AAS: Given what we know about the conditions on
Mars, past and present, what sort of life forms
might you expect to see?
CC: I think if there were anything there, it would be
very simple and it would probably use quite basic
sources of energy. One example could be microbes
that use hydrogen and carbon dioxide to make
methane. Methane hasn’t actually been detected
on Mars, but that is one of the most primitive
types of energy-gathering. Those are the sorts of
things you would be looking for if you were going
to hunt for life.
AAS: How about complex life? Could anything larger
have lived in the water?
CC: It seems unlikely; Mars became very dry about
3.9 billion years ago. There has been episodic
water since then, but the main phase of large
bodies of water, lakes and rivers, seems to have
been over about 3.8 to 3.9 billion years ago.
[Complex] multi-cellular life only appears in the
rock record on the Earth about 600 million years
ago. I think that what you would probably be
looking for are micro organisms, not complex life.
AAS: What are the chances of microbial life forms
still existing on Mars?
CC: It would all depend on whether there is liquid
water under the surface. The problem with Mars
is that it’s very much a frozen world now. People
have seen what might be brine seeps, seeping
water onto the surface of the Red Planet, even
today. Whether these places are inhabited is
difficult to know, they could be habitable but
actually have no life in them. In other words, be