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Lec 11 Life in the Solar System

Lec 11 Life in the Solar System - Life in the Solar System...

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Life in the Solar System
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Life in the Solar System 1. Study processes that produce current conditions on planets (n e ) 2. Life elsewhere in Solar System? (f l )
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Planet Temperatures Factors in Planet temperature: Greenhouse gas? N 2 , O 2 CO 2 , H 2 O CH 4 , CFC s no yes yes (Life) Reflecting Light (Albedo) Clouds, Rock, Ice, Snow Two extremes: Runaway Greenhouse Runaway Glaciation
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Greenhouse effect
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Terrestrial Planet Atmospheres CO 2 (%) N 2 (%) O 2 (%) H 2 O (%) Pressure (bar) T avg (ºC) T avg (K) Venus 96 ~ 3 trace < 0.1 90 477 750 Abiotic Earth 96 ~ 3 trace ? 60 290 563 Mars 95 2.7 0.16 -- 0.0061 ~ –50 ~ 220 Biotic Earth 0.03 79 21 1.0 15 288
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T = 279K Rapid Rotation, Albedo Apply to Venus, Mars Venus Mars d 0.72 AU 1.52 AU A 0.80 (!) 0.215 T avg 220 213 (no greenhouse) T avg 750 220 (actual) (1 – A) L d 2 1/4 Recall from Chap. 3
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Venus: Basic Facts Sister Planet: R = 0.95 R d = 0.72 d BUT HOT! Clouds: Sulfuric Acid droplets Radar Active surface Age < Age of Planet But no large-scale plates
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View of Venus from Radar Mapping
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Evolution of the Atmosphere Ultraviolet no oceans H O Escape d < d H 2 O higher in atm CO 2 remained in atm Thick atm, Greenhouse Hot! Runaway Greenhouse Example of positive feedback
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Mars: Basic Facts Smaller R = 0.53 R Less Massive M = 0.11 M Less Dense ρ = 0.71 ρ Mars year = 687 Earth days Mars day = 24.5 Earth hours Seasons 2 small moons (captured asteroids)
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Mars
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Ancient Volcanoes Olympus Mons The largest volcano in the solar system 24 km high Scarp is 550 km in diameter
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Polar Ice Caps Image from the Hubble Space Telescope during close approach of Earth and Mars.
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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 H 2 O but pressure is too low Active in past, but not now: Fossil river beds Liquid H 2 O for ~ 1 × 10 9 yr (and perhaps more recently) Life? Survive another 0.7 × 10 9 yr in frozen lakes? Analogy to Antarctic lakes
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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
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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
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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
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