Life on Mars?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• The Viking Labeled Release experiment vs. GCMS controversy

Could life have arisen independently on Mars?

What is LIFE? – A primer

Life (as we know it) needs:– Energy– CHON– Water– Not much time to get going apparently!

Obviously, Earth was sufficient, what about Mars?

Early Mars was similar to Earth

Energy can come from many sources

Organic matter is ubiquitous in cosmosCarbonaceous 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”?

Earth-life shows a wide range of metabolic variation

• Heterotroph– Aerobes– SRBs– Methanogens

• Phototrophs– Cyanobacteria– Photosynthetic bacteria

• Lithotrophs– H2 oxidizers

– Fe oxidizers

– CH4 oxidizers [Nealson, 1997]

Potential Martians?

Extremeophiles

• Earth organisms have resistance to extremes of: – Heat/cold [Stetter, 1996; Junge et al., 2004]

– UV and ionizing radiation [Battista et al., 1999; Wynn-Williams et al., 1999]

– Low water activity– Salinity– Low oxygen/no oxygen

Can live deep within the Earth [Weiss et al., 2000]

Mars, too?

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?

Ejecta

Meet the Viable Organisms• Deinococcus Radiodurans

• Bacillus Subtilis

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

Traumas

• A trip from one planetary body to another would have four main threats to survival to the organisms:

• Dynamical Stress• Excess Temperature• Radiation• Chemical Attack

Dynamical Stress & Excess Temperatures• Vikery & Melosh (1997) determine that a 1-30+ km impactor can

propel rock off of a planetary surface and into space.– Upon impact the ground can boil up to 2800ºK

– However reflected shock waves are phase shifted by 180º allowing some ejecta to remain totally or partially un-shocked, and the temperature to remain below 100º C

– As and example, ALH84001 is believed to have not been heated above 40ºK (although some disagree with this conclusion)

– When rising through the atmosphere, heating lasts less than 10s and does not permeate to the core, even though the exterior bores get baked.

Radiation• Organisms would have been subjected to UV, X-ray

background, GCR, and Natural Radioactivity (which was much more potent in the first several 100 million years)

• The combined Radiation effect is given by:τ(a)=ln(N°/Nd)/(σFGCR/a + σ FA/a)

• The main factor in DNA damage in this case is the fact that the extreme cold slows down the metabolism, and therefore the DNA repair mechanisms of the bacteria.

• Applying conservative numbers it was determined that a viable survival time of 100,000 years was reasonable for non-vacuated pores*.

*Exposure to the Vacuum of space consistently demonstrated the lowest bacterial survival rate

Comprehensive Equation(Mileikowsky et. al, 2000)

*Note the similarity in logic to the Drake Equation

Main Conclusions

• Transfer of ejecta between planets was common during the first 0.5 Ga of our solar system. If RNA/DNA life existed on either or both Earth and Mars, then natural transfer of viable microorganisms was frequent.

• After the first 0.5 Ga, transfer of ejecta continued at a lower rate and so did transfer of viable microorganisms.

The Problems of Panspermia

• Could sufficiently robust organisms that could survive an interplanetary trip, (such as our two examples) have evolved on Mars or Earth in the first 500-700 Ma?

• Can Mars sustain any life that had evolved on Earth after 3.8Ga?

• Would any life brought from Mars to Earth after 3.8Ga survive for long in Earth’s eco-system (huge spacecraft design implications)

• Biggest Problem: How do you PROVE Panspermia?

Evidence for life on Mars? YES!

ALH84001

• Meteorite is from Mars• Carbonate globules of Martian origin • PAHs associated with carbonate

globules• Magnetite crystals

McKay et al., 1996

Thomas-Keprta et al., 2001

Friedmann et al., 2001

A closer look at the magnetite

• 6 criteria for biogenicity of magnetite crystals[Thomas-Keprta et al., 2000]

A closer look at the magnetite

• 5 criteria for biogenicity of magnetite chains [Friedmann et al., 2001]

1) Uniform crystal size and shape within chains

2) Gaps between crystals

3) Orientation of elongated crystals

4) Halo around chains

5) Flexibility of chains

Granted– ALH84001 is from Mars– Features seen are not of terrestrial origin

But,– Carbonates & magnetites could have been

produced abiologically [Golden et al., 2001]

– PAHs are ubiquitous in the cosmos– Magnetotactic bacteria recent invention on Earth

[Nealson and Cox, 2002]

Evidence for life on Mars? NO!

ALH84001

The Viking Labeled Release Experiment

The Proposal

Detection of Metabolically Produced Labeled Gas: The Viking Mars Lander 

GILBERT V. LEVINBiospherics 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.

How Did It Work

• 0.5 cm3 of Mars soil is placed inside a test cell.• After 24hrs the sample was injected with 0.115ml of

nutrient.• Approximately 7 sols after the first nutrient injection, a

second nutrient injection was made, and incubation was continued for an additional 6 sols.

• After each nutrient addition, radioactive gas evolved into the headspace above the sample equilibrated with the gas volume in the detector chamber and was measured.

• A control sample was first sterilized, then given nutrient, and then had its evolved gas measured for metabolized 14C.

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).

Results• The rate of gas evolution was constant until approximately 10% of the

added radioactivity had been released (these observations were replicated several times at both Viking sites).

• The sterilized control sample released virtually no gas, and one heated to 50 ºC evolved 60% less gas.

• “The Labeled Release (LR) life detection experiment aboard NASA's 1976 Viking Mission reported results which met the established criteria for the detection of living microorganisms in the soil of Mars.” –Gilbert Levin

Yes! We Did Detect LifeThe GCMS is overrated!• Organics, including amino acids, have been found in

meteorites from space. When a NASA spokesman was asked (Huntress, 1996) how this can be reconciled with Viking he replied that the GCMS was sent so long ago it may not have been sensitive enough to detect the low amounts of organic matter in the meteorite

• The GCMS discovered no organics in a particular Antarctic soil that was KNOWN to have life (Levin, G. 1997).

The Oxides• Levin’s critic’s say: The atmosphere of Mars produces H2O2 that

precipitates onto the Martian soil. The H2O2 and other oxidants produced are in the soil sample and thought to have oxidized the LR organic substrates to release radioactive gas. It was proposed that the oxidant(s) also released the oxygen detected in the Viking GEx experiment. This oxidative chemistry destroyed any organics or life.

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.

The Anomalously Fast RxnSkeptics 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:

It’s a Conspiracy

• NASA did discover life on Mars in 1976 but scientists are just out-thinking themselves.

• The results can be explained biologically• A comprehensive non-biological explanation

cannot be duplicated.• No proof of an oxidative surface has EVER been

shown, and this is the crux of the skeptics argument.

Labeled Release? – No! It’s a Sham

1. No organic compounds were found in Martian soil analyzed by the Viking Gas Chromatograph Mass Spectrometer (GCMS). (Biemann et al. 1976)

2. The regolith of Mars contains one or more oxidants responsible for decomposition of organic compounds supplied in the LR medium that can also be shown to be responsible for the immediate release of molecular oxygen.(Klein, 1978; Hunten 1978). KO2, ZnO2, Ca(O2)2 could all explain the release of Oxygen (Yen et. al. 1999)

3. The explanation in #2 above is consistent with #1 above (Biemann, 1977)

4. In an experiment where the LR nutrient mixture was added to UV irradiated hematite samples, 14CO2 was evolved. (Ponnamperuma et. al. 1977)

5. The kinetics of the experiment were duplicated when formate (an ingredient of the nutrient) was exposed to H2O2 and Fe2O3. (Oyama et. al. 1978)

6. Adding certain clay minerals to the LR nutrient resulted in many of the same findings seen in the experiment (Banin and Rishpon, 1979)

Summary of dissenting opinions (Klein, 1999):

What kind of Microorganisms?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.”

•The initial rxn is so rapid and so intense that it would suggest a large biological load in the samples.

•Viking’s organic analysis indicator was sensitive enough to detect 106 cells of E. Coli but didn’t detect anything.

Yeast (mg. WET WT.) LR Response

CO2 Produced per hour ~30 μl ≥0.1 μl

Equivalent number of cells

7.7x106 2x104

Equivalent E. Coli Cells 1.25 x109 3.2x106

Klein 1978

This should be detectable by GCMS

LR Experiment Conclusions• The LR experiment’s results demonstrated a chemical reaction

and not a biological one. • The experiment was predicated on Earth-centric soil conditions,

and could not have predicted the specific nature of the Martian soil, prior to the Viking landing.

• Although the experiment did work as designed, its results can be explained by several natural reactions.

• No biological analog can be found on Earth that can mimic all of the results seen. Furthermore, keep in mind that that any putative Martian organism was taken from its undisturbed natural environment and subjected to a “large” increase in temp in the ambient environment of the experiment, and yet continued metabolizing vigorously.

• The vast majority of the science community does not accept the LR experiment as proof of life

Conclusion 1

• Evidence supports supposition of life existing on Mars– All of ALH84001 data put together

(But especially the magnetite crystals)

– Viking labeled release experiment – Tenacity of life

Conclusion 2

• There is no conclusive, direct evidence of life of Mars– Viking data inconclusive– ALH84001 evidence can all be explained by other

means

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