Exobiology: Laboratory tests of the impact related aspects of Panspermia

The idea that life began elsewhere and then naturally migrated to the Earth is known as Panspermia. One such possibility is that life is carried on objects (meteorites, comets and dust) that arrive at the Earth. The life (bacteria) is then presumed to survive the sudden deceleration and impact, and then subsequently develop here on Earth. This step, the survivability of bacteria during the deceleration typical of an object arriving at Earth from space, is studied in this paper. To this end a two-stage light gas gun was used to fire projectiles coated with bacteria into a variety of targets at impact speeds of 3.8 to 4.9 km s(-1). Targets used were rock, glass, metal and aerogel (density 100 kg m(-3)). Various techniques were used to search for bacteria that had transferred to the target material during the impact. These included taking cultures from the target crater and ejecta, and use of fluorescent dyes to mark sites of live bacteria. So far only one sample has shown a signal for bacteria surviving an impact. This was for bacteria cultured from the ejecta spalled from a rock surface during an impact. However, this result needs to be repeated before any firm claims can be made for bacteria surviving a hypervelocity impact event.