Ever since I was a kid my dreams have been crazy as hell. Last night, I had a dream where I was dropping my kid off at school, but there were people on both sides of the road standing waiting for a wedding. I see the couple and nope right out. Turning around a curb, suddenly I was in a fucking baseball stadium and rows of seats cut me off. I had to get home so I got out of my car? I'm walking down the stairs when I hear "oh, there it is!" I look up where the person was pointing to the sky. I see some rocket like thing, and assumed it was fireworks. It stopped, I hear three dreaded bomb falling noise, and then it slams into a seat a few rows down from the wedding. I hit the deck because I don't want to die. But instead of exploding it sprays enough glitter throughout the stadium I ended up with a mouth full. Then I get out of there, call my mom, explained what happened, head to their house which is now a bunker in new York City and they refuse to believe what I went through. Then I woke up.
That doesn't make sense, if that were the case it wouldn't be relevant anymore as humans simply walking on the continent would introduce incredible amounts of bacterias and viruses.
Even with the sterile processing of Moon and Mars rovers have observed this. It's impossible to prevent, only reduce.