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The Outer Planets
Cosmic Abundance of Elements
Hydrogen
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 Rings
Silicate dust, 10,000 times more transparent than window glass.
Moons
Their densities
tell us that they
are 1/2 rock &
1/2 ice.
A typical, heavily
cratered, terrain.
Saturn’s moon,
Tethys
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.
IoIo
• Images\iovol_vgr.gif
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.
Neptune’s Largest Moon:
Triton
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.
Atmosphere:
This is seen on Earth with the
condensation of water at dew
point.
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
Titan
Size:5150 km
Mass: 1.3x1023
Callisto
Size: 5268
Mass: 1.1x1023
Ganymede
Size: 4800
Mass: 1.5x1023
Observações da alta atmosfera
Composition of Titan’s stratosphere
Molecule
N2
CH4
H2
CO
CH3D
C2H6
C2H2
C3H8
C2H4
HCN
HC3N
CH3C2H
C4H2
C2N2
CO2
Abundance
65-98%
2-10%
0.2-0.6%
6-150 ppm
5-180 ppm
13-20 ppm
2-5 ppm
0.5-4 ppm
0.09-3 ppm
0.2-2 ppm
80-250 ppb
4-60 ppb
1-40 ppb
5-16 ppb
1.5-14 ppb
Derived from radiative transfer analyses of Voyager, ISO and ground-based data.
Oceans?
hν
H2
CH4
 + 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.
haze
Oceans containing methane explain the near
saturated tropospheric conditions,
provide a source for methane, and don’t require
a penchant for being lucky.
C2H2
C2H6
Ocean (CH4, C2H6, N2)
Flasar et al. Science 221, 55
Lunine et al. Science 222, 1229
Production Rate
Species
Flux
Depth*
Phase
C2H6
5.8x109 cm-2 s-1
600 m
liquid
C2H2
1.2x109 cm-2 s-1
100 m
solid
C3H8
1.4x108 cm-2 s-1
20 m
liquid
HCN
Haze
2.0x108 cm-2 s-1
1.5x10-14 g cm-2 s-1
20 m
60 m
solid
solid
* Depth assuming global coverage & 4.5 Gyr of production
Taken from Lunine et al. 1989. Based on Yung et al. 1984, Raulin (1984)
Expected Surface Scenario
Sagan & Dermott 1982
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Titan’s Surface
HST images
Peter Smith et al.
U. of Arizona
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Testing Cassini
(Jet Propulsion Laboratory, California)
We can see the main antenna.
All the instruments (e.g. the
cameras) are covered.
Huygens Probe,
European Space
Agency
We can see the
shield that
protects the
instruments
against the heat
of entry into the
atmosphere.
In 2005, the desent of Huygen’s
into Titan’s atmosphere.
At 170 km altitude, Huygens
releases the shield and begins
measurements.
15 October 1997
Cassini-Huygens spacecraft,
on a Titan IV rocket, waiting
for takeoff.
A perfect takeoff
that saved fuel.
ISS Images
Huygens DIRS Descent Movie
Ice
Mountains

View of Landing Site
Landing Site
Huygen’s DISR
Images
PI: Marty Tomasko
University of Arizona
Foreground stones are 6 inches
More DISR
Images.
DISR
Washes flow downhill
Tomasko et al. Nature 438, 765
Huygens aterrizou ~30km
ao sul das dunas

Imagem do Cassini Radar (no modulo orbital)
Sitio de
aterrissagem
Larry Soderblom
Tropical Dunes
Washes in Xanadu
Cassini RADAR
Lakes
Seas
Titan
~ 1 m of surface CH4
~ 4 m of atmospheric CH4
Cassini Radar
60o N latitude line
2.7 km of water on the surface
2.5 cm of atmospheric water
Earth
Cryovolcanism
Sotin et al. Nature 435, 786 (2005)
A Mystery about Titan
Where is the ethane (C2H6)?
C2H6
N2, CH4
Atmosphere
A Mystery about Titan
Where is the ethane (C2H6)?
C2H6
N2, CH4
Atmosphere
Titan’s Two Kinds of Clouds
Ethane
(C2H6)
40
20
Methane
(CH4)
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Summary
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