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From the Mine

he planet Neptune was discovered by Johann Gottfried Galle of the Berlin Observatory on September 23, 1846. With an orbital period of 164.79

years, it completed its first orbit since its discovery on July 12, 2011. To commemorate this event, this special issue of Argentus: The Neptunian Anniversary is being published on July 12, 2011.

I open the issue with a discussion of Neptune’s discovery and then jump ahead to Michael A. Burstein’s personal discovery of the planet with the help of a catchy little song.

Marianne Dyson has graciously agreed to allow me to reprint portions of the chapter on Neptune from her book Space and Astronomy: Decade by Decade, in which Chris McKitterick discusses the research he did when he decided to set parts of his novel Transcendence in the Neptunian system. Chris discusses Triton in his article which leads to Mike Brotherton’s article on the moons of Neptune and Diane Turnshek’s article on a plan to discover more moons of Neptune.

When Voyager 2 flew past Neptune in 1989, Bill Higgins had a front row seat as he was sitting at the Jet Propulsion Laboratory watching as the results streamed in from four light hours away. More recent discoveries about Neptune come thanks to the work done with the Hubble Space Telescope, and Christian Ready has contributed an article and images the discuss and demonstrate the Hubble’s use with regard to the planet.

When I asked Brother Guy Consolmagno for an article, he asked if it would be okay to send me an interview with one of the foremost experts on Neptune, Heidi Hammel. Naturally, I jumped at the offer. Dr. Hammel was also pulled into this project by Christian Ready, who double checked some of the technical details about Neptune for his article on the Hubble Space Telescope with her. Clearly, when Neptune’s second orbit is complete in 2176, I should skip the middlemen and invite Dr. Hammel to contribute directly.

Sprinkled liberally throughout are NASA images of Neptune as well as artwork by a variety of fan artists, who have a tendency of seeing the mythological side of the planet’s name.

From the Mine ..................................................................................... 1 One [Neptunian] Year Ago .................................................................. 2 Neptunian Nomenclature .................................................................... 6 A Brief Description of the Planet Neptune........................................... 8 Neptune............................................................................................. 10 Neptune, Triton, and the Sensawunda; or Why I Set My Novel (Partly) at the Edge of the Solar System ....................................................... 11 Triton and the Satellites .................................................................... 15 Discovery of Neptune’s Thirteen Moons ........................................... 18 Phone Call from a Turquoise Giant................................................... 22 Unlocking Neptune’s Secrets with the Hubble Space Telescope...... 33 Neptune’s First Birthday.................................................................... 45

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Artwork Kurt Erichsen…32, 34, 38, 42 Al Eugster…8 Brad Foster…39 Sue Mason…5 Mo Starkey…Cover Steve Stiles…44, 49

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One [Neptunian] Year Ago

Steven H Silver rom time immemorial, humans knew there to exist seven planets… the Moon, Mercury, Venus, Mars, the Sun, Jupiter, and Saturn. This understanding of

the solar System began to be challenged with the theories of Nicholas Copernicus and Galileo Galilei, who helped demote Earth from the center of the universe and placed the Sun in the center of the solar system.

The Problem with Uranus

On March 13, 1781, William Herschel, a British astronomer, charting the night sky from his garden in Bath, noticed a previously unknown comet. Subsequent observations over several nights revealed that the comet traveled in a planetary orbit rather than a cometary one. He eventually shared his discovery with the British Astronomer Royal, Nevil Maskelyne and, while Herschel and Maskelyne wrestled with the categorization of the object, Russian astronomer Andrei Leksel computed a nearly circular orbit, which was confirmed by the computations of Johann Bode. It wasn’t long before Herschel was credited with the discovery of the first planet to be found since ancient times. Although Herschel initially wanted to name the new planet Georgium Sidus, after the king of England, popular opinion was opposed and Bode suggested the name which eventually stuck, Uranus. Interestingly, a Swedish astronomer, Erik Prosperin, who had also worked out calculations for Uranus’ orbit, suggested the name Neptune, as well as Astraea and Cybele.

In 1821, Alexis Bouvard published a chart of tables indicating the locations of Jupiter, Saturn, and Uranus. While his tables for the first two planets were accurate, the third was rife with discrepancies when compared to later observations. Bouvard came to believe that that the discrepancies were the result of an unknown mass, probably a planet, orbiting beyond Uranus. In 1837. Bouvard’s nephew, Eugène, confirmed his uncle’s suspicions in a letter to George Airy, who was of the opinion that the discrepancies were a matter of an incorrect calculation of Uranus’ mass. Bouvard died in 1843, his calculations still incorrect.

Adams

In 1841, a student at Cambridge, John Couch Adams, happened across a copy of Airy’s Report of 1831-1832 to the British Association for the Advancement of Science. A note in the book discussed the problems with Bouvard’s 1821 tables. Adams determined that when he finished his degree, he would tackle the problem that had been vexing Bouvard. Adams received his degree and a Fellowship in 1843 and began to turn his attention to the Uranus issue, eventually determining a placement for an eighth planet.

By October 1845, Adams believed he had solved the problem and arranged to deliver his calculations to the Astronomer Royal, now George Airy. Several of Adams colleagues who saw the calculations and were impressed by his work suggested that he pursue other avenues to prove his calculations were correct, however, a young man who was still trying to make a name for himself, despite receiving various accolades, Adams wanted to go straight to the top. Unfortunately, Airy had been convinced for years that Bouvard’s hypothetical planet was non-existent.

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Moreover, Airy appeared to be highly dismissive of the claims made by an unproven mathematician (not just Adams, but anyone without a reputation) and wound up somewhat dismissive of Adams’s work. Airy failed to follow up on the calculations and suggestion to look for a new planet. Airy’s dismissal of Adams’s calculations appears to have disheartened the mathematician who did not take his figures to other astronomers to use in a search. One of Adams’s friends, who had encouraged him, James Challis, would eventually become involved in the search using Adams’s calculations after Airy began to reconsider the possibility of a trans-Uranian planet.

Leverrier

In France, Urbain Jean Joseph Leverrier received his degree in 1831 and immediately began to build his reputation as a mathematician. In 1837, Leverrier was recommended for the position of répétiteur in astronomy at École Polytechnique. For his first paper in the new position, Leverrier chose to investigate the stability of the solar system. Building on the prior work of Lagrange, Leverrier’s paper, Sur les variations séculaires des orbites planetaires appeared in late 1839. The paper focused mostly on the inner planets, and Leverrier followed up by studying Mercury at the suggestion of François Arago, the director of the Observatoire de Paris and secretary of the Académie des sciences.

Over the next few years, Leverrier continued his studies, eventually becoming interested in cometary orbits. When his research into a comet discovered by Francesco de Vico on August 22, 1844 proved that it was not the same as a comet Tycho Brahe had observed in 1585, but rather one that was discovered by Philippe de La Hire in 1678, Arago

suggested that Leverrier turn his attention to the perturbations in the calculated orbit of Uranus.

Agreement

Leverrier published his Premier mémoire sur le théorie d’Uranus on November 10, 1845. When Airy read the work the following month, he noted that for first the first time, the theory of Uranus was placed on a satisfactory foundation. Leverrier’s work demonstrated that Bouvard’s equations were rife with errors and in June of 1846, he followed up with Recherches sur le mouvements d’Uranus.

Airy had begun to closely follow Leverrier’s work and had suggested to Challis that he follow up on the work that Adams had done. However, Airy’s attitude towards Challis had the effect of turning Challis from a detailed study of the night skies based on Adams’s predictions. Airy also wrote to Leverrier with follow-up questions about his work, which substantially agreed with the mathematics of Adams’s.

Eventually, in August 1846, Challis worked with Adams to conduct a search for a planet beyond Uranus, searching for anything down to eleventh magnitude (Adams had predicted the planet would be about ninth magnitude). The search included more than 3,000 stars. At the end of the month, Leverrier published Sur la planète qui produit les anomalies observées dans la movement d’Uranus—Détermination de sa masse, de son orbite et de sa position actuelle.

Without knowing of Challis’s search or Adams’s calculations, Leverrier wrote to Johann Gottfried Galle at the Berliner Sternwarte on September 18, 1846. Galle received the letter, which provided the calculations for the

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new planet on September 23, 1846. Galle, an assistant at the observatory, sought the permission of the director, Johann Franz Encke, to search for the planet. Although he initially said “no,” throughout the day, Galle persisted and Encke finally gave permission to Galle to perform a search with the assistance of a student, Heinrich d’Arrest, who had overheard the discussions.

Using a 9-inch Fraunhofer refractor, Galle began calling out star placements to d’Arrest who checked them against Hora XXI of the Berlin Academy’s Star Atlas, a new chart which was not widely disseminated. Shortly after they began, Galle described an eighth magnitude star at right ascension 22h53m25s.84. D’Arrest responded, “That star is not on the map!”

Naming and Controversy

With the discovery of an eighth planet, the French suddenly began to suggest that Uranus be referred to as Herschel and the eighth planet be called Leverrier. Just as the rest of the world had been opposed to naming the seventh planet Georgium Sidus, the idea of naming the eighth planet Leverrier never was popular. Galle suggested naming the planet Janus, and Challis, who continued his search for some time after the discovery, but before word reached him, offered up Oceanus. Leverrier’s first suggestion had been, in fact, Neptune, and he claimed it had the support of the Bureau des Longitudes. By December, Friedrich Georg Wilhelm von Struve was using the name Neptune at the Russian Academy of Sciences and the name stuck.

Although Galle discovered Neptune using the calculations provided by Leverrier, it wasn’t long before Adams’s predictions became known. On October 3, 1846, John

Herschel, the son of Uranus’ discoverer, published a letter in the Athenaeum which noted “The remarkable calculations of M. Le Verrier” were confirmed by “a similar investigation…independently entered into, and a conclusion as to the situation of the new planet very nearly coincident with M. Le Verrier’s arrived at (in entire ignorance of his conclusion), by a young Cambridge mathematician, Mr. Adams…”

At the same time, Airy and Challis began to make Adams’s calculations public. This wasn’t necessarily an effort to gain Adams any specific fame or recognition for his efforts, but quite possibly an effort to claim the discovery of Neptune for English, despite the fact that Airy had dismissed Adams’s calculations and Challis’s two month search had proven fruitless (although Challis had spotted the planet twice and failed to recognize it as such).

The scientific community, particularly the French, gave little credence to Adams’s, Airy’s, and Challis’s claims. Leverrier and Arago both questioned why nothing had been said about Adams’s calculations until after Galle announced his discovery, despite prior communications between Leverrier and Airy. Arago noted that “Mr. Adams has no right to figure in the history of the discovery of the planet Le Verrier, neither by a detailed citation, nor by the slightest allusion.”

Other astronomers searched for and found the planet, including the American William Lassell, who discovered the moon Triton on October 10. More importantly, Sears Cook Wallace began tracking down sightings of the planet prior to its discovery by Galle (the earliest known of which was made by Galileo Galilei while observing Jupiter and its moons on January 6, 1613). Few of these pre-discovery

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sightings were in line with the calculations made by either Leverrier or Adams leading Benjamin Pierce of Harvard University to declare Neptune’s “discovery by Galle must be regarded as a happy accident,” just as Pluto’s discovery by Clyde Tombaugh was regarded following its 1930 discovery.

Leverrier and Adams met for the first time in June of 1847 at the British Association for the Advancement of Science and afterward both traveled to John Herschel’s home, at Collingwood. The two were not just cordial to each other, but struck up a lifelong friendship and eventually Adams was according recognition for his work in determining the location of Neptune, even if his calculations did not lead to its discovery.

Adams’s Role Revisited

Beginning in the 1960s, the Royal Greenwich Observatory claimed that the letters exchanged between Airy, Adams, and Challis were unavailable. They were last seen by Olin J. Eggen, who used them to write articles about Airy and Challis. Although Eggen claimed not to have them, following his death in October 1998, the documents, along with many other books belonging to the observatory, were found in his apartment in Chile.

After examining the letters, William Sheehan, Nicholas Kollerstam, and Craig B. Whiff published a paper, “The Case of the Pilfered Planet: Did the British Steal Neptune?” in the November 22, 2004 issue of Scientific American. In this article, the men claimed that an examination of the actual letters led them to believe that the case of Adams’s claims of deduction were overstated by Airy, Challis, and Adams after Galle’s discovery. The article notes that while

Adams did some work, it was much more vague than they led people to believe, that Airy was entirely justified in dismissing Adams’s notes, and that Challis was not as much of a bungler on the search as previously believed, but rather lacked the important Hora XXI chart that Galle and d’Arrest had access to. The article notes that the discovery of Neptune had a private side, which both Leverrier and Adams completed, and a public side, at which Adams failed.

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Neptunian Nomenclature

Name Origin of Name Date Discovered Discoverer Despina Neptune V S/1989 N 3

named for Despoina, the daughter of Demeter and Poseidon. Her name means “The Lady” and was used in place of her real name, which was only revealed to those who were initiated into the mysteries of her cult.

July 1989 Stephen P. Synnott & Voyager Imaging Team

Galatea Neptune VI S/1989 N 4

One of the daughters of Nereus and Doris, Galatea was in love with Acis. When Acis was slain by the Cyclopes Polyphemus, Galatea took his blood and her tears and formed the river Acis in Sicily.

July 1989 Stephen P. Synnott & Voyager Imaging Team

Halimede Neptune IX S/2002 N 1

One of the daughters of Nereus and Doris. August 14, 2002 Matthew J. Holman, John J. Kavelaars, Tommy Grav, Wesley C. Fraser, Dan Milisavljevic

Laomedeia Neptune XII S/2002 N 3

One of the daughters of Nereus and Doris. August 13, 2002 Matthew J. Holman, John J. Kavelaars, Tommy Grav, Wesley C. Fraser, Dan Milisavljevic

Larissa Npetune VII S/1981 N 1

A Thessalian nymph. Two towns (one in Thessaly, one in Peneus) are named for her and her image appeared on coinage issued by Larissa, Thessaly.

May 24, 1981 Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky, and David J. Tholen

Naiad Neptune III S/1989 N 6

a collective name for the nymphs who were responsible for fountains, wells, springs, streams, and brooks.

September 1989 Voyager Imaging Team

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Name Origin of Name Date Discovered Discoverer Neptune Roman god of the sea, known as Poseidon in Greek mythology. The

brother of Jupiter (Zeus) and Pluto. September 23, 1846

Johann Galle, Urbain Le Verrier, John Couch Adams

Nereid Neptune II

The second discovered moon of Neptune. It was given the collective name of the daughters of Nereus and Doris, for whom many of the other moons were named. The Nereids were responsible for the waters of the Mediterranean, much as the Naiads were responsible for inland water.

May 1, 1949 Gerald P. Kuiper

Neso Neptune XIII S/2002 N 4

One of the daughters of Nereus and Doris. August 14, 2002 Matthew J. Holman, Brett J. Gladman

Proteus Neptune VIII S/1989 N 1

Early Greek sea god, known as a shape-shifter, eventually depicted as a son of Poseidon and herdsman of Poseidon’s seals.

June 16, 1989 Stephen P. Synnott & Voyager Imaging Team

Psamanthe Neptune X S/2003 N 1

One of the daughters of Nereus and Doris, she was the wife of Proteus and the goddess of sandy beaches.

2003 Scott S. Sheppard, David C. Jewitt, Jan Kleyna

Sao Neptune XI S/2002 N 2

One of the daughters of Nereus and Doris, Sao was known as a protector of sailors.

August 14, 2002 Matthew J. Holman, John J. Kavelaars, Tommy Grav, Wesley C. Fraser, Dan Milisavljevic

Thalassa Neptune IV S/1989 N 5

The daughter of Aether and Hemera, possibly the mother of Aphrodite, Uranus, and Zeus, she is the personification of the Mediterranean Sea.

September 1989 Richard J. Terrile & Voyager Imaging Team

Triton Neptune I

The messenger of the sea and the son of Poseidon, Triton is often represented as a merman. He can use a conch shell to summon or calm the waves.

October 10, 1846 William Lassell

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A Brief Description of the Planet Neptune

Michael A. Burstein

ow did you first learn about the planet Neptune? I

can’t say for sure when I first learned about it, but my guess is that it was through the Schoolhouse Rock song “Interplanet Janet.” For those of you too old or too young to know what I’m talking about, Schoolhouse Rock was a series of educational songs and cartoons that were broadcast on Saturday mornings in the 1970s. Each song focused on a different subject, in one of four topics: American history, mathematics, grammar, or science.

“Interplanet Janet” was the song about the solar system. The premise of the song was that an alien named Janet visited every major body in the solar system from the sun to the planet (yes, planet) Pluto. Many years after I first heard the song, I went back to listen to it again, and was surprised by the paucity of information it provided about the planets—particularly, the outer planets.

For example, this is what the song said about Neptune: “Uranus is built on a funny tilt/And Neptune is its twin.” In retrospect, it’s not surprising that the song said little more. For one thing, you’re not going to be able to fit an entire

treatise on a planet into a children’s song. For another, the song and video were released in 1978, the year after the Voyager mission spacecraft were launched.

It wasn’t until August 1989, when Voyager 2 reached Neptune, that we really began to expand our understanding of the planet. If you ever have the chance, compare the Neptune sections in a typical college astronomy textbook from before and after 1989; the lack of information in the earlier textbook compared with the explosion of information in the later textbook is instructive.

So what do we know about Neptune today?

Let’s start with some basics. Neptune is a gas giant, so called because it is one of the largest planets in the solar system—its radius is almost four times that of Earth—and is composed mostly of hydrogen and helium. However, the planet appears blue due to the presence of methane gas in its atmosphere. Neptune’s atmosphere has an average rotation period of about 17.3 hours, but its magnetic field—and presumably, its interior—rotates once every 16.1 hours. This means that Neptune is the only outer planet whose atmosphere rotates more slowly than its interior. The planet is about 30 times further away from the sun than Earth, and it takes about 165 Earth-years for it to complete one orbit around the sun.

Neptune is a cold planet, with an average surface temperature of only about 60°K. Because it’s so cold, before 1989 many scientists thought that it would be somewhat boring. After all, energy is required for most geologic and gaseous processes, and a planet that was low in temperature was expected to lack the heat needed for an interesting atmosphere.

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It turns out that there is a lot more going on in Neptune’s atmosphere than we expected. Apparently, Neptune’s interior is hot due to energy left over from its formation, and this heat produces the clouds and storms that we see in Neptune’s atmosphere. The most dramatic of these that we saw was the Great Dark Spot, about the size of Earth, and photographed by Voyager in 1989. Even today, many pictures of Neptune will show this feature, although the Spot was actually gone by 1994, when the Hubble Space Telescope was used to look for it.

Oddly, Neptune’s upper atmosphere is warmer than that of its sister planet Uranus—odd, because Neptune is further away from the sun. Also odd is the fact that Neptune radiates almost three times more heat than it receives from the sun. The weather on Neptune is intense and can change drastically within seconds. Wind speeds can reach up to 1500 km/h, roughly half the speed of sound in the atmosphere. Consider that the speed of sound in Earth’s atmosphere is approximately 1200 km/h, or 750 miles per hour. So comparable winds on Earth would blow at a speed of 375 miles per hour. Given that the top wind speeds of a hurricane on Earth have never broken about 200 miles per hour, even scaled down the storms on Neptune are much more intense than anything ever seen on our planet.

Neptune’s magnetic field, about 100 times stronger than Earth’s, gives us clues about its interior. The field is inclined to the axis of rotation at about forty-six degrees and is off-center. This implies that Neptune’s interior may have thick layers of clouds made of water. If ammonia is dissolved into these clouds, it might create a layer of electrically conducting ions that could lead to the odd

properties of the magnetic field. Research still has to be done.

Another thing that makes Neptune interesting are its moons. Neptune has 13 moons that we know of, but only two of them, Triton and Nereid, are visible from Earth. Neptune’s largest moon, Triton, orbits Neptune in the opposite direction of Neptune’s rotation, and is one of the few objects in the solar system (besides Earth, Io, and Enceladus) to be geologically active. Voyager 2 photographed geysers of nitrogen gas erupting from below the surface. As for the moon Nereid, its orbit is so elongated that its closest approach to Neptune is 1.4 million km and its furthest is 9.7 million km. As of now, only eight of Neptune’s moons have names; they are named for water deities of Greek mythology.

Finally, Neptune is also surrounded by five dark rings, three narrow and two broad. From Earth, we can only see partial ring arcs, as in many places the rings are too thin to see without being close by. Neptune’s ring system has only added to the mystery of how ring systems develop; as of yet, we still do not have a comprehensive theory to explain all our observations.

Ever since its discovery in 1846, Neptune has provided astronomers with surprises and mysteries. May it keep doing so as it begins a new orbit around the sun.

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Neptune

Marianne Dyson

xcerpt from Marianne Dyson's book, Space and Astronomy: Decade by Decade (Facts On

File, 2007), Chapter 9, 1981-1990, "Voyage to Uranus and Neptune" pages 206-207. Reprinted with permission.

Voyager 2 launched in 1977 and used a gravitational assist (sling-shot) from Jupiter in 1979 to bend its path toward Saturn, then from Saturn in 1982 to Uranus, and from Uranus in 1986 to Neptune in 1989. Without gravitational assists, Voyager 2 would have taken about thirty years to reach Neptune instead of twelve.

In August 1982, Voyager 2 completed its fly-by of Saturn and headed for distant Uranus. The trip took six and a half years and the fly-by lasted just six hours in January 1986.

The quick fly-by of Uranus was followed by a three-year trip to Neptune, then the most distant planet from the Sun. Arriving in August 1989 the Voyager 2 found a storm about half the size of Earth. This Great Dark Spot1 generated an ultraviolet aurora and winds up to 1,500 mph (2,400 kph), stronger than on any other planet. High cirrus clouds of natural gas cast shadows on clouds below. One of the most surprising and puzzling discoveries was that Neptune 1 Hubble photos showed the spot had dissipated by 1994.

has an internal heat source that drives the winds, whereas Uranus does not. It remains a great mystery why Neptune is the same temperature as Uranus despite being so much farther from the Sun. Neptune’s weak magnetic field was found tilted and offset from the planet’s center. This suggests that matter is not evenly distributed inside the planet, and that the magnetic field derives from a shallow spherical shell, not deep in the core like on Earth.

Voyager 2 found six new moons (Nereid and Triton were previously discovered) during its encounter. It discovered three debris rings and two broad rings. Neptune’s largest moon, Triton, displayed two types of “ice” volcanoes in the Voyager images. The first are calderas about one thousand feet (300 m) deep and hundreds of miles/kilometers across. They produced ocean-sized floods of ice as recently as a half billion years ago. The second type erupted explosively, ejecting nitrogen ice and gas at speeds of 560 mph (900 kph). Astronomers estimate that these volcanoes have been active within the last three hundred years. Triton’s relatively high density and retrograde orbit offer strong evidence that it is a captured object. If true, then tidal forces may have melted Triton and made its surface liquid for as long as a billion years after its capture. Triton’s surface temperature is now the coldest of any known world in the Solar System at -391° F (-199° C).

Voyager 2 was the first spacecraft to visit Uranus and Neptune and answered many questions about these giant worlds. After its encounter with Neptune, the spacecraft dove below the ecliptic plane and headed out of the Solar System.

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Neptune, Triton, and the Sensawunda; or Why I Set My Novel (Partly) at the Edge of the Solar System

Christopher McKitterick

've been fascinated with astronomy since childhood, and bought my very first telescope—an Edmund Astroscan, a 4" f/4 Newtonian reflector—at age 12 using money

earned washing dishes at the Polly Cook-It Restaurant in Ortonville, Minnesota. Its little weighted-ball tube rode smoothly over three felt pads, ready to view the instant one set it down. A simple carry strap bolted to the little tripod and tube so one could carry it around like a shoulder bag. I can hardly remember what a 3° field of view was like anymore—that's binocular territory! Over the next year or two, I used that little 'scope to find all the bright, dramatic Messier objects and most of the planets. It also served as a projector to cast images of the spotty Sun onto paper, where I traced the active surface (this was during the last active cycle, a while back, ahem). Not being able to pick Neptune out among the litter of stars glowing in the eyepiece field was one reason I moved up to a serious (for

the time) telescope, a Crown 6" f/8 Newtonian on a beefy German equatorial mount.

In junior-high, I would often set my alarm for 2:00am on the weekends—even in mid-winter mornings—and lug those 80 pounds of telescope up the big hill that shadowed our neighborhood. In the snow. Because we lived miles from a small town, the skies were utterly black up there, half a mile from the nearest house light. Absolutely gorgeous skies, with the Milky Way so bright in contrast to the darkness that I could read my planisphere in the light cast by the distant stars of our galaxy. Often, the Northern Lights whooshed across the sky, spikes and curtains of light obscuring the stars but amazing and beautiful in their own way; this was western Minnesota, after all. Gosh, I miss living beneath such skies.

It was there, beneath those starry skies, silent and gorgeous and all mine, far above the mundane world of petty teenage jealousies and bullying and tedious schoolwork, where I first saw the spiral arms of the Whirlpool Galaxy, the glowing bubble of the Ring Nebula, the moons of Jupiter, the rings of Saturn, and where I finally picked out the green disk of Neptune among the stars. There and then I fell in love with this magic of discovering entire worlds and suns and galaxies hidden by distance; that's when I grew determined to become an astronomer one day. This was also about the time I discovered science fiction and began to seriously write—also to build

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liquid-fuel rockets and date girls, but that's another story.

The degree in astrophysics got derailed around the time I discovered the dearth of jobs in the field combined with GTAs who had difficulty communicating in English. What was left to someone so impassioned (or afflicted) with exploring the skies? This combined love of astronomy and disease of writing led to my life in SF, of course. Most of my work is set off-world, giving me the excuse to do a lot of research into astounding and wonderful locales. When staring through an eyepiece, alone in the night, one can't help but imagine what it's like to actually be there, hiking the Martian highlands or Lunar maria, jetting through the clouds of our gas giant planets, or riding some massively powerful engines through the spiral arms of distant galaxies.

Most fitting for this issue of Argentus is my novel Transcendence (Hadley Rille Books, 2010), in which Neptune and Triton serve not only as setting, but even pose for the cover art. Check out the gorgeous piece by Greg Martin, where we cruise through the clouds of Neptune and see Triton in crescent phase just above the title:

One of the characters in the book serves as Neptunekaisha Coordinator of Protection; that is, she's the head of corporate security in the region around Neptune. Here's where she works:

Clarisse Chang’s security station hung stationary in Neptune’s upper atmosphere, nearly in orbit around the pale blue gas giant—high enough from the planet’s center of mass that onboard gravity barely exceeded Earth’s. Even at this altitude, winds could be potentially destructive. Roiling clouds swept past like mountains, as if the station were hurtling across smooth white and blue terrain, flying over hundred-kilometer valleys and then crashing through liquid cliffs. The tiny disk of the sun shone at a steep angle, tingeing the sky’s horizons a faint purple while, overhead, stars pricked pure blackness. Triton, Neptune’s largest moon, was rising. For a moment, its disk partially eclipsed the sun’s.

The image on the cover of the book is pretty much what Clarisse sees out her window when she goes to work each day. But out there on Triton is where the transformative feature of the novel is buried:

A tenuous breeze hissed across Liu Miru’s suit as he crossed a ridge of nitrogen ice. Neptune filled the sky, lighting Miru’s path about as brightly as, though shades bluer than, the full Moon on Earth. Thoughts of Earth reminded him that somewhere in the recesses of space, not far away now, an invading warship from that world blazed nearer. This was seventy-two hours before the end of the human race as he knew it.

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Triton was a largely worthless world that had revealed most of its secrets long before he arrived. But Project Hikosen gave him purpose. When he first saw the object—which he was careful not to call “alien” to anyone but himself—it had seemed that he’d awakened from a long sleep.

Soon, the tractor-worn path turned off the ridge. Miru stopped for a moment and looked to the foreshortened horizon across pockmarked terrain, the peculiar “grapefruit” texture of Triton’s Eastern Hemisphere, methane and nitrogen ice encrusting the rock. He drew a deep breath and turned toward the shallow excavation. Unmarked, it looked like nothing more than a test dig.

Miru’s heart rate increased as he climbed down a gleaming staircase melted from the ice. As he descended the few meters into the pit, the wind quieted and the walls constricted the dome of stars overhead. His breathing seemed to grow louder within his helmet. He reached the bottom of the excavation and stared at the object. Silence ruled down here, except for the mechanical sounds of his breathing apparatus and the crunch of ice crystals beneath his boots.

NKK scientist Liu Miru is exploring a great ball of star-stuff buried in the ice at the moment when a system-wide war is about to erupt, threatening all of human civilization, and the only way to save humankind is to find a way to use it before all is lost.

Why would I choose to place the crucial artifact way out here at the edge of the Solar System? Among other things, science fiction is an ongoing conversation between authors and fans, and this is my reply to a couple of works that deeply influenced young-Chris. Surely you recall Arthur C. Clarke's story, "The Sentinel," where astronauts discover an artifact on the Moon that can only be opened by using the "savage might of atomic power"—and doing so turns off the signal it has been transmitting for eons, letting whoever placed it there know that humankind has not only left the Earth but has also developed nuclear power. I also took inspiration from Algis Budrys's book, Rogue Moon, and its mysterious Lunar artifact that tests the men who enter it, usually killing them but ultimately transforming those who survive. And of course I was inspired by the cold beauty of Neptune and desolate Triton, their symbolic distance and isolation. A space-faring human civilization can only send people to Neptune after overcoming a myriad of technical, cultural, and political challenges; we are far from doing so right now or any time in the near future, not only because we lack the basic infrastructure to do so in a realistic time-frame for human travels to make the trip safely, but primarily because we lack the motivation and will… and we have to wonder if a culture increasingly immersed in fleeting communication technology and instant gratification will ever be capable of doing so. I argue that, yes, there will always be explorers and those who seek to learn more about our universe, even if the majority settle into intellectual morass.

We could debate whether or not intelligence normally arises from species that survive conflict and come to dominate their environment, but any species that evolves to the point that it is capable of sending live people to

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worlds will be viewed by other galactic civilizations as A) scary and dangerous, B) ready to welcome into galactic culture, or C) both. Let's hope for one of the latter! Not that my book or those works that inspired me offer an answer.

When I was first researching Transcendence, I wanted to set it not only on an Earth that demonstrates what happens to us as humans as we lose real human contact, but also on worlds as distant and foreboding as imaginable. Enter Neptune and its mysterious satellite Triton. The Voyager 2 images are astounding, and I'm sure you'll read more about that mission and see those photos elsewhere in this issue; if not, a quick search of the interwebs will provide great wonder. Go ahead and take a look; I'll wait. The combination of truly alien landscape, thin exotic atmosphere, and close proximity to a giant planet set my imagination alight, and after that, the rest of the book came to life.

When Neptune completes its first orbit since we discovered it this July 12—two days after the Campbell Conference and Awards Banquet—you know I'll be in a dark field somewhere outside Lawrence, Kansas, telescope pointed at the far reaches of Solar System. My personal 'scopes cannot reveal images anywhere near as jaw-dropping as those Voyager 2 and Hubble provide, but I'll have found it by myself, that little greenish-blue disk and the companion pinprick orbiting it. There's something uniquely rewarding about finding a celestial object using one's own hands to steer an instrument and one's own eyes to observe what it reveals that no 12-megapixel NASA glamour-shot can offer.

That's sensawunda you can't get anywhere else, and why astronomy is still my first love. I may have abandoned my

dream of becoming a professional astronomer, but by continuing to drag out my light-bucket to pick gems from the starfields, I continue to find inspiration for my fiction—where an author can explore places no human will likely set foot in our lifetime. I will always be an astronomer first, I think, and a writer as a way to express the delight and joy I find in these studies.

"The Golden Age of science fiction is 12," Peter Graham wrote in the Void fanzine back in 1957; Peter Nicholls suggests 14 in 1979's The Science Fiction Encyclopedia. Discovering astronomy and science fiction together at that impressionable age range is why I'm writing this article, today, about a novel set in Neptune's gravity field, and why I still seek to recapture that feeling of wonder at the beauty of the universe whenever I set down to write or cart around optics that weigh more than I do.

Where will you be in mid-July on this auspicious day? Do you have an old C-8 Celestron gathering dust in the garage? Maybe your local observatory hosts a weekly public-viewing night? If you search just a little, I guarantee that you'll find a way to peer up through our protective skin of atmosphere, across 4.5 billion kilometers of void, at a world we have barely begun to explore. One day, we shall fly through those blue blue skies and crunch across the icy surface of Triton. I'll be there with you in spirit!

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Triton and the Satellites

Mike Brotherton

ot-at-all-superstitious Neptune has 13 known moons, which are also often referred to as satellites. There won’t be a quiz, but for the record they are, in order

from innermost to outermost moon: Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Triton, Nereid, Halimede, Sao, Laomedeia, Psamathe, and Neso. Coming up with a sea-themed mnemonic to remember that would be impressive, but let’s move on.

Neptune’s largest moon, Triton, was discovered by amateur British astronomer William Lassell in 1846, a mere 17 days after the discovery of Neptune itself. Neptune has only a single moon that is easily visible, and the name Triton, who was a son of Neptune, makes a lot of sense. That name was a long time coming, not becoming official until the twentieth century.

Triton is a big moon, about two-thirds the size of Earth’s own oversized moon, and masses more than a hundred times that of all of Neptune’s other moons combined. It’s also incredibly interesting and is the best-studied moon of Neptune, so let’s focus on Triton a while before discussing the other satellites.

Triton is noteworthy in a number of ways, and in its ensemble of properties, quite unlike any other object in the solar system. First, Triton has a retrograde orbit. That is, it orbits Neptune in the opposite direction Neptune spins. All the other large moons in the solar system are prograde,

and probably formed in a disk around the protoplanets they were orbiting. There are other retrograde moons to be found, Amalthea around Jupiter, which is regarded as a captured asteroid. Triton is likely a captured dwarf planet, an object that formed on its own and later wandered too close to Neptune, perhaps violently too close. Even for a giant like Neptune, capturing such a large object may have required a collision, and Triton might have bounced off Neptune’s atmosphere or catastrophically encountered one of Neptune’s other moons. Another possibility is that Triton, like the smaller Pluto, had its own moon, and the capture launched Triton’s own moon out into space.

That would have been pretty cool to have seen, but even cooler are Triton’s icy cold temperatures, something like -400 degrees Fahrenheit. Triton is icy, and icy tends to be shiny, and Triton winds up reflecting back into space the vast majority of sunlight that might have otherwise heated it. A place so cold seems like it should be frozen and dead, but that’s not the case. When it flew by in 1989, Voyager 2’s cameras spotted ice geysers exploding off Triton’s surface. These are probably spouting liquid nitrogen, methane, and dust, much of which freezes into a fountain of falling ice. Some of the nitrogen helps give Triton a very thin atmosphere, only about one part in a hundred thousand as dense as ours on Earth. And Triton has at least one polar ice cap (the other pole was not photographed by Voyager 2), that would seem to be frozen nitrogen. That’s pretty strange.

One of the strangest things about Triton, at least to some astronomers, is that parts of its surface strongly resemble that of a cantaloupe. It could be referred to as the big, retrograde, super-cold ice geyser cantaloupe moon.

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Triton, showing its cantaloupine surface features.

Neptune has another dozen moons that we know of, and likely others we have not yet discovered. They are all much, much smaller than Triton, with the largest being a few hundred kilometers across and the smallest only dozens, although that’s a little misleading since they’re all irregular shaped and not even round. They’re all composed of rock and ice and are typically very dark

objects, reflecting only a small portion of the light they receive. They are named after Roman and Greek sea deities and nymphs. It would not be too unreasonable to think of them as big inactive comets with fancy names that happen to be orbiting around Neptune.

Neptune’s third largest moon at 340 kilometers across, Nereid was discovered by Gerard Kuiper in 1946. Nereid is notable for having an extremely eccentric orbit (an eccentricity of 0.75 makes its orbit look a lot more like a stretched rubber band than a circle). It’s likely that something unusual happened in Nereid’s past to give it such an extreme orbit.

Neptune’s fourth largest moon, Larissa, was discovered accidently by a team of astronomers in 1981. They were interested in a star that would be occulted by Neptune, which might allow them to detect the presence of rings, which had previously been done for Uranus. Well, something else got in the way, and the discovery of a new moon was announced.

Wait! Didn’t we skip the second largest moon a couple of moons ago? Well, it was skipped historically, too. Proteus, has an orbit too close

to Neptune to have been easily discovered by Earth-based telescopes, and did not have the fame-seeking qualities to wander in front of a star and occult it while astronomers were peering in that direction. Proteus was not spotted until Voyager 2’s fly-by.

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The importance of Voyager 2 cannot be overstated when it comes to our understanding of Neptune and its satellites. No other spacecraft before visited this system, and proximity is priceless. In addition to Proteus, Voyager 2 discovered Neptune’s inner four tiny moons.

Fly-bys don’t last long and Voyager 2 didn’t get the chance to do a complete census of everything orbiting Neptune. Ground-based telescopes have been improved dramatically over the last few decades, and more importantly digital analysis techniques have made big leaps as well. Such improvements permitted two teams of astronomers to discover another half dozen, small, irregular satellites with large orbits (everything beyond Nereid). Three of these, Halimede, Psamathe and Neso, have retrograde orbits like Triton. These newly discovered moons comprise the outer parts of the Neptunian system.

That’s the census of the moons of Neptune. It’s one big, super strange and interesting moon in Triton, probably captured, with a bunch of small dark little irregular moons. This information suggests a catastrophic history. A captured moon would be likely to have an eccentric orbit initially, and disrupt the orbits of existing moons, likely causing crashes between them. Due to their very similar colors, it has been suggested that Halimede is a chip off of Nereid, for instance. These interactions would help give Triton a more circular orbit, and the debris from the collisions might have once formed bright rings around Neptune. Some of the moons may have reformed from the debris in the system, and constitute little more than big piles of rubble today.

Neptune probably had a simple system of small moons after its formation, but the interloper Triton caused a

version of “When Worlds Collide” as it crashed the party. Triton is our best-studied example of a dwarf planet like Pluto or Eris, and we have Neptune to thank for that, even if it cost us studying Neptune’s original system.

Just for fun, can you remember Neptune’s moons in order? I came up with this mnemonic that might help: Nasty thieves despise gallant Lords, preferring trendy neer-do-wells, hip sexy ladies, psychologically naïve. Thirteen words is tough, and three “N” moons doesn’t seem fair.

Proteus

Nereid

Larissa

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Discovery of Neptune’s Thirteen Moons

Diane Turnshek

“It is the modest, not the presumptuous, inquirer who makes a real and safe progress in the discovery of divine truths.” – Henry St. John, First Viscount Bolingbroke (1678–1751)

he pattern of discovery of Neptune’s moons illustrates how science itself has advanced. Only seventeen days after Neptune was found in 1846,

Triton, the largest moon, was discovered by one man, British astronomer William Lassell. He had made his fortune in the beer industry allowing him the free time and funds necessary to pursue his interest in astronomy. Like

the great scientists of his era, he furthered the field by the lone pursuit of knowledge.

Triton, with a diameter of 2700 kilometers and a thin atmosphere of nitrogen and small amounts of methane and carbon dioxide, revolves around Neptune in a retrograde orbit. Nearly every body in our solar system revolves around the Sun and rotates on its axis counterclockwise as seen from the North. When a moon orbits in the opposite direction that the planet rotates, like the two tiny moons of Mars, it indicates that the satellite wasn’t formed with the planet, but was captured at a later date. Several moons share that honor in the flock orbiting Neptune. They’re considered to be captured Kuiper Belt Objects (KBOs).

Triton is a dense, geologically active moon with polar caps, geysers and icy lava flows. Smooth, flat plains that are not heavily cratered indicate past volcanic activity. Triton is as large as Pluto and tidally locked to Neptune. Triton’s retrograde orbit is slowly decaying and it will eventually bring the moon so close to the gas giant that the planet’s differential gravitational forces will rip the moon into another ring.

Gerard P. Kuiper discovered Nereid in 1949. He was regarded by many as the father of modern planetary astronomy. He postulated that planetesimals, formed at the birth of the solar system, may someday be found orbiting in the icy reaches just beyond the orbit of Neptune, but he died before they were discovered. These Kuiper Belt Objects (KBOs) have been found to orbit 30 to 55 AU from the Sun in a disk aligned with the plane of the solar system. Kuiper also introduced the idea that Pluto and short-period comets came from this region. Besides the Kuiper Belt, astronomical objects bearing his name include the Kuiper

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Airborne Observatory (named to honor the work he did with infrared spectroscopy), a minor planet, several binary stars, and craters on the Moon, Mercury, and Mars. His discoveries are credited to his extraordinary eyesight and his complete dedication and devotion, the long hours of work and the seriousness with which he approached his studies, demanding near perfection of himself and the researchers around him.

Neried has the most eccentric orbit of any moon that we’ve found in the solar system. It is almost seven times further at its greatest distance from the planet than the closest point. Triton’s capture (millions of years ago) is the likely cause of Neried’s disrupted orbit.

Proteus, Thalassa, Despina, Galatea, Larissa and Naiad were seen when Voyager 2 passed the system in 1989. From Earth, they are so close to the planet that they are hidden in the glare.

Proteus is the second largest moon of Neptune, but not completely spherical and extremely dark with only 6% of sunlight reflecting off the surface--a sharp contrast to Triton’s extremely bright surface that reflects 70%. At 5 x 109 kg, Proteus is thought to be just under the mass limit for a moon to form a spherical shape.

Larissa had originally been spotted by a team of scientists using ground-based telescopes in 1981. Harold Reitsema, William Hubbard, Larry Lebofsky, and David Tholen were looking for a ring around the planet Neptune by monitoring the luminosity of a star as the planet eclipsed it. A quick fluctuation in the brightness, a decrease of only a few seconds, indicated not a ring, but a small moon. Larissa wasn’t seen again until Voyager 2 passed by.

Stephen Synott and the Voyager 2 Team share the credit for Despina, Galatea, and Proteus, and Richard Terrile and the Voyager Imaging Team share discovery of Thalassa. One of the satellite discovery papers from Voyager 2 has fourteen authors.

Halimede, Laomedeia, and Sao were discovered in 2002 by science teams using Earth-based telescopes. Distant and tiny, they were missed by Voyager 2 and are most likely captured satellites, orbiting Neptune up to 125 times the distance from the Earth to the Moon. Halimede has a retrograde orbit. The 4-m Blanco telescope at CTIO in Chile and the 3.6-m CFH telescope on Mauna Kea in Hawaii were used. Again, the discovery papers have numerous authors.

Matthew Holman and his team found distant Neso, then lost it again and the International Astronomical Union refused to acknowledge their find. Persistence paid off and the team reestablished Neso’s position a year later in 2003. Psamathe has a similar orbit to Neso. These two moons are thought to originally come from one moon that broke apart. The 8.3-m Subaru telescope on Mauna Kea was used in this search-and-find mission by astronomers Scott S. Shepard, David C. Jewtt, and Jan Kleyna.

The discovery process has changed over the years, reflecting the way science is being done today. The solitary discoverers are all but gone. This is one of the points in Robert Park’s “Seven Warning Signs of Bogus Science,” originally written to advise federal judges, but useful for us all. He says, “The image of a lone genius who struggles in secrecy in an attic laboratory and ends up making a revolutionary breakthrough is a staple of Hollywood's science-fiction films, but it is hard to find examples in real

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life. Scientific breakthroughs nowadays are almost always syntheses of the work of many scientists.” Does this mean astronomical discoveries can no longer be made outside the large groups of astronomers with doctorates working at research institutions? Not at all. A new discovery method has arisen to make use of the raw talent and enthusiasm of ordinary people who enjoy astronomy’s universal appeal.

The key was to realize that many people wish to experience firsthand the excitement of scientific inquiry. Discovery often requires searching through vast data sets. Humanity is not yet at the stage where we can direct computers and robots to find all the answers we seek. We still need human hands to guide the search and human eyes to find the natural patterns. We have more data than we can reduce in a timely fashion and this has given rise to citizen science, programs that educate and engage people in the pursuit of the answers to the questions about the universe. There’s excitement in this kind of investigation and scientists have learned the value of sharing.

Citizen science has enjoyed enormous success, especially in astronomy. The government funds the organization of science networks to classify galactic mergers, look for new lunar features (and debris from spacecraft), track variable stars, monitor solar flares and find supernovae. Privately-funded programs extend the list to, for example, the search for extraterrestrial radio messages. Even in a city, young scientists can go outside, look at magnitudes of certain stars and report on the local light pollution levels for international efforts like the Great World-Wide Star Count and Globe at Night. New programs come online often in this international scientific community. Citizens are introduced to the background concepts via online tutorials

and then work on whatever survey experiments they find appealing for as long as they wish. Galaxy Zoo alone can boast that 150,000 citizens classified millions of galaxies from the Sloan Digital Sky Survey and users found a new class of object now known as Galaxy Zoo peas. The Zooniverse portal and Citizen Science Alliance attract visitors from all over the planet, skilled volunteers in scientific endeavors directed by scientists.

Next spring, a new citizen science project will unfold, designed to identify interesting solar system objects (new asteroids, comets, and KBOs), features on the planets (storms, meteor impacts, geysers) and potentially find new planetary satellites. Coordinated by Max Mutcher, this program will use archival images from the Hubble Space Telescope (HST), 10,000 datasets taken over the course of fifteen years. He knows very well the excitement of discovery—in 2005 he found Nix, a moon of Pluto, using this same archival data method. He will oversee nine others in the development of a web interface that allows citizen scientists access to HST archival images through the Zooniverse with specific tasks set up for the public to accomplish.

One of the team members, Dr. Alberto Conti, the NASA Multimission Archive Scientist at the Space Telescope Science Institute has shared some pictures and the procedure that is being implemented. The first step: process the data from the Hubble Wide Field Planetary Camera 2 creating a calibrated, searchable database. Uniformly-processed and well-documented, this “Planet Pipeline” will be ready for both astronomers and citizen scientists. A citizen science user may choose to explore several regions, for instance the area around a planet. The

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following image is a photograph and an overlay diagram depicting moon positions for the same date.

A user could drag the diagram over the photograph and align the visible moons. Images taken directly before and after can be compared, making obvious any movement of objects in the field. Software will be available to determine magnitude, mass, distance from planet and orbital characteristics. Artifacts in the data must be recognized, cosmic ray strikes for instance. In the following panel of photos of Saturn’s moon Rhea, ghostly images that are

visible in one frame and gone in the next are not real—they are caused by ultra-energetic, charged particles striking the camera.

Can you spot some?

As the months progress, testing of the tutorials and software will take place, first by the science team, next by experienced Zooniverse users, then with novice users, for instance visitors at science museums. Incentives are provided for citizen scientists, including possible inclusion on the author list of research papers that use their images. Can it get better than that?

What would you like to explore today?

(Click one.)

• Asteroids? • Moons? • A planet?

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Phone Call from a Turquoise Giant

by William S. Higgins

September 1989

hree billion miles is a heck of a long distance call. Even so, thousands of Earth dwellers reached out and touched Voyager 2 as it swept past Neptune

during the week of 24 August. I was lucky enough to be a part of it when the National Space Society asked me to be an announcer on "Dial-A-Planet" for the encounter.

Dial-A-Planet was a natural extension of the "Dial-A-Shuttle" service that the National Space Society ran. Every time a Shuttle mission lifted off (unless it was classified), a team of NSS announcers is ready at the Johnson Space Center in Houston to keep the phone lines hot with information. When there was space-to-ground chatter, callers could hear it live. When astronauts were asleep or busy, or the spacecraft was out of tracking range, Dial-A-Shuttle played a variety of short taped features which explained aspects of the mission or reported on its latest progress. The announcer broke in every now and then to identify Dial-A-Shuttle, plug NSS, or provide live commentary. Dial-A-Shuttle ran from STS-7 until 1994, and developed a following among space enthusiasts who relied on (900) 909-NASA for fresher information and more detail than other news media give. It made sense to try covering the Neptune encounter. But, of course, there are differences. Voyager has no "voice," so there would be no live audio coming from the spacecraft. On the other hand, we could expect much of scientific novelty to be pouring

down the data stream in the three days we planned to operate. It's the nature of a fly-by mission to report a lot in a short time, so we could provide a service by telling callers about the latest results in the "quick look" science.

I arrived early in Pasadena to attend part of the AIAA's conference on Solar System Exploration. I made it a point to attend a session which featured many of the leading theorists and observers working on planetary rings. By this time, Wednesday, 23 August, Voyager 2 had picked up two rings: a brighter one with a radius of 63,000 kilometers, and a dimmer one at 52,000 kilometers from the center of the planet.

According to the best guess the speakers could make from their ground-based telescope observations, both had been suspected of being partial, dotted-line rings or "ring arcs." Voyager was gradually showing that both rings were complete, in the sense of having material all the way around their circumference. However, ring particles were clumped, especially in the outer ring, so that as you walked along its circumference, you'd see thicker and thinner amounts of material. This accounted for the "arc" impression—at some locations in the ring, there just wasn't enough dust to block the light of a passing star as seen from Earth. This had the theorists very excited, because it's a new kind of situation in the world of ring studies. Imagine a bunch of particles (boulders, gravel, sand, or specks of dust, it doesn't matter) orbiting Neptune in a clump. Some of them are gonna be moving a little faster than others. In time they will race ahead, and the clump will no longer be a clump; particles will be stretched out along its entire length. Rings around the other outer planets look pretty continuous. The only way to maintain a clumped structure

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would be to speed up slow particles and slow down fast ones with an external force, such as the gravity of a passing moon, perhaps. It was suggestive that the orbits of two of the new little satellites Voyager had found were just inside the rings (1989 N3 at the inner, and 1989 N4 at the outer ring). The theory guys had gleefully been playing games with hypothetical moons in various peculiar orbits to try to get clumps.

But the mood in that seminar room on Wednesday afternoon was very much one of "wait and see." They knew that anything they said could be obsolete the next week. They were anxious to see the results of important Voyager experiments such as stellar occultation of the rings, radio occultation, and post-encounter images taken with the Sun behind the rings. What keeps the rings narrow? What keeps them clumped? How did they originate, and how have they evolved? Are Neptune's and Uranus's skinny dark rings a late stage of evolution, and Saturn's bright wide ones early? Or is it the other way around? The ring astronomers had no answers, or maybe too many answers, to their favorite questions. They were hoping Neptune would help them pin down the possibilities in the years to come.

Thursday morning I reported for work on Dial-A-Planet. D.A.P. was set up in a room on the Caltech's student union, where a table was piled high with multiple cassette players, mixing board, patch boxes, telephone hardware, and an intricate tangle of wires. Another pair of cassette decks sat on a nearby table for editing. A nineteen-inch TV monitor served as our window to Neptune, showing us the "NASA Select" satellite feed from JPL. We had a copy stand for our "station identification" text and a whiteboard

which got updated every hour with Voyager's speed and distance from Neptune. Peter Kappesser was the wizard who had hooked all this together, a most skilled and experienced announcer who could probably do this with his eyes closed. David Brandt of NSS headquarters, who had arranged for these facilities, had already figured out that coffee was available in the wonderful greasy-spoon-style cafeteria next door.

The rhythm of our activities was set by JPL' s video schedule. The most important event of each day would be the 10 AM press conference. Five or six scientists would present results, with a different mix of experiments each day. The exception was the imaging team, which was always represented since it cut across such a wide mix of disciplines. The rest of the day, there would be a live update once an hour which included long interviews with investigators, who could go into a little more detail and background than was possible in the press conference. These sessions were good for pulling juicy quotes to use in our taped features. The hourly "Blue Room" updates ran all night Thursday. Maybe you saw some of them if you watched the video on PBS or on satellite.I felt a bit out of my element as the only green announcer on D.A.P. Bev Freed, who also runs the NSS's bulletin board in Pittsburgh, was a great help coaching me in what to do. I started working with timelines and outlining features I wanted to try writing, with one eye on the clock. I wanted to be planted firmly in front of the TV when the press conference started.

The tape wasn't properly recording the press conference, so we had to rely on our own summaries rather than recorded quotes. I was taking notes furiously all through

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the press conference, and as soon as it was over I started scribbling out a few paragraphs of highlights copy. As I finished a page of copy, I would tear it off my pad and hand it to Pete Kappesser, who would read it in between tapes. Pretty exciting.

By Thursday morning Voyager had not yet passed the "bow shock" of the magnetosphere , somewhat to the surprise of experimenters. I was only vaguely aware of what a bow shock was, but I was about to learn. The frustrated imaging people studying Neptune's clouds were having a lot of trouble measuring wind speeds, because they couldn't find a cloud feature they were sure kept its identity from picture to picture. They were able to see shadows cast by the high white clouds on the lower blue layer, and measured their height to be about 50 kilometers above the blue haze. (Rip. Hand to Peter.) The outer ring had been photographed (well, "imaged") along 90 percent of its length now, and looked indeed like it was a complete 360-degree ring. Two new satellites (1989 N5, 90-kilometer radius, 50,000 kilometers orbital radius, and 1989 N6, 50-kilometer radius, 48,200 kilometers from Neptune's center) were announced. (Rip.) The "old" moon 1989 N1, known for a couple of weeks now, was dark, mottled, and 400 kilometers in diameter, awfully big—bigger than Nereid!-- for something that's so irregular in shape. You expect big objects to be spherical, but N1 is rather heart-shaped.(In case you're wondering, it takes a couple of years to think up names for new satellites, then get the blessing of the International Astronomical Union.) Triton (I suppose you might have called it 1846 N1) still didn't look like much, but we could see a bright pinkish area covering much of the southern hemisphere, and a darker, more bluish area further north. We knew the best was yet to come. (Rip. )

Now I could take a little time to record the summary in my own voice, so we could play it periodically through the afternoon and evening. I was pretty self-conscious on the mike, reading my copy with an exaggerated slowness and lack of feeling. Barring the odd talk show, I hadn't been on the radio for fifteen years, and I'm afraid I sounded like a somnolent classical DJ... except that DJ's have hearty masculine baritone voices, not a squeaky nasal tenor. Oh, well. Time for lunch.

After lunch I decided to tackle the problem of learning what Voyager had been up to in the days before I arrived. I knew the AIAA had a Jet Propulsion Laboratory display over in a nearby building which included a bulletin board full of Neptune images that had already been released to the press. Heading over with my clipboard, I read the captions on all the pictures carefully, making notes and sketches that might be helpful in preparing feature tapes. I also used my trusty camera to take slides of the images. A handy music stand served as an impromptu tripod. This session was especially enlightening about Neptune's atmosphere. The planet had a number of large distinct features. There was the Great Dark Spot, a football-shaped storm nearly the size of the Earth, and the white cloud that always seemed to be present near its bottom edge. There was the Lesser Dark Spot, or "D2," further south. It always seemed to have brighter clouds in its interior, and it moved around the planet faster than the GDS. There was a fast-moving white spot nicknamed "Scooter" between the latitude of the GDS and the latitude of D2. And there were always thin white cirrus clouds in a band very near the south pole. Neptune's atmosphere seemed to have blue features (GDS and D2), in which you couldn't see much detailed structure, and white features which were detailed enough, but which

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changed so fast they couldn't be used to get any wind-speed information by comparing successive pictures.

White clouds were probably made of tiny methane (CH4) crystals freezing out high in the atmospheres. Each of the major features stayed at a different latitude, but they moved from east to west at different rates, which meant that winds blew at wildly different speeds at different latitudes. The way to infer Neptune's "true" rotation rate was to look at the feeble radio waves associated with its magnetic field, since the magnetic field originates in the planet's core. The radio waves vary in strength as the gas giant revolves, with a period that turned out to be about 16 hours. Scooter moved from west to east in slightly less time, which means it's in a belt of winds blowing eastward. The Great Dark Spot, by contrast, took 18.3 hours to complete a revolution at its latitude nearer the equator. So it is actually being blown "backward" at staggering speed by westward winds.

Thursday evening was Voyager's busiest period, as its closest approach to Neptune was to occur just before 9 PM PDT. Of course, its radio signals took over four hours to cross the distance to Pasadena, so we wouldn't learn about it until 1 AM or so. It would also take several days for all the scientific measurements to come back, because lots of pictures and instrument readings were being stored on Voyager's tape recorder for playback later. Still, there was plenty to report as I worked on a Thursday evening summary. David Krebs was exhibiting iron-man behavior, having been on-mike for hours and refusing all offers of relief. But Pat Jones and Vickie Caffey were ready to take over for the midnight shift. I also managed to complete a report on rings and occultation studies that I'd been

working on intermittently all day. Voyager's photopolarimeter, a sensitive light meter, was tracking the bright star Sigma Sagittarii as it passed behind the rings. It could turn up very fine details of the rings'structure, measuring the outermost ring to be 17 kilometers in width ,with a broader low-density zone of about 50 kilometers around it. Details of the inner ring, or any undiscovered ring, would have to wait for more careful statistical analysis of the photopolarimeter's jagged data traces.

Visitors dropped in all evening, both space activists and curious Caltech denizens. The most welcome were a squad of NSS officials led by Lori Garver, because they brought pizza with them. After this spontaneous dinner and the 11 PM video update, I went back to my motel, because I knew I'd have to be fresh for the press conference the next morning.

I did stop and call Kathy Cochrane, the Planetary Society volunteer coordinator for the Chicago area. She was running "Live from Neptune," an event featuring lectures and live Voyager video at the Scitech museum back home in Naperville. I had helped line up some speakers for the affair, so I had a strong interest in how it was going. I was delighted to find that they'd gotten large crowds, and there were still fifty people hanging around even at two in the morning Naperville time. This should be a boost to the struggling new hands-on science center. I told Kathy some tales of Pasadena, then went upstairs to sleep through the closest approach.

Friday morning, back at Caltech, I began to sort through some tapes collected during the night's hourly updates. Magnetospheres and plasma science were never my

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strong point, but I began to understand what Voyager's experiments were looking for. And some of Friday's press conference dealt with such matters.

The first landmark in Neptune's magnetic environment was the bow shock, the location where the solar wind streaming through space first feels the push of the planet's field. Solar wind flow is slowed down suddenly here, dropping from supersonic to subsonic speed and becoming very turbulent. Voyager crossed the bow shock around noon Thursday, later than experimenters were expecting. This suggested a weak magnetic field equivalent to a dipole of about 0.2 gauss. The turbulence within the bow shock showed up as a drop in low-frequency radio emissions, a rapid fluctuation in magnetometer readings, and a change in the number and energy of electrons and ions striking the spacecraft. As recorded data were transmitted over the next few days, scientists expected to see Voyager's encounter with radiation belts close to the planet and to measure the tilt, if any, of its magnetic field.

Most of the excitement of Friday's press conference, however, was focused on Triton. The largest moon of Neptune, nearly the size of the Earth's Moon, was known to have a tenuous atmosphere, and to move around the planet in a perfectly circular but retrograde orbit—it goes around clockwise, rather than counterclockwise, as seen from Neptune's north pole. This behavior is almost unknown in the solar system, and suggests that something mighty strange happened to Triton in its earliest years. Maybe it collided with something and went into a crazy orbit. If so, Neptune would have generated tidal forces on Triton that could modify its orbit into the present circular one. But tidal forces would also tend to create friction and

warm Triton up. You'd expect it to be molten for a long time after the rest of the bodies in the solar system had cooled off and hardened.

Sure enough, Friday's images showed that there had once been a lot of activity on the surface of Triton. These were not the best pictures Voyager had taken—recorded color and high-resolution images would be beamed back late Saturday—but they were the first to show a lot of detail. And the detail was spectacular.

Triton's bright region turned out to be a southern polar cap that reflects about 90% of the sunlight reaching it. It covered a variety of terrain, some flat, some rough, and showed mysterious elongated streaks of darker material here and there. The ragged edges of the icecap are being eaten away as Triton enters its summer, and patches of darker surface beneath showed through.

North of the icecap was a region of rough terrain covered with many roundish depressions. These were too irregular in shape and too uniform in size to be impact craters. This zone was crisscrossed with linear features hundreds of kilometers long, probably fault lines where cracks had formed in Triton's icy crust and the material within had oozed outward. Such cracks are familiar to geologists from images of other icy moons. The dimpled surface and network of lines soon got the area dubbed "cantaloupe terrain."

Another notable feature in the mid-latitudes was the presence of "lakes." Flat, smooth, low-lying regions had probably started as depressions in the landscape, which became covered with liquid at some time when there was

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an episode of melting. The liquid material froze, becoming the smooth surfaces we were looking at. One lake—the scientists were also using the word for a frozen lava flow, "caldera"—had an impact crater right in the middle. Another caldera showed several different levels of smooth surface in a step-like arrangement, suggesting that melting, flow, and freezing had occurred on several occasions. I supposed this happened during Triton's peculiar thermal evolution, while it was warming and cooling and trying to shed its tidally-generated heat.

The atmosphere of Triton showed up in one image where a dim gray haze hovered above the edge of the moon. Some reflecting stuff was suspended above the surface, probably ice crystals or something hanging in the atmosphere. There wasn't much to say about it, but we would learn more Saturday after the results of Triton occultation measurements came out.

I noticed that the Voyager guys danced around the question of what Triton was made of. They were pretty sure that the core of the planet was small and rocky, surrounded by a thick shell of water ice. But layers near the surface were poorly understood. Lawrence Soderblom said that the crust was probably a mixture of substances, maybe methane, ammonia, and/or nitrogen, but that it would take a lot of laboratory work to determine what mixture would give an ice with soft, mushy physical properties that matched the patterns of flow and fracture in Voyager's pictures.

Pete Kapesser had two cassette recorders going during the press conference. This way he could cover any gaps in the audio from having to change tapes. Midway through, when

he'd filled his first tape, Pete slapped it into the editing deck and went to work slicing out "sound bites" from the tape and building short features around them. By the time the press conference ended, he had several tapes ready for airing.

Bev Freed knew I sounded sort of tense on-mike. "Let's try something," she said. "I'm going to interview you." I reviewed all the numbers and facts in my notes on the press conference while she plugged in an extra headset. Then we launched in. We talked about Triton. We talked about the magnetopause. It was relaxed, it was spontaneous. It was exactly like going to a scientific seminar, then coming back to my office and giving my officemate a five-minute summary. All these years I've been attending colloquia and seminars, I was really rehearsing for Dial-A-Planet and didn't realize it!

We spent most of Friday afternoon that way. JPL would do an update on the hour, and we carried the audio from that. A few tapes would play. Then the "Bev and Bill Show" would return, usually rehashing whatever was in the update. After ten minutes or so we'd play more tapes until the top of the hour, and the cycle began again. Meanwhile everybody was carving up the press conference and update tapes to make more short stories.

Leonard David, editor of Ad Astra, dropped by with photos of Triton, which I took and spread on the sidewalk outside. The sunlight gave me good illumination for my camera. Like any good tourist, I was accumulating a slide set so I could tell the folks back home all about my trip. ("I just got back from Neptune, and, boy, are my feet cold!")

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We attended the NSS fundraiser Friday evening, where Star Trek people mingled with space people in a Caltech courtyard. Gene Roddenberry, Walter Koenig, and Grace Lee Whitney met with admirers; Buzz Aldrin and Hans Mark were there; Charlie Walker and Lori Garver spoke briefly. Our hosts, the members of OASIS (the Los Angeles-area NSS chapter), were really hustling, working to keep food and drink flowing to the chattering guests. I was pleased to renew friendships with activists, artists, and engineers I'd gotten to know while organizing the Space Development Conference.

Late in the evening, just before heading back to my motel, I drove to downtown Pasadena to look in on the Students for the Exploration and Development of Space. I knew a few SEDS members from conferences, and more from their correspondence on computer nets. I ran right into Ted Kenny and a bunch of SEDS movers-and-shakers in the hotel lobby, but things were breaking up, and it turned out to be a cameo appearance for me. I needed my sleep—Saturday morning I was going to JPL!

The Jet Propulsion Laboratory, at the feet of the mountains north of Pasadena, started out as the Army's rocket-design shop in the forties, but has found its niche as the Earth's premier designer and operator of deep-space probes. It was closed to the public during the Neptune encounter. But I had a friend who had a friend. Greg Ruffa, a space industry veteran who's now at the University of Minnesota, was in town for a meeting, and we were sharing a hotel room. Greg sits on the Space Science and Astronomy Committee of the American Institute of Aeronautics and Astronautics. Several members of this committee are from JPL. Dr. Pete Mason arranged for the group to visit JPL

Saturday, and kindly allowed Greg to add me to the list. Dr. Mason is a specialist in low-temperature physics; he managed the development of the liquid-helium cryostat system that kept the Infrared Astronomy Satellite cold for a year or so.

A winding road up into the hills... a lot of cars parked on the sides of the road... a bunch of TV network trailers with satellite dishes... in the distance, a bunch of buildings with much bigger satellite dishes... Yeah, this must be the place.

We met Pete Mason in the reception area, and he got us visitors' badges with nifty color pictures of Voyager on 'em. He'd arranged for a small briefing room with monitors tuned to the NASA video. Between updates, Pete told us about the Shuttle experiment he's working on. His group is trying to measure the properties of superfluid helium in the absence of gravity.

I stepped outside the building for a bit and browsed through the souvenir tent. With so many visitors on site, the JPL giftshop had a prime opportunity to move T-shirts, jewelry, and other Voyager merchandise. Of course I stocked up. It'll be a "Voyager Christmas" among my friends and family in 1989...

When the press conference started on the TV, the small talk died down and the kibitzing scientists in our room concentrated on the show. Occasionally some graph or image would provoke an "ooh" or a "wow" from one of the committee members.

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Nereid was a washout. Voyager never got closer than four million kilometers to it, and it was in quarter-phase. The best image looked no better then a quarter Moon looks to you on an overcast night. Images of other moons looked better, though they were sketchy. 1989 N1 showed dark and light markings, flat and bumpy spots, and irregular shape. 1989 N2 could be seen in similarly vague detail in a couple of images.

There was a lot of new information on Triton, though no new images of it were presented on this day. Results from the ultraviolet spectrometer (UVS) told us something about the chemicals in Triton's atmosphere. As Voyager approached Triton, the UVS slit had been aimed at its sunlit side. It recorded definite emission lines from molecular nitrogen and ionized nitrogen.

In a second study, the UVS had been trained on a bright star, Beta Canis Majoris, looking at two different colors in the ultraviolet as Triton came between Voyager and the star. Before the eclipse, the spectrometer was staring through hard vacuum, and could see both colors pretty well. As the edge of Triton got closer to the star, the line of sight passed through the top of its atmosphere. Light from the star grew a little dimmer as some was absorbed by the mixture of gases. Gradually the line of sight moved closer and closer to Triton, where it encountered more and more atmosphere and the light intensity decreased even further. At last it crossed the opaque solid surface of Triton, and the starlight winked out completely.

Thus by the amount of starlight absorbed, scientists could tell the amount of gas in its path at any given level. Now here's the gimmick: Of the two colors the UVS was

watching, one is strongly absorbed by methane, and the other is absorbed by nitrogen. Both colors were bright at the start of the measurement. About 800 kilometers from the center of Triton, the "nitrogen" wavelength started to get dimmer; the "methane" wavelength was still pretty bright. So there was enough nitrogen in the way to block some light, but not enough methane to notice. The "nitrogen" light got steadily dimmer all the way down to the surface. Not until the line of sight reached the lower levels of the atmosphere did the "methane" light show some dimming, indicating that nearer the surface there was enough methane to do some absorbing. Comparing the absorption of the two colors tells you about the relative amount of these two gases.

On Saturday morning the UVS team was willing only to say that the atmosphere was "mostly nitrogen" with "some methane." Twenty percent? Five percent? One percent? Despite cajoling by reporters, they refused to guess. Whatever they said would probably be proved erroneous after they'd gotten a chance to do more careful analysis. They needed to untangle the pressures, variation with altitude, and light-path geometry from the data. Until then, they'd clam up. I realized that this was a good example of the "instant science" problem. The Voyager investigators had the whole world peering over their shoulders while they worked on their raw data. Imagine what your job would be like if you had to give an international press conference every morning to discuss your progress—on projects that wouldn't be complete for a year!

There were reports from the plasma science and charged-particle experiments on the Neptunian magnetosphere. Voyager had crossed the "cusp" near the magnetic poles

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and the plasma sheet at the magnetic equator, discovering in the process that the magnetic poles were tilted at some large angle to the rotational poles. "More than thirty degrees" was the best estimate so far. The field was declared to be "rather humble" compared to the magnetic fields of other planets. A radiation belt existed around Neptune, reaching no further than the orbit of Triton, but the moon's role in confining the trapped radiation was not clear. The cutoff was much broader than the size of Triton's radiation "shadow" itself, so Triton somehow does more than simply absorb radiation hitting it. But the radiation does damage the ices on the surface of Triton, probably darkening the surface and lending it color. More work for

the laboratory people who stick batches of strange frozen mixtures into particle accelerators to see what happens.

All week we had heard about "the inner ring" and "the outer ring." Bradford Smith presented a new picture that showed both clearly, but bore faint traces of a ring inside the inner ring, and a suggestion of another one between the (old) inner ring and the outer one. It was grainy and speckled from background noise, because it had been a four-minute exposure. The sun was now somewhat behind the rings, from Voyager's point of view, and forward-scattered sunlight was beginning to show up tiny dust particles.

It was well after noon by the time the press conference ended. Speeches by NASA and JPL administrators were scheduled for 1 PM, and I knew Dial-A-Planet would carry the audio from them, so I figured I had time for lunch with Greg Ruffa, Pete Mason, and the other committee

members. The JPL cafeteria was fairly crowded with guests, reporters, and employees. Carl Sagan was a few people behind me in the lunch line; I tried not to turn and stare. I did speak to Trudy Bell, of IEEE Spectrum magazine, at the salad bar to let her know I admired her science writing. With video monitors hanging everywhere, somebody said it reminded him of a sports bar. We amused ourselves speculating what an "astronomy bar" would be like. I left them to continue their tour of JPL and headed for Caltech.

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Back at the Dial-A-Planet studios, I did more editing, gradually getting better at picking good quotes out of the interview and press-conference tapes and writing introductions for them. I spent a while operating the board, too. I would play a few tapes, then read the ID's: "You're listening to Dial-A-Planet, a service of the National Space Society, coming to you from studios at the California Institute of Technology in Pasadena. Dial-A-Planet is two dollars for the first minute, and forty-five cents for each minute thereafter." It got easier with practice, and certainly was getting to be fun. Not much time remained, however, as our service was scheduled to end early Sunday morning, and no new video updates were coming from JPL.

I felt that I had learned the job fairly well, for a beginner, and would be ready to work a planetary encounter the following weekend and do a really good job. Too bad there wasn't gonna be one. Call me if there's ever a Pluto fly-by.

Lori Garver, David Brandt, and Bev Freed left for the Paramount studios. Gene Roddenberry, a member of NSS's Board of Governors, had arranged for a fundraising dinner on the Star Trek set. Personally, I'd be nervous about spilling something. But those 23rd-century computers look like you could just hose 'em off and they'd be as good as new. I gather the event went well, and everybody got to sit in Captain Picard's chair.

Sunday morning Greg Ruffa and I got up and headed for Planetfest in downtown Pasadena, arriving in time to catch the morning press conference on video monitors there. (I was no longer obligated to do this, since Dial-A-Planet had shut down, but by this time I was thoroughly hooked.)

There were problems with the video signal that gave us green scientists showing us red-and-green pictures of Neptune. I noticed an American flag next to JPL's podium that seemed to have green and white stripes. I guess it reminded us that we were dealing with a completely alien world.

Final word on the magnetic field was that it's really cranked over, tilted "minus fifty degrees." This means that the magnetic axis is tilted fifty degrees to the spin axis, but it's also upside down. On Neptune, a compass needle would point south. Not toward the south pole, either, but more toward someplace like the Falkland Islands or Hobart, Tasmania.

Studies of the atmosphere by several instruments took up much of the briefing. Infrared and ultraviolet filter scans by the photopolarimeter, images of clouds from the TV system, and detailed temperature measurements from the infrared spectrometer were the pieces of the puzzle.

Neptune's air (at least at the top of the atmosphere, where we could see it) is warm near the equator, warm near the poles, and cool in the middle latitudes. This is similar to the situation at Uranus. Wind shear was peculiar, too. Near Neptune's equator, wind at lower levels of the atmosphere blows more slowly than at higher levels. But near its poles, low levels were faster than high ones! Near 45 degrees south latitudes, wind speed didn't change much with level at all—there was a chance that this region might be a window into the deeper levels of the planet's atmosphere.

My head began to spin as a third dimension was added: east-to-west wind speeds. At different latitudes, the air we

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can see travels at radically different speeds. The Great Dark Spot moves westward at 325 meters per second, but further south, the Lesser Dark Spot (D2) moves eastward at 20 meters per second. So latitude, depth, velocity, and temperature are all going to go into models of the atmospheric dynamics which will keep gas-giant specialists busy for decades to come.

The third, innermost ring announced Saturday popped out nicely Sunday in a pair of images showing all three major rings at a vary large sun angle. The "fourth ring" of Saturday now appeared to be a broad, dim disk of dust bounded on the inside by the second-outermost ring and on the outside by an invisible circle halfway to the outermost ring.

Once I had soaked up the press conference, I felt ready to tackle Planetfest. The Planetary Society had taken over a convention center and was staging lectures, movies, and demonstrations hither and yon. The exhibit area seemed the best place to spend the limited time we had. I collected a few more souvenirs in the huckster area.

Some of the PlanSoc merchandise was overpriced, but their Voyager frisbee was a good buy. Kim Poor's company was doing a brisk business in astronomical art prints, and dealers in books, patches and pins seemed happy.

JPL and NASA had supplied a lot of planetary-exploration displays, along with people to stand in front of them. I quickly discovered that these were mostly not PR people, but JPL scientists and engineers who'd volunteered to explain things. This was delightful, as it gave Greg and me a chance to ask fairly technical questions. I met a comet-

probe navigator, a Martian volcano lady, and a Jupiter propulsion guy, and picked up some valuable tips on getting information about JPL probes in the future.

Somehow we tore ourselves away from the posters, the models, the robots, and all the fun, and Greg drove me to the airport. Voyager 2 was millions of miles from Neptune. Its next goal—the heliopause, where the solar wind bangs into the interstellar wind—was billions of miles away. I felt a bit sorry for the little robot, sailing into the loneliness of the void, never to see a human face again.

On the other hand, it was better than being stuck in Los Angeles traffic.

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Unlocking Neptune’s Secrets with the Hubble Space Telescope

Christian Ready

Waiting in the darkness

n the night of August 25, 1989, I was in the observatory at Villanova University waiting for something remarkable to happen. The 15-inch

telescope was pointed at an eclipsing binary star in the northern sky. Over the course of the evening, the two stars would complete an orbit around a common center of gravity.

This wasn’t the remarkable bit; we observed eclipsing binaries all the time.

On this night, Voyager 2 was making its closest approach to Neptune. As images were sent back from Voyager 2 to NASA’s Jet Propulsion Laboratory in Pasadena, California they were broadcast in real-time across the country from PBS affiliate WHYY in Philadelphia. As an undergraduate astronomy major—and Philly-area native—I was especially excited to watch “Neptune all Night” live on PBS. I set up a television in the observatory, turned the brightness down to its lowest level, and watched the raw, unprocessed images of an alien world appear on TV.

Throughout the night, I would gaze just above the “teapot” in the constellation Sagittarius, in the direction of Neptune. I imagined the tiny Voyager 2 spacecraft racing above the methane cloudtops, taking images that would arrive at Earth four hours hence.

The rest, of course, is history. Voyager 2 revealed a planet far different from the cold, dormant world anticipated by scientists. Despite receiving 97% less sunlight than Jupiter, Neptune was alive with 900-mile-per-hour winds, billowing clouds of methane and acetylene in the -260F cloud tops, and an earth-sized anticyclone south of its equator dubbed the “Great Dark Spot.” Despite being way out in the boondocks of the solar system, Neptune was a very active planet!

A few hours later it was over. Voyager 2 continued past Neptune, taking images and measurements of the planet, its rings, and its moons as they all shrank into the background. Voyager 2 sped on into the night, destined to eventually leave the solar system and travel among the stars.

Planetary scientists wanted to know more about Neptune, and Voyager had sent back a great deal of data to be analyzed. But no new missions to Neptune were planned. Fortunately, the Hubble Space Telescope would launch the following year, offering a new opportunity to study Neptune with a clarity unattainable by any ground-based telescope.

At some 5,000 times farther away than Voyager 2 at its closest approach, Hubble would not reveal Neptune at the same level of detail. But Hubble had two key advantages over Voyager 2. First, it had better ultraviolet and infrared capabilities. Second, Hubble could study Neptune over a long period of time, watching the planet change over the next two decades.

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Early HST observations

Hubble was used to study Neptune in 1991. Even with the flaw in its primary mirror, Hubble still delivered images that were superior to any telescope on the ground. Individual cloud features could be identified and tracked as they moved within the planet’s atmosphere. The Great Dark Spot was not detected, but it wasn’t clear if this was due to Hubble’s myopic vision or if the storm itself had dissipated. There was, however, a telltale clue: During the Voyager 2 encounter, a bright cloud complex was clearly seen in the outer regions of the Great Dark Spot. By the time of Hubble’s first observations in 1991, the bright clouds were not seen. Other bright clouds were detected, but none at the same latitude as the Great Dark Spot. If its companion clouds were missing, perhaps the Great Dark Spot itself had disappeared as well?

1991 HST Observations, taken prior to the first servicing mission that would correct its optics. Bright cloud features similar to those found by Voyager 2 were tracked, but none near the same latitude as the Great Dark Spot, an early indicator that it had probably dissipated the previous year. Images taken by the Wide Field / Planetary Camera (WFPC) using red filters (F899N). Image credit: J. Westphal, NASA

Otherwise, Neptune seemed largely unchanged when viewed two years after Voyager. Cloud patterns were generally similar, and the winds were still blowing at

roughly the same speed. The only thing different was that an Earth-sized dark spot had apparently gone missing.

A new second look

In December 1993, Hubble received its first servicing mission, bringing its vision into focus. A new primary camera—the Wide Field and Planetary Camera 2 (WFPC2) —contained internal corrective mirrors and replaced WFPC1. An additional instrument, the Corrective Optics Space Telescope Axial Replacement (COSTAR) replaced one of Hubble’s instruments to restore focus to the three remaining scientific instruments. Hubble was back in business—and this time, with prescription mirrors.

The following June, Hubble was turned back to Neptune. A prominent band of clouds at 30 degrees north latitude was spotted encircling the planet, while new clouds and prominent features were detected at southern latitudes.

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Now you see them, now you don’t. Above: Voyager 2 captured the Great Dark Spot (GDS) and a smaller, southern dark spot (DS2) during its fly-by in 1989. Below: The first HST images of Neptune after the first servicing mission that restored Hubble’s focus shows neither dark spot, despite observing Neptune during a full 16-hour rotation.

But the new observations confirmed what was long suspected: The Great Dark Spot had disappeared! Not only that, but a second, smaller dark spot in the south that had also been spotted by Voyager 2 was missing as well.

A new Great Dark Spot emerges

The surprises from Neptune were just beginning. On October 10, October 18, and November 2, 1994, Dr. Heidi Hammel used Hubble to observe a series of large-scale weather changes in Neptune’s upper atmosphere. New formations of clouds would form and dissipate over just a few days.

Neptune’s clouds as seen on October 10 (upper le)), October 18 (lower center), and November 2 (upper right), 1994. The images are a combination of images taken at visible and near-infrared wavelengths. Credit: NASA

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But the most interesting surprise was just emerging in the northern limb, where a new dark spot had formed.

Located at 32 degrees North latitude, this new feature was designated the Northern Great Dark Spot. Because Neptune’s northern hemisphere was tilted away from Earth, this new spot was seen at an oblique angle. Nevertheless, the new spot appeared to have commonalities with its predecessor: They had similar shape and size, and featured high-altitude methane clouds, with winds reaching 1,500 miles per hour.

A new dark spot at 30 degree’s latitude in Neptune’s northern hemisphere. With its northern hemisphere tilted away from Earth, the spot was observed at an oblique angle. Credit: NASA

Like its predecessor, the new northern spot was also something of a mystery: Would this new storm dissipate soon, or would it remain for several more years? What is the mechanism that generates these storms, and once formed, how long do they last?

1996: Dark spots abound

A team of astronomers led by Dr. Lawrence Sromovsky used Hubble to study Neptune in even further detail in March and again in August of 1996.

When Hubble is used to take an image or spectrum of an object, it doesn’t take it in full color. Instead, filters are used to only observe objects in a single “color” of the spectrum. This allows astronomers to examine chemical features that are detectable at those specific colors. Combining them builds a composite-color image that reveals more details than would be seen all at once, without filters.

Neptune in 1996, taken over the course of a full rotation. High-altitude clouds appear white, while the dark blue band along the equatorial region is formed by Neptune’s equatorial jet, where winds reach 900 mph. The green band in the south represents a region of mid-altitude clouds where the atmosphere absorbs blue light. The green band itself, then, would appear as a dark-blue band to the naked eye. Credit: L. Sromovsky, NASA

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The observations captured Neptune over the course of a full 16-hour rotation, allowing the team to track cloud and weather formations over a single Neptunian day.

In many ways, the weather on Neptune was largely unchanged from the previous Hubble observations. Higher-altitude clouds appeared in white, while the highest of its cloud tops appeared in yellow.

The new dark spot discovered by Dr. Hammel in 1994 was still detected, but by 1996 a

bright companion had become noticeably brighter. But the best was yet to come: Hubble had detected a new third dark spot!

The Northern Great Dark Spot, discovered by Hammel, et al in 1994 at 32 degrees North latitude (designated NGDS-32). By 1996, NGDS-32’s companion clouds had brightened, and a new spot was discovered at 15 degrees North latitude (NGDS-15). The two spots were at different longitudes, and aren’t visible in the same hemisphere. HST images taken in blue filters by Hammel (1994) and Sromovsky (1996). Credit: NASA. Images adapted from Sromovsky.

This third dark spot, located at 15 degrees North Latitude, was designated NGDS-15. But this new spot was different in that there were no bright companion clouds associated with it. In the Voyager images, bright clouds were clearly

seen with the Great Dark Spot, especially in Voyager 2’s orange filter. Likewise, Hubble’s images of NGDS-32 revealed bright companion clouds as well, when viewed in red filters. But no such clouds would appear near NGDS-15.

Above: The Great Dark Spot (GDS) as seen by Voyager 2 in clear (top left) and in orange (top center) filters. Bright companion clouds are visible near GDS. In the Hubble images of NGDS-32, the spot is clearly seen in blue (bottom left) and its companion clouds show up in red filter (bottom center) By contrast, NGDS-15 (bottom right) doesn’t seem to have any bright companion clouds. Voyager images showing Neptune at a similar inclination as Neptune appeared during the HST observations were selected for comparison purposes, as indicated upper right.

To see this a little more clearly, Sromovsky’s team created two projection “maps” of Neptune. This is the same

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technique cartographers use to create a rectangular map of Earth.

The first projection shows Neptune as seen through a blue filter, where the spots show up the best. The second projection is a false-color image that combines the blue images with red and near-infrared filters, recast as green and red colors, respectively. The result is an image that ”compresses” what would otherwise be a wavelength range of colors too broad for the human eye to (completely) detect into a range that can be clearly studied.

Since bright companion clouds preferentially reflect more light at these redder wavelengths, they should be visible if they exist. However, the only cloud companion that appears is the one associated with NGDS-32. NGDS-15 didn’t seem to have any companions at all.

Above: Both dark spots are clearly seen in blue filter. The filter used is designated F467M, which is a medium-bandpass filter centered at 467 nanometers, the wavelength of blue(ish) light. A composite-color image combining HST blue (F467M), red (F673N ) (represented in green color), and near-infrared (FQCH4-890nm) (represented in red color) clearly shows a bright companion for NGDS-32, but none for NGDS-15. The green band in the south isn’t really green, but

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represents a region where the atmosphere absorbs blue light. Likewise, the yellow-colored clouds at NGDS-32 aren’t truly yellow, but there is something about them that is different from the other bright clouds that appear white. Credit: L. Sromovsky, NASA

So, dark spots on Neptune seem to come and go, sometimes with bright companion clouds, sometimes without. Elsewhere on the planet, bright clouds form and dissipate. The question, of course, was why?

1998: A little brighter

During the 1998 observations, neither dark spot was detected, although strangely, NGDS-32’s bright companion remained. At the same time, however, Neptune appeared to be increasing its cloud formations.

Keep in mind, Neptune is 50% farther away than Uranus and receives 60% less sunlight. And yet, rather than a cold, barren world, Neptune appeared to not only be churning with clouds and storms, but appeared to be getting even more active.

The mechanism driving Neptune’s weather is its warm interior, which radiates more than 2½ times as much energy as it receives from the Sun. The internal “machine” is very efficient, capable of driving the fastest winds found anywhere in the solar system. But was this buildup of cloud

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formations a temporary phenomenon, or would more follow?

2002: Neptune’s spring awakening

Like Earth, Neptune undergoes seasonal changes as it orbits the Sun. But with a 165-year-long orbit, each season can last over four decades.

By 2002, as Neptune was approaching its equinox, significant changes were noticed in its atmosphere. The entire planet continued to brighten, especially in its southern hemisphere. Hubble was witnessing the coming of a new season on Neptune for the first time.

To put the brightening in perspective, Sromovsky’s team combined several images of Neptune as it completed a full rotation in 1996, 1998, and 2002. The results clearly show how bright Neptune had become in just a few years.

HST images of Neptune during a full rotational period in 1996, 1998, and 2002. In the far right column, the images were averaged together and smoothed to reveal the average brightness pattern of the atmosphere. Credit L. Sromovsky, NASA

Neptune’s clouds and bands were clearly getting wider and brighter. It seems reasonable to assume that this is due to the coming springtime on Neptune. But are these changes truly seasonal, or are they the result of some other phenomenon, such as an increase in its internal heat source? Or both? The truth is, we don’t yet know, and more observations are needed.

So much universe, so little time

Every year, astronomers are invited to submit proposals to the Hubble Space Telescope. The good news is that there are plenty of interesting things in the universe that Hubble is suited to look at, but the bad news is that there is only one Hubble Space Telescope. As Hubble became more

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capable after each servicing mission, competition for its precious observing time grew more intense.

Snapshots of the South Polar Feature

Catching Neptune over a full 16-18-hour rotation was quickly becoming less and less likely. Fortunately, astronomers Kathy Rages, Heidi Hammel, and G. W. Lockwood were able to take advantage of a new observing technique, called the Snapshot program.

Snapshots are brief observations, usually lasting 30 minutes or less, that are slipped into any gaps in Hubble’s schedule. If the target is visible, and Hubble doesn’t have anything else it can do at the moment, a snapshot observation could be taken. Such observing programs aren’t ideal, but Rages and her team managed to get a series of interesting observations this way.

In the last week of June 2001, a bright cloud feature called the South Polar Feature (SPF) made a chance appearance during the Snapshot program. The SPF is a region located 70 degrees south latitude where bright clouds can suddenly form. In fact, these clouds are so bright they can be the single brightest feature of Neptune at any given time.

A bright cloud formation called the South Polar Feature (SPF), captured by HST in 2001. The bright cloud formation appeared

quickly, then gradually faded. The SPF was on the far side of the planet in the first image in the sequence, then captured while in view in the subsequent images. Credit K. Rages, H. Hammel, G.W. Lockwood, NASA.

Over the course of 36 hours, the SPF feature quickly appeared, then gradually faded. In a stroke of luck, Hubble captured the first South Polar Feature appearance since the Voyager encounter.

One of the strange things about the SPF is that it’s always there, or at least, certainly has been since Voyager 2’s encounter. Other features such as dark spots come and go and are seen at different locations on the planet, but the SPF is always at the same southern latitude. Occasionally bright cloud complexes form there—sometimes very bright clouds. But the exact nature of the SPF remains something of a mystery.

There is nothing quite like the SPF anywhere else on Neptune, but fundamental questions remain. What is the SPF? How long has it been there? How long will it last? Only time, and future telescopes, will tell.

False vs. natural colors: more than meets the eye

Most of Hubble’s images of Neptune are taken with individual filters that isolate features of the atmosphere. Combining these images rarely yields a true color image, but rather one that allows scientists to study the composition and distribution of features in Neptune’s atmosphere. Careful examination of these features yields insight into their nature such as their composition, wind speed, and altitudes.

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In August 2003, however, Erich Karkoschka and his team used Hubble’s Space Telescope Imaging Spectrograph (STIS) to take images of Neptune in natural and near-infrared colors alike.

Neptune as seen in natural (left) and enhanced colors (right). Space Telescope Imaging Spectrograph (STIS) images of Neptune were chosen to present an image very close to what the unaided eye would see. Features such as the light haze in the lower le) or the dark-blue band at the south are much more easily viewed in enhanced colors and near-infrared wavelengths (right). Credit: E. Karkoschka, NASA

The natural color image was created with filters chosen such that when combined, produce an image that appears very close to what the human eye can see. The planet appears in its familiar ice blue color, but details are difficult to discern.

Neptune’s blue color is due to the abundance of methane in its atmosphere. Methane absorbs red light, so sunlight reflected back into space is “stripped” of its red component. Thus, Neptune appears blue in color to the eye.

But when viewed at red and near-infrared colors, some features stand out as orange/red “bright” spots, because there are clouds present that reflect these colors back into space.

Karkoschka and his team used Hubble’s Advanced Camera for Surveys to produce a similar set of images of Uranus. Comparing both sets reveals remarkable differences between the two ice giants that would otherwise go unnoticed by the unaided eye.

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In natural colors, Uranus and Neptune appear to be largely similar in nature to one another. It is only at enhanced colors and near-infrared wavelengths can the differences between the two worlds be readily seen.

Uranus’s rotational axis is tilted nearly 90 degrees to Neptune’s axis. Both worlds have bands of clouds and haze that run parallel to their equators, but Uranus’s bands are much more distinguished than Neptune’s.

In space, Hubble is able to view these planets at wavelengths that are otherwise not detected from within Earth’s atmosphere. Two planets that otherwise appear to be similar in nature turn out to be very different worlds indeed.

A two-decade glimpse

With seasons lasting as long as four decades, Neptune’s springtime will last far beyond the expected lifetime of the Hubble Space Telescope. Springtime on Neptune will last at least another two more decades, followed by another 120+ years of Neptune’s Summer, Autumn, and Winter.

The positions and orbits of the outer planets in 1993 and present day are superimposed in this representation. The position of Neptune as seen from 1993 through the present day is highlighted. The positions of Voyager2 in 1993 and 2011 are shown at lower right.

Hubble yielded tremendous insight into a world that was little understood just 23 years ago. An ice giant assumed to

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be cold and featureless was instead a world rife with rapidly changing clouds and the solar system’s most extreme weather.

Understanding Neptune better will require more observations over a long time. A very long time. Today, Hubble continues to perform well. With the completion of its last servicing mission in 2009, Hubble is at the pinnacle of its capabilities.

And yet, Hubble’s days are numbered. As a result, astronomers are clamoring for observing time like never before; each year, for every proposal accepted, more than ten are rejected. With a whole universe to explore, and precious few years remaining, Hubble may not observe Neptune again for quite some time, if ever.

Hubble’s Legacies

When launched, the James Webb Space Telescope (JWST), will be the largest, most powerful telescope ever launched into space. Like Hubble, James Webb will rewrite astronomy textbooks as it peers deep into the farthest regions of the universe and, closer to home, our own solar system.

Unlike Hubble, James Webb will be an infrared telescope, detecting the heat signature of objects. Back on Earth, the largest ground-based telescopes with advanced technologies such as adaptive optics are beginning to compete with Hubble at longer, redder wavelengths.

However, JWST will be able to help us understand more about Neptune’s upper atmosphere, which is best observed at infrared wavelengths. At the moment, there is very little known about Neptune’s upper atmosphere, and JWST will offer new insights into this still very mysterious planet.

But no telescope can—or is planned to—match Hubble in its blue-light capabilities. And that’s a shame, because features like the Great Dark Spots are best detected at these shorter, bluer wavelengths. Once Hubble’s mission is complete, it will be a very long time before these features of Neptune can ever be studied in detail again.

Acknowledgements

I am deeply indebted to Dr. Heidi Hammel of the Space Science Institute, Dr. Larry Srmovosky of the University of Wisconsin - Madison Space Science and Engineering Center, and Dr. Kathy Rages of the SETI Institute for their

generous assistance. Their stories, clarifications, and corrections are greatly appreciated.

Special thanks to Ms. Jeri Smith-Ready and Mr. Robert Staeger for their helpful suggestions, copy editing, and helping me sound coherent.

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Neptune’s First Birthday

An interview with Dr. Heidi Hammel, conducted by Br. Guy Consolmagno SJ

lanet Neptune was discovered on September 23, 1846, by the Berlin Observatory astronomers Johann Galle and Heinrich D’Arrest. They had famously been

informed by the French astronomer Urbain Le Verrier that calculations of the perturbations in the orbit of Uranus suggested a planet could be found in a particular spot of the sky; when Galle and D’Arrest pointed their telescope at that spot, they found the planet, first try out. (John Couch Adams in Cambridge had made similar calculations, but couldn’t find any observer to listen to him and take a look.)

Once Neptune was found, people started looking at earlier observations when it should have been visible and discovered that it had actually been seen, but not recognized as a planet, by Jérôme Lalande in 1795 and John Herschel (son of the discoverer of Uranus) in 1835. In fact, one observation of Jupiter and its moons made by Galileo in 1613 also includes a star that is now thought to be Neptune!

With all these observations, it was quite easy to trace out the orbit of Neptune and calculate its period to be 164.79 years, or 60,190 days. On July 12, 2011, exactly 60,190 days will have passed since Neptune was discovered. Thus on that night it celebrates its first Neptune-year since it was recognized by fellow dwellers in its solar system.

But what’s happening today with Neptune? Who better to ask than the world’s leading expert on the planet, Heidi Hammel.

Dr. Hammel achieved world-wide fame in 1994 as the lead scientist on the team using the Hubble Space Telescope to observe the impact of Comet Shoemaker-Levy into Jupiter. Her images not only were published in newspapers and television world-wide, her gracious presence and clear explanations to the reporters made her an instant media star… one that was recognized by the world’s largest association of planetary astronomers, the Division for Planetary Sciences of the American Astronomical Society, who awarded her the Sagan Medal in 2002 for her contributions to the public understanding and enthusiasm for planetary science. She even was the subject of a biography, Beyond Jupiter, by Fred Bortz, written to inspire school children (especially girls aged 9-12) to consider a career in science.

After graduating from MIT in 1982, she went to the University of Hawaii where she earned her PhD in physics and astronomy in 1988. After that she worked at the Jet Propulsion Laboratory and MIT. In 2005 she joined the board of directors of The Planetary Society. Now a senior research scientist with the Space Science Institute, her work concentrates on observing and understanding the outer planets. She has been an author on more than 300 papers, going back to her undergraduate days at MIT.

It was at MIT when I first met Heidi, while she was a student and I was a research post-doctoral fellow. But it wasn’t in the planetary sciences department where we crossed paths… in fact, I was also trying out a future career by appearing in the MIT Musical Theatre Guild’s production of Fiddler on the Roof. While I was on stage as the Rabbi (blame my beard!) Heidi was in the orchestra pit, playing the drums.

P

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We’ve stayed in touch over the years, meeting up at various scientific meetings around the world. This conversation occurred via Skype from my office in the Vatican Observatory south of Rome, and her home in Connecticut.

Were you aware that this is the first anniversary of the discovery of Neptune—in Neptune years?

If I had not been aware, then the number of calls from reporters would have alerted me, because you are not the only one to call me! Sometime this week I will also be talking to the BBC, and I have some other emails awaiting in my in-box.

I am happy that you have actually responded to me, then! This is what happens when you’re the world’s leading expert on a planet.

I guess so! [Laughs] One of them, anyway.

What’s hot in Neptune? By that, I mean, not only what are the big mysteries, but it seems that in your most recent work you’ve doing a lot talking about hot spots in Neptune. What’s that all about?

We’re able to do thermal imaging of Neptune now, because we finally have big enough telescopes and big enough detectors that are arrays instead of single channel bolometers. Now we can do infrared imaging, and with the large telescopes we have enough spatial resolution to

actually map out where some of the heat is coming from on the planet.

What are some of the telescopes that you are using?

Gemini [a pair of 8.1 meter telescopes in Hawaii and Chile], and the VLT [the Very Large Telescope array, a set of four 8.2 meter telescopes in Chile]. Glenn Orton is really the expert on this… he’s been doing the VLT work, and I have been doing some of the Gemini work.

What we see is that down on the south pole of Neptune is a very bright spot, and we really don’t know much about the details of that or why it’s there. But it’s quite evident in the imaging that there’s this tightly confined spot...

We first thought it was the pole itself. When we look in the near-infrared images from Keck -- which are reflected light, not thermal emission -- there is a very tiny confined spot at the south pole. So when we got our thermal images (which don’t have as much resolution) with a bright polar spot, we initially that maybe that was the pole itself. But in some of the images, the spot seems to shift around, as if it is something that is close to the pole but not quite at the pole. But we’re not really sure, we don’t have enough data.

So it’s a mystery. Why is there a bright polar spot there? What’s causing it and why should it be moving? It’s very hard to answer these questions with the limited data that we have.

Why does it matter?

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The specific question of whether Neptune has a hot spot on its pole or not is really arcana that only people like me or Glenn Orton care about.

The broader question is really, what drives atmospheric circulation on a planet that gives rise to that structure? We don’t have a good explanation for that yet. What drives atmospheric circulation on any planet? It’s a complex interplay of the sunlight falling on the planet, with whatever heat might be generated within a planet, along with (in the case of Earth and Venus and Mars) the surface interactions with the atmosphere.

So to have a planet that is doing something that you can’t explain yet, really points to knowledge that still needs to be understood about atmospheric circulation, something we don’t really have in our arsenal yet. We don’t understand planetary atmospheres well enough to really explain this yet. If you don’t understand the physics and chemistry of what’s going on there, why not?

And to me, that’s important. We certainly care about the planetary atmosphere in which we live and are enveloped!

Is there anything else going on in Neptune that’s really interesting right now?

The thing about Neptune is that, every time we look at it, it looks different, and we don’t have a clue why. You know, when Voyager flew by, it had the big dark spot. OK… so planets have big spots. Jupiter has this big red spot, it’s been there for 400 years. Neptune has a big dark spot, right? Except… five years later, that big dark spot was gone.

I remember the day it disappeared. Tim Dowling, who does modeling of planetary circulation, came up to me and said, “I am so excited, I can finally make the great dark spot on Neptune!” And I said, “I’ve got bad news for you, buddy… it’s not there anymore.” And he looked absolutely crestfallen.

It’s easy to make spots. It’s not easy to make them go away. And there’s no good explanation for that yet.

It’s also not easy to make them drift around, and in fact Neptune’s great dark spots do that. They drift around, they come, they go, it’s just… they’re very complex and there’s very little understanding at this point of what drives that complexity.

Neptune right now is one of those planets where, the more you look, the more confused you get. I am sure at some point the confusion will give way to solutions. But we’re very much still in the confused stage.

When I was young, we learned about rocky planets and gas giant planets. Somewhere along the line that got shifted to rocky planets, gas giants, and ice giants. What was the logic behind that?

What happened is, people actually started to learn something about Uranus and Neptune!

When you and I went to MIT, there had never been a fly-by of these planets, we didn’t have modern telescopes, so we just assumed that they were smaller versions of Jupiter and Saturn.

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Well, guess what -- they’re not. Their chemistry is quite different, their internal structure is quite different, the dynamics in their atmospheres is quite different, and so basically it became not sensible to call them gas giants; because they’re not.

They have thick mantles of briny fluid; water, we believe. There’s an outer envelope of hydrogen and helium; but the bulk composition, the main components that these planets are made of, is not hydrogen and helium. Not like Jupiter or Saturn. They aren’t gas balls.

Now, if you talk to Fran Bagenal [a fellow planetary scientist who was a student at MIT while Heidi and I were there], she’ll give you a big earful about how it’s wrong to call them ice giants, because it’s not ice really. And she’s right. It’s liquids, they’re water balls. But then, if you talk about water balls, people get all confused, because they think that then you’re talking about oceans, and it really isn’t oceans unless you consider oceans under very, very high pressures, once you’re down deep inside these planets.

The bottom line is that we’ve learned enough to actually distinguish this class of planets from the gas giant class.

What's your opinion of the model developed by a team of celestial mechanics experts in Nice, commonly called the Nice Model, that suggests Neptune and Uranus were formed much closer to the Sun, and that in planetary migration Neptune moved from being inside, to being outside, the orbit of Uranus?

I think it’s a really cool idea! What a neat concept! It explains a lot of what we see in planetary science. It

explains the whole idea of this late heavy bombardment where all of a sudden everything was stirred up and that’s why we have a whole bunch of delivery of volatiles to the inner part of the solar system. That’s where all the water in the inner solar system came from, this period of time where these two planets were swapped around and stirred things up a lot. So you could say that Uranus and Neptune, and Neptune in particular, is responsible for life on Earth!

Is there a visible chemical difference between Uranus and Neptune (beyond the different states of their upper atmospheres that might be attributed to their relative distances from the Sun) that could test this theory one way or another?

That’s one reason we want to send probes into these atmospheres. There’s really nothing you can tell by just looking at them remotely. You need to do in-situ measurements of things that don’t chemically react to understand the isotopic abundances. The stuff that chemically reacts -- basically everything you see -- that stuff is not going to tell you about primordial conditions. What you need is the isotopes of things that don’t chemically react. I’m talking about noble gases, like xenon and neon. But because they don’t chemically react, you can’t see any chemical signature of them, remotely. So you need to have an in-situ measurement. That’s why we want to send a probe into one of these ice giants.

For the kind of chemistry that we’re talking about, you absolutely need to have a gas-chromatograph mass spectrometer in the planet’s atmosphere itself. You need a probe like the Galileo probe.

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What are the odds we’ll be able to do that in the near future?

The most recent Decadal Survey [a regular ten-year survey of planetary scientists to set priorities for future research; the latest came out just this past year] looked closely at the issue of exploring ice giants and identified ice giant in-situ measurements as a very high priority.

They did also talk about an in-situ measurement of Saturn as well. We’ve measured Jupiter with the Galileo probe [launched from the Galileo orbiter, it plunged into Jupiter’s atmosphere in 1995], and we’d like to measure Saturn next because we have so much remote information with the Cassini spacecraft. However, the next priority after that is an ice giant, Uranus or Neptune.

Now, if you’re going to go to all the effort to get out to an ice giant -- and it’s not easy, it takes a lot of effort -- if you’re going to go to all that effort, would you want to do it as a fly-by like Voyager did, or would you want to actually try to do an orbiter where you can go into orbit, study the atmosphere for longer than a couple of days, and study the rings and the moons and all that? The feeling of the Decadal Survey is that an orbiter is really preferred over a fly-by.

So which is more feasible to do in the next decade? There is an opportunity to do a Uranus orbiter in the next decade, it’s not technologically feasible to do a Neptune fly-by. Basically, to go into orbit around Neptune, you’d need aero-capture technology that we don’t have right now. And so, it would have to be developed, and it’s just not feasible to do that in the next decade.

So at this point, the planetary community has recommended that a Uranus mission have a higher priority than a Neptune mission. But, that said, the planetary community has a lot of very clever people, and a lot of those clever people are very interested in Neptune. So I wouldn’t rule anything out. [Laughs]

What does Neptune tell us about exoplanets?

Many of the exoplanets that we are finding are Neptune-sized bodies. So Neptune is even more relevant in today’s world of 1200 exoplanet candidates. Neptune itself represents a class of planets that we have not fully explored in our solar system. And so it is just out there waiting to have its secrets unveiled.

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Mike Brotherton is the author of the science fiction novels Star Dragon (2003) and Spider Star (2008), both from Tor books. He’s also a professor of astronomy at the University of Wyoming and investigates active galaxies using the Hubble Space Telescope and nearly every observatory that will give him time on their facilities. He is the founder of the NASA and National Science Foundation funded Launch Pad Astronomy Workshop for Writers, which brings a dozen award-winning professional writers to Wyoming every summer. He blogs about science and science fiction at http://www.mikebrotherton.com.

Michael A. Burstein graduated from Harvard College with a degree in Physics, and in 1993 he earned a Master's in Physics from Boston University. The following year, he attended the Clarion Science Fiction and Fantasy Writer's Workshop. Burstein's first published story, "TeleAbsence," which appeared in the July 1995 issue of Analog, was nominated for the Hugo. Burstein won the John W. Campbell Award for Best New Writer at LoneStarCon2. He is the founder and president of the Society for the Preservation of Pluto as a Planet.

Br. Guy Consolmagno SJ is staff astronomer and curator of meteorites at the Vatican Observatory, located in the Pope’s summer gardens outside of Rome.

Marianne Dyson was one of the first women flight controllers for NASA and is an award-winning author of children’s books and science and science fiction stories for adults (now available on Kindle). Her first book, Space Station Science: Life in Freefall (Scholastic, 1999, 2nd ed Windward, 2004), won the Golden Kite award from the Society of Children’s Book Writers and Illustrators. Her third book, Home on the Moon: Living on a Space Frontier

(National Geographic, 2003), won the American Institute of Physics Science Writing award. She has a degree in physics and a second degree black belt in Kuk Sool. Contact her through http://www.mdyson.com or via Facebook or Twitter.

Bill Higgins enjoys speaking and writing about spaceflight, science, technology, and history. He works as a radiation safety physicist at Fermilab, near Chicago. He is a volunteer in NASA's Solar System Ambassador program, and has also been active with the National Space Society for over 25 years. His blog, "Eponymously Yours, W. Skeffington Higgins," may be found at http://beamjockey.livejournal.com.

Chris McKitterick’s short work has appeared in Analog, Artemis, Captain Proton, Extrapolation, Mythic Circle, Ruins: Extraterrestrial, Sentinels: In Honor of Arthur C. Clarke, Synergy SF, Tomorrow SF, Visual Journeys, and elsewhere, and he was honored to edit the special science fiction issue of World Literature Today. Chris recently finished a far-future novel, Empire Ship, and his debut novel, Transcendence, just appeared from Hadley Rille Books. He is Director of the Center for the Study of Science Fiction (sfcenter.ku.edu) and lives in Lawrence, Kansas, where he teaches writing and SF, restores old vehicles, and watches the sky. Visit Chris at his website (sff.net/people/mckitterick), blog (mckitterick.livejournal.com), or on Facebook. Christian Ready worked at the Space Telescope Science Institute in the 1990's as a Program Coordinator. There, he helped support the verification of the Hubble Space Telescope following its first servicing mission. Afterward, Christian supported HST observations using the Wide Field

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Planetary Camera 2 (WFPC2) installed during the first servicing mission. He later worked at NASA's Goddard Spaceflight Center in Greenbelt, MD where he supported spacecraft flight operations and science observations on the Rossi X-Ray Timing Explorer. He continues to provide public education and outreach on astronomy to the public.

Steven H Silver is the publisher of the Hugo-nominated fanzine Argentus, founder of the Sidewise Awards for alternate history, and publisher of ISFiC Press. His short fiction has appeared both on-line and in print. He is currently serving as one of the vice-chairs of Chicon 7, the 2012 Worldcon.

Diane Turnshek teaches astronomy at the University of Pittsburgh, St. Vincent College and Carnegie Mellon University, where she also coordinates physics outreach. She hosts a monthly public lecture series at Allegheny Observatory. In her outreach role, she has visited schools, libraries, camps, Scouts and Congress and podcasted with Gateworld.net (“The Science of StarGate 1 and 2”) and 365Daysof Astronomy.org. She’s been adjunct faculty in the Writing Popular Fiction MFA Program at Seton Hill University since 2002. Diane consults with people who wish to use accurate science, from SF authors to opera companies. Find her short fiction in Analog and elsewhere. She has four delightful sons and a sweet dream guy.

Neptune

Aphelion 4,553,946,490 km

Perihelion 4,452,940,833 km

Semi-major Axis 4,503,443, 661 km

Orbital Period 60,190 days or 164.79 years

Equatorial Radius 24,764 km

Polar Radius 24,341 km

Volume 6.254x1013km3 or 57.75 Earths

Mass 1.0243x1026 kg or 17.147 Earths

Density 1.638 g/cm3

Equatorial Surface Gravity 1.14g

Axial Tilt 28.32°

Atmosphere 80% Hydrogen, 19% Helium,1.5% Methane

©2011 Argentus, Inc. Argentus is published annually by Steven H Silver with occasional special editions (of which this is the third). You can reach him at 707 Sapling Lane, Deerfield, IL 60015-3969 or via e-mail at shsilver@sfsite.com. His LiveJournal is at shsilver.livejournal.com and his website is at www.sfsite.com/~silverag. He’s also on Facebook. ISSN 2159-6727 (print) ISSN 2159-6735 (online)