No. 99: May-Jun 1995
Scientists are already convinced that cratering events on the moon and Mars have propelled rocky debris in the direction of the earth, and that some of these fragments have landed here in the guise of meteorites. A logical question is: Can life forms and/or chemical precursors of life be transported thus across the far reaches of the solar system? Can one planet infect another ballistically? An analysis by M.K. Wallis and N.C. Wickramasinghe is rather warm towards this idea:
"The mass of escaping ejecta from the presumed 10-km comet that caused the 180-km Chicxulub crater, with a radius of roughly 10 km and 1 m deep, amounted to ~300 Mm3 , of which one third may have been rock and 10% higher-speed ejecta that could have transited directly to Mars. It may have taken 10 Ma to impact Mars but...the probability is not exceedingly low but 0.1-1%.
"The survival and replication of microorganisms once they are released at destination would depend on the local conditions that prevail. Although viability on the present-day Martian surface is problematical, Earth-to-Mars transfers of life were feasible during an earlier 'wet' phase of the planet, prior to 3.5 Ga ago. The Martian atmosphere was also denser at that epoch, with several bars of CO2 , thus serving to decelerate meteorites, as on the present-day Earth. Since the reverse transfer can occur in a similar manner, early life evolution of the two planets may well have been linked."
(Wallis, Max K., and Wickramasinghe, N.C.; "Role of Major Terrestrial Cratering Events in Dispersing Life in the Solar System," Earth and Planetary Science Letters, 130:69, 1995)
Comment. Now we know why the "face on Mars" looks so human!!