New doubts over Mars water
2008-03-01 21:09
Washington - It made a big splash when
scientists announced in 2006 that images from a Nasa spacecraft
indicated water apparently had flowed on the surface of Mars in
the past decade, but new research casts doubt on that finding.
Other scientists on Friday said new images and computer
simulations strongly indicated that a landslide of sand and
gravel was a more likely explanation for the bright deposits in
gullies previously touted as evidence of recent water flow.
"We started off not thinking that we were going to debunk
anything.
"I absolutely thought it was going to be liquid," Jon
Pelletier, a professor of geosciences at the University of
Arizona who led the new study, said in a telephone interview.
Using previous images from Nasa's Mars Global Surveyor and
newer, higher-resolution readings from Nasa's Mars
Reconnaissance Orbiter, the team created three-dimensional
pictures of one of the geological formations showing downhill
flow in a crater.
Computer simulations
The scientists then ran computer simulations of what
conditions might have caused such a formation.
Flows of liquid
water did not really match the formation in the computer models
but flows of dry, granular material like sand and gravel
matched it almost perfectly, they reported in the journal
Geology.
"What we'd hoped to do was rule out the dry flow model -
but that didn't happen," University of Arizona planetary
sciences professor Alfred McEwen said in a statement.
Pelletier said his research cannot absolutely rule out that
liquid water created the flow formation, measuring about 500m long and up to 100m wide.
Another possibility is that flows of thick mud containing
about 50% to 60% sediment with a consistency
similar to molasses or lava might be responsible.
Hot topic
"The simplest explanation is that it is dry, granular
flow," Pelletier said. "We think that the simpler explanation
is probably the correct one."
The presence of water on Mars is a hot topic for
scientists.
They have presented strong evidence of huge
deposits of frozen water at the Martian poles and point to
geological features that indicate that large bodies of water
have flowed on the planet's surface in the distant past.
Water is a key to the question of whether life, even in the
form of mere microbes, ever existed on Mars.
On Earth, all
forms of life require water to survive.
Kenneth Edgett of Malin Space Science Systems in San Diego,
who was involved in the 2006 study suggesting the flows were
liquid, declined to comment.