QUESTION:
I noticed as I watch that there is a particular interest in the water levels
of the planet, and the idea that water on Mars means that life could/did
exist.  Now I don't know... but could there be a possibility of life on Mars
that is not water based, as life here on Earth is?  Has the prospect been
considered that some other form of life, as we do not recognize it, may
exist now or existed in the past?

ANSWER from Bruce Jakosky on June 17, 1997:
Can life use a substance other than water as its medium?  It's pretty clear
that some liquid must be involved in life.  It's needed to fill in the
volume of cells, and yet allow for nutrients to be transported in and waste
products to be transported out.  With the types of life we know about on
Earth, it would be impossible to imagine a different liquid filling this
role.

Looking out at other planets, though, there are other possible liquids that
could exist.  These might include liquid methane and ethane (as are thought
to occur on the surface of the Saturn satellite Titan, for instance).  One
cannot rule out these liquids as sustaining life, even though there are
arguments that suggest that water is more suited for life.

Of course, water is much more abundant in the universe than any of these
other liquids would be.  This means that water will be much more available
for life, and that an organism that could use water has many more places
where it could live than an organism that would require a different liquid.

On Mars, it's not clear that any liquid other than water even would be
present. There is a lot of evidence for water--channels that almost
certainly were carved by water, water ice polar caps, water vapor in the
atmosphere, and so on. There is no evidence for any other liquids.  So, if
there is life on Mars, it almost certainly would be water based.