What mechanism acts as a barrier against the survival of terrestrial bacteria accidentally introduced to the Martian surface?

Answer

Intense ultraviolet (UV) radiation and high-energy cosmic rays sterilize the surface layers.

The thin Martian atmosphere offers minimal shielding, allowing harsh surface radiation to penetrate deeply enough to kill any terrestrial microbes or spores that might be present.

What mechanism acts as a barrier against the survival of terrestrial bacteria accidentally introduced to the Martian surface?
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