In a blow
to hopes for finding water and life on Mars, scientists think bright streaks
detected inside Martian gullies after 1999 were not spurts of water, but rather
avalanches of dust.
Water is
thought to have covered much of Mars in the
past, but whether or not the life-giving substance has shown up in the
recent past is a matter of debate among scientists.
The strange,
streaky formations were not present in Mars Global Surveyor 1999 images of the
gullies. Seven years later, however, the bright streaks made their debut in new
images, prompting Michael Malin of Malin Space Science Systems and his
colleagues to conclude that a recent burst of Martian
groundwater might be responsible.
But Jon
Pelletier, a geoscientist at the University of Arizona (UA) in Tucson, and his team now say "pure liquid water" is unlikely to have made such
formations in the Centauri Montes region of Mars.
"The
dry granular case was the winner," Pelletier said, referring to a dusty
mode of creation. "I was surprised. I started off thinking we were going
to prove it's liquid water."
Pelletier
and his colleagues' findings, which are based on Mars
Reconnaissance Orbiter images taken by High Resolution Imaging Science
Experiment (HiRISE) camera, will be detailed in the March issue of the journal Geology.
Since 2006,
HiRISE has provided the most detailed images of Mars ever taken from orbit,
giving Pelletier a chance to offer a second opinion on the existence of liquid
water that might still support life beneath the Red
Planet's surface.
"What
we'd hoped to do was rule out the dry flow model," said Alfred McEwen, a
UA professor and leader of the HiRISE team. "But that didn't happen."
Although
the new study doesn't rule out a watery creation of the bright streaks,
Pelletier and McEwen said a bone-dry avalanche of dust and rocks is the most
likely culprit.
Their
conclusions stem from work with 3-D maps created with HiRISE image data.
"This
is the first time that anyone has applied numerical computer models to the
bright deposits in gullies on Mars," Pelletier said.
When he
compared the bright
deposit and its HiRISE image to the predictions made by the model, the dry
avalanche model was a better fit.
"There
are other ways of getting deposits that look just like this one that do not
require water," Pelletier said.
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