MAR 98-050

Interplanetary Biological Transfer: Impact Resistance of Bacteria Entrapped in Small Meteorites
C. A. H. Roten, A. Gallusser, G. D. Borruat, S. D. Udry, G. Niederh, A. Croxatto, O. Blanc, S. De Carlo,
C. K. Mubenga-Kabambi and D. Karamata.
Contact: Claude-Alain Roten, Institut de Genetique et de Biologie Microbiennes, Rue Cesar-Roux 19, Lausanne, Switzerland Ch-1005. claude-alain.roten@igbm.unil.ch

The Martian origin of at least twelve meteorites, ejected into a solar orbit after a primary hypervelocity meteorite impact and subsequently captured by the Earth, clearly demonstrate that regular exchanges of crust fragments between planets take place in the solar system. Recently described, putative biological traces in one of these ejecta led to the debated proposal that life was present in Martian surface rocks. As interplanetary transfers of biological know-how may provide an explanation for the presence of life on at least two solar system bodies, survival in conditions mimicking final steps of interplanetary transfer of life forms entrapped in crust fragments was investigated with respect to small meteoroids.=20

From observations on the free fall of small impactors, analogous ballistic experiments can be designed and help to investigate if living cells can withstand the terminal low velocity impact. We have established that a series of different living cells survived an initial acceleration of 100 000 g and an impact in sand with a velocity of 300 to 750 meters per second. Based on these experiments and on the observation that the interior of small meteoroids remains cold during the fall, we propose, for the first time, that various kinds of organisms entrapped in small impactors can withstand (i) the heat produced by the Earth’s aerobraking, reducing the preatmospheric velocity (usually between 10 and 70 kilometers per second) to that of a free fall (125 to 250 meters per second), and (ii) the subsequent non-explosive impact. The significance of our observations for the origin and the early development of life in the solar system will be discussed.