Astrobiology Workshop, Macquarie University July 12-13 2001

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Estimated flux of rocks bearing viable lifeforms exchanged between Earth and Mars

Michael Paine (The Planetary Society Australian Volunteers)

It has been suggested that a possible mechanism for transfer of life between Earth and Mars is through rocks ejected by major asteroid impacts. Recent work on this subject is reviewed. An estimate is provided on the quantity of rocks that are exchanged by the impact process and the likelihood that these rocks have delivered viable lifeforms to the other planets. Averaged over millions of years, it is estimated that each year about 150kg of Earth rocks reach Mars year under conditions that are conducive to survival of microbes within the rocks. It is therefore highly likely that Earth-life has reached the surface of Mars for hundreds of millions of years. The main uncertainty appears to be the ability of these microbes to colonise Mars once they reach the surface. Similar estimates apply to Mars rocks reaching the Earth.