From: Steven L. Wilson, Sr <Ndunlks@aol.com>
Date: Wed, 28 Jun 2000 15:21:13 -0400 (EDT)
Fwd Date: Wed, 28 Jun 2000 20:37:23 -0400
Subject: UpDate: Flash Floods Carving Channels On Mars? - Wilson, Sr


Source: Science (vol 288, p 2330)

 From New Scientist magazine, 01 July 2000


Fount of life

Even now, flash floods may be carving channels on Mars


There was great excitement last week when news leaked out that a
spacecraft has seen signs that water might have recently flowed
on Mars's surface. But experts are puzzled by how water could be
liquid in the frigid Martian climate and warn that concrete
proof will be hard to come by.

"If these results prove true, that there is water on Mars near
the surface, it has profound implications for the possibility of
life on Mars," NASA's associate administrator for space science
Ed Weiler told a press conference in Washington DC last week.
"Just about any place biologists find liquid water, organic
molecules and energy, they find life, whether it's on the
surface of the Earth or 10 000 feet below."

The debate about water on Mars began in earnest when the Mariner
9 spacecraft photographed the planet in 1972. The images showed
features that looked like giant flood channels and river
valleys. But it seemed impossible that liquid water carved these
in the recent past since the average surface temperature on Mars
is around ­50 °C and seldom rises above freezing. However, there
could have been liquid water on the planet more than a billion
years ago, when the climate would have been much warmer.

But pictures taken since March 1999 by a camera on the Mars
Global Surveyor spacecraft suggest that water has flowed on Mars
much more recently, says Mike Malin of Malin Space Science
Systems in San Diego, chief scientist for the camera. He and his
colleague Kenneth Edgett have seen rock formations at around 150
sites that seem to have formed relatively recently, during
sudden floods.

None of the formations has been around long enough to be scarred
by craters or shrouded in wind-blown sand, making them a million
years old at most. "The features appear to be so young that they
might be forming today," says Malin.

The formations are gullies on crater and valley walls. Each is a
deep V-shaped channel, typically a few kilometres long, with a
collapsed region at the top and a pile of debris at the bottom.
Their shapes resemble terrestrial gullies formed by water rather
than dry landslides or lava flows. "On Earth, there's no
question these are created by water," says Malin.

He and Edgett think the channels form because there is a layer
of water more than 100 metres below the Martian surface that is
kept liquid by the pressure of the overlying rock. When exposed
in a cliff face, this water freezes. More water then builds up
behind the dam, until it eventually bursts through the ice. This
flash flood would carve a channel.

"These observations are very compelling," says Maria Zuber, a
planetary scientist at the Massachusetts Institute of
Technology. But some things are puzzling, she adds. The features
appear on the coldest regions of Mars, near the poles and on
slopes facing away from the Sun. "It's so cold on Mars--you're a
hundred degrees away from the melting temperature. But there
might be very high pressures that make melting occur."

"I find it really exciting," says Steve Squyres of Cornell
University in Ithaca, New York. "The pictures make a compelling
case that water has leaked out of the ground recently on Mars.
But I think it might be an over-interpretation to suspect that
these things are tapping into a really large, subsurface
reservoir." Because the gullies are small, he thinks local
melting of ground ice due to the Sun or the planet's internal
heat might be responsible.

A definite answer will be a long time coming. "I don't think you
can really test this hypothesis fully without actually going to
the place from which the water is believed to have emerged,"
says Squyres. "But nature has played a very cruel trick on us
here, and put these things on the most unimaginably difficult
places to reach on the planet." For instance, they're on steep
and probably crumbly slopes that existing robots couldn't
navigate. "I'm not sure that even a human in a spacesuit could
climb up to these things," he adds.

In the meantime, the Global Surveyor team plans to check future
snapshots of the same gullies. If they change, this would
strengthen the case that water is still flowing today.

Hazel Muir