Survival of seeds in hypervelocity impacts

摘要

Panspermia ('seeds everywhere') postulates that life naturally migrates through space.Laboratory studies of Panspermia often examine the survival of Earth's species under the conditionsthought to occur during transfer through space. Much of this research has centred on bacteria, but herewe consider seeds themselves. We simulated the extreme accelerations necessary for their hypotheticalejection from a planetary surface and the impacts associated with their arrival on another planet. Seedsof tobacco, alfalfa and cress were fired into water at speeds in the range 1-3 km s~(-1), corresponding toimpact shock pressures of circa 0.24-2.4 GPa. No seeds remained intact and able to germinate, even atthe lowest speeds. Although fragmentation occurred, even at 3 km s~(-1)the size of some of the fragmentswas about 25 % that of the seeds. Thus, whilst the seeds themselves did not survive extreme shocks, asubstantial fraction of their mass did and might successfully deliver complex organic materials afterimpact. These results are discussed with respect to ancient Panspermia and the potential ofcontemporary impacts to eject living organisms into space.