Survival of life on asteroids, comets and other small bodies

The ability of living organisms to survive on the smaller bodies in our sol ar system is examined. The three most significant sterilizing effects inclu de ionizing radiation, prolonged extreme vacuum, and relentless thermal ina ctivation. Each could be effectively lethal, and even more so in combinatio n, if organisms at some time resided in the surfaces of airless small bodie s located near or in the inner solar system. Deep within volatile-rich bodi es, certain environments theoretically might provide protection of dormant organisms against these sterilizing factors. Sterility of surface materials to tens or hundreds of centimeters of depth appears inevitable, and to gre ater depths for bodies which have resided for long periods sunward of about 2 A.U.