These are the opening words to David Bowies brilliant song Life on Mars and although the song is great Bowie couldn’t have been more wrong. As I write this Europe’s latest mission, ExoMars has just been launched by a Russian Proton rocket and is on its way to the Red Planet to look for the signs of life.
I won’t go into details here about the mission and how it will work but I would like to use this space, (no joke intended!), to think a bit about what it would mean if we found, or indeed didn’t find, life on Mars. OK, just a few details then! Exo Mars will arrive in October and consists of an orbiter and a lander called Schiaparelli. Now they will not be looking for little green men or in fact, little green anythings. What the mission is designed to test for is the gases that could indicate that there is biological activity on Mars.
Over the years we have heard that large quantities of methane have been detected and then we have heard that there is no methane. The latest seems to be that there might be methane or at least in some areas some of the time. The Viking landers in the 1970s tested for chemical signs of life but this was also inconclusive. One experiment showed a definite positive result and the other showed a definite negative which is about as inconclusive as you can get. About as inconclusive as asking a politician for a simple yes or no answer!
So let’s jump a year forward in time and look at what we might ind and what that finding would mean. Scenario number one- we find no signs of life at all. This would not in fact be a final, conclusive answer. As Carl Sagan said- “Absence of evidence is not evidence of absence”. So that would mean that it was possible that Mars is completely dead, that we hadn’t looked in the right way or that we were just unlucky. By “hadn’t looked in the right way” I mean that the experiments were wrong in that they were testing for life as we know it and that Martian life is different in some way. If we later found life that was different from Earth life then that would tell us a lot about how life develops.
Scenario number two is that we find life and that it is the same as Earth life. This would mean that life probably got knocked off Earth or Mars in a meteorite impact and landed on the other planet. The most likely route is Mars to Earth as Mars cooled and became hospitable before Earth and it is smaller so it is easier to knock bits off it by hurling rocks at it.
The bits you knock off also fall inwards which also requires less energy than going the other way. Tests have also showed that it is possible for bacteria to survive inside rocks, in space and during entry into Earth’s atmosphere. Also this happened a lot in the early Solar System, partly because there were a lot of rocks flying about and partly because Bruce Willis hadn’t been born yet. We don’t know whether this has happened but we know it is possible. It could also mean that life is pretty much the same everywhere and that would make the origin of life rather inconclusive. If it is the same everywhere then we can’t tell if it started one place and got transfered somewhere else, or if it is the same even though it originates independantly on different planets.
Alternatively, we find life that clearly does not have a common origin with life on Earth which would mean that wherever the conditions are suitable, life appears. Discovering life on Mars, or any other planet or moon, would be a huge thing but discovering that life is almost innevitable wherever the conditions are right would have huge implications.