The question of life on Mars is a hard one to answer.

Making a firm 'no' is almost impossible, as one could always argue that we're looking for the wrong thing in the wrong place and that actually, over the hill and under a different rock, is a different form of life we've just not detected yet.

However - DNA has been long held as a good marker for the sort of life we might be able to understand.

Of course, if one says "it might not have DNA...it might have something else" - then the question is, how exactly does one go looking for something. It's like going through a haystack, without knowing if there is any needles in it, nor what a needle looks like, is made of or how it reacts to things.

Searching for familiar life markers is a sensible place to start - if that is a negative then perhaps we can speculate as to what other markers any potential life might have.

Doug