Chapter 10 Mars€¦ · 63 moons have now been found orbiting Jupiter, but most are very small The...

Chapter 10Mars

Friday, March 12, 2010

Mars’s orbit is fairly eccentric which affects amount of sunlight reaching itMars can be either in the direction of the Sun (conjunction) or not (opposition)

10.1 Orbital Properties


MarsRadius: 3394 kmMoons: 2- Deimos, Phobos

Mass: 6.4 x 1023 kgDensity: 3900 kg/m3

Length of day: 24.6 hours

10.2 Physical Properties

EarthRadius: 6378 kmMoons: 1Mass: 5.79 x 1024 kgDensity: 5520 kg/m3

Length of day: 24 hours


From Earth, we can see polar ice caps that grow and shrink with the seasons- seasonal capsChanging polar ice caps are frozen carbon dioxide

10.3 Long-Distance Observations of Mars


• Residual Caps: mostly carbon dioxide, but possibly contain water ice- permanently frozen• BIG temperature difference in the residual caps is caused by shifting dust cover during the southern summer- frequent dust storms, with high winds makes surface look like it is changing

10.3 Long-Distance Observations of Mars


Major feature: Tharsis bulge, size of North America and 10 km above surroundingsMinimal cratering; youngest surface on Mars

10.4 The Martian Surface


This map shows the main surface features of Mars. There is no evidence for plate tectonics.



• Northern hemisphere (left) is rolling volcanic terrain

• Southern hemisphere (right) is heavily cratered highlands; average altitude 5 km above northern

• Assumption is that northern surface is younger than southern

• Means that northern hemisphere must have been lowered in elevation and then flooded with lava



Valles Marineris: Huge canyon, created by crustal forces Top right: Grand

Canyon on same scale

• 4000 km long• Maximum 120 km wide, 7 km deep



Mars has largest volcano in solar system: Olympus Mons

• 700 km diameter at base• 25 km high• Caldera is 80 km in diameter

Three other Martian volcanoes are only slightly smaller



Was there running water on Mars?

Runoff channels resemble those on EarthLeft: MarsRight: Louisiana

10.5 Water on Mars


Current thinking: Open water (rivers, lakes) once existed on Mars

10.5 Water on Mars


10.5 Water on Mars

This may be an ancient Martian river delta (Or it may not)


Recently, gullies have been seen that seem to indicate the presence of liquid water; interpretation is still in doubt

10.5 Water on Mars


Viking landers both landed in low-latitude northern plainsRocky surface, red due to iron content

Viking 1:

10.5 Water on Mars


The landing site for Opportunity was chosen to maximize the chances of finding water, or evidence for water

10.5 Water on Mars


Discovery 10-1: Life on Mars?

Viking landers looked for evidence of living organisms; did not find anything conclusive


Discovery 10-1: Life on Mars?

Two Martian meteorites found in Antarctica show possible signs of microbial life, but evidence is disputed


Martian atmosphere is mostly carbon dioxide, and very thinToo thin to retain much heat; temperature drops sharply at night

10.6 The Martian Atmosphere


Mars may be victim of runaway greenhouse effect in the opposite sense of Venus’s:

As water ice froze, Mars became more and more reflective and its atmosphere thinner and thinner, freezing more and more water and eventually carbon dioxide as well.

10.6 The Martian Atmosphere


• No seismic studies have been done

• From behavior of crust, it is estimated to be 100 km thick

• No magnetic field, so core is probably not metallic, not liquid, or both

10.7 Martian Internal Structure


Mars has two tiny moons: Phobos (left, 28 km x 20 km) Deimos (right, 16 km x 10 km) Both probably captured from the asteroid belt

10.8 The Moons of Mars


• Mars’ orbit is more eccentric than Earth’s• Rotates in 24.6 hours; axial tilt similar to Earth’s• Atmosphere very thin, mostly carbon dioxide• Temperature averages 50 K below Earth’s, but seasons are otherwise similar• Mars landers have yielded substantial amounts of data

Summary of Chapter 10


• Northern and southern hemispheres are very different• South is higher and heavily cratered• North is lower and relatively flat• Major features: Tharsis bulge, Olympus Mons, Valles Marineris• Crater ejecta provide evidence for permafrost layer under surface (easily liquidized)• Two small moons, probably captured asteroids

Summary of Chapter 10 (cont.)


Chapter 11Jupiter


11.1 Orbital and Physical Properties

This figure shows the solar system from a vantage point that emphasizes the relationship of the jovian planets to the rest of the system


Three views of Jupiter: From a small telescope on Earth; from the Hubble Space Telescope; and from the Cassini spacecraft



• Mass: 1.9 × 1027 kg (twice as much as all other planets put together)• Radius: 71,500 km (112 times Earth’s)• Density: 1300 kg/m3—cannot be rocky or metallic as inner planets are• Rotation rate: Problematic, as Jupiter has no solid surface; different parts of atmosphere rotate at different rates• From magnetic field, rotation period is 9 hr, 55 min



Major visible features:Bands of clouds; Great Red Spot

11.2 The Atmosphere of Jupiter


• Atmosphere has bright zones and dark belts• Zones are cooler, and are higher than belts• Stable flow underlies zones and bands, called zonal flow• Simplified model:



Real picture is much more complicated

Here: Wind speed with respect to internal rotation rate



Composition of atmosphere: Mostly molecular hydrogen and helium; small amounts of methane, ammonia, and water vaporThese cannot account for color; probably due to complex chemical interactions



No solid surface; take top of troposphere to be at 0 kmLowest cloud layer cannot be seen by optical telescopesMeasurements by Galileo probe show high wind speeds even at great depth—probably due to heating from planet, not from Sun



Great Red Spot has existed for at least 300 years, possibly much longerColor and energy source still not understood- possibly sustained by large scale atmospheric motion



Lightning-like flashes have been seen; also shorter-lived rotating stormsOne example: Brown Oval, really a large gap in clouds




Recently, three white storms were observed to merge into a single storm, which then turned red. This may provide some clues to the dynamics behind Jupiter’s cloud movements.


No direct information is available about Jupiter’s interior, but its main components, hydrogen and helium, are quite well understood. The central portion is a rocky core.

11.3 Internal Structure


Discovery 11-1: A Cometary ImpactJuly 1994: Comet Shoemaker-Levy 9, in fragments, struck Jupiter, providing valuable information about cometary impacts


Discovery 11-2: Almost a Star?Jupiter is much too small to have become a star—needs 80 times more mass!But its energy output was larger in the past; could have been 100 times brighter than the Moon as seen from EarthDwarf star in Jupiter’s place probably would have made stable planetary orbits impossibleJupiter played invaluable role in sweeping solar system clear of debris before too much reached Earth—otherwise life might not have been possible


Jupiter is surrounded by belts of charged particles, much like the Van Allen belts but vastly larger.

Magnetosphere is 30 million km across

11.4 Jupiter’s Magnetosphere


Intrinsic field strength is 20,000 times that of EarthMagnetosphere can extend beyond the orbit of Saturn

11.4 Jupiter’s Magnetosphere


63 moons have now been found orbiting Jupiter, but most are very smallThe four largest are the Galilean moons, so called because they were first observed by Galileo:• Io, Europa, Ganymede, CallistoGalilean moons have similarities to terrestrial planets: orbits are roughly circular, largest is somewhat larger than Mercury, and density decreases as distance from Jupiter increases

11.5 The Moons of Jupiter



Jupiter with Io and Europa. Note the relative sizes!


Interiors of the Galilean moons:



Io is the densest of Jupiter’s moons, and the most geologically active object in the solar system:• Many active volcanoes, some quite large

• Can change surface features in a few weeks

• No craters; they fill in too fast—Io has the youngest surface of any solar system object



Orange color is probably from sulfur compounds in the ejecta



Cause of volcanism: Gravity!Io is very close to Jupiter and also experiences gravitational forces from Europa. The tidal forces are huge and provide the energy for the volcanoes.



Europa has no craters; surface is water ice, possibly with liquid water below

Tidal forces stress and crack ice; water flows, keeping surface relatively flat



Ganymede is the largest moon in the solar system—larger than Pluto and MercuryHistory similar to Earth’s Moon, but water ice instead of lunar rock



Callisto is similar to Ganymede; no evidence of plate activity



Jupiter has been found to have a small, thin ring

11.6 Jupiter’s Ring


• Jupiter is the largest planet in the solar system• Rotates rapidly• Cloud cover has three main layers, forms zone and band pattern• Great Red Spot is a very stable storm• Pressure and density of atmosphere increase with depth; atmosphere becomes liquid and then “metallic”



• Relatively small rocky core (but still about 10x size of Earth)• Still radiating energy from original formation • 63 moons, four very large• Io: Active volcanoes, due to tidal forces• Europa: Cracked, icy surface; may be liquid water underneath• Ganymede and Callisto: Similar; rock and ice



Chapter 12Saturn


Mass: 5.7 × 1026 kgRadius: 60,000 kmDensity: 700 kg/m3—less than water!Rotation: Rapid and differential, enough to flatten Saturn considerablyRings: Very prominent; wide but extremely thin




View of rings from Earth changes as Saturn orbits the Sun


Saturn’s atmosphere also shows zone and band structure, but coloration is much more subdued than Jupiter’s

Mostly molecular hydrogen, helium, methane, and ammonia; helium fraction is much less than on Jupiter

12.2 Saturn’s Atmosphere



This true-color image shows the delicate coloration of the cloud patterns on Saturn


Similar to Jupiter’s, except pressure is lowerThree cloud layersCloud layers are thicker than Jupiter’s; see only top layer



Wind patterns on Saturn are similar to those on Jupiter, with zonal flow



Jupiter-style “spots” rare on Saturn; don’t form often and quickly dissipate if they do



12.2 Saturn’s AtmosphereThis “dragon storm” was first spotted in 2004; it is believed to be a long-lived phenomenon but is usually hidden under the clouds


12.2 Saturn’s AtmosphereAs expected for a planet with an atmosphere, there is a vortex at Saturn’s south pole.


Interior structure similar to Jupiter’s

12.3 Saturn’s Interior and Magnetosphere


Saturn also radiates more energy than it gets from the Sun, but not because of cooling:

• Helium and hydrogen are not well mixed; helium tends to condense into droplets and then fall

• Gravitational field compresses helium and heats it up



Saturn also has a strong magnetic field, but only 5% as strong as Jupiter’s

Creates aurorae:



Saturn has an extraordinarily large and complex ring system, which was visible even to the first telescopes

12.4 Saturn’s Spectacular Ring System


Overview of the ring system:



Ring particles range in size from fractions of a millimeter to tens of metersComposition: Water ice—similar to snowballsWhy rings?

• Too close to planet for moon to form—tidal forces would tear it apart



Closest distance that moon could survive is called Roche limit; ring systems are all inside this limit




This backlit view shows the fainter F, G, and E rings


Voyager also found radial “spikes” that formed and then dissipated; this probably happens frequently



Strangest ring is outermost, F ring; it appears to have braids and kinks



F ring’s oddities probably caused by two shepherd moons, one of which can be seen here:



Details of formation are unknown:• Too active to have lasted since birth of solar system• Either must be continually replenished, or are the result of a catastrophic event



Saturn’s many moons appear to be made of water iceIn addition to the small moons, Saturn has: • Six medium-sized moons (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus)• One large moon (Titan) which is almost as large as Ganymede

12.5 The Moons of Saturn


Titan has been known for many years to have an atmosphere thicker and denser than Earth’s; mostly nitrogen and argonMakes surface impossible to see; the upper picture at right was taken from only 4000 km away




The Huygens spacecraft has landed on Titan and is returning images directly from the surface


Discovery 12-1: Dancing Among Saturn’s Moons

The Cassini spacecraft uses multiple “gravitational slingshots” to make multiple close passes around Saturn’s moons. Precise orbits are decided on the fly.


• Iapetus is tidally locked- “two-faced” moon



• Saturn, like Jupiter, rotates differentially and is significantly flattened• Saturn’s weather patterns are in some ways similar to Jupiter’s, but there are far fewer storms• Saturn generates its own heat through the compression of “helium raindrops”• Saturn has a large magnetic field and extensive magnetosphere



• Saturn’s most prominent feature is its rings, which are in its equatorial plane• The rings have considerable gross and fine structure, with segments and gaps; their particles are icy and grain- to boulder-sized• Interactions with medium and small moons determine the ring structure• The rings are entirely within the Roche limit, where larger bodies would be torn apart by tidal forces



• Titan is the second-largest moon in the solar system• Titan has an extremely thick atmosphere, and little is known about its surface or interior• Medium-sized moons are rock and water ice; their terrains vary• These moons are tidally locked to Saturn• Several of the small moons share orbits, either with each other or with larger moons



Chapter 13Uranus and Neptune


Uranus was discovered in 1781 by Herschel; first planet to be discovered in more than 2000 yearsLittle detail can be seen from Earth; arrows point to three of Uranus’s moons:

13.1 The Discoveries of Uranus and Neptune



Slightly more detail can be seen in this image taken by Voyager 2 at a distance of 1 million km


Neptune was discovered in 1846, after analysis of Uranus’s orbit indicated its presence

Details of Neptune cannot be made out from Earth either; arrows again point to moons:




More detail is visible in these Voyager 2 images, also taken from a distance of 1 million km:


Uranus and Neptune are very similar



Uranus Neptune

Mass 14.5 x Earth 17.1 x Earth

Radius 4.0 x Earth 3.9 x Earth

Density 1300 kg/m3 1600 kg/m3



Peculiarity of Uranus: Axis of rotation lies almost in the plane of its orbit. Seasonal variations are extreme.



Outer atmospheres of Uranus and Neptune are similar to those of Jupiter and Saturn

Uranus and Neptune are cold enough that ammonia freezes; methane dominates and gives the characteristic blue color

13.3 The Atmospheres of Uranus and Neptune


Band structure of Neptune is more visible; it had a “Dark Spot” similar to Jupiter’s storms (now vanished)

13.3 The Atmospheres of Uranus and Neptune


Uranus and Neptune both have substantial magnetic fields, but at a large angle to their rotation axes.

The rectangle within each planet shows a bar magnet that would produce a similar field. Note that both Uranus’s and Neptune’s are significantly off center.

13.4 Magnetospheres and Internal Structure


Magnetic fields of Uranus and Neptune must not be produced by dynamos, as the other planets’ fields are

Interior structure of Uranus and Neptune, compared to that of Jupiter and Saturn:

13.4 Magnetospheres and Internal Structure


13.5 The Moon Systems of Uranus and Neptune



Uranus has 27 moons, five of which are major: Miranda, Ariel, Umbriel, Titania, and OberonSimilar to Saturn’s medium-sized moons, except that all are much less reflectiveUmbriel is the darkest


Neptune has 13 moons, but only two can be seen from Earth: Triton and NereidTriton is in a retrograde orbit; Nereid’s is highly eccentricTriton’s surface has few craters, indicating an active surface



Nitrogen geysers have been observed on Triton, contributing to the surface features

Triton’s fate: the moon is spinning towards Neptune- Roche Limit



Also, there appear to be ice volcanoes



Uranus and Neptune have faint ring systems, recently detected via stellar occultation

13.6 The Rings of the Outermost Jovian Planets


Neptune has five rings: three narrow and two wide

13.6 The Rings of the Outermost Jovian Planets


Pluto- Irregularities in Uranus and Neptune’s orbit suggested another planet- Tomaugh discovered Pluto- Irregularities do not exist- Pluto’s mass, radius and density are closer to a icy moon than a planet


• Uranus and Neptune were discovered in the last 350 years• Uranus and Neptune are similar: gaseous and cold• Uranus’s spin axis is almost in the plane of its orbit• Surface features are hard to discern on Uranus but are more obvious on Neptune• Uranus has no excess heat emission, but Neptune does



• Uranus’s midsized moons are similar to those of Saturn• Neptune’s moon Triton has a retrograde orbit• Uranus and Neptune both have faint ring systems



Chapter 10 Mars€¦ · 63 moons have now been found orbiting Jupiter, but most are very small The...

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Transcript of Chapter 10 Mars€¦ · 63 moons have now been found orbiting Jupiter, but most are very small The...