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THERE鈥檚 a better chance than ever that any water found on Mars will hold
signs of life, according to a new computer model. The model, originally
developed to describe Antarctica鈥檚 Lake Vostok, suggests any existing lakes
under Mars鈥檚 icy poles must have formed on the surface of the planet when it was
warm and maybe habitable.

Features such as riverbeds on Mars indicate that water flowed on the planet鈥檚
surface when it was much warmer than it is today. Many scientists suspect liquid
water might still exist somewhere on Mars, possibly in lakes under the ice at
the Martian poles.

But how these lakes would have formed at the poles is not clear. On Earth,
they can be created when ice several kilometres thick is warmed from below by
geothermal heat. This warming, combined with the pressure and insulation of the
ice above, is enough to melt the ice.

For the same thing to happen on Mars, the insulating ice sheet would have to
be 4 to 6 kilometres thick. Measurements by NASA鈥檚 Mars Global Surveyor
spacecraft indicate that the ice caps at the poles are 3 to 4 kilometres thick
at most.

But now Natalia Duxbury at the Jet Propulsion Laboratory in Pasadena,
California, and her colleagues have used a computer model developed to describe
Lake Vostok to show how lakes could form on Mars. If there was once even a
shallow lake鈥攋ust 63 metres deep鈥攐n the warm Martian surface, it
could have survived the cooling of the planet without totally freezing, says
Duxbury. 鈥淚f there is water under the Martian ice, it has to be from an open
濒补办别.鈥�

鈥淐learly, if it was on the surface in the past, there鈥檚 a greater chance for
life,鈥� says microbiologist Charles Cockell from the British Antarctic Survey in
Cambridge. But he adds there are still a lot of 鈥渋fs鈥� in the theory. 鈥淚t鈥檚 all
extreme speculation.鈥�

Lake Vostok covers around 14,000 square kilometres under the Antarctic ice.
Duxbury thinks it may have formed more than 30 million years ago, when the
Antarctic had a mild climate. At that time the lake must have been at least 53
metres deep, otherwise it would have frozen as the Antarctic became cold. If
Lake Vostok formed from a surface lake exposed to balmy temperatures and
sunlight, traces of life from that time might still be there today.