Martians? Life on Mars

1. Martians?Life on Mars ASTR 1420 Lecture 13 Chapter 8

2. Mars • Northern low land and southern mountains  impact origin?

3. Geography of Mars • Olympus Mons = tallest mountain in the Solar System!

4. We saw evidence of liquid water on the Mars!

5. Climate History of Mars • We saw evidence of liquid water on the Mars. • Why was Mars warmer and wetter in the past? • If Mars had about 400 times more CO2, then it could have liquid water on the surface via a stronger greenhouse effect and denser atmosphere. • If the composition of outgassed material was the same as Earth’s, then it should have enough H2O to fill oceans hundreds meters deep. • However, the Sun was dimmer in the past  CO2 alone could not have warmed the ancient Mars’ atmosphere high enough… • Possible solutions • enhanced greenhouse effect by other gases such as methane • Mars never had an extended period of warmth  liquid water only after major impacts… Mars was never Earth-like, but it was certainly warmer and wetter!

6. Small size of Mars • Small size • lost internal heat rapidly… • outer core solidified • weakened magnetic field • became vulnerable to solar winds • being stripped off • Large enough to have volcanism and outgassing in the beginning… • H2O got also dissociated by solar UV radiation: 2H2O  H2 + O2 • H2 got escaped quickly while O2 rusted the rocks and lost to space over time…

7. Martian climate: • After losing its atmosphere and H2O, has the climate of Mars unchanged for the past 2-3 Gyr? • No. The climate had changed with period of hundreds of thousands years!

8. Cause of Seasons on Earth

9. Cause of Seasons on Earth

10. Seasons on Mars Current obliquity of Mars = 25.19°

11. Monsoonal winds on Mars • During the northern summer : wind blows from N  S • During the southern summer : wind blows from S  N • These global winds oftentimes cover the entire planetary surface!

12. Global dust storm

13. Ice ages of Earth  due to the change of obliquity. 22° - 25° : small range due to the stabilizing effect of the large Moon Mars does not have a large moon and closer to Jupiter  a much wider range of obliquity change, 0° - 80° Larger obliquity  warm summer pole  more CO2 sublimation  stronger greenhouse effect  warmer temperature. On-going short-term climate changes of Mars Even with this increased seasonal enhanced greenhouse effect, average T cannot maintain surface liquid water, but high enough to have liquid water just beneath the surface!

14. Is Mars habitable? • Mars has • chemical elements • energy  Sun light + chemical energy(?) • Current surface of Mars is not habitable due to no liquid water • However, during the high obliquity periods, Martian surface might have been habitable! • Subsurface has been habitable throughout the period until now. Time to search!

15. Evidence of Life on Mars? • There are some scientific claims already about the existence of life on Mars  on-going debate! • Three groups of claims • Based on Viking lander data • From Martian atmosphere studies • From Martian meteorites

16. I. Viking Experiments Examine the soil of Mars to see if there are any living microbes.  Two Viking landers in 1976 Four experiments carbon assimilation experiment gas exchange experiment labeled release experiment gas chromatography

17. 1. Gas chromatography – Mass spectrometer (GCMS) A device that separates vapor components chemically via a gas chromatograph and then feeds the result into a mass spectrometer, which measures the molecular weight of each chemical  it can separate, identify, and quantify a large number of different chemicals.  However, the GCMS measured no significant amount of organic molecules in the Martian soil. In fact, Martian soils were found to contain less carbon than lifeless lunar soils returned by the Apollo program.

18. 2. Gas Exchange Experiment Mix the soil with organic nutrients and check for any released gas (e.g., O2 for terrestrial photosynthesis) • O2 was released! • But, similar result from an experiment with no sunlight!?! • O2 detection even after a thermal treatment of the soil • Non-biological process

19. 3. Labeled Release Asample of Martian soil was inoculated with a drop of very dilute aqueous nutrient solution. The nutrients (7 molecules that were Miller-Urey products) were tagged with radioactive 14C. • The air above the soil was monitored for the evolution of radioactive 14CO2 gas as evidence that microorganisms in the soil had metabolized one or more of the nutrients. • The experiment was done by both Viking probes, the first using a sample from the surface exposed to sunlight and the second probe taking the sample from underneath a rock; both initial injections came back positive. • 2nd experiment a week later showed nothing! Could Martian microbial life forms make a positive LR result and yet showed no traceable amount of organic molecules??

20. 4. Carbon Assimilation Experiment Mix Martian soil with terrestrial CO2 and CO (14C) : if these gases were used by life, then 14C would get incorporated into the soil • Yes! Some 14C were incorporated! The amount of carbon fixed is small by terrestrial standards; highest yields were observed in the light, but some dark activity was also detected; and heating the surface material to 90°C for nearly 2 hours had no effect on the reaction, but heating to 175°C for 3 hours reduced it by nearly 90%.

21. II. ALH84001 ALH84001: a 1.93kg meteorite found in Allan Hills, Antarctica on December 27, 1984

22. ALH84001 : Magnetite Magnetobacteriamagnetite is known in similar crystals on Earth only when deposited by bacteria Top: macroscopic chain of magnetite crystals produced by bacteria on Earth. Bottom: Similar chain found in ALH84001 These are smaller than it was thought free-living terrestrial organisms could be, an objection that has shrunk with the study of nano-bacteria.

23. ALH84001 : nano-fossils

24. nano-fossils electron micrographs showing tiny structures that look remarkably like microorganisms or microfossils.

25. nano-fossils

26. Another microfossil-like structure from ALH84001

27. Methane on Earth = Life Methane on Earth • http://www.nasa.gov/centers/goddard/news/topstory/2005/methane.html

28. Sources of Terrestrial Methane

29. III. Methane on Mars Methane detected from observations made by NASA IRTF and Keck telescopes (2003)

30. Methane on Mars Destruction of CH4 Replenishment of CH4

31. Possible Methane sources on Mars

32. Curiosity : No Methane in Martian Atmosphere • Sample Analysis at Mars (SAM, Tunable Laser Spectrometer) analyzed Martian air and found little to no methane (Nov 2012)

33. Methane measurements and Curiosity ?!?!

34. In summary… Important Concepts Important Terms ALH84001 nano-fossil • Seasons of Mars • Reason for Mars climate change • Viking Experiments • Evidence of Life from ALH84001 • Chapter/sections covered in this lecture : 8.1-8.5 • Life on Jovian Moons : next class!!