Lec 11 Life in the Solar System

runaway glaciation also positive feedback thin

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Unformatted text preview: ach of Earth and Mars.! Runaway Glaciation (also positive feedback)! Thin atmosphere led to Weak Greenhouse ! Cold temperature led to freeze-out of greenhouse gases Temperature range now: T = 175 - 300 K! Some places warm enough for liquid H2O! but pressure is too low! ! Active in past, but not now: Fossil river beds! ! Liquid H2O for ~ 1 × 109 yr (and perhaps more recently)! ! Life?! Survive another 0.7 × 109 yr in frozen lakes?! Analogy to Antarctic lakes! Antarctica as a model for early Mars! Dry valleys: Mean T = –20 ºC! Annual precipitation ~ 2 cm! But T > 0ºC for a few days in summer.! ⇒ Lakes are not frozen solid (though always ice-covered)! Algae & bacteria photosynthesize in lakes! Also lichens in rocks! Lake Vostok below ice for about 0.5 Myr! Were there similar situations on Mars?! If life arose on Mars, it might have lasted a while! ! Viking Mission! 2  spacecraft !1976! !1.! !Chryse Planitia !22º N. Lat! !2.! !Utopia Planitia !48º N! ! Cameras, …! ! Organic Matter Analysis! 3 life detection experiments! Sampler arm! Organic Matter Analysis! •  Could detect carbon molecules! –  Few/billion if more than 2 Carbons! –  Few/million if 1 or 2! –  100 to 1000 times less than desert soils! –  Could be left over, brought by asteroids, …! •  No organic molecules found! Life Detection Experiments! •  All assumed microscopic soil organisms! –  Fairly near surface (shallow trench)! –  Either heterotrophs! •  Feed and look for signs of metabolism! –  Or autotrophs! •  Look for signs of photosynthesis! –  If signs of life, do a control experiment! •  Sterilize first! Gas Exchange Experiment (GEX)! •  Most earth-biased! –  Assumed Martians would like chicken soup! –  Pressurized, warmed to 10 C! –  First mode: humidify! •  N2, Argon, CO2...
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This note was uploaded on 04/05/2013 for the course UGS 302 taught by Professor Staff during the Spring '08 term at University of Texas.

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