Astronomy 340 Fall 2005 4 October 2005 Class

Astronomy 340 Fall 2005 4 October 2005 Class #9

Salient Martian Features n RMars = 3396 km (REarth = 6378 km) q q n Atmospheric Composition q q n Higher surface area to mass ratio More efficient cooling Lower internal heat flow, less volcanism No plate tectonics 95% CO 2 (same as Venus) Pressure = 0. 006 bar (Earth = 1, Venus = 89) TSurface hey, it’s cold! q q q Mean solar constant 0. 431 (Earth =1) Summer T ~ 273 K (max) Winter (polar) T ~ 150 K ground is permanently frozen to 1 km

Soil Composition

Mars Missions n n n Current Missions q Spirit and Opportunity (rovers) q 2001 Mars Odyssey (orbiter) q Mars Global Surveyot (orbiter) q Mars Express (polar orbit) q Mars Reconnaissance Orbiter (just launched) Planned q Phoenix q Mars Science Laboratory Past q Mariner flybys/orbiters q Viking landers q Pathfinder

NASA Mars Missions -- Goals n n Determine whether life ever arose on Mars Characterize the Climate of Mars Characterize the Geology of Mars Prepare for Human Exploration

Where to land? n n Equatorial maximum solar radiation Low elevation maximum atmosphere to slow descent, low shear Relatively flat to preserve airbag Radar-reflective, hard surface for rovers

Where to land? n Parachute to slow descent, followed by bouncing airbag….

Gusev Crater

Spirit Landing Site Golombek et al 2005 Nature 436 44 n Nice and flat….

Opportunity landing site – and some space junk

Rock size distribution on landing sites

Surface Composition Bibring et al. 2005 Science 307 1576 n Ices/Frosts q q n Hydrated Minerals/Ferric Oxides q q n CO 2 veneers over polar ice caps H 2 O ice w/ dust Significant presence – detected via 3μm feature Primarily in older craters (younger craters lack hydrated minerals) Igneous Rocks q Standard olivines

Water on Mars n n Canals? Background origin of H 2 O on Earth q Outgassing via internal processes volcanic n q n External origin via hydrated impactors (comets? ) Maintaining liquid H 2 O on surface…. q Temperature n n q n n Liquid H 2 O unstable at 150 K < T < 220 K But ice on stable at poles Pressure n n Formation via accretion of hydrated protoplanetary material Sublimation of polar ice atmospheric pressure insufficient to maintain water in atmosphere Dissociation of H 2 O, loss of H Current conditions not favorable for liquid H 2 O on Martian surface or significant H 2 O in atmospere But…. .

Water on Mars n n n Polar Ice Caps Mariner 9 (1972) images of obvious channels that look like river beds major amounts of surface water in past Atmospheric chemistry q q Trace H 2 O content via outgassed volatiles 80 -160 m of water outgassed North Polar Ice Cap in summer

Water on Mars n Water channels q Outflow channels n n n q Valley networks n n q n Catastrophic floods (108 m 3 s-1 vs 104 m 3 s-1) “sudden” appearance Volcanism, internal pressure, ? ? ? Look like river systems groundwater Fretted channels Remote sensing/imaging

Gusev Crater Haskin et al 2005 Nature 436 66 n n Gusev plain an old lake bed? Primarily igneous rock (olivine basalt) q q Veins/plugs aqeous solutions plausible Composition measured via near-IR spectrometer

Gusev crater Haskin et al 2005 Note inclusions – need water to form

Gusev Crater Haskin et al 2005 Nature 436 66 q q q Veins/plugs aqeous solutions plausible Composition measured via near-IR spectrometer Various geochemical effects of aqeous solutions n n n E. g. ratio of Al 2 O 3 vs SO 3 Increased ratio of salts, oxidation of Fe 2+ Conclusions: running water, but no pools/oceans Inverse correlation – mixing with evaporative component with high S content

Gusev Crater Haskin et al 2005 Nature 436 66 n n Gusev plain an old lake bed? Primarily igneous rock (olivine basalt) q q q Veins/plugs aqeous solutions plausible Composition measured via near-IR spectrometer Various geochemical effects of aqeous solutions n n n E. g. ratio of Al 2 O 3 vs SO 3 Increased ratio of salts, oxidation of Fe 2+ Conclusions: running water, but no pools/oceans

Frozen Equatorial Sea? Murray et al. 2005 Nature 434 352 n n What are these cracked “plates”? Lava? The authors think not… Edges much younger than rest of plate – lava doesn’t do this Crater density suggests age ~ 5 Myr Resemblance of plates to pack-ice in Arctic

a. Mars 13. 7 m resolution b. Antarctica c. Martian ice raft?

Phobos & Deimos n Low inclination, equatorial orbits