Could meteorites from Earth end up on Mars?

Andrew Pontzen from UCL took on Brian's cosmic question...

Andrew - I think the answer is yes. There could certainly meteorites from Earth on Mars. Just for people who haven’t looked into this before, it is a fact that we have found meteorites that we are pretty confident have come from Mars right here on Earth. And the reason we think they’ve come from Mars is because we can study their chemical composition and so on, and we find that they just don’t have a chemical composition that’s typical of meteorites that are whizzing around in the solar system - not the normal meteorites. They have a chemical composition that matches that we know Mars has. So we are pretty confident that those things have come directly from Mars.

When you look at why? Why would there by chunks of mars landing here on Earth? You find out that the only sensible explanation for it is collisions of giant comets, or something like that, with Mars. Chips off a bit of Mars which then flies around a bit in the solar system for a few million years and, eventually, happens to find it’s way to Earth and it lands. Then it’s actually very useful because we can start learning stuff about Mars. And there’s absolutely no reason why the reverse process couldn’t have happened.

The thing to bear in mind though, especially if you’re interested in water say, is that the quantities of material involved here are absolutely tiny. You are talking about absolutely tiny amounts of stuff. So, even if a bit of water found it’s way from Earth to Mars through that route, it’s not going to be something that’s supporting little green men on Mars somewhere.

Chris - Well that’s a relief. Sarah Madden…

Sarah - Is it possible that life from Earth could get to Mars via the same kind of route by meteors?

Andrew - It’s entirely possible. I think a lot of people are thinking very seriously about where did life come from? Could it originate in space even? Or if it did originate here on Earth, could it then be transferred to other planets through space?

At first, a lot of people were hugely sceptical of this but, it is now known that here on Earth that there are bacteria that we call “extremophiles” that can survive in incredibly extreme environments. So, even though you’d think any living thing that was chipped off the Earth in some giant cataclysmic collision, and then flew around in space for a while, would surely die. Actually, maybe not. Maybe life could survive in those environments and could have found it’s way to Mars in exactly that way.