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NASA Images Suggest Water Still Flows in Brief Spurts on Mars
WASHINGTON - NASA photographs have revealed bright new deposits seen in
two gullies on Mars that suggest water carried sediment through them
sometime during the past seven years.
"These observations
give the strongest evidence to date that water still flows occasionally
on the surface of Mars," said Michael Meyer, lead scientist for NASA's
Mars Exploration Program, Washington.
Liquid water, as
opposed to the water ice and water vapor known to exist at Mars, is
considered necessary for life. The new findings heighten intrigue about
the potential for microbial life on Mars. The Mars Orbiter Camera on
NASA's Mars Global Surveyor provided the new evidence of the deposits
in images taken in 2004 and 2005.
"The shapes of these
deposits are what you would expect to see if the material were carried
by flowing water," said Michael Malin of Malin Space Science Systems,
San Diego. "They have finger-like branches at the downhill end and
easily diverted around small obstacles." Malin is principal
investigator for the camera and lead author of a report about the
findings published in the journal Science.
The atmosphere of
Mars is so thin and the temperature so cold that liquid water cannot
persist at the surface. It would rapidly evaporate or freeze.
Researchers propose that water could remain liquid long enough, after
breaking out from an underground source, to carry debris downslope
before totally freezing. The two fresh deposits are each several
hundred meters or yards long.
The light tone of the deposits
could be from surface frost continuously replenished by ice within the
body of the deposit. Another possibility is a salty crust, which would
be a sign of water's effects in concentrating the salts. If the
deposits had resulted from dry dust slipping down the slope, they would
likely be dark, based on the dark tones of dust freshly disturbed by
rover tracks, dust devils and fresh craters on Mars.
Mars
Global Surveyor has discovered tens of thousands of gullies on slopes
inside craters and other depressions on Mars. Most gullies are at
latitudes of 30 degrees or higher. Malin and his team first reported
the discovery of the gullies in 2000. To look for changes that might
indicate present-day flow of water, his camera team repeatedly imaged
hundreds of the sites. One pair of images showed a gully that appeared
after mid-2002. That site was on a sand dune, and the gully-cutting
process was interpreted as a dry flow of sand.
Today’s
announcement is the first to reveal newly deposited material apparently
carried by fluids after earlier imaging of the same gullies. The two
sites are inside craters in the Terra Sirenum and the Centauri Montes
regions of southern Mars.
"These fresh deposits suggest that
at some places and times on present-day Mars, liquid water is emerging
from beneath the ground and briefly flowing down the slopes. This
possibility raises questions about how the water would stay melted
below ground, how widespread it might be, and whether there's a
below-ground wet habitat conducive to life. Future missions may provide
the answers," said Malin.
Besides looking for changes in
gullies, the orbiter's camera team assessed the rate at which new
impact craters appear. The camera photographed approximately 98 percent
of Mars in 1999 and approximately 30 percent of the planet was
photographed again in 2006. The newer images show 20 fresh impact
craters, ranging in diameter from 7 feet (2 meters) to 486 feet (148
meters) that were not present approximately seven years earlier. These
results have important implications for determining the ages of
features on the surface of Mars. These results also approximately match
predictions and imply that Martian terrain with few craters is truly
young.
Mars Global Surveyor began orbiting Mars in 1997. The
spacecraft is responsible for many important discoveries. NASA has not
heard from the spacecraft since early November. Attempts to contact it
continue. Its unprecedented longevity has allowed monitoring Mars for
over several years past its projected lifetime.
NASA's Jet
Propulsion Laboratory, Pasadena, manages the Mars Global Surveyor
mission for the NASA Science Mission Directorate, Washington.
For more information about NASA's Mars missions, visit:
