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The Moons of the Jovian Planets

Goals• Saturn’s Titan and Enceladus• Neptune’s Triton• A tour of neglected moons• Energy and life

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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% N2, CH4 clouds.

AtmosphereLow pressure icesWater oceanHigh pressure iceSilicate core

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Saturn’s Titan – the basics

Atmospheric MethaneIt 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

CH4 + photons CH, CH2 C2H6

Methane (CH4) and ethane (C2H6) 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.

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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 N2 atmosphere probably originated from outgassing?

Radar-smooth surfaces due to lakes of methane/ethane?

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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.

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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?

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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 N2 emerging from underneath solid N2?

Triton of Neptune

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Europa Titan

Ganymede Enceladus

Callisto Triton

Jovian satellite all-stars

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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?

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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.

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Energy from redox!Consider the reaction of burning hydrogen gas with oxygen:

2H2 + O2 2H2OBreak this down into steps:

2H2 4H+ + 4e- Hydrogen donates electrons (Increasing its charge, making it more positive)

4e- + O2 2O-2 Oxygen accepts the electrons (Reducing its charge to a negative number)

4H+ + 2O-2 2H2O Chemists say the oxygen is reduced and the hydrogen is oxidized—Redox!

More redox energy sources:

C6H12O6+ 6O2 6CO2 + 6H2O + energy

2Fe+2 + ½O2 + 2H+ 2Fe+3 + H2O + energy

THIS is why we look for water-rock interfaces in planetary cores.

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Cold temperatures

H2O freezes 273 K 32ºF

CO2 deposits/sublimates 195 K -109ºF

O2 condenses/vaporizes 90 K -300ºF

N2 condenses/vaporizes 77 K -321ºF

Mars: min: 186 Kmean: 227 Kmax: 268 K

Europa: 102 KGanymede: 110 KCallisto: 134 KTitan: 94 KEnceladus: 75 KTriton: 38 K