8/6/2019 Bio Signatures of Anticipated Life on Mars and Their Detection - Houtkooper & Schulze-Makuch 2007

1/1

European Space AgencyEuropean Mars Science and Exploration Conference: Mars Express & ExoMarsESTEC, Noordwijk, The Netherlands, 12 - 16 November, 2007

BIOSIGNATURES OF ANTICIPATED LIFE ON MARS AND THEIR DETECTION BY MSL ANDEXOMARS Joop M. Houtkooper 1, Dirk Schulze-Makuch 2. 1Center for Psychobiology and Behavioral Medicine,Justus-Liebig-University of Giessen, De Maalkom 7, 1191LP Ouderkerk Amstel, The Netherlands. 2School of Earth and Environmental Sciences, Washington State University, USA. joophoutkooper@gmail.com

Anticipated Life on Mars: The hydrogen peroxide-water hypothesis [1] offers an explanation for thehitherto puzzling aspects of the Viking Landerbiology experiments. The lack of detected organics inthe GCMS and the evolution of oxygen in the GExexperiment point to the possibility of organisms usinga mixture of hydrogen peroxide and water in theirintracellular fluid.

H 2O 2-H 2O mixtures: Such mixtures have severalproperties attractive in Martian ambient conditions:The freezing point of the eutectic is -56.5 oC, with thetendency to supercool below that temperature, H 2O2 is a source of oxygen and energy, and the mixture ishygroscopic, enabling organisms to attract watervapor from the atmosphere well below saturatedconditions.

The compatibility of H 2O2 with biochemistry maybe questioned, but even terran biochemistry has anumber of uses for H 2O2, as a messenger molecule, asa defence by antibodies, in the metabolism of

Acetobacter peroxidans , with the most extremeexample known being the 25% H 2O2 solutionproduced by the insect Brachinus crepitans .

Properties of the anticipated organisms: First, theorganisms are well able to grow without liquid waterat Martian ambient temperatures. Furthermore theymay well have an excess oxidative content and theirability to scavenge water vapor from the atmospheremay also be a disadvantage: Under water vapor richconditions, such as saturation at above zerotemperatures, they may have no defence againsthyperhydration. Obviously, the organisms have toproduce their H 2O2 from the atmosphere, of whichthe H 2O2 content is in the ppb range. Moreover, thecontact between the H 2O2 and the proteins in the cellmay require an active stabilization mechanism,possibly in conjuction with the H 2O2 production. Theactive stabilization mechanism may be similar insome way to the damage repair mechanism in Deino-coccus radiodurans , which requires an activemetabolic state.

Explaining the Viking results: The lack of detected organics can be explained by the gradualheating to pyrolysis, by which the organismsdecomposed into CO 2, H 2O, O 2, N 2 and little else. Inthe GEx experiment, the added moisture caused the

organisms to hyperhydrate and perish as well. Theexcess oxidative content of organisms explains theevolved O 2. Moreover, the presence of organismsmay explain the diminished reponses in the "coldsterilization" tests and the lack of response of samplesstored for 3 months in the dark at above zerotemperatures, possibly because of energy use byactive cellular stabilization.

The MSL and ExoMars instruments: MSL andExoMars may reveal indicators of biology. The MSLwill have the SAM searching for carbon compounds,both in soil samples and in the atmosphere. The soilsamples will be heated to get the GCMS to work. Alaser spectrometer will analyze isotopic abundances.Environmental monitoring will measure humidity.

ExoMars will carry GEP to monitor the environmentfor a few Martian years. The Pasteur package on therover will contain a GCMS and a microscopicspectrometer. Organics and oxidants should bedetected and an antibody-based life-marker chip maydetect present life if a biochemistry similar to ours isinvolved.

Adding water is no option: Most biologyexperiments use liquid water. The resulting com-bination of humidity and temperature is unmartianand may cause the anticipated organisms to perish.The same may well have happened when heating thesamples in the Viking GCMS. This limits the pos-sibilities of detection. Still, imaging and microscopicspectroscopy, in the visual and UV to detectabsorbing/photosynthetic pigments, and in the IR topossibly detect a Raman signature of H 2O2 arepossibilities. However, metabolism should not beneglected: Organisms which produce H 2O2 from H 2Oand CO 2 using photosynthesis or thermal gradientshave to produce reducing species such as CO, CH 4 and CH 2O. Scavenging O 2 from the little present inthe atmosphere is another possibility. Thesemetabolic processes may result in signatures in thesurface boundary layer of the atmosphere in the formof diurnal rhythms. Monitoring of the atmospheric(isotopic) composition with high precision would becalled for.

References: [1] Houtkooper, J. M., and D. Schulze-Makuch, (2007) IJA 6: 147-152.doi:10.1017/S1473550407003746.