- posted 18 years ago
Meridiani Planum: "Drenched"
NASA Science News
March 2, 2004
Long ago, parts of Mars were soaked in liquid water, say scientists
analyzing data from NASA's Mars rover Opportunity.
March 2, 2004: Some rocks at Opportunity's landing site in Meridiani Planum
on Mars were once soaked in liquid water. Members of the Mars Exploration
Rovers' international science team presented the evidence today to news
reporters at NASA Headquarters in Washington, DC.
"Liquid water once flowed through these rocks. It changed their texture, and
it changed their chemistry," said Cornell University's Steve Squyres, the
principal investigator for the science instruments on Opportunity and its
twin, Spirit. "We've been able to read the tell-tale clues the water left
behind, giving us confidence in that conclusion."
Here are some of the clues that water formerly pervaded an outcropping of
rocks where Opportunity has been working:
(1) The rover's alpha particle X-ray spectrometer found lots of sulfur in
the outcrop. Related clues from that instrument and the miniature thermal
emission spectrometer suggest the sulfur is in the form of sulfate salts
(similar to Epsom salts). On Earth, rocks containing so much salt either
formed in water or, after formation, were soaked in water a long time.
Above: These spectra show that a rock dubbed "McKittrick" near the Mars
Exploration Rover Opportunity's landing site at Meridiani Planum, Mars,
possesses the highest concentration of sulfur yet observed on Mars. [More]
(2) The rover's Moessbauer spectrometer detected jarosite, a hydrated iron
sulfate mineral that could result from the target rock spending time in an
acidic lake or acidic hot springs environment.
(3) Pictures from Opportunity's panoramic camera and microscopic imager show
many thin, flat holes--"about the size of pennies," says Squyres--in an
outcrop rock selected for close-up examination. These holes, or "vugs,"
match the distinctive appearance of Earth-rock vugs that form where crystals
of salt minerals grow inside rocks that sit in briny water then disappear by
eroding or dissolving.
The cameras have revealed spheres the size of BBs embedded in outcrop rocks.
Researchers call them "blueberries"-- although they're not blue, they're
gray. The spherules are not concentrated at particular layers within the
rock, as they would be if they originated outside the rock and were
deposited onto accumulating layers while the rock was forming. Instead, the
spherules are scattered. This means they are probably what geologists call
"concretions" that formed from accumulation of minerals coming out of
solution inside a porous, water-soaked rock.
(5) Some of the spherules in pictures from the microscope appear to have
stripes that correspond to layering of the matrix rock around them. This
would be consistent with the interpretation that the spherules are
concretions that formed inside a wet rock.
There is still much to learn: When was the area wet? And how long did the
wet conditions last? How was the water collected--e.g., in a salty lake or
sea? How deep was the water? Scientists and engineers plan to keep
Opportunity busy in the days ahead looking for more clues that might answer
some of these questions.
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