ON EARTH CAVES ARE WET, ON MARS CAVES ARE?

To make solutional caves, one needs three basic ingredients: 1) soluble rock, 2) rock heterogeneity (e.g. fractures, bedding planes, solubility, or permeability), and 3) a solvent. Mars is now thought to have relatively near subsurface water ice at mid to high latitudes (Boynton et al, Feldman et al., & Mitrofanov et al., 2002) and highly soluble evaporite sulfates in large crater basins (Gellert et al., 2004). We believe that impact events into evaporite basins, at latitudes where subsurface water ice is present, could provide two additional factors, namely massive fracturing of the target terrain and impact-imparted heating to release large amounts of frozen subsurface volatiles, thus providing the liquid solvent. These components could produce a type of catastrophic cave formation (speleogenesis) unlike any that have been identified so far on Earth. Such a scenario provides cavities for possible microbial habitat (or at least traps for interesting material) and also could release subsurface volatiles and extant near- or mid-surface microbiota (or geochemical traces of past biota) that do not survive on the harsh modern-day Martian surface. Such releases may have left analyzable traces in the vicinity of certain impact sites.

Cockell and colleagues (2002) have advanced the idea of a surface transient biohabitat as the result of impacts here on Earth (e.g. Haughton Crater, Devon Island, Canada) and speculated about similar events on Mars. We extend this idea to the subsurface and posit the simultaneous release of large amounts of subsurface frozen volatiles, with other compounds and particulates (especially organics), and possibly life or traces of life while unique caves are formed almost instantaneously.

We explore this scenario in terms of new advances in speleogenetic mechanisms in gypsum and halite karst (Stafford, 2007, Klimchouk, 2007) and parallels that we can draw from our work in relevant Earth caves (e.g. Boston et al., 2001, 2006; Spilde et al., 2005, Northup et al., 2001, 2003, etc). Any such identifiable sites on Mars would be of extreme interest for both planetary geology, climatology, and astrobiology. We have a few suggestions….