Survivability of bacteria ejected from icy surfaces after hypervelocity impact.

Both the Saturnian and Jovian systems contain satellites with icy surfaces. If life exists on any of these icy bodies (in putative subsurface oceans for example) then the possibility exists for transfer of life from icy body to icy body. This is an application of the idea of Panspermia, wherein life migrates naturally through space. A possible mechanism would be that life,here taken as bacteria, could become frozen in the icy surface ofone body. If a high-speed impact occurred on that surface, ejectacontaining the bacteria could be thrown into space. It could thenmigrate around the local region of space until it arrived at a second icy body in another high-speed impact. In this paper we consider some of the necessary steps for such a process to occur,concentrating on the ejection of ice bearing bacteria in the initial impact, and on what happens when bacteria laden projectiles hit an icy surface. Laboratory experiments using high-speed impacts with a light gas gun show that obtaining icy ejecta with viable bacterial loads is straightforward. In addition to demonstrating the viability of the bacteria carried on the ejecta, we have also measured the angular and size distribution of the ejecta produced in hypervelocity impacts on ice. We have however been unsuccessful at transferring viablebacteria to icy surfaces from bacteria laden projectilesimpacting at hypervelocities.