Would a Mars probe in the Sahara desert detect human civilisation?

Dominic - Well that's a great question because NASA do actually test some of their spacecraft in the New Mexico desert or if they want a really harsh environment, they might try the Atacama Desert at high altitude in Chile. And that's a useful test bed for a couple of reasons: it provides a similar physical environment to what you might find, for example on Mars, and so you can test for practical issues like whether your wheels are going to get clogged up with mud when you drive around on Mars; It also means you can see if you can detect the really quite sparse life forms, the bacteria that you find in the sand of the desert, and the answer is that yes, you can. You really need to draw a distinction between two different objectives that you can have when you're searching for extraterrestrial life. You can either be searching for anything that seems to be alive, so anything from bacteria upwards, or you could be searching for signs of intelligence, searching for intelligent life like ourselves. And you can divide the current search programmes for extraterrestrial life into those two categories. So if you're sending rovers to Mars and looking at soil samples, you're really talking about looking for bacteria rather than looking for little green men. But if you're looking at the signals from radio telescopes to see if you can detect alien television signals perhaps coming from alien planets, then that is looking for intelligence, rather than direct traces of life itself. Having said that, I think if you were to land a rover in the desert, you probably would be able to detect that there was something quite funny going on on this planet because you would smell the air and you would notice it had quite a large oxygen content, and you would wonder where that oxygen was coming from and think that maybe you needed some plants and some photosynthesis to make that oxygen. And you would probably also notice that this planet had quite a lot of radio noise coming from it, from planes, from communication satellites, and of course from radio and television transmitters. So you would think it was quite an odd planet, I think.

Ben - So, the odds are, it would pick up some very tantalising clues of our existence, even if it landed somewhere where there are no humans for hundreds of miles.

Dominic - I think it would, yes.