MODELING IMPACT-INDUCED SUBSURFACE CAVITY FORMATION ON MARS: ASTROBIOLOGICAL AND GEOLOGICAL IMPLICATIONS

The Martian subsurface could be the last refuge for a hypothetical Mars biosphere in which caves or vugs as well as the near-subsurface fracture habitat serves as possible microbial repositories (Boston, Ivanov, and McKay, 1992; Boston, et al., 2001 & 2006). From this hypothesis, the following questions arise, do caves exist on Mars and how are they formed, could an impact crater ejecta blanket allow for an underlying near-subsurface microbial habitat? We suggest one possible mechanism for cave formation (“catastrophic speleogenesis”) involving an impact event and rapid melting/volatilization of subsurface ice to produce solutionally created voids (Boston, et al., 2006). The plausibility of a surface biological habitat created as a result of heat imparted by a crater ejecta blanket deposited around the impact crater site has been suggested for Earth with implications for similar events on Mars (Cockell, et al., 2002). We extend this idea to include subsurface cave habitats created as a result of the impact event itself. We are quantitatively constraining these theories through computer-based modeling simulations of impactors into relevant rock and ice terrains. This allows us to account for possible cave formation at many different localities as well as a generalized representation of the interaction between the ejecta blanket and the underlying material. We consider subsurface and surface composition, amount and spatial distribution of energy imparted and associated heat, certain impactor properties, atmospheric effects, and possible biological implications. We have incorporated Martian surface material data from MER and other orbital and lander missions into our thinking. Based on modeling results, we can predict a first order result of what materials vaporize and are subsequently released into the surrounding atmosphere. Modeling results will be applied to the interpretation of orbiter and MER imaging to identify possible sites of subsurface cavity formation and aid in the site selection for future Mars missions.