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.
Image right:
A new gully deposit in a crater in the Centauri Montes Region. Image credit:
NASA/JPL/Malin Space Science Systems + Full image and caption
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.
Image left: A
new gully deposit in a crater in Terra Sirenum. Image credit: NASA/JPL/Malin
Space Science Systems + Full image and caption
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.
Image right:
A colorized view of a new crater on the upper north flank of the Martian
volcano Ulysses Patera. Image credit: NASA/JPL/Malin Space Science Systems + Full image and caption
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 verdana 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 and agency programs, visit:
