1. Stephen Eikenberry 21 Feb 2019 AST 2037
Life on Mars - II
Stephen Eikenberry
21 Feb 2019
AST 2037

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

3. Modern Search for Water on Mars

4. Modern Search for Life on Mars
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)

5. Viking & Life on Mars 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

6. Viking: Atmosphere/Soil Tests
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 …

7. Viking: Gas Exchange
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  !

8. Viking: Labeled Release
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

9. Viking: Pyrolitic Release
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!!

10. Viking: Pyrolitic Release
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

11. Viking: Life on Mars?
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 …

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

13. ALH 84001

14. Life on Mars: ALH 84001 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 …

15. ALH Martian Origin
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.)

16. ALH Timeline
Radio-isotope dating (as for Earth rocks) implies rock formed about 4 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

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

18. ALH 84001: Carbonate
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 of life …

19. ALH 84001: Iron Pyrite
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 of life …

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

21. ALH Fossils!
Electron microscopy reveals what appear to be fossil nanobacteria in ALH84001 carbonate globules (!!!!)
Life on Mars!
In 1996, Bill Clinton even has a press conference to announce it!

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

23. ALH 84001: Really “Fossils”? 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

24. ALH 84001: Really “Fossils”?
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 (though recent results refute this refutation!)
Still could be fossils, but …

25. ALH 84001: Life on Mars? Intriguing evidence
The “too small” arguments – Earth-centric bio-bias? (Even in an Earth-type life scenario, could “RNA World” be a viable explanation, for instance?)
But … none of it is really solid; alternate (non-biological) explanations seem to work too
Jury still out …

26. Mars Missions & Life on Mars
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?

27. Future Searches for Life on Mars
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 …