Bacterial Spores in Granite Survive Hypervelocity Launch by Spallation: Implications for Lithopanspermia

Abstract

Bacterial spores are considered good candidates for endolithic life-forms that could survive interplanetary transport by natural impact processes, i.e., lithopanspermia. Organisms within rock can only embark on an interplanetary journey if they survive ejection from the surface of the donor planet and the associated extremes of compressional shock, heating, and acceleration. Previous simulation experiments have measured each of these three stresses more or less in isolation of one another, and results to date indicate that spores of the model organism Bacillus subtilis can survive each stress applied singly. Few simulations, however, have combined all three stresses simultaneously. Because considerable experimental and theoretical evidence supports a spallation mechanism for launch, we devised an experimental simulation of launch by spallation using the Ames Vertical Gun Range (AVGR). B. subtilis spores were applied to the surface of a granite target that was impacted from above by an aluminum projectile fired at 5.4 km/s. Granite spall fragments were captured in a foam recovery fixture and then recovered and assayed for shock damage by transmission electron microscopy and for spore survival by viability assays. Peak shock pressure at the impact site was calculated to be 57.1 GPa, though recovered spall fragments were only very lightly shocked at pressures of 5-7 GPa. Spore survival was calculated to be on the order of 10(-5), which is in agreement with results of previous static compressional shock experiments. These results demonstrate that endolithic spores can survive launch by spallation from a hypervelocity impact, which lends further evidence in favor of lithopanspermia theory.

PCR-based analysis of microbial communities during the EuroGeoMars campaign at Mars Desert Research Station, Utah

“…Despite this extremely challenging situation for life, there are organisms on Earth which are potentially able to survive space travel: it has been shown that different micro-organisms can survive launch by spallation from a hypervelocity impact (Horneck et al 2008a;Fajardo-Cavazos et al 2009) and hypervelocity atmospheric transit (Fajardo-Cavazos et al 2005). Thus, it has been suggested that, for example, bacterial spores situated on or within meteorites could survive interplanetary transport (Fajardo-Cavazos et al 2009) and hypervelocity entry from space through Earth's atmosphere (Fajardo-Cavazos et al 2005;reviewed in Olsson-Francis & Cockell 2010). However, DNA may be the sensitive target of spores exposed to ultrahigh shock pressures (Moeller et al 2008).…”

Resistance of Microorganisms to Extreme Environmental Conditions and Its Contribution to Astrobiology

“…The analyses of the combined stresses can be most closely simulated in the laboratory via hypervelocity ballistics experiments. The results demonstrated that microbes could survive rapid acceleration to Mars escape velocities and subsequent impact into surfaces of different compositions [156,157]. Thus, there is a body of evidence suggesting that microbes can survive the conditions of interplanetary transfer from Mars to Earth or from any Mars-like planet to other habitable planets in the same solar system.…”

Ionizing Radiation and Life

“…The theory of (litho)panspermia, that life can be transferred between planetary bodies within meteorites, has matured over recent years (see up-to-date reviews by Burchell, 2004, andNicholson, 2009) with the results of simulations of planetary ejection by low-angle impact (Nyquist, 1983) or spallation (Melosh, 1984), orbital transfer dynamics calculations (Gladman et al, 2005), and experimental work on microbial survival of the associated shock pressures and temperatures (Fajardo-Cavazos et al, 2009), and resistance to the space environment (Horneck et al, 1994(Horneck et al, , 2001). On the whole, such experiments find that non-negligible proportions of microbial populations could indeed survive the shock of ejection or reentry and if protected from solar UV can tolerate the vacuum and desiccation of the space environment for protracted periods, thus supporting the conjecture of biological transfer within the Solar System.…”