LOS ANGELES - New photographs from space suggest that water occasionally
flows on the frigid surface of Mars, raising the tantalizing possibility that
the Red Planet is hospitable to life, scientists reported Wednesday.
Kenneth Edgett, a scientist at Malin
Space Science Systems in San Diego, Calif., gestures during a news
conference at NASA Headquarters in Washington, Wednesday, Dec. 6, 2006 to
discuss the possibility that liquid water flowed on the surface of Mars as
recently as several years ago, raising the possibility that the Red Planet
could harbor an environment favorable to life. [AP]
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The new images, taken by NASA's Mars Global Surveyor before it lost contact
with Earth, do not actually show flowing water. Rather, they show changes in
craters that provide the strongest evidence yet that water coursed through them
as recently as several years ago, and is perhaps doing so even now.
"This is a squirting gun for water on Mars," said Kenneth Edgett, a scientist
at San Diego-based Malin Space Science Systems, which operates a camera on the
Global Surveyor.
The news excited scientists who hunt for extraterrestrial life. If the
finding is confirmed, they say, all the ingredients favorable for life on Mars
are in place: liquid water and a stable heat source.
In all of its Mars exploration missions, NASA has pursued a "follow the
water" strategy to determine if the planet once contained life or could support
it now.
Scientists believe ancient Mars was awash with pools of water. And at
present-day Mars' north pole, researchers have spotted evidence of water ice.
But they have yet to actually see water in liquid form.
"This underscores the importance of searching for life on Mars, either
present or past," said Bruce Jakosky, an astrobiologist at the University of
Colorado at Boulder, who had no role in the study. "It's one more reason to
think that life could be there."
Some researchers were skeptical that liquid water was responsible for the
surface feature changes seen by the spacecraft. They said other materials such
as sand or dust can flow like a liquid and produce similar results.
"Nothing in the images, no matter how cool they are, proves that the flows
were wet, or that they were anything more exciting than avalanches of sand and
dust," Allan Treiman, a geologist at the Lunar and Planetary Institute in
Houston said in an e-mail.
The findings will appear in Friday's issue of the journal Science.
The Global Surveyor previously spotted tens of thousands of gullies that
scientists believed were geologically young and carved by fast-moving water
coursing down cliffs and steep crater walls. Scientists decided to retake photos
of thousands of gullies in a search for evidence of recent water activity.
Two craters in the southern hemisphere that were originally photographed in
1999 and 2001 were examined again in 2004 and 2005, and the images yielded
changes consistent with water flowing down the crater walls, according to the
study.
Scientists said five to 10 pools of water rushed down the craters in each
case. In both craters, scientists found bright, light-colored deposits several
hundred yards long in gullies that weren't present in the original photos. They
concluded that the deposits - possibly mud, salt or frost - were left
there when water recently cascaded through.
Edgett said a combination of factors, including the shape and color of the
deposits, led the team to believe it was recent water action and not dust that
slipped down the slope. He said dust would leave dark deposits.
Water cannot remain a liquid on Mars for long because of subzero surface
temperatures and low atmospheric pressure that would turn water into ice or gas.
But scientists theorize that liquid water is being shot up to the surface from
an underground source, like geysers.
The Global Surveyor, managed by NASA's Jet Propulsion Laboratory, abruptly
lost radio contact with Earth last month. Several attempts to locate the
spacecraft, which has mapped Mars since 1996, have failed and scientists fear
the mission was likely at an end.
Mars formed more than 4.5 billion years ago and scientists generally believe
it went through an early wet and warm era that ended after 1.5 billion to 2.5
billion years, leaving the planet extremely dry and cold.
NASA's durable twin rovers have sent scientists strong evidence that the
planet once had liquid water at or near the surface, based on observations of
alterations in ancient rocks. The images from the Global Surveyor suggest the
process is still occurring.
"We're now realizing Mars is more active than we previously thought and that
the mid-latitude section seems to be where all the action is," said Arizona
State University scientist Phil Christensen, who was not part of the current
research.