The Icy Moons and the Extended Habitable Zone
Europa Interior Models
Other Types of Habitable Zones Water requires heat and pressure to remain stable as a liquid
Extended Habitable Zones You do not need sunlight. You do need liquid water You do need an energy source. Examples: Black smokers Europan ocean?
Europa All these worlds are yours... Except Europa. Attempt no landings there. Arthur C. Clarke, 2010: Odyssey Two
Titan and the Moons of Saturn
Telesto Titan Prometheus Dione Titan
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Recap Life is a disequilibrium process O 2 on Earth is maintained by plants/ photosynthesis Metabolisms get energy from disequilibrium.
Redox Reactions H 2 è 2H + + 2e - (reduction) 1/2 O 2 + 2H + +2e - è H 2 O (oxidation) Aerobic respiration 2Fe ++ + 1/2 O 2 + 2H + è 2Fe +++ +H 2 O C 6 H 12 O 6 + 6O 2 è 6H 2 O + energy
Equilibrium Temperatures Recall that T EQ ~ (L * /d 2 ) 1/4 Planet Distance (AU) T EQ (K) Mercury 0.38 400 Venus 0.72 291 Earth 1.00 247 Mars 1.52 200 Jupiter 5.20 108 Saturn 9.53 80 Uranus 19.2 56 Neptune 30.1 45
Saturn and its Satellites Saturn is nearly twice as far from the Sun as Jupiter Saturn gets ~30% of Jupiter s sunlight: It is commensurately colder Prometheus Saturn has 62 known satellites (plus the rings) 7 major 24 regular 4 Trojan 38 irregular Others in rings Titan Titan is nearly as large as Ganymede
Titan The second-largest moon in the Solar System The only moon with a substantial atmosphere 90% N 2 + some CH 4, Ar, C 2 H 6, C 3 H 8, C 2 H 2, HCN, CO 2
The Atmosphere of Titan 1.5 bar pressure, T=95 K Condensation sequence: Jovian Moons: H 2 O ice Saturnian Moons: NH 3, CH 4 NH 3, CH 4 gaseous at lower temperatures 2NH 3 + sunlight è N 2 + 3H 2 CH 4 + sunlight è CH, CH 2
The Intrigue Free CH 4 requires replenishment Liquid methane on the surface? Hazy atmosphere/clouds may suggest methane/ ethane precipitation. (Liquid natural gas anyone?) This atmosphere may resemble the early terrestrial atmosphere.
Near-IR image penetrates the haze and sees surface features
Near-IR image (933 nm)
The Sea?
The Lake?
Part of the Cassini mission Landed on Titan 1/14/05 The Huygens Probe
A Coastline? Rivers? The View from Above
é Panoramic view from 8 km The surface in true color è Rocks are probably water ice The Surface
Lessons At 8 km, the atmosphere is saturated with CH 4 Surface features look like lakes and riverbeds H 2 O rocks show evidence of erosion Titan is a dynamic world, with CH 4 and C 2 H 6 precipitation Photochemical smog due to organic molecules Titan has all the building blocks for life
Life on Titan? Probably not. Titan is cold. But C 2 H 2 (acetylene) could be a source of energy. Titan does have subsurface water oceans heated tidally, beneath a thick crust of water ice (Science 319, 1649 3/21/08)
Enceladus
Enceladus up close
Tiger Stripes Enceladus
Tiger Stripes IR-bright emission near the south pole of Enceladus
Geysers Gas and dust plumes from occultation photometry. V=600 km/s March 2008 Cassini flyby
Geyser Plumes backlit
Cassini Enceladus Flyby 12 March 2008 Came within 30 km of surface Flew through geysers at 120 km altitude Geysers suggest subsurface water at 0C
Enceladus Model Ocean 10 km thick Below 30-40 km ice Science, 4/4/14
Mimas Closest of the large moons.
Mimas Librates (wobbles) 6 km wobble suggests a liquid interior, or an oval core See http://www.sciencedaily.com/ releases/ 2014/10/141016143656.htm Science, 2014; 346
What s Next? EJSM: Europa/Jupiter System Mission (LaPlace) Europa orbiter Jupiter orbiter http://sci.esa.int/science-e/www/area/index.cfm?fareaid=107 2026 lunch date proposed TSSM: Titan/Saturn System Mission Titan orbiter Balloon floating in Titan s atmosphere Saturn orbiter, focussing on Enceladus Launch in 2020s; orbital insertion 7 years later
Triton Further Out
Implications for N H Planets (and moons) create their own habitable zones Habitable zones change with time Venus and Mars were probably habitable (but are not in the CHZ) Earth is habitable Europa, Callisto, Titan, Enceladus, Mimas, and other icy satellites are potentially habitable N H > 1 seems reasonable
Implications for f l Life started at least once in the Solar System The basic ingredients for biochemistry are common in the Solar System We will not know whether life started more than once in the Solar System without more detailed investigations. f l = 1 seems reasonable
N Update N = N * f s f p n H f l N * = 4 x 10 11 f s = 0.2 f p = 1.0 n H = 2 f l = 1.0 N = 1.6 x 10 10