Upload
caitlin-johnston
View
216
Download
0
Tags:
Embed Size (px)
Citation preview
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! Voyager 2 image of Titan
• sunlight 1/100 of Earth -180°C
• A lot of organic molecules
CH4, C2H2, C2H6, C3H8, …, argon, CO2, etc.
• Always covered with thick haze/smog
• Cassini/Huygens in 2004+
Cassini + Huygens (2004- )
Titan’s landscape from Huygens descending image…
looks like a dried streambed!Water ice as rocks…
Taken at an altitude of ~8 km.
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 !
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 55km smaller than Ganymede…• NH3 + CH4 + solar UV photons organic molecules…• Drizzle of methane and ethane. Possible lakes/oceans of methane
Ganymede : 2631 km radiusTitan : 2576 km radius 55km
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
-183C
Possible ethane world?
Origin of Atmosphere
Image of Titan taken from Cassini orbiter
• 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?1. distance from the Sun2. effect of their host
planets
• 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 Namib desert from Space Shuttle
made of hydrocarbon sediments.
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!
Earth Titan
liquid water liquid methane
silicate rocks water ice rocks
molten lava volcano ice/slush volcano
silicate sand dunes organic particulate dunes
Active 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!
• Tiger stripes = fresh ices cracks or grooves
6th largest moon of Saturn
Enceladus
Cryovolcanism
feeding a ring of Saturn
Iapetus : An Intelligence Test for Earthlings?
3rd largest moon of Saturn
a large brightness change (10+ times) over one rotation period!
Strange Surface• Heavily terraformed?
• Equatorial bulge (how???)
Iapetus = Alien’s Starship?
?
No, Iapetus is in fact Deathstar!
Triton: Surprising possibility of potential habitability
• Cryovolcanism…
largest moon of Neptune
Triton’s cantalope skin
Possibly formed by diapirism (i.e., slow boiling pattern)
• 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 oceaneven at -230°C, possible habitable world!
Triton: Surprising possibility of potential habitability
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• 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.
Important Terms• icy volcanism (cryo-volcanism)
Chapter/sections covered in this lecture : 9.3Next lecture : Exo-planets!