What are the risks of contaminating Mars with Earth life forms, or vice versa?
Actually, it is arguable that this has already been happening for billions of years. During his study of known Martian meteorite ALH84001, Cal Tech’s Joseph Kirschvink showed that large parts of the rock were never heated above 40C (104F), proving the theory of University of Arizona researcher Jay Melosh that it is possible for rocks to be ejected from one planet’s surface and land on another’s surface without being excessively heated. More importantly, this discovery showed that not all rocks ejected from either Mars or Earth are sterilized — a fact that, when combined with the known ability of microorganisms to remain alive in a dormant state for millions of years, means that Earth life has probably already traveled to Mars, and if life ever existed on Mars, it has already traveled to Earth.
