Life on Mars - II

Stephen Eikenberry

11 October 2012

AST 2037

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Life on Mars??

Mars has long been a “favorite” location for extra-terrestrial life

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

elmfu

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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)• 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

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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 …

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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 !

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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

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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!!

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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

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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 …

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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 ?!

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ALH 84001

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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 … 14

ALH 84001 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.)

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ALH 84001 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

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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!

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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 …

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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 …

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

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ALH 84001 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!

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ALH 84001 Fossils!

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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

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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 …

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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 …

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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?

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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 …

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