1. 1 The Moons of the Jovian Planets Goals Saturn’s Titan and Enceladus Neptune’s Triton A tour of neglected moons Energy and life

2. 2 Saturn’s Titan – the basics Size: 1.48× Earth’s moon, mass: 1.8× Earth’s moon; Temperature: -180ºC (-290ºF); Interior: ices, possibly a fluid water ocean; Atmosphere 1.5 Earth’s; 90-98% N 2, CH 4 clouds. Atmosphere Low pressure ices Water ocean High pressure ice Silicate core

3. 3 Saturn’s Titan – the basics Atmospheric Methane It should be photo-disassociated by solar UV by now. Its persistence means something is replenishing it. What is doing this? It is so cold on Titan that methane would also be liquid. Titan might have huge oceans of methane that slowly evaporate. Atmospheric methane would also result in interesting chemistry CH 4 + photons  CH, CH 2  C 2 H 6 Methane (CH 4 ) and ethane (C 2 H 6 ) could occur as liquids at Titan’s temperature and pressure. Are there drizzling methane and ethane rains on the surface of Titan? A biological source of the methane has not been eliminated.

4. 4 Remote views of Titan’s surface The Cassini flyby mission mapped much of the surface in radar, and observed surface shifting by 30 km in 2 years (hence, subsurface oceans); Dunes and craters have been observed. Surface volcanism has been proposed, with water as the magma? The N 2 atmosphere probably originated from outgassing? Radar-smooth surfaces due to lakes of methane/ethane?

5. 5 Titan’s surface! Huygens probe was released from Cassini on 15 Jan 2005. It reached the surface, and landed on dry land. Ultimately, although organic compounds occur in great quantities, it is difficult to imagine the chemistry of life occurring at the extremely low temperatures on Titan.

6. 6 Enceladus of Saturn Vital stats – –Size: 249 km radius—0.14× Earth’s moon; – –Mass: 0.002× Earth’s moon; – –An extraordinarily surprisingly active world, with water geysers occurring at its southern pole; – –Is it possible that a habitable zone occurs under its crust? – –How much real estate do you need for life?

7. 7 Vital stats – –Size: 0.78× Earth’s moon – –Mass: 0.29× Earth’s moon; – –Retrograde orbit, probably a captured Kuiper Belt Object; – –Tidal forces are slowing it in its orbit—a far distant descent into Neptune may be inevitable; – –Very cold: -230ºC (-380ºF); – –Geysers of N 2 emerging from underneath solid N 2 ? Triton of Neptune

8. 8 Europa Titan Ganymede Enceladus CallistoTriton Jovian satellite all-stars

9. 9 Jupiter (64), Saturn (62), Uranus (27), Neptune (13)! Probably dead, but many show indications of drama! Some of Saturn’s midsize moons Some of Saturn’s small moons Some of Uranus’s small moons MimasDione Phoebe Iapetus Hyperion Miranda What else have we missed?

10. 10 Energy and Life In order to be able to tap into energy in a useful way, you must have a disequilibrium. Example: a hot room has energy in it, but you cannot tap into it as an energy source. But a hot room next to a cold room can be tapped into as an energy source. Hence, drafts! Equilibrium conditions – –Reactions can occur, but they are balanced by reverse reactions. – –No overall changes occur with time. Disequilibrium conditions – –Even if energy is available, you need to be able to tap into it. – –Voltage drops.

11. 11 Energy from redox! Consider the reaction of burning hydrogen gas with oxygen: 2H 2 + O 2  2H 2 O Break this down into steps: 2H 2  4H + + 4e - Hydrogen donates electrons (Increasing its charge, making it more positive) 4e - + O 2  2O -2 Oxygen accepts the electrons (Reducing its charge to a negative number) 4H + + 2O -2  2H 2 O Chemists say the oxygen is reduced and the hydrogen is oxidized—Redox! More redox energy sources: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy 2Fe +2 + ½O 2 + 2H +  2Fe +3 + H 2 O + energy THIS is why we look for water-rock interfaces in planetary cores.

12. 12 Cold temperatures H 2 O freezes273 K32ºF CO 2 deposits/sublimates 195 K-109ºF O 2 condenses/vaporizes 90 K-300ºF N 2 condenses/vaporizes 77 K-321ºF Mars: min: 186 K mean: 227 K max: 268 K Europa: 102 K Ganymede: 110 K Callisto: 134 K Titan: 94 K Enceladus: 75 K Triton: 38 K