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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 0.653 0.952 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 0.653 0.952 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