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ASTR/GEOL-2040: Search for life
in the Universe: Lecture 21
• Studying Titan’s interior?
• Enough methane?
• Cryovolcanism, life
Advantages of fly-bys…
• Measuring thickness of atmosphere
• 1.6 bar
Titan
• Titan’s pressure of 1.6 bar
– Bennett & Shostak, p. 319
– “fairly comfortable even without space suit”
– Why? What’s the problem at low pressures?
A.
B.
C.
D.
Can’t hear normally
Can’t balance properly
Body tissue would burst
Water would boil
Neil Armstrong?
1930-2012
• Titan’s pressure of 1.6 bar
– “fairly comfortable even without space suit”
• Atmosphere 200 km thick
– Radius 2576 km + 200 km = 2776 km
– Larger than Ganymede, radius 2634 km
– Keeping with its name
Titan
• Titan’s pressure of 1.6 bar
– Bennett & Shostak, p. 319
– “fairly comfortable even without space suit”
– Why? What’s the problem at low pressures?
A.
B.
C.
D.
Can’t hear normally
Can’t balance properly
Body tissue would burst
Water would boil
Titan: looks big
• Titan’s pressure of 1.6 bar
– “fairly comfortable even without space suit”
• Atmosphere 200 km thick
– Radius 2576 km + 200 km = 2776 km
– Larger than Ganymede, radius 2634 km
– Keeping with its name
Another + for fly-bys…
• Measuring thickness of atmosphere
• Can also measure …
Lect 18: Galilean satellites
• Orbital periods: • Distances:
–
–
–
–
1.769 d
3.551 d
7.155 d
16.69 d
–
–
–
–
422,000 km (Io)
671,000 km (Europa)
1070,000 km (Ganymede)
1883,000 km (Callisto)
Kepler’s law
Orb. period
P  2 r / GM
3
M is mass
of Jupiter
8
Another + for fly-bys…
• Measuring thickness of atmosphere
• Can also measure Titan’s mass
Why is the mass important
A. To tell whether Titan can have atmosphere
B. How strong a magnetic field it could have
C. How large is its rocky core
D. How large it its iron core
E. How thick it its crust?
Lect. 18, p. 21
•
•
•
•
Callisto: 1.83 x 103 kg/m3
Chondritic meteorites: 3.10 x 103 kg/m3
Ice: 0.95 x 103 kg/m3
r = x rdense + (1-x) rlight
 x=0.41
We is the mass important
A. To tell whether Titan can have atmosphere
B. How strong a magnetic field it could have
C. How large is its rocky core
D. How large it its iron core
E. How thick it its crust?
How do we do this?
• Kepler’s law useful if orbit around Titan
• Or trajectory affected by Titan
• Simple if we make relative statements
• Example 1: Saturn’s mass relative to Jupiter
• Example 2: Titan’s mass relative to Saturn
(i) Saturn’s satellites
• Orbital periods P: • Distances r:
– 1.37 d
– 15.9 d
– 238,000 km (Enceladus)
– 1220,000 km (Titan)
•
P  2 r 3 / GM
M  r3 / P2
Orbital periods: •
– 1.769 d
– 3.551 d
– 7.155 d
– 16.69 d
Distances:
– 422,000 km (Io)
– 671,000 km (Europa)
– 1070,000 km (Ganymede)
– 1883,000 km (Callisto)
Ratio:
M S  rTi tan 

 
M J  rCal 
3
2
 PTi tan 
3
2

  0.65 0.95  0.27 0.91  0.30
 PCal 
14
M S  rS 
  
M J  rJ 
3
 PS

 PJ
2

  0.653 0.952  0.27 0.91  0.30

Saturn is
A. 30% more massive than Jupiter
B. 30% less massive than Jupiter
C. about 3 times more massive than Jupiter
D. about 3 times less massive than Jupiter
E. neither of the above
15
M S  rS 
  
M J  rJ 
3
 PS

 PJ
2

  0.653 0.952  0.27 0.91  0.30

Saturn is
A. 30% more massive than Jupiter
B. 30% less massive than Jupiter
C. about 3 times more massive than Jupiter
D. about 3 times less massive than Jupiter
E. neither of the above
 6x1026 kg
=100 times Earth’s mass
16
(ii) Same to get Titan’s mass
M T  rSatellite 

 
M S  rTi tan 
3
2
 PSatellite   10,000 km 

  

 PTi tan   1220,000 km 
3
 0.8 d 


 16 d 
2
MT
3
2
 0.008 0.05  5.5 10 7 0.0025  0.00022
MS
 1.3x1023 kg
17
Titan
• Titan’s pressure of 1.6 bar
– “fairly comfortable even without space suit”
• Atmosphere 200 km thick
– Radius 2576 km + 200 km = 2776 km
– Larger than Ganymede, radius 2634 km
– Keeping with its name
• What sustains it?
Titan’s atmosphere
• Infrared spectrum from Voyager
Most abundant inTitan’s
atmosphere:
A.
B.
C.
D.
E.
N2
O2
Ar
H2
CH4
Most abundant inTitan’s
atmosphere:
A.
B.
C.
D.
E.
N2
O2
Ar
H2
CH4
Tritan
Venus?
Solar
nebula
• Wet:
22
Earth: 1 atm = 1 hPa = 105 Pa, so its 1/1000
Table
• From
1700 K
to 20 K
• Refractory
minerals:
T50>1100K
23
Origin of N2
Lect. 19, p.16
Bermuda triangle
• N2 trapped in the ice (as clathrates)
• Lab experiments: N2 and Ar trapped equally
• Original ratio: Ar/N2 ~ 0.06
A.
B.
C.
D.
Ar/N2 ~ 0.6
Ar/N2 ~ 0.06
Ar/N2 ~ 0.006
Ar/N2 << 0.0006
Lect 20: Atmospheric composition
• N2, CH4, and H2 most important
gas
concentration
N2
0.97
CH4
0.049
H2
0.0011
CO
0.00006 (6e-5)
Ar
0.0000432
C2H6
0.000011
C2H2
0.000003 (3e-6) [ethyne]
[ethane]
Origin of N2
Lect. 19, p.16
Bermuda triangle
• N2 trapped in the ice (as clathrates)
• Lab experiments: N2 and Ar trapped equally
• Original ratio: Ar/N2 ~ 0.06
A.
B.
C.
D.
Ar/N2 ~ 0.6
Ar/N2 ~ 0.06
Ar/N2 ~ 0.006
Ar/N2 << 0.0006
Actually
0.00004
4e-5
nd
2
model: 2NH3  N2 + 3H2
• Would be very slow at 94K
• if reaction in equilibrium!
Lect 4: Energy sources on Earth
•
•
•
•
Reducing atmosphere:
H2, H2O, NH3, CH4,
Discharges
Steam
28
2NH3  N2 + 3H2 not directly
• NH3  NH2 + H
• NH2 + NH2  N2H4
Hydrazine (famable)
• N2H4  N2+2H2
Methane: similar story
• CH4  CH3+H (methyl molecule)
– has an unpaired electron  highly reactive
– chemists call thisCa2H“radical”
2
• CH3+CH3  C2H6 (ethane)
– Readily absorbs ultraviolet
– C2H6  C2H2 + 2H2 (C2H2 ethyne)
Continue
losing H
• Longer carbon
chains
• HCC + HCCH
 HCCCCH+H
• Never regain
any methane
– irreversible
Haze = Smog
• Aerosols
• Wet haze
• Photochemical smog/haze
Why not on Ganymede?
• Warmer, so methane not liquid
Ganymede too
warm for liquid
methane?
Other implications
• How to explain the 5% methane in
Titan’s atmosphere?
• 5 x 1013 molecules m-2s-1 destroyed
• 1.3 x 10-12 kg m-2s-1
Evaporation from
huge lakes?
• Discovered by Huygens (1629 – 1695)
Do we have enough in
the lakes, Daniel?
• Discovered by Huygens (1629 – 1695)
Delivery via comets?
• on Earth: Krypton, xenon: delivered by comets
• Titan: no krypton nor xenon found
• Why not?
A. Comets negligible, insufficient delivery
B. Lost because of thermal escape
C. Not enough rocky material, no radioactive decay
Delivery via comets?
• on Earth: Krypton, xenon: delivered by comets
• Titan: no krypton nor xenon found
• Why not?
A. Comets negligible, insufficient delivery
B. Lost because of thermal escape
C. Not enough rocky material, no radioactive decay
Wait: what’s this?
• Discovered by Huygens (1629 – 1695)
Volcanoes?
• How does it work?
• Not too cold?
Cryovolcanism
• Titan’s interior not warm enough to melt rock
– So: need low temperature volcanisms
• Driven by melting, vaporizing water, ammonia, methane
• May help explain mystery of replenishing methane
Historical background
• Discovered by Huygens (1629 – 1695)
Historical background
• Discovered by Huygens (1629 – 1695)
Historical background
• Discovered by Huygens (1629 – 1695)
Analogies
Core•
Rocky planet
xx
Iron
Mantle
Silicate rocky shell
Crust
Rock
Outgassing
CO2
Eruption of …
Lava
Aerosols
Dirt
Dunes
Sand
Cycles
Water
Icy body
Analogies
Rocky planet
Icy body
Iron
Rock
Mantle
Silicate rocky shell
Liquid water
Crust
Rock
Water ice
Outgassing
CO2
CH4
Eruption of …
Lava
Slush
Aerosols
Dust
Haze
Dunes
Sand
Organics
Cycles
Water
Methane
Core•
xx
Life on Titan?
• Would methane-based life be
A. Fast
B. Slow
Life on Titan?
• Would methane-based life be
A. Fast
B. Slow
because chemical reaction speed
decreases with decreasing temperature
Life on Titan?
• Methane-based
– ?faster/slow
• Chemical reactions slow  “slow life”
– But what if bonds are weaker?
A. Maybe reactions not so slow after all
B. Reactions too fast
C. Reactions slower still
Life on Titan?
• Methane-based
– ?faster/slow
• Chemical reactions slow  “slow life”
– But what if bonds are weaker?
A. Maybe reactions not so slow after all
B. Reactions too fast
C. Reactions slower still
Life on Titan?
• Methane-based
– ?faster/slow
• Chemical reactions slow  “slow life”
– ? But what if bonds are weaker
• Maybe based on weaker chemical bondings
– Maybe not so slow
• But less able to dissolve other chemicals
– Outlook is bleak
Other ideas
•
•
•
•
•
•
Heat from occasional impacts
Warm pockets persist for ~1000 yr
Life? But at least interesting chemistry
Volcanic cones ~1000 – 1500 m high
Hot springs
…
Bacteria in apolar
environment!?
• Discovery of bacteria in oily lake in
Caribbean island of Trinidad: Pitch Lake
The lesson so far…
• In the ocean, like in Europa?
– Not just water, lots of ammonia
• Also: do amino acids form?
– Equally left/right handed ones?
• Inspiration about life as we don’t know it
Next time
•
•
•
•
Outer solar system’s bodies
More on icy bodies
Pluto
Organics on/in comets
• Longstaff: pp 297 – 303
• BS: 319 – 326