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Life around Saturn,
and beyond
ASTR 1420
Lecture 14
Sections 9.3
Saturn’s Moons
• 62 Moons, 53 named (18 above). Mostly icy, some with rocky cores.
• Titan is the 2nd largest moon in our Solar System & only one with a “real”
atmosphere with N2, CH4, CO2 (1.5 bar!)
• 98% of N2 : (N2=77% at Earth)
• No appreciable O2
Titan, the Masked!
• sunlight 1/100 of Earth
• A lot of organic
CH4, C2H2, C2H6, C3H8, …,
argon, CO2, etc.
• Always covered with
thick haze/smog
• Cassini/Huygens in
Voyager 2 image of Titan
Cassini + Huygens (2004- )
Titan’s landscape from Huygens descending image…
Taken at an altitude of ~8 km.
looks like a dried streambed!
Water ice as rocks…
Interior of Titan
• Satellite gravity
• Similar to Callisto, Titan’s
interior is not
• It has a subsurface ocean
at very low temperature
 mixture of water and
• Controversial… : some
believe that it should have
a rocky core + icy mantle…
• A lot of NH3 !
Titan’s Atmosphere
Ganymede : 2631 km radius
Titan : 2576 km radius  55km
• Multi-layer of haze
• Titan once was believed to be the largest moon in the solar system because of
its extended haze layer (~200 km).
• Titan’s solid surface is only 55km smaller than Ganymede…
• NH3 + CH4 + solar UV photons
organic molecules…
• Drizzle of methane and ethane. Possible lakes/oceans of methane
Liquid Flow
Methane river
 A feature most
likely formed by a
liquid methane
flow. Taken by
Huygens probe.
Theoretical models
predict that a single
methane rainstorm
can produce several
inches of rain…
Methane World
Cassini pictures of Saturn's moon Titan taken in 2004 and 2005
show that a large methane lake suddenly appeared after what
looked like a heavy rainstorm
Sea of Methane on Titan
A Cassini radar image juxtaposed with an image of the Lake Superior
Lots of Natural Gases, but no Oxygen to burn with!
• Temperature range for liquid:
water: 0 to 100C, methane: -182C to -164C, ethane: -183C to -89C
Possible ethane world?
Origin of
Image of Titan taken from Cassini orbiter
• 10 times more extended
than Earth’s
• Key factor  size
• How does Titan have an
atmosphere when even
a larger moon
Ganymede doesn’t?
1. distance from the Sun
2. effect of their host
• Ganymede does not have an atmosphere  at Jupiter’s
distance, only water ice could condense…, but at Saturn’s
distance, ices such as methane and ammonia could condense!
• Due to the stronger gravity of Jupiter, impacts were generally
stronger at Jupiter’s moons than Saturn’s moon. Stronger
impacts more easily blew away atmospheres…
More surface feature : Sand Dunes
Windblown dunes
made of hydrocarbon sediments.
Namib desert from Space Shuttle
Titan : summary
• Very similar features with very different composition and temperature!
liquid water
liquid methane
silicate rocks
water ice rocks
molten lava volcano
ice/slush volcano
silicate sand dunes
organic particulate dunes
• A lot of liquid hydrocarbons!
about 200°C colder than liquid water  much slower chemical reaction  slower
• A lot of organic material (e.g., organic sand dunes!)
• Possible life in the upper atmosphere (acetylene [C2H2] based) or in the
subsurface liquid ocean!
• interesting to see if we can find right- and left-handed amino acids in life!
Active Enceladus
• Tiger stripes = fresh ices
 cracks or grooves
6th largest moon of Saturn
• Ice geysers  subsurface liquid water +
ammonia mixture
• Although we expect some tidal heating, it is
hard to explain all these activities.
• possible subsurface habitable zone!
feeding a ring of Saturn
Iapetus : An Intelligence Test for Earthlings?
a large brightness change (10+ times)
over one rotation period!
3rd largest moon of Saturn
• Heavily terraformed?
Strange Surface
• Equatorial bulge
Iapetus = Alien’s Starship?
No, Iapetus is in fact Deathstar!
Triton: Surprising possibility of potential habitability
largest moon of Neptune
• Cryovolcanism…
Triton’s cantalope
Possibly formed by diapirism
(i.e., slow boiling pattern)
Triton: Surprising possibility of potential habitability
• Retrograde motion = Triton orbits Neptune
“backward”  captured moon!
• Crater count  Triton’s surface is 10-100
million years old.
• Active ice geysers!!
• Remnant internal heat from the capture may
drive the geological activity…
possible subsurface liquid ocean
even at -230°C, possible habitable world!
Cosmic Messengers
Signal from Pioneer
• A signal from the Pioneer 10 spacecraft, sent from a distance of more than
6 billion kilometers. The spacecraft transmitted the signal with a power of
only one watt (about the power of X-mas tree light)!
In summary…
Important Concepts
Important Terms
• At least six potentially habitable
jovian moons!
 Europa, Ganymede, Callisto,
Titan, Enceladus, and Triton
• icy volcanism (cryo-volcanism)
• Origin of Titan’s atmosphere
• Prominent characteristics of Titan,
Enceladus, Iapetus, and Triton.
Chapter/sections covered in this lecture : 9.3
Next lecture : Exo-planets!