General Astronomy

General AstronomyThe Solar System

The Smaller ObjectsThe Smaller MembersThe smaller members of the System are composed of the:

Minor Planets (Asteroids)CometsMeteoroidsDust and GasTitus-Bode "Law"In 1766, Johann Titus notices a peculiar pattern in the distances to the known planets; in 1772, Bode brings it into prominence:

N(4+N)/10ObjectAU00.4Mercury0.430.7Venus0.761.0Earth1.0121.6Mars1.5242.8485.2Jupiter5.29610.0Saturn9.519219.6Uranus19.338439.0Neptune30.676877.2Pluto39.4Known to Titusand BodeAsteroids.

AsteroidsThe discovery of Uranus in 1781 was found to fit nicely into "Bode's Law"A search for the 'missing planet' was organized since nothing at 2.8AU had been foundOn January 1, 1801, Piazzi (a Sicilian astronomer) noted a new object which he watched until February 11. He wrote Bode of his discovery, but by the time Bode looked for it, the object was too near the direction of the Sun for observation.In November, Gauss predicted the location of this object based on Piazzi's observations; it was found on Dec 31, 1801Piazzi named the object "Ceres" after the protecting goddess of SicilyThe missing planet had been found at a distance of 2.77 AUAsteroidsIt came as a surprise, when Olbers found another, Pallas, in March 1802In short succession, came the discoveries of:Juno (1804)Vesta (1807)

By 1890, more than 300 'planets' had been found. All where Bode's "Law" said one should be located.

AsteroidsOrbitsMost minor planets, or asteroids, orbit the sun in the same direction as the rest of the system

Most are reasonably close to lying in the ecliptic planeThe average inclination is 9About two dozen, have inclinations over 25

The distances lie in a range from 2.3 to 3.3 AU

Lagrangian PointsIn 1772, Lagrange realize that there were two peculiar point in Jupiter's orbit where the balancing of forces would permit asteroids to remain indefinitely:*JupiterTrojans(Western)Trojans(Eastern)6060These are named after Homeric heroes. The custom is to name the eastern group after Greeks and the western group after the Trojans. (This custom began after several names had been assigned; so there is one Greek spy in the Trojan group and one Trojan spy in the Greek group)Kirkwoods Gaps

The asteroid orbits are not evenly distributed throughout the asteroid belt between Mars and Jupiter.There are several gaps where no asteroids are foundThese correspond to resonances of the orbits with the orbit of Jupiter.Non-Belt Asteroids

Apollo-Amor Objects:Not all asteroids orbit within the asteroid belt.Asteroids with elliptical orbits, reaching into the inner solar system.Some potentially colliding with Mars or Earth.Trojans: Sharing stable orbits along the orbit of Jupiter.Asteroid NamesOnce a minor planet is discovered and found to make at least one orbit about the Sun, it is given both a name and a number.The number is the next value in the sequence of discovery; the name is left to the discoverer:

1 Ceres2 Pallas433 Eros1566 Icarus

433 ErosMission to another world

The NEAR spacecraft was sent to the asteroid 433 Eros.It arrived and went into orbit and was eventually landed on the asteroid.

433 Eros is an airless, irregular rock

433 Eros: Boulders and CratersThe NEAR spacecraft in orbit

433 Eros: TouchdownAt a height of 123 meters, this photo spans 6 meters. The rock at the top is about 4 meters across.The bottom is where the transmission ended as the spacecraft landed on the asteroid on 12 FEB 2001

Ida and DactylDactyl is the small "moon" orbiting asteroid Ida

Exploring the AsteroidsDawnThe Dawn spacecraft was launched September 27, 2007Went into orbit around Vesta on July 17, 2011Dawn left Vesta orbit on September 5, 2012Went into orbit around Ceres in April 2015

VestaVesta

A wall structureAnd Marcia craterVesta

Marcia craterCeres

Ceres

Ceres

A 4 mile highmountain

Ceres:

Occators LightsCeres Topography

CometsCometsComets were once thought to bring tidings of bad fortune. It was, for King Harald, when Halley's comet appeared in 1066 and he lost the English throne to William of Normandy.

The ancient Chinese named them 'Broom Stars'

In any event, they are beautiful and spectacular visitors to our night sky.

StructureThe current model of a comet is known as the Dirty Snowball ModelComets are composed of:NucleusComaHydrogen CloudTailIon TailDust TailJetsStructureThe Nucleus is ice, dirt andFrozen gases a Slush ball!As the heat of the Sun warms the comet, the Hydrogen Cloud formsMore warmth and the Coma makes the comet 'fuzzy'Deep Impact

In December 2004, a Delta II rocket launched the combined Deep Impact spacecraft which left Earth's orbit toward the comet. In early July 2005, 24 hours before impact, the flyby spacecraft pointed high-precision tracking telescopes at the comet and released the impactor on a course to hit the comet's sunlit side.

The impactor is a battery-powered spacecraft that operates independently of the flyby spacecraft for just one day. It is called a "smart" impactor because, after its release, it takes over its own navigation and maneuvers into the path of the comet. A camera on the impactor captures and relays images of the comet's nucleus just seconds before collision. The impact is not forceful enough to make an appreciable change in the comet's orbital path around the Sun.

After release of the impactor, the flyby spacecraft maneuvered to a new path that, at closest approach passes 500 km (300 miles) from the comet. The flyby spacecraft observed and recorded the impact, the ejected material blasted from the crater, and the structure and composition of the crater's interior. After its shields protected it from the comets dust tail passing overhead, the flyby spacecraft turned to look at the comet again. The flyby spacecraft took additional data from the other side of the nucleus and observed changes in the comet's activity. While the flyby spacecraft and impactor did their jobs, professional and amateur astronomers at both large and small telescopes on Earth observed the impact and its aftermath.Deep Impact The approach

Deep Impact: The Collision

Preliminary FindingsComet Temple I has a very fluffy structure weaker than a bank of powder snowDistinct layers with impact craters and topographyMuch carbon-containing molecules substantial amount of organic moleculesVery porous provides a good heat insulator for the coreConsiderable water presentWhat are good little comets made of?

These "comet soup" ingredients are pictured above: (in the back from left to right) a cup of ice and a cup of dry ice; (in measuring cups in the middle row from left to right) olivine, smectite clay, polycyclic aromatic hydrocarbons, spinel, metallic iron; (in the front row from left to right) the silicate enstatite, the carbonate dolomite, and the iron sulfide marcasite.

Materials are courtesy of Dr. George Rossman of the California Institute of Technology's Geology and Planetary Sciences department.The Nucleus

This is the nucleus of Halley's Comet as seen by the Hubble Space Telescope

It is a chunk of ice and sand grains and other frozen gasesRosettas MissionSummer 2014, the Rosetta spacecraft intercepts and goes into orbit about comet 67P/ChuryumovGerasimenko at that time between the orbits of Mars and Jupiter after travelling for 10 years, 5 months and 4 days.

Rosetta

Philae as seen by Rosetta

The first probe ever to land on the surface of a comet performed some serious science before going into hibernation. Philae lander found organic molecules in the comet's atmosphere and discovered that the frigid object's surface is as hard as ice.On Nov. 12, 2014, Philae became the first probe to softly land on the face of a comet. After being released from the orbiter, the lander actually bounced off Comet 67P/Churyumov-Gerasimenko twice before coming to its current less-than-ideal resting spot. Because of the low sunlight conditions, Philae went into hibernation after only about 57 hours on the comet when its battery depleted.Before shutdown, one of Philae's instruments managed to "sniff" the first organic molecules detected in the atmosphere of the comet scientists still aren't sure what kind of organics carbon-containing molecules that are the building blocks of life on Earth were found.

Philaes Final resting place

(in the shadows)

Rosetta and Philae

Rosetta spacecraft captured these images of Philaes bouncing landing during its historic touchdown on Nov. 12, 2014The Tail

Gas TailIonized GasesBlue emitted lightDust TailSand & dirtWhite reflected lightJetsGas pockets breaking through the crust

Two Types of TailsIon tail: Ionized gas pushed away from the comet by the solar wind. Pointing straight away from the sun.Dust tail: Dust set free from vaporizing ice in the comet; carried away from the comet by the suns radiation pressure. Lagging behind the comet along its trajectory0

Gas and Dust Tails of Comet Mrkos in 19570Comet Hale-Bopp in 1997

0Fragmentation of Comet Nuclei

Comet nuclei are very fragile and are easily fragmented.Comet Shoemaker-Levy was disrupted by tidal forces of JupiterTwo chains of impact craters on Earths moon and on Jupiters moon Callisto may have been caused by fragments of a comet.Fragmenting Comets

Comet Linear apparently completely vaporized during its sun passage in 2000.Only small rocky fragments remained.Comet Orbits

Comet TypesShort Period CometsPeriodic, returning in less than 200 yearsMostly orbit in the same direction as the rest of the Solar System objectsTend to be in or near the ecliptic planeLong Period CometsMay not be periodic (or have such a long period that it takes thousands of years to orbit.May come from any angle to the eclipticMay have any directionKuiper BeltThe short-period comets appear to share the ecliptic plane and the general direction of motion. Their origin is in a belt about 30-50AUThe numbers of icy-bodies (comets) are estimated to be in the millions.If nudged by Neptune's gravity, some are occasionally moved from their orbits and sent toward the SunMany astronomers now consider Pluto to be "just another" KBO (Kuiper Belt Object)Oort CloudThe long-period comets can come from any direction and at any angle. This suggest that their origin is spherically-distributed about the sun.Their origin is now considered to be in a cloud, or shell, about the Sun at a distance of about 50,000 AUTheir numbers are estimated to be in the billions.

Image from JPLThe BIG Picture

Meteors

"I would more easily believe that two Yankee professors would lie than that stones would fall from heaven" - Supposedly said by Thomas Jefferson after hearing of meteorite exploding over Weston, Connecticut on December 14, 1807.Chunks of rock and iron floating in space, their name reflects where they are found:

MeteoroidIn space

MeteorIn the SkyMeteoriteOn the ground

Bolides(Fireball)MeteoritesMeteorites come in several flavors:

Stony meteorites are commonly made of familiar minerals like plagioclase, pyroxene, and olivine. It is believed that they were formed in the outer parts of asteroid belt. Stony meteorites look a lot like Earth rocks, and are often not recognized as meteorites. Their outer surfaces are usually melted as they pass through our atmosphere, giving them dark "fusion crusts."

Iron meteorites are made almost entirely of iron metal with some nickel. As with stony meteorites, iron meteorites also have fusion crusts and show distinct molten metal shapes and flow markings

Some meteorites are mixtures of iron and fragments of rock; they are called stony-iron meteorites. Probably formed at the boundary between the metal core and the rocky mantle of an asteroid.

Their sizes range from dust to grains of sand to the size of housesMeteor ShowersAs Earths on its orbit intersects the dust trail of a comet, we observe meteor showers (or sometimes storms)These appear to radiate outward from a given constellation (the radiant) and are named accordingly. For example, the Leonides.The best time to see them is after midnight:MidnightDawnMeteor Showers

Most meteors appear in showers, peaking periodically at specific dates of the year.

Meteoroid OrbitsMeteoroids contributing to a meteor shower are debris particles, orbiting in the path of a comet.Spread out all along the orbit of the comet.Comet may still exist or have been destroyed.Only few sporadic meteors are not associated with comet orbits.0

Radiants of Meteor ShowersTracing the tracks of meteors in a shower backwards, they appear to come from a common origin, the radiant. Common direction of motion through space. The Perseid Meteor Shower

The Leonid Meteor Shower in 2002Earth ImpactsEarth retains the poorest record of impact craters amongst terrestrial planetsWhy? Plate tectonicsErosionSedimentationLifeOceans are relatively young and hard to exploreMany impact structures are covered by younger sediments, others are highly eroded or heavily modified by erosion. Few impact craters are well preserved on the surface

There are about 160 known impact cratersEarth's Known Impact Craters

1992 Peekskill FallOn October 9, 1992, a fireball was seen streaking across the sky from Kentucky to New York.

1992 Peekskill, NY

Chicago/Trinity Park, IL Sunday, March 30, 2003

Colby Navarro was sitting in her computer room about midnight Thursday, chatting on the phone with a friend, when she heard a boom that sent plaster shards from her ceiling falling to her carpeted floor. "It scared the living daylights out of me for sure," said Navarro. "I first thought a gunshot went off and ducked to the ground, but then I saw the 4- to 5-inch diameter hole in my ceiling. Then there was a burning smell." What crashed through Navarro's ceiling was a meteorite about the size of a grapefruit that landed less than 2 feet from where she was sitting. She touched it. It was warm and smoking and smelled like fireworks. Wabar, Saudi Arabia (0.072mi)

Wolfe Creek, Australia (0.55mi)

Barringer Crater, Arizona (0.75 mi)

It is estimated that the meteorite that produced the Barringer Crater was still traveling at 11 km/second when it struck what is now the Arizona desert 49,000 years ago. Roter Kamm, Namibia (1.6mi)

Brent, Canada (2.4 mi)

Spider, Australia (8.1mi)

Manicouagan, Canada (62mi)

Popigai, Russia (62 mi)

Vredefort, South Africa (125-185mi)

Tunguska, Siberia 1908

Chesapeake Crater, VAMarine impact event, about 35 Myr old, with typical inverted sombrero shape due to multi-layer nature of target region: soft sediments + hard rockIts existence explains several geological features of the area including the saline groundwater and higher rate of subsidence at the mouth of the Chesapeake Bay. Inner basin (the head of the sombrero) is about 25 miles wide - Outer basin (the brim of the sombrero) extends to about 53 miles.

Mystery Structure #1

Gosses Bluff Crater, AustraliaComplex crater with a central peak ring (143 million years old)

Crater diameter: 22 km Mostly eroded away only spotted by the different color of the vegetation

Inner ring: 5 kmRound bluff that is fairly easy to spot.Mystery structure #2

Aorounga crater, ChadComplex crater with a central peak ringCrater diameter: 12.6 km Buried under rocks and sand for a long time, it has been uncovered again by recent erosion.

Possible craterAorounga may be part of a crater chainMystery structure #3

Clearwater, Canadatwo craters, both 290 Million years agoClearwater West: 22.5 miles Complex structure

Clearwater East:16 miles

Probably they were made by a double asteroid, like ToutatisMystery structure #4

Chicxulub Structure, Mexico65 Myr old (end of dinosaurs!)Structure diameter: 106 miles Crater is not really visible at the surface

Dino Killer?A large body of scientific evidence now exists that support the hypothesis that a major asteroid or comet impact occurred in the Caribbean region at the boundary of the Cretaceous and Tertiary periods in Earth's geologic history. Artist: Don Davis

Such an impact is suspected to be responsible for the mass extinction of many floral and faunal species, including the large dinosaurs, that marked the end of the Cretaceous period. Until now, the remains of such an impact crater have escaped detection. The Cenote Ring off Yucatan represents a prime candidate for the impact site of a global catastrophic event.

Evidence for ChicxulubIn 1980 , Nobel laureate Luis Alvarez, his geologist son Walter Alvarez, nuclear chemist Frank Asaro, and paleontologist Helen Michael published on their discovery of high levels of the element Iridium in a clay layer separating marine sediments of Cretaceous and Tertiary age.

The thin clay layer that marks the boundary between the Cretaceous and Tertiary rocks. This layer has been found at many localities around the Earth. (Courtesy of Canadian Museum of Nature, Ottawa)

This three-dimensional map of local gravity and magnetic field variations shows a multi-ringed structure called Chicxulub named after a village located near its center. The impact basin is buried by several hundred meters of sediment, hiding it from view. This image shows the basin viewed obliquely from approximately 60 above the surface looking north, with artificial lighting from the south. (Courtesy of V. L. Sharpton, LPI)Chicxulub, Yucatan Peninsula, MexicoThis leads to the idea of a mass extinction at the K-T boundary by the impact of an asteroid (~10 Km diameter).The crater that remains is about 150 300 Km diameter.

No land animal > 25 Kg survived.EarthImpact?

Earth's Recent 2nd Moon2006 RH120 was discovered on 14 September 2006 by the 27-inch Schmidt camera of the Catalina Sky Survey .

Preliminary orbital calculations indicated it was captured by Earth's gravity

Analysis shows the body must be a dense rocky body or at least regularly shaped.

One hypothesis is that the object is a piece of lunar rock ejected by an impact.

However, the object was later confirmed to be minor planet.

The object made four Earth orbits before being ejected after the June 2007 perigee.

At that perigee, it dipped inside the Moon's orbit to a distance of approximately 200,000 miles.

Douglas R. Allen, Dordt College