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Extended survival of several organisms and amino acids under simulated martian surface conditions |
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| Authors: | AP Johnson LM Pratt S Tronick |
| Institution: | a Department of Molecular and Cellular Biochemistry, Indiana University, 1001 E. 10[th] Street, Bloomington, IN 47405, United States b Department of Geological Sciences, Indiana University, 1001 E. 10[th] Street, Bloomington, IN 47405, United States c Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States d Center for Environmental Biotechnology, Department of Microbiology, University of Tennessee, 676 Dabney Hall, Knoxville, TN 37932, United States e Department of Nuclear Medicine, Albert Einstein College of Medicine, 1575 Blondell Avenue, Room 103, Bronx, NY 10461, United States f Department of Nuclear Medicine, Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1695A Eastchester Road, Bronx, NY 10461, United States g Department of Natural Resource Sciences, McGill University, Macdonald Campus, 21,111 Lakeshore, Ste. Anne de Bellevue, Quebec, Canada H9X 3V9 h Department of Geosciences, Princeton University, B79 Guyot Hall, Princeton, NJ 08544, United States i Department of Biology, Nematology Section, University of Ghent, Ldeganckstraat 35, 9000 Gent, Belgium j SETI Institute, 515 N. Whisman Rd., Mountain View, CA 94043, United States k NASA Ames Research Center, MS 239-20, Moffat Field, CA 94035, United States l BAER Institute, NASA Ames Research Center, Mail Stop 239-20, Bldg. N239 Rm. 371, Moffett Field, CA 94035, United States m NASA Ames Research Center, Moffat Field, CA 94035, United States |
| Abstract: | Recent orbital and landed missions have provided substantial evidence for ancient liquid water on the martian surface as well as evidence of more recent sedimentary deposits formed by water and/or ice. These observations raise serious questions regarding an independent origin and evolution of life on Mars. Future missions seek to identify signs of extinct martian biota in the form of biomarkers or morphological characteristics, but the inherent danger of spacecraft-borne terrestrial life makes the possibility of forward contamination a serious threat not only to the life detection experiments, but also to any extant martian ecosystem. A variety of cold and desiccation-tolerant organisms were exposed to 40 days of simulated martian surface conditions while embedded within several centimeters of regolith simulant in order to ascertain the plausibility of such organisms’ survival as a function of environmental parameters and burial depth. Relevant amino acid biomarkers associated with terrestrial life were also analyzed in order to understand the feasibility of detecting chemical evidence for previous biological activity. Results indicate that stresses due to desiccation and oxidation were the primary deterrent to organism survival, and that the effects of UV-associated damage, diurnal temperature variations, and reactive atmospheric species were minimal. Organisms with resistance to desiccation and radiation environments showed increased levels of survival after the experiment compared to organisms characterized as psychrotolerant. Amino acid analysis indicated the presence of an oxidation mechanism that migrated downward through the samples during the course of the experiment and likely represents the formation of various oxidizing species at mineral surfaces as water vapor diffused through the regolith. Current sterilization protocols may specifically select for organisms best adapted to survival at the martian surface, namely species that show tolerance to radical-induced oxidative damage and low water activity environments. Additionally, any hypothetical martian ecosystems may have evolved similar physiological traits that allow sporadic metabolism during periods of increased water activity. |
| Keywords: | Exobiology Mars Regoliths Search for extraterrestrial life Photochemistry |
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