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.