Life on Mars - II Stephen Eikenberry 11 October 2012 AST

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

Modern Search for Water on Mars elmfuhttp:// elmfu 3

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 O 2 O 2 aggressively combines with rocks on a short timescale So … do not expect free O 2 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 CH 4 in large amounts (unless life replenishes it in atmosphere) Not much seen on Mars 4

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 5

Viking: Atmosphere/Soil Tests Atmosphere analysis showed no evidence for methane or silane (SiH 4 ) 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 … 6

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  ! 7

Viking: Labeled Release Take Martian soil, add nutrients with “normal” C 12 replaced by radioactive C 14 Wait a few days and check to see if C 14 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 8

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!! 9

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 10

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 … 11

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

ALH

Life on Mars: ALH 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 … 14

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+% CO 2 ; 3% N 2 ; etc.) 15

ALH Timeline 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 16

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! 17

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 if life … 18

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 if life … 19

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

ALH Fossils! 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! 21

ALH Fossils! 22 E Coli on Earth Fossil from Mars

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 23

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 Still could be fossils, but … 24

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

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? 26

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 … 27