  Potential microbial contamination of Martian moons, Phobos and Deimos, which
can be brought about by transportation of Mars ejecta produced by meteoroid
impacts on the Martian surface, has been comprehensively assessed in a
statistical approach, based on the most probable history of recent major
gigantic meteoroid collisions on the Martian surface. This article is the first
part of our study to assess potential microbial density in Mars ejecta
departing from the Martian atmosphere, as a source of the second part where
statistical analysis of microbial contamination probability is conducted.
Potential microbial density on the Martian surface as the source of
microorganisms was estimated by analogy to the terrestrial areas having the
similar arid and cold environments, from which a probabilistic function was
deduced as the asymptotic limit. Microbial survival rate during hypervelocity
meteoroid collisions was estimated by numerical analysis of impact phenomena
with and without taking internal friction and plastic deformation of the
colliding meteoroid and the target ground into consideration. Trajectory
calculations of departing ejecta through the Martian atmosphere were conducted
with taking account of aerodynamic deceleration and heating by the aid of
computational fluid dynamic analysis. It is found that Mars ejecta smaller than
0.03 m in diameter hardly reach the Phobos orbit due to aerodynamic
deceleration, or mostly sterilized due to significant aerodynamic heating even
though they can reach the Phobos orbit and beyond. Finally, the baseline
dataset of microbial density in Mars ejecta departing for Martian moons has
been presented for the second part of our study.
