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ASTR/GEOL-2040: Search for life in the Universe: Lecture 22

This lecture explores atmospheric escape and the study of Martian meteorites in the search for life in the universe. Topics covered include atmospheric loss on Mars and Venus, the escape velocity on Mars, stripping by solar wind, and the history of Martian meteorite ALH 84001.

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ASTR/GEOL-2040: Search for life in the Universe: Lecture 22

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  1. ASTR/GEOL-2040: Search for life in the Universe: Lecture 22 • Atmospheric escape • Martian meteorites • ALH 84001 Axel Brandenburg (Office hours: Mondays 2:30 – 3:30 in X590 and Wednesdays 11-12 in D230)

  2. Modern stromatolites (Lect 14)

  3. Stromatolites are • Iron-reducing lithotrophs extracting energy from the rocks they are living on • Photosynthesizing cyanobacteria growing on top of each other • Hydrothermal alkaline vents harboring methanogens that life of hydrogen and CO2 • sedimentary rocks in Western Australia where the oldest microfossils have been found

  4. Στρώμαλίθος

  5. More evidence for early lifeAccumulation of organics • Photosynthesizing cyanobacteria • Grow on top of each other • Layered structure

  6. Martian atmosphere

  7. Comparison Mars really does have a problem

  8. Lecture 13: Water loss on Venus • Same reason as for Mars • UV light: H2O  H2 + ½ O2  photolysis • H2 lost through thermal escape • Why?

  9. Thermal escape? • Escape velocity? • Apollo 8 (Borman, Lowell, Anders) • ½ mve2=GMm/R • ve=(2GM/R)1/2 = 11.2 km/s • ½ mvH2=kBT • H2 is so light M: mass of Earth R: radius of Earth

  10. Thermal escape velocity on Mars? • ve=(2GM/R)1/2 = 11.2 km/s • 4 times higher on Mars • 2 times higher on Mars • Same on Mars as on Earth • 2 times lower on Mars • 4 times lower on Mars

  11. Both M and R are lower • But density about the same • Density = r = Mass/Volume ~ M/R3 • So M ~ rR3 • ve= (2GM/R)1/2 ~ (2GrR3/R)1/2 • ve= (2GrR2)1/2 ~ (2Gr)1/2 R • ve~ R

  12. Again: escape velocity on Mars? • ve=(2GM/R)1/2 = 11.2 km/s on Earth • 4 times higher on Mars • 2 times higher on Mars • Same on Mars as on Earth • 2 times lower on Mars • 4 times lower on Mars

  13. Again: escape velocity on Mars? • ve=(2GM/R)1/2 = 11.2 km/s on Earth • 4 times higher on Mars • 2 times higher on Mars • Same on Mars as on Earth • 2 times lower on Mars • 4 times lower on Mars

  14. Stripping by solar wind • Lightest molecules are seen to escape • Mars lost 99% of its atmosphere

  15. Meteorites from ejecta?

  16. Meteorites from Moon or Mars? • Ejecta from impacts thought implausible… • Apollo: 1969 – 1972 • ALHA81005 first lunar meteorite (lunar highlands) • 31 g • EETA79001 • gases agreed w/ Viking • weathered basaltic rock, 8 kg

  17. Initial classification

  18. Mineralogical comparison

  19. Martian atmosphere in meteorite & many other isotopes

  20. 3rd most abundant element in Martian atmosphere? • Hydrogen • Helium • Neon • Argon • Nitrogen

  21. 3rd most abundant element in Martian atmosphere? • Hydrogen • Helium • Neon • Argon • Nitrogen

  22. ALH – Allan Hill – post office? 50,000 yr 4.55 Gyr

  23. Allan Hills nearest post office?

  24. But it fell in Antarctica Sherghati 1865, El-Nakhla 1911, Chassigny 1815 + ungrouped ones  pyroxene [Greek: fire+stranger]

  25. Post offices in Antarctica

  26. ALH – Allan Hill, EET – Elephant Moraine

  27. in 1996: Mars 6 (press conf) in 1997: Mars 12, Moon 15 in 2010: Moon 134 in 2014: Mars 132 Martian meteorites

  28. Martian meteorites

  29. ALH 84001’s History • 4.1 Gyr solidified from molten rock in southern highlands • 4.0 – 4.1 Gyr: affected by nearby impact, but not ejected (shock metamorphism) • 3.9 Gyr: infiltrated by water  carbonate grains at +18oC, according to oxygen isotope • 0.016 Gyr = 16 Myr: blasted into space • 0.013 Myr = 13,000 yr: fell in Antarctica • 1984 found, 1993 recognized as Martian,  1996 01 – 0.2 mm

  30. Wednesday • More on ALH 84001 • Methane • Meteorites • RGS pp. 109 – 119

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