Life on Mars?. Abhi Tripathi Andy Czaja ESS 250 Winter 2004. Agenda. The Indirect Evidence: Could life have arisen independently on Mars? Can life sustain itself on Mars at the present? Could life have been brought to Mars via panspermia? The Direct Evidence The ALH84001 controversy
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The Indirect Evidence:
The Direct Evidence
Could life have arisen independently on Mars?
Life (as we know it) needs:
Obviously, Earth was sufficient, what about Mars?
Energy can come from many sources
Organic matter is ubiquitous in cosmos
Carbonaceous chondrites [Cody et al., 2002]
Mars only 11% mass of Earth [Sleep and Zahnle, 1998]
Cooled to habitable levels earlier than Earth
Atmosphere of several bars of CO2/N2
Thick enough and temperate enough to support liquid water
Gullies and outflow channels indicate H2O
Can Life Sustain Itself on Mars at the Present?
Analogues of Earth “diversitility”?
Can live deep within the Earth [Weiss et al., 2000]
Could Life Have Been Brought to Mars Via Panspermia?
Theoretical analysis performed by Mileikowsky et. al 2000, find it overwhelmingly likely that any microorganisms living near the surface of a planet in our solar system would be transported to another planet inside the ejecta from an impact.
Craterology and orbital trajectory simulations (Gladman et.al 1996) tell us that during the first 500-700 Ma, 0.7% of ejecta leaving Mars had hit the Earth 1Ma after impact and launch.
But how much of that ejecta can sustain viable organisms?
Deinococcus radiodurans's can withstand radiation 3,000 times what it would take to kill a human. That's 1.5 million rads of gamma radiation.
Bacillus Subtilis’ which has been studied before with regards to its ability to survive in space (Webster & Greenberg 1985)
*Note that there is no reason to believe that these bacteria were common on a primitive Earth or Mars, but they are common in nature today
τ(a)=ln(N°/Nd)/(σFGCR/a + σ FA/a)
*Exposure to the Vacuum of space consistently demonstrated the lowest bacterial survival rate
*Note the similarity in logic to the Drake Equation
McKay et al., 1996
Thomas-Keprta et al., 2001
Friedmann et al., 2001
[Thomas-Keprta et al., 2000]
5 criteria for biogenicity of magnetite chains
[Friedmann et al., 2001]
Uniform crystal size and shape within chains
Gaps between crystals
Orientation of elongated crystals
Halo around chains
Flexibility of chains
Detection of Metabolically Produced Labeled Gas: The Viking Mars Lander
GILBERT V. LEVIN
Biospherics Incorporated, Rockville, Maryland 20853
Received May 5, 1971
A qualitative, nonspecific method will test for life on Mars in 1976 by supplying radioactive substrates to samples of the planetary surface material. If microorganisms are present, they may assimilate one or more of the simple labeled compounds and produce radioactive gas. The compounds have been selected on the basis of biological theory and terrestrial results. The measurement of radioactive gas evolved as a function of time constitutes evidence for life. A control performed on a duplicate, but heat sterilized, sample will confirm the biological nature of the results. The shape of the response curve obtained from the viable sample may provide information on the physiological state and generation period of the organisms. Data obtained from a wide variety of terrestrial soils demonstrate a rapid response and high sensitivity for the experiment. Its ability to make comparative studies of soil microorganisms is also demonstrated. Instruments have been developed to conduct the experiment automatically and a breadboard version of the instrument designed for the Viking mission is under construction. The Mars experiment is described and simulated return data are given.
The labeled release (LR) experiment seeks to detect metabolism or growth through radiorespirometry. The radioactive nutrient used for the test consists of seven simple organic substrates (formate, glycolate, glycine, D- and L-alanine, D- and L-lactate), each present at 2.5 x 10-4 M and each equally and uniformly labeled with 14C (8 µc/µmole).
The GCMS is overrated!
BUT: A study (Krasnopolsky, V., et. al 1997) of Earth-based IR telescopic measurements made through the entire column of the Martian atmosphere, showed no spectrographic feature for H2O2.
H2O2 and other proposed derivatives do not approximate the thermal sensitivity of the Martian agent causing the LR responses. At 50°C, 90% H2O2 decomposes at only 0.001% per hour (Schumb, W.C et. al 1995). Of numerous attempts to simulate those results with H2O2, none reported has succeeded under conditions consistent with those on Mars.
Skeptics Logic: If microorganisms were present on Mars they would be in far lesser numbers than in terrestrial soils. Hence, their response would be less, especially considering the harsh Mars environment.
But look at the data:
Summary of dissenting opinions (Klein, 1999):
Gilbert Levin further contends, “…a combination of known properties of microorganisms, perhaps even those possessed by a single species, could reproduce all aspects of the LR data.”
This is a huge claim and Sagan once pointed out that the science community's stance should always be, “…the more extraordinary the claim, the more extraordinarily well tested the evidence must be.”
This should be detectable by GCMS
(But especially the magnetite crystals)
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