快猫短视频

MELTING glaciers rather than flowing surface water could have carved out the
Red Planet鈥檚 distinctive valleys.

Branching networks of small valleys have led many scientists to conclude that
rivers of running water once flowed freely across the surface of Mars. But this
would mean that the Red Planet once had a much warmer climate than it does today
and, apart from its valleys, there is no evidence to suggest that Mars was ever
warm
(快猫短视频, 17 April 1999, p 48).

But Pascal Lee, a planetary scientist at NASA鈥檚 Ames Research Center in
Mountain View, California, says the answer may be found on Devon Island in the
Canadian Arctic, where he is studying valleys carved by glacial meltwater. 鈥淲hat
we鈥檝e been finding on Devon Island,鈥� says Lee, 鈥渋s a wide variety of valley
types, from canyons to little networks of small valleys, that bear an uncanny
resemblance to specific counterparts on Mars.鈥�

In particular, he says, the Martian valleys 鈥渃ut through a desert that
otherwise has very little sign of water flowing nearby鈥�. The constant width and
depth of Martian valleys over long distances, their flat floors and steep walls
are all distinctive features also found on Devon Island, but uncommon on river
networks.

Lee believes that other Martian landforms, notably some large canyons on the
west end of Vallis Marineris, could actually have been carved by flowing glacial
ice. Devon Island also has canyons like these, he told the 31st Lunar and
Planetary Institute Science Conference in Houston, Texas, last week.

If Lee is correct, Mars may have had a cold climate, in which snowfall piled
up to form glaciers that later melted in the heat generated inside the planet.
Mars expert Jim Head of Brown University, Rhode Island, welcomes Lee鈥檚 work,
saying the analogy to Devon Island is helping him visualise how melting snow
might have produced valleys on Mars.