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Saturn System Gas Giant: Smaller Than Jupiter… About 95 Earth Masses

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Saturn System Gas Giant: Smaller Than Jupiter… About 95 Earth Masses Saturn system Satellites of Saturn Gas giant: smaller than Jupiter… about Large number ~60 moons 95 Earth masses Enceladus: 500km diameter moon, orbital radius 240,000km Titan: 5150km diameter - second largest moon in the Solar system after Ganymede • orbital radius 1.2 million km • orbital period (Saturn) 16 days • rings: extend from 6,000-120,000 km above the equator • orbital period of Saturn ~30 years of Saturn… made up of mostly small icy particles • orbital radius is 9.6 AU - planet formed in a still colder Solar flux ~1% of value at Earth part of the protoplanetary disk in which hydrocarbon ices as well as water ice were present Temperature in absence of greenhouse effect ~80K Extraterrestrial Life: Spring 2008 Extraterrestrial Life: Spring 2008 Both satellites are of interest for astrobiology: Atmospheric properties Titan atmosphere: Enceladus: possible existence of liquid water in the subsurface - plumes mean that it is easily Dense atmosphere extends several hundred km high accessible to measurements! Surface pressure is ~1.5 times Earth pressure, surface Titan: no evidence for liquid water, but many similarities temperature ~90K to the early Earth - may provide information on the chemistry that preceded life on Earth P " #T The ESA Huygens probe landed on Titan early in the 1.5 times higher 3 times lower than Earth Cassini mission than Earth (90K rather than 300K) Solv!ing : density at Titan’s surface is about 5 times the terrestrial value Extraterrestrial Life: Spring 2008 Extraterrestrial Life: Spring 2008 Differences between Titan and Ganymede Atmosphere: Jovian moon Ganymede is similar in size to Titan, but • 98% nitrogen N has no atmosphere… 2 • 2% methane CH4 • small amount of H Temperature in the protoplanetary disk: 2 Atmospheric haze is due to • Jupiter - water ices hydrocarbons - literally smog • Saturn - hydrocarbon ices Appears Titan started with a large reservoir of material that can survive (in modified form) in the atmosphere Interpretation: methane and ammonia (NH3) released from for a long time the surface are broken up in the high atmosphere… hydrogen escapes whereas N2 is retained. Short lifetime of CH4 (10s of millions of years) in the atmosphere suggests reservoir: lakes, seas, ocean Extraterrestrial Life: Spring 2008 Extraterrestrial Life: Spring 2008 1 Cycle with methane Atmosphere largely obscures Titan’s surface in the optical and other or infra-red - surface maps from Cassini’s radar and from hydrocarbons camera on the Huygens probe playing the same Radar image colored to role that water does emphasize smooth areas on the Earth of terrain near the pole - these may be lakes of hydrocarbons Release of carbon in the upper atmosphere from destruction of methane leads to formation of heavier organic compounds which then rain out of the atmosphere Low sunlight means desert-like conditions - lots of methane in the atmosphere but ~1cm precipitates out per year Extraterrestrial Life: Spring 2008 Extraterrestrial Life: Spring 2008 Surface from River channels an altitude of Sand dunes about 10km Impact craters Lakes during the … Huygens probe descent Topography looks Dry river quite a lot like channels? Earth No very clear sign of volcanic activity Extraterrestrial Life: Spring 2008 Extraterrestrial Life: Spring 2008 View from the surface: dry Liquid water? at the Huygens landing site, No evidence for liquid water - much too cold on the with icy pebbles surface. Atmosphere contains: Speculations: • simple molecules (HCN, C2H6) • subsurface lakes or oceans, heated by internal heat • polymers of quite from radioactive decay uncertain make-up • liquid water in volcanic hotspots (`tholins’) - maybe • transient (~1000 years) water in regions heated by polymers of HCN impacts Gas phase reactions seem Unless life without water is possible, seems unlikely that to occur at high altitude, conditions for habitability are satisfied on Titan. with condensed materials in the lower atmosphere and on the surface Extraterrestrial Life: Spring 2008 Extraterrestrial Life: Spring 2008 2 Pre-biological chemistry Future exploration possibilities In increasing complexity: Numerous more Cassini flybys • simple organic molecules 4 candidate `flagship’ missions to the • complex molecules (polymers) outer planets: • amino acids • Europa orbiter • replicating molecules • Jupiter orbiter • life • Enceladus orbiter • Titan explorer First three are either definitely present on Titan or seem probable - opportunity to study these processes on another world Titan proposal includes an orbiter, a lander, and possibly a balloon to study the surface chemistry in detail If selected, launch from 2015 onwards… Extraterrestrial Life: Spring 2008 Extraterrestrial Life: Spring 2008 3.
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