Most importantly, if life was found on Mars and it was convincingly shown to have had a separate origin to life on Earth (i.e. no panspermia) then this would se

Most importantly, if life was found on Mars and it was convincingly shown to have had a separate origin to life on Earth (i.e. no panspermia) then this would severely impact upon our understanding of how common life in the universe is. When we've only got one example and it's us, our estimate of the probability of life evolving on a given planet (given suitable conditions) could literally be anything from 100% to any arbitrarily low number you might like to think of. If we check two life-plausible planets and find separate life on both, the probability is suddenly way biased towards the high end of the scale. (A statistician can figure that one out for me.)