Presentation Transcript

1. Life on Mars - II Stephen Eikenberry 11 October 2012 AST 2037

2. Life on Mars?? • Mars has long been a “favorite” location for extra-terrestrial life

3. http://www.youtube.com/watch?v=Hah5c_kTqh0&feature=relmfu Modern Search for Water on Mars

4. What could we see from Earth? • Radio signals (communication) • But only present on Earth itself for <100 years • Look for O2 • O2 aggressively combines with rocks on a short timescale • So … do not expect free O2 in large amounts (unless life replenishes it in atmosphere) • Not much seen on Mars • Look for methane • UV solar radiation breaks it down on short timescale • So … do not expect free CH4 in large amounts (unless life replenishes it in atmosphere) • Not much seen on Mars Modern Search for Life on Mars

5. Two Viking landers arrived at Mars in 1976 • Identical landers, both stationary (no rover) • Cameras and various sensors • Included several exo-biology experiments to look for life Viking & Life on Mars

6. Atmosphere analysis showed no evidence for methane or silane (SiH4) • Soil tests • Take a Martian soil sample and bake it • Look for amino acids, or other carbon compounds • Did not find ANY (!) • So little carbon, scientists struggled to explain why (less than the Murchison meteorite) • Theory: UV rays plus CO2 produce oxygen temporarily; this oxygen breaks down organic compounds at the surface of Mars, so none left • Irony: first active test for life on Mars by humans would first KILL any life it finds … Viking: Atmosphere/Soil Tests

7. Take Martian soil, add “chicken soup” (broth of yummy nutrients) • Wait a few days and check to see if the composition of the gas changes due to respiration/metabolism • Cool result: found evidence of oxygen enhancement after nutrient exposure!! • But: repeat experiment after “cooking” soil to sterilize it  same result  ! Viking: Gas Exchange

8. Take Martian soil, add nutrients with “normal” C12 replaced by radioactive C14 • Wait a few days and check to see if C14 shows up in gas due to respiration/metabolism • Cool result: found evidence of C14 enhancement after nutrient exposure!! • But: repeat experiment  reaction stops  ! • Explanation: hydrogen peroxide in soil reacts to release C, but gets used up in first round of reactions Viking: Labeled Release

9. Problem with previous experiments: what if “yummy” nutrients for Earth life is not-yummy for Martians? • Add C14-labeled gas to Martian atmosphere w/Martian soil • Pump out atmosphere; heat up soil to break down & release volatiles; look for C14 • If any found, it must have been metabolized from gas into something in the soil • Cool result: found evidence of C14!! Viking: Pyrolitic Release

10. But … • Skeptical at this point aren’t we? • Try this experiment on Earth in sterilized soil, but with naturally occurring organic compounds • Find similar results • So … no real proof of life Viking: Pyrolitic Release

11. All 3 Viking exo-biology experiments showed “success” in finding evidence of life • But … most were inconsistent after further testing • The pyrolytic release experiment is consistent with life – but also consistent with no life • Inconclusive … Viking: Life on Mars?

12. Meteor found in Allen Hills, Antarctica in 1984 • One of 14 meteors on Earth thought to originate as a Martian rock • What ?! Life on Mars: ALH 84001

13. ALH 84001

14. Basic idea: • Asteroid hits Mars, knocking chunks of debris (including Mars rocks) into space • Rocks wander around space for awhile • Some rocks get captured by Earth gravity, and land as meteors • It could happen … Life on Mars: ALH 84001

15. Isotope abundances change depending on origin point (distance from Sun) • Isotope abundances in these meteors closely match Mars • Pockets of gas in ALH84001 match composition of Mars atmosphere (90+% CO2; 3% N2; etc.) ALH 84001 Martian Origin

16. Radio-isotope dating (as for Earth rocks) implies rock formed about 4.6 billion YA; igneous  from volcano • C14 dating of surface indicates it has been on Earth for about 13,000 years • Weird isotopes indicate exposure to cosmic rays for a duration of 16 million years • Timeline: • 4 GYA rock forms on Mars (some evidence that it came from Valles Marineris region) • 16 MYA rock blasted into space, exposed to cosmic rays • 13,000 YA rock lands in Antarctica ALH 84001 Timeline

17. 4 pieces of evidence for Martian life embedded in ALH84001 • Carbonate nodules • Crystals of iron pyrite • Traces of poly-aromatic hydrocarbons (PAHs) • Fossils! ALH 84001: Life on Mars

18. Carbonate globules are present in ALH84001; formed in water medium ~1 GY after rock matrix • These are often created in Earth rocks by life (bacteria) • Metabolism converts CO2 plus minerals into carbonate • Could be a sign if life … ALH 84001: Carbonate

19. Very small iron pyrite grains are present inside the carbonates in ALH84001 • These are often created in Earth rocks by life (bacteria) • Could be a sign if life … ALH 84001: Iron Pyrite

20. Complex hydrocarbons – building blocks of life on Earth! • Could be a sign if life … ALH 84001: PAHs

21. Electron microscopy reveals what appear to be fossil nanobacteria in ALH84001 carbonate globules (!!!!) • Life on Mars! • Bill Clinton even has a press conference to announce it! ALH 84001 Fossils!

22. ALH 84001 Fossils! E Coli on Earth Fossil from Mars

23. Caveats to ALH84001 scenario • Carbonates can also form non-biologically; typically at high temperatures • ALH84001 pyrites can also form non-biologically, and small fracture evidence indicates high temperature (!) • PAHs are found on meteors in general ALH 84001: Really “Fossils”?

24. The ALH84001 fossil is TINY compared even to small bacteria on Earth – not sure life can be that small • Some indication that the sampling process for microscopy may have CREATED the “fossil” structures • Still could be fossils, but … ALH 84001: Really “Fossils”?

25. Intriguing evidence • But … none of it is really solid; alternate (non-biological) explanations seem to work too • Jury still out … ALH 84001: Life on Mars?

26. Anything new? • Water on Mars Redux • Find evidence of shorelines • There WAS standing water on Mars at some point • But, when? How long? Could these have been volcanic/meteoric melt of permafrost, lasting a few years/centuries? Mars Missions & Life on Mars

27. What next? • Future Mars missions include more advanced “biology labs” on rovers • Also include “sample return” missions, to bring Mars material back to even more advanced labs on Earth • Will we find Life (or fossil life) on Mars? Stay tuned … Future Searches for Life on Mars