Tests conducted with tardigrades suggest that there is something in Martian dirt that dramatically reduces biological activity.

'War of the Worlds' in reverse? Mars dirt could help fight off a microbial invasion from Earth

Source: space
Source Link: https://www.space.com/space-exploration/search-for-life/war-of-the-worlds-in-reverse-mars-dirt-could-help-fight-off-a-microbial-invasion-from-earth