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Life around Saturn, and beyond. ASTR 1420 Lecture 15 Sections 9.3. Saturn’s Moons. 62 Moons, 53 named (18 above). Mostly icy, some with rocky cores. Titan is the 2 nd largest moon in our Solar System & only one with a “real” atmosphere with N 2 , CH 4 , CO 2 (1.5 bar!)

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Life around Saturn, and beyond

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life around saturn and beyond

Life around Saturn,and beyond

ASTR 1420

Lecture 15

Sections 9.3

saturn s moons
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 molecules

CH4, C2H2, C2H6, C3H8, …, argon, CO2, etc.

Always covered with thick haze/smog

Cassini/Huygens in 2004+

Titan, the Masked!

Voyager 2 image of Titan

titan s landscape from huygens descending image
Titan’s landscape from Huygens descending image…

looks like a dry streambed!

Water ice as rocks…

interior of titan
Satellite gravity measurement…

Similar to Callisto, Titan’s interior is not differentiated!

It has a subsurface ocean at very low temperature  mixture of water and ammonia

Controversial… : some believe that it should have a rocky core + icy mantle…

A lot of NH3 !

Interior of Titan
titan s atmosphere
Titan’s Atmosphere
  • 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 60km smaller than Ganymede…
  • NH3 + CH4 + solar UV photons organic molecules…
  • Drizzle of methane and ethane. Possible lakes/oceans of methane
liquid flow
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
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
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
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 atmosphere
10 times more extended than Earth’s

Key factor  size (gravity)

How does Titan have an atmosphere when even a larger moon Ganymede doesn’t?

distance from the Sun

effect of their host planets

Origin of Atmosphere

Image of Titan taken from Cassini orbiter

  • 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
More surface feature : Sand Dunes

Windblown dunes

Namib desert from Space Shuttle

titan summary
Titan : summary
  • Very similar features with very different composition and temperature!
  • A lot of liquid hydrocarbons!

about 200°C colder than liquid water  much slower chemical reaction  slower metabolism

  • 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!

Complex organic aerosols consisting of CHN and hydrogen gas (H2), which escapes into space. Ethane and methane partly condense, forming clouds and hazes that precipitate, replenishing the lakes and bearing many organic species in solution. (Nature 454, 587-589; 31 July 2008)

active enceladus
Tiger stripes = fresh ices  cracks or groovesActive Enceladus
  • 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!

6th largest moon of Saturn

enceladus creates saturn s e ring
Enceladus creates Saturn’s E-ring

Cassini (2006) : 2007-03-27 APOD

strange surface
Equatorial bulge (how???)Strange Surface
  • Heavily terraformed satellite?
triton s cantalope skin
Triton’s cantalope skin
  • Possibly formed by diapirism (i.e., slow boiling pattern)
triton surprising possibility of potential habitability1
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!
signal from pioneer
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
In summary…

Important Concepts

Important Terms

icy volcanism (cryo-volcanism)

  • At least six potentially habitable jovian moons!
  • Europa, Ganymede, Callisto, Titan, Enceladus, and Triton
  • 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!