Even clumps of viable bacteria, if they are introduced as micrometre-sized meteoroids, could survive flash heating in the atmosphere.
The asteroids, meteoroids and apparently all comets originated in the explosion of planets (or moons).
The sputtering model considered here may require significant modification for the case of highly fluffy and porous meteoroids.
Second, the time meteoroids have been travelling in space exposed to cosmic rays is relatively short, typically millions of years.
This kinetic energy goes into heating the meteoroid and the surrounding atmosphere.
Classical work on meteoroid ablation suggests that these particles should be annihilated by atmospheric deceleration.
As the evaporation of molecules from the surface of the meteoroid increases, a vapour cloud starts to form around the meteoroid.
Heating of the meteoroid by direct impact causes it to lose mass by fragmentation and, as the temperature rises, evaporation and melting of its surface.
