Question: is there life on other planets?

Paul Roche answered on 13 Jun 2010:

I personally think we will find evidence of life on other planets in our Solar system, although it will most likely be something like bacteria or microbes, not “little green men”.

There are several places where we think liquid water exists (under the surface on Mars, and below the icy surfaces of some of the moons of Jupiter, like Europa, Ganymede and Callisto, and also the moon Titan that orbits Saturn), and that is one of the vital keys to life (as far as we know, from our experience with life on Earth – but maybe we don’t know as much about life as we think we do).

Conditions on Mars were once warmer and wetter than they are now, so some primitive forms of life may have evolved there as well, and various future missions will look for the chemical signatures of this. But it will really take humans to explore the surface properly, and look for evidence of fossils that might show that some form of bacteria etc. may once have developed on the Martian surface (before most of the atmosphere evaporated away, leaving the cold and apparently lifeless planet than we now see).

Beyond our Solar system, I think there is a very high chance that intelligent life has evolved in many places throughout our galaxy – but our galaxy is much older than the solar system, so much of this life may have evolved and become extinct before our Siun and planets were even formed. And the galaxy is very, very big – even at the speed of light it would take over 100,000 years to cross it from one side to another – so any life out there is likely to be very, very far away. So even if there are aliens out there, they are likely to be very widely spread, and (unless they have cracked the problem of travelling faster than light, which our current knowledge of physics says we just can’t do), they are very unlikely to ever reach us – unless they are prepared to spend thousands of years travelling…