[Vautrin]

With billions of planets in the universe, it would be unlikely that only on Earth life would have evolved.

It would be unlikely that other high life forms would look, think, or feel the way humans do. There may be some things the same, but a lot of differences as well.

It could well be that life had existed on Mars - but as we still have no tangible direct proof it is easier to come up with possible life forms, than to make a good prediction on what life forms would have lived on Mars.