The Outer Planets

The Outer Planets

Cosmic Abundance of ElementsHydrogen H 1 1,000,000

Helium He 2 80,000

Carbon C 6 363

Nitrogen N 7 112

Oxygen O 8 851

Neon Ne 10 117

Sodium Na 11 2

Magnesium Mg 12 32

Aluminum Al 13 3

Silicon Si 14 45

Sulfur S 16 16

Argon Ar 18 1

Calcium Ca 20 2

Iron Fe 26 36

Nickel Ni 28 2

Major Constituents

Gas Formula Jupiter Saturn

Hydrogen H2 86% 92%

Helium He 14% 7%

Methane CH4 0.2% 0.2%

Ammonia NH3 0.02% 0.02%

Water H2O ~0.2% (?) ~0.4% (?)

Interiors: Big H2 Atmospheres

Jupiter vs Saturn

Jupiter’s Ammonia Clouds:

Belts: Dark bands

Zones: Bright bands

Great Red Spot

White Ovals

The GRS has lived at least 300 yrs. Ovals have been seen to survive tens of years

Jupiter’s clouds result from convection.

1) Hot air expands.

2) Lighter than the rest of the air, it rises.

3) As it rises, it cools and condenses forming clouds.

4) When it is cooler than the ambient air, it sinks.

Great Red Spot

Saturn’s Clouds

Uranus

Absorption of sunlight at red wavelengths by methane renders the planet blue.

Neptune

Neptune emits more energy from its interior than does Uranus. This energy drives weather. The colder temperatures cause methane to condense in the upper atmosphere – these are the clouds that we see.

Jupiter’s RingsSilicate dust, 10,000 times more transparent than window glass.

Moons

A typical, heavily cratered, terrain.

Saturn’s moon, Tethys

Their densities tell us that they are 1/2 rock & 1/2 ice.

Jupiter’s Moons

Europa

Few craters

A terrain containing elements that were recently dislodged can be seen to neatly fit together if rotated and translated in position.

Io

• Images\iovol_vgr.gif

Io

What fuels Io?

Each time Ganymede orbits once, Europa orbits twice, and Io orbits 4 times.

Plumes fountain 500 km above the Surface

Io’s surface is almost devoid of craters, for it is being repaved at a rapid rate.

The glow of warm lava.

A pool of lava (black) covered with sulfur deposits (orange). This is called Tupan Patera after the Brazilian thunder god.

Images taken from the Galileo spacecraft.

Io is hot

Lava flows on Io exceed 1500 K in temperature. Lavas this hot are not sulfur (which would evaporate immediately). This is hotter than present lavas on Earth (1300-1450 K). Instead these lavas are likely ultramafic (rich in Mg and Fe), similar to the lavas that occurred on early Earth.

Present hypothesis, a ~100 km thick crust floats on top of a worldwide ocean of magma 800 km deep.

Triton Neptune’s Largest Moon:

Triton

On Triton the main component of the atmosphere, nitrogen, exits in vapor pressure equilibrium.

That is, it exists as an ice on the surface and as vapor in the atmosphere, in the same way that water exists as liquid and ice on Earth’s surface and as a gas in the atmosphere.

The amount of gas depends on the temperature. Less exists at cooler temperatures.

This is seen on Earth with the condensation of water at dew point.

Atmosphere:

1.6x10-7 bar 38K Nitrogen

Summary

• Giant planets are large gas planets with nearly solar elemental abundances.

• They have small ice-rock cores. • Their moons are ½ rock and ½ ice. • Most moons display heavily cratered terrains. Io, Europa,

Triton and Titan are exceptions. • All jovian planets sport rings of differing thicknesses,

compositions & character. • Titan supports an atmosphere second only to Venus’

(considering bodies with proper surfaces). It is rich with organics, and its origin is unknown.

• The Cassini mission to the saturnian system is in route and functioning well.

Titan: a moon with an atmosphere

Saturn’s largest moon compared to Jupiter’s largest moons

GanymedeSize: 4800Mass: 1.5x1023

CallistoSize: 5268Mass: 1.1x1023

TitanSize:5150 kmMass: 1.3x1023

Observações da alta atmosferaObservações da alta atmosfera

Composition of Titan’s Composition of Titan’s stratospherestratosphere

MoleculeMolecule Abundance Abundance

NN22 65-98% 65-98%CHCH44 2-10% 2-10%HH22 0.2-0.6% 0.2-0.6%COCO 6-150 ppm 6-150 ppmCHCH33DD 5-180 ppm 5-180 ppmCC22HH66 13-20 ppm 13-20 ppmCC22HH22 2-5 ppm 2-5 ppmCC33HH88 0.5-4 ppm 0.5-4 ppmCC22HH44 0.09-3 ppm 0.09-3 ppmHCNHCN 0.2-2 ppm 0.2-2 ppmHCHC33NN 80-250 ppb 80-250 ppbCHCH33CC22HH 4-60 ppb 4-60 ppbCC44HH22 1-40 ppb 1-40 ppbCC22NN22 5-16 ppb 5-16 ppbCOCO22 1.5-14 ppb 1.5-14 ppb

Derived from radiative transfer analyses of Voyager, ISO and ground-based data.

Oceans?Oceans?CH4

C2H6

C2H2

haze

+ CH4 -> other hydrocarbons

Methane in atmosphere is depleted in107 years.

Either methane is supplied or we are witnessing Titan at a particular moment in its history.

Oceans containing methane explain the near saturated tropospheric conditions,provide a source for methane, and don’t requirea penchant for being lucky.

Flasar et al. Science 221, 55Lunine et al. Science 222, 1229

Ocean (CH4, C2H6, N2)

hν

Production RateProduction Rate

SpeciesSpecies FluxFlux Depth*Depth* PhasePhase

CC22HH66 5.8x105.8x1099 cm cm-2-2 s s-1-1 600 m600 m liquidliquid

CC22HH22 1.2x101.2x1099 cm cm-2-2 s s-1-1 100 m100 m solidsolid

CC33HH88 1.4x101.4x1088 cm cm-2-2 s s-1-1 20 m20 m liquidliquid

HCNHCN 2.0x102.0x1088 cm cm-2-2 s s-1-1 20 m20 m solidsolid

HazeHaze 1.5x101.5x10-14-14 g cm g cm-2-2 ss-1-1 60 m60 m solidsolid

Taken from Lunine et al. 1989. Based on Yung et al. 1984, Raulin (1984)

* Depth assuming global coverage & 4.5 Gyr of production

Expected Surface ScenarioExpected Surface ScenarioSagan & Dermott 1982Sagan & Dermott 1982

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Titan’s Surface

HST images

Peter Smith et al.

U. of Arizona





Testing Cassini(Jet Propulsion Laboratory, California)

We can see the main antenna.

All the instruments (e.g. the cameras) are covered.

Huygens Probe,European SpaceAgency

We can see the shield that protects the instruments against the heatof entry into theatmosphere.

In 2005, the desent of Huygen’s into Titan’s atmosphere.

At 170 km altitude, Huygens releases the shield and beginsmeasurements.

Cassini-Huygens spacecraft, on a Titan IV rocket, waiting for takeoff.

15 October 1997

A perfect takeoff that saved fuel.

ISS Images

Huygens DIRS Descent Huygens DIRS Descent MovieMovie

View of Landing Site

Ice Mountains

Landing Site

Huygen’s Huygen’s DISR ImagesDISR Images

PI: Marty TomaskoPI: Marty TomaskoUniversity of University of

ArizonaArizona

Foreground stones are 6 inches

DISR

More DISRImages.

Washes flow Washes flow downhilldownhill

Tomasko et al. Nature 438, 765

Huygens aterrizou ~30km Huygens aterrizou ~30km

ao sul das dunasao sul das dunas

Imagem do Cassini Radar (no modulo orbital)

Sitio de aterrissagem

Larry Soderblom

Tropical DunesTropical Dunes

Washes in XanaduWashes in Xanadu

Cassini RADAR

Lakes

Seas

TitanTitan

60o N latitude line

~ 1 m of surface CH~ 1 m of surface CH44

~ 4 m of atmospheric CH~ 4 m of atmospheric CH44

Cassini Radar

2.7 km of water on the surface 2.5 cm of atmospheric water EarthEarth

Sotin et al. N

ature 435, 786 (2005)

CryovolcanismCryovolcanism

A Mystery about TitanA Mystery about TitanWhere is the ethane Where is the ethane

(C(C22HH66)?)?

N2, CH4

Atmosphere

C2H6

A Mystery about TitanA Mystery about TitanWhere is the ethane Where is the ethane

(C(C22HH66)?)?

N2, CH4

Atmosphere

C2H6

Titan’s Two Kinds of Clouds

40

20



Ethane(C2H6)

Methane(CH4)

SummarySummary

Titan, Saturn’s largest moon, has an atmosphere10 times thicker than Earth’s.

This atmosphere is mainly of N2 and contains a lot of organic material.

Titan sports a methane cycle, with clouds, rain & seas.

Methane is the source of organic material in Titan’s atmosphere and on its surface.

It’s not entirely clear how and when Titan outgassed its methane, but the dearth of ethane suggests that it happened within 1 billion years.

The complexity of the organic chemistry is unclear.

Um Balão para Titã

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The Outer Planets