ASTR/GEOL 3300: ET Life

1. ASTR/GEOL 3300: ET Life • Logistics: • HW#7 due next Monday! • Check for Exam key on www by early next week. • Guest speakers coming up (October 18, Dr. Hynek “The future of Mars exploration”); Oct. 22 Dr. McCollom “hydrothermal systems on planets” • Plan for Today: • Finish up Mars: Ice, water, & climate • The search for life on Mars • SOON: we visit the other planets

5. Ground Ice • Odyssey neutron spectrometer is finding ground ice today!

6. Earth gas Mars Liquid Water Is Unstable on Mars Surface Today • Temp too low & pressure too low for surface liquid H2O (or CO2) today. • Lots of evidence for past water. • Suggests climate change: • higher P, T in past. • Past greenhouse? • Mars surface has since frozen up!

7. weak magnetic field today Long-Term Climate Change • Mars probably had a warm, wet past. • Had a thicker greenhouse atmosphere. • Most CO2 & H2O was lost to space: • Impacts. • Stripping by solar wind(after magnetic field lost). • UV dissociation of H2O(O then rusted surface rocks). • No CO2 cycle.

8. high P,T Subsurface Water on Mars? • Mars’ surface has frozen up, but liquid water is predicted deep underground today! • What are the implications for life?

9. Mars Gullies: Recent Water! • Gullies may suggest “recent” (~1 Myr) shallow subsurface water!

10. tilt Recent Climate Change • Changes in tilt could cause “recent” climate change. • High tilt = warm poles, and warmer average temperature. • “Recent” warm climate could explain gullies! • Is Mars subsurface still habitable?

16. OPINION Question: • What makes Mars (apparently) uninhabitable? • OR, do you think it’s still possible for life to exist there? Where?

17. gas Mars Pop Q: Mars Water • Where is it possible for liquid water to exist at Mars today? • High in the atmosphere. • In the equatorial regions. • In the polar regions. • Deep underground. • None of the above.

18. gas Mars Pop Q: Mars Water • Where is it possible for liquid water to exist at Mars today? • High in the atmosphere. • In the equatorial regions. • In the polar regions. • Deep underground. • None of the above.

19. tilt Recent Climate Change • Changes in tilt could cause “recent” climate change. • High tilt = warm poles, and warmer average temperature. • “Recent” warm climate could explain gullies! • Is Mars’ subsurface still habitable?

20. Life on Mars???

21. Mars Geology & Climate: Summary • Some "recent" water; lots of past water. • Mars has “died out”: • Was active, warm, & wet during Noachian; activity waned during Hesperian. • Abundant ground ice today, with water deep underground. • Consistent with the intermediate size of Mars: • Lost most of its heat early, so activity level waned. • Lost greenhouse over time. • Could life have arisen on Mars during the Noachian? • Could it have retreated underground, or into rocks (endoliths)? • Could “recent” climate change (tilt changes) bring it to surface?

22. Viking: Search for Life • Twin Viking landers searched for life (1976).

23. Viking Life-Detection Experiments • Carbon Assimilation Experiment: • “Fed” soil 14CO & 14CO2, and found 14C was incorporated by the soil! • BUT heating to 175°C (which should kill any organisms) did not eliminate the positive response, so probably just geochemical reactions incorporated the C-rich gases. • Gas Exchange Experiment: • “Fed” soil wet nutrients and found O2 and other gases released! • BUT positive response continued upon heating, and in the dark, and when exposed to H2O only, so again probably just geochemical reactions.

24. Viking Life-Detection Experiments • Labeled Release Experiment: • “Fed” soil organics labeled with radioactive isotopes, and found radioactive gases were released! • Amount of released gas decreased as nutrients were used up, and stopped when soil was heated to 160°C! • This seems a positive result! BUT probably doesn’t really indicate life, considering the next result… • GCMS (Gas Chromatograph / Mass Spectrometer): • Heated soil to vaporize organics & measure abundance. • No organic materials found in soil to parts per billion! • Organics on Mars surface are readily destroyed by UV light & oxidants in the soil.

25. Viking Results: Summary • 3 Viking experiments gave results consistent with life. • For two, “positive” results continued at temps high enough to kill life. • Chemical reactions by soil oxidants can explain the results. • In hindsight, the Viking life detection experiments were not well designed!

26. Meteorites from Mars • Some meteorites all have similarly strange isotope ratios: • Not from asteroids, Earth, or Moon. • Chemistry of air bubbles trapped in one of these matches Viking measurements of Mars atmosphere! • These “SNC” meteorites must be from Mars!

27. Mars Meteorite ALH84001 • The Mars meteorite that changed planetary science! • 1996: thought to possibly show signs of life! • Evidence of life within now severely weakened.

28. ALH84001: 4 Lines of Possible Evidence for Life • Carbonate Globules: • Alternating layers of Fe-, Mg-, Ca-rich carbonates: minerals out of equilibrium, which have biological origin. • BUT could be deposited by high-temperature fluids. • PAHs (Polycyclic Aromatic Hydrocarbons): • Complex C-molecules, on Earth typically remnants of dead organisms. • BUT can form inorganically, or could be terrestrial contamination of meteorite.

29. ALH84001: 4 Lines of Possible Evidence for Life • Magnetite crystals: • On Earth, observed hexagonal crystals, sometimes aligned in chains, are characteristic of biological origin. • BUT these have now been produced in the lab inorganically. • Nanobacteria?: • Segmented, rod-shaped structures that resemble terrestrial bacteria. • BUT these may be artifacts of sample preparation. ALH84001 made by terrestrial bacteria

30. Discussion Question • Should we continue the search, or does the weight of the Viking and ALH84001 evidence say that there is no (and has not been) any life on Mars?

31. If yes, then where would YOU search for evidence of past life?

32. Martian “Frozen Sea”? • Ice now protected by volcanic ash? • A good place to search for preserved life?

33. Methane in Mars’ Atmosphere • Ground-based & Mars Express orbiter indications of CH4. • Life (methanogens) is a possible source: • CO2 + 4H2 CH4 + 2H2O or 2H2O + 3CO  CH4 + 2CO2 • BUT may just be minor volcanic outgassing… (how?)

34. Ancient Mars???

35. In the not too distant future…

36. That’s it for Mars… Now, there’s the rest of the solar system, and beyond!

37. Venus

43. Venus: Earth’s Evil Twin "Venus Is the Planet Most Like Hell."-Carl Sagan • Similar size to Earth: • Similar internal heat (WHY?). • Thick CO2 atmosphere: • Pressure = 90 bar (WHY?). • Searing hot from greenhouse warming: • ~460 °C (~860 °F) • SO2 clouds: • sulfuric acid rain. • Only traces of water. • Why no CO2 cycle? • no oceans! • Why no oceans? • runaway greenhouse! • Why no continents?

44. Magellan radar(bright = rough or metallic) Soviet Venera lander

46. uplands • highlands Venus Physiography • lowlands

47. Varied volcanic styles: Some extremely runny lava. Some more stiff. Lowland plains volcanism: Basaltic (?) Covers much of surface. Volcanism on Venus