In what could turn out to be a landmark discovery in the
history of Mars exploration, imaging scientists using data from
NASA’s Mars Global Surveyor spacecraft have recently observed
features that suggest there may be current sources of liquid
water at or near the surface of the red planet.

The new images, available at
or , show the smallest
features ever observed from martian orbit — about the size of a
sport-utility vehicle. NASA scientists compare the features to
those left by flash floods on Earth.

“We see features that look like gullies formed by flowing
water and the deposits of soil and rocks transported by these
flows. The features appear to be so young that they might be
forming today. We think we are seeing evidence of a groundwater
supply, similar to an aquifer,” said Dr. Michael Malin, principal
investigator for the Mars Orbiter Camera on the Mars Global
Surveyor spacecraft at Malin Space Science Systems, San Diego,
Calif. “These are new landforms that have never been seen before
on Mars.”

The findings will be published in the June 30 issue of
Science magazine.

“Twenty-eight years ago the Mariner 9 spacecraft found
evidence — in the form of channels and valleys — that billions
of years ago the planet had water flowing across its surface,”
said Dr. Ken Edgett, staff scientist at Malin Space Science
Systems and co-author of the paper in Science. “Ever since that
time, Mars science has focused on the question, ‘Where did the
water go?’ The new pictures from Global Surveyor tell us part of
the answer — some of that water went under ground, and quite
possibly it’s still there.”

“For two decades scientists have debated whether liquid
water might have existed on the surface of Mars just a few
billion years ago,” said Dr. Ed Weiler, associate administrator
for space science at NASA Headquarters. “With today’s discovery,
we’re no longer talking about a distant time. The debate has
moved to present-day Mars. The presence of liquid water on Mars
has profound implications for the question of life not only in
the past, but perhaps even today. If life ever did develop
there, and if it survives to the present time, then these
landforms would be great places to look.”

The gullies observed in the images are on cliffs, usually in
crater or valley walls, and are made up of a deep channel with a
collapsed region at its upper end (an “alcove”) and at the other
end an area of accumulated debris (an “apron”) that appears to
have been transported down the slope. Relative to the rest of
the martian surface, the gullies appear to be extremely young,
meaning they may have formed in the recent past.

“They could be a few million years old, but we cannot rule
out that some of them are so recent as to have formed yesterday,”
Malin said.

Because the atmospheric pressure at the surface of Mars is
about 100 times less than it is at sea level on Earth, liquid
water would immediately begin to boil when exposed at the martian
surface. Investigators believe that this boiling would be
violent and explosive. So how can these gullies form? Malin
explained that the process must involve repeated outbursts of
water and debris, similar to flash floods on Earth.

“We’ve come up with a model to explain these features and
why the water would flow down the gullies instead of just boiling
off the surface. When water evaporates it cools the ground —
that would cause the water behind the initial seepage site to
freeze. This would result in pressure building up behind an ‘ice
dam.’ Ultimately, the dam would break and send a flood down the
gully,” said Edgett.

The occurrence of gullies is quite rare: only a few hundred
locations have been seen in the many tens of thousands of places
surveyed by the orbiter camera. Most are in the martian southern
hemisphere, but a few are in the north.

“What is odd about these gullies is that they occur where
you might not expect them — in some of the coldest places on the
planet,” Malin indicated. “Nearly all occur between latitudes 30
degrees and 70 degrees, and usually on slopes that get the least
amount of sunlight during each Martian day.”

If these gullies were on Earth they would be at latitudes
roughly between New Orleans, Louisiana, and Point Barrow, Alaska,
in the northern hemisphere; and Sydney, Australia, to much of the
Antarctic coast in the south.

The water supply is believed to be about 100 to 400 meters
(300 to 1,300 feet) below the surface, and limited to specific
regions across the planet. Each flow that came down each gully
may have had a volume of water of, roughly, 2,500 cubic meters
(about 90,000 cubic feet) — about enough water to sustain 100
average households for a month or fill seven community-size
swimming pools. The process that starts the water flowing remains
a mystery, but the team believes it is not the result of volcanic

“I think one of the most interesting and significant aspects
of this discovery is what it could mean if human explorers ever
go to Mars,” said Malin. “If water is available in substantial
volumes in areas other than the poles, it would make it easier
for human crews to access and use it — for drinking, to create
breathable air, and to extract oxygen and hydrogen for rocket
fuel or to be stored for use in portable energy sources.”

“This latest discovery by the Mars Global Surveyor is a true
‘watershed’ — that is, a revolution that pushes the history of
water on Mars into the present,” said Dr. Jim Garvin, Mars
Program Scientist, NASA Headquarters. “To follow up on this
discovery we will continue the search with Mars Global Surveyor
and its rich array of remote sensing instruments, and in 2001,
NASA will launch a scientific orbiter with a high spatial
resolution middle-infrared imaging system that will examine the
seepage sites in search of evidence of water-related minerals.

“Furthermore, NASA is in the process of evaluating two
options for a 2003 mission to Mars, both of which could provide
independent information concerning the remarkable sites
identified by Malin and Edgett.”

NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif.,
manages the Mars Global Surveyor mission for NASA’s Office of
Space Science, Washington, D.C. JPL is a division of the
California Institute of Technology in Pasadena. Malin Space
Science Systems built and operates the camera system.

JPL’s industrial partner is Lockheed Martin Astronautics,
Denver, Colo., which developed and operates the spacecraft.

For more information on the Mars Global Surveyor mission,