Download Lecture 08b: Other Jovian moons - Sierra College Astronomy Home

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.
Atmosphere
Low pressure ices
Water ocean
High pressure ice
Silicate core
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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
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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Triton of Neptune
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?
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Jovian satellite all-stars
Europa
Titan
Ganymede
Enceladus
Callisto
Triton
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What else have we missed?
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
Dione
Phoebe
Mimas
Iapetus
Hyperion
Miranda
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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  2H2O
Break this down into steps:
2H2  4H+ + 4e4e- + O2  2O-2
Hydrogen donates electrons
(Increasing its charge, making it more positive)
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
CO2 deposits/sublimates
O2 condenses/vaporizes
N2 condenses/vaporizes
Mars:
Europa:
Ganymede:
Callisto:
Titan:
Enceladus:
Triton:
273 K
195 K
90 K
77 K
32ºF
-109ºF
-300ºF
-321ºF
min: 186 K
mean: 227 K
max: 268 K
102 K
110 K
134 K
94 K
75 K
38 K
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