...we eventually get around to building a research vessel to another
planet, Mars for example, that can take soil samples and bring them back to
Earth.  But what we didn't take into account were the various previously
benign viruses present on the equipment taken on the previous exploratory
missions to Mars, which were released onto the planet and have been hanging
around there in the radiation, mutating and growing more virulent, just
waiting to be scooped up in a soil sample and returned to Earth.

So what then, huh?

Amanda
VFP Writing The Screenplay