Panspermia - The Survival of Micro-Organisms During Hypervelocity Impact Events

The possible spread of life between planetary bodies has significant implications for any future discoveries of life elsewhere in the solar system, and for the origin of life on Earth itself. Litho-Panspermia proposes that life can survive the shock pressures associated with giant impacts which are sufficiently energetic to eject life into space. As well as this initial ejection, life must also survive the impact onto another planetary surface.

The research presented shows that the micro-organisms Nannochloropsis oculata phytoplankton and tardigrade Hypsibius dujardini can be considered as viable candidates for panspermia. Using a Two-Stage Light Gas Gun, shot programmes were undertaken to impact frozen organisms at different velocities to simulate oceanic impacts from space. It is demonstrated that the organisms can survive a range of impact velocities, although survival rates decrease significantly at higher velocities.

These results are explained in the context of a general model for survival after extreme shock, showing a two-regime survival with increasing shock pressure which closely follows the pattern observed in previous work on the survival of microbial life and spores exposed to extreme shock loading, where there is reasonable survival at low shock pressures, but a more severe lethality above a critical threshold pressure (a few GPa). Hydrocode modelling is then used to explore a variety of impact scenarios, and the results are compared with the experimental data during a thorough analysis of potential panspermia scenarios across the universe.

These results are relevant to the panspermia hypothesis, showing that extreme shocks experienced during the transfer across space are not necessarily sterilising, and that life, could survive impacts onto other planetary bodies, thus giving a foothold to life on another world.