I’ve always found the idea of panspermia oddly comforting. Growing out of the work of Swedish chemist and Nobel Prize winner Svante Arrhenius, panspermia assumes that life can move between worlds by natural means, and implies that planets with the right conditions will wind up with living things on them. That idea of all but universal life, and the weird notion that we might all be in some way ‘related,’ was exhilarating to thinkers like Fred Hoyle and Chandra Wickramasinghe, who went on to suggest that the influx of life from space triggers continuing changes on Earth today, which might involve epidemics and new diseases.

Now comes a variant called lithopanspermia, which questions whether rocks blasted off a planetary surface by impacts might not be the transfer vehicles for microorganisms that travel between planets and perhaps further. After all, we have found Martian meteorites in Antarctica, forty or so to date, so the real question becomes the survival possibilities. Can a microorganism survive the impact of the original projectile into its home world and the journey through space, which in the case of Martian meteorites ranges from between one and twenty million years?

A study in the latest issue of Astrobiology makes the case that survival is possible. Endolithic cyanobacteria and epilithic lichens can withstand incredibly harsh conditions here on Earth and become prime candidates for investigating their potential passage through space. The team simulated shock pressures of the sort the organisms might have experienced when being blasted off the Martian surface, with results that support space transport at least within planetary systems. From the paper (internal references deleted for brevity):

A vital launch window for the escape from Earth’s gravity field may only be achieved by very large impact events that blow out at least part of the atmosphere… The direct ejection and escape of rocks from Earth is very difficult because of the required very high escape velocity (11 km/s) and the decelerating effect of Earth’s dense atmosphere. Therefore, “mega-impacts,” which occurred frequently only during the “early heavy bombardment phase,” i.e., before 3.75 billion years ago…, would be required to transfer sufficiently large fragments of moderately shocked rocks into space. Our results enlarge the number of potential organisms that might be able to reseed a planetary surface after “early,” very large impact events… and suggest that such a re-seeding scenario on a planetary surface is possible with diverse organisms.

Re-seeding a planetary surface is an interesting scenario in itself. It implies that a major asteroid strike might not spell complete doom for life on the planet, no matter how devastating the effects on the surface below. Rocks eventually falling back to their home world have the potential for launching life processes all over again. And, of course, the concept of life moving between entirely different planets receives another boost from this work, which gives “…further support to the hypothesis of lithopanspermia for a viable transport from Mars to Earth or from any Mars-like planet to another habitable planet in the same stellar system.”

The paper is Horneck et al., “Microbial Rock Inhabitants Survive Hypervelocity Impacts on Mars-Like Host Planets: First Phase of Lithopanspermia Experimentally Tested,” Astrobiology Vol. 8, No. 1 (2008), pp. 17-44 (available online).