Risks threatening viable transfer of microbes between bodies in our solar system
Planetary and Space Science, 48 (11):
1107--1115 (2000)Abstract
A fraction of the number of ejecta expelled from a planet by comet
or asteroid impacts end up landing on another planet. If microorganisms
were living in the ground before impact, they would be transported
inside ejecta to the target planet. During that perilous trip, they
would be subject to four main categories of threat to their survival:
dynamical stress, excess temperature, radiation, chemical attack
and vacuum. The effect of these, in the form of survival fractions
as a function of time, as well as approximate numbers of arriving
ejecta with viable flight times, have been investigated in a quantitative
study we have made. The result shows that viable transfer from Mars
to Earth and vice versa was highly probable during the first 0.5
Ga, and also probable, but with lower frequency, thereafter. Here
we follow up with considerations about the consequences of the result
regarding the question of whether the ancestor cell of all life on
Earth must have originated on Earth, or whether it could have originated
on Mars, its descendants thereafter moving to Earth. Some other possible
consequences are also discussed. (C) 2000 Elsevier Science Ltd. All
rights reserved.