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Physical Chemistry

Mars Was Wet

Results from rover Opportunity show almost unequivocal signs of water

by Elizabeth K. Wilson
March 8, 2004 | A version of this story appeared in Volume 82, Issue 10

Credit: NASA/JPL/Cornell
Mars rover Opportunity's examination of the outcropping nicknamed El Capitan shows evidence of water-deposited sulfate salts.
Credit: NASA/JPL/Cornell
Mars rover Opportunity's examination of the outcropping nicknamed El Capitan shows evidence of water-deposited sulfate salts.

Scientists announced on March 2 the stunning discovery that martian rocks examined by the rover Opportunity were once "soaked in liquid water."

Steven W. Squyres, astronomy professor at Cornell University and head of the science team for Opportunity and its companion rover, Spirit, told reporters at the National Aeronautics & Space Administration's headquarters in Washington, D.C., that numerous lines of evidence point nearly unequivocally to large amounts of water on Mars. "That doesn't mean life was there, but Mars was a habitable place at one time," he said.

Whether the rocks were laid down in a briny sea or deposited by water percolating to the martian surface is still unknown, but rover team scientists intend to answer that question in a week or two.

For the past three weeks, Opportunity has used its instruments to examine an outcropping of rock inside the small crater in which it landed. A section of the rock known as El Capitan is "shot through" with flat holes about a centimeter long and a millimeter wide, Squyres said. "It was as if a bunch of objects the size and shape of pennies were embedded and went away," he said.

Similar structures on Earth are formed when minerals dissolved in water seep through and precipitate inside rock. Eventually, the crystals dissolve or are eroded away, leaving tabular holes. And curious spherules--dubbed "blueberries" by scientists--embedded within the rocks likely were deposited by water.

Previously, Opportunity had detected a high concentration of sulfur on the rock's surface, in particular, on a section of the outcropping called Guadalupe. The rover then used a grinding tool to expose rock underneath, where its -particle X-ray spectrometer also found extraordinarily high levels of the element. The only explanation, the scientists said, is that the rock is composed largely of sulfate salts, a telltale sign of liquid water.

The salt concentration in Guadalupe may be as high as 40%, Benton C. Clark III, rover scientist and chief scientist of space exploration at Lockheed Martin Space Systems Astronautics Operations in Denver, said at the briefing.

"This is an astounding amount of salt," Clark said. "This can no longer be considered a volcanic outcrop of some kind. The only way you can form such a large concentration of salt is to have water."

The rover's Mössbauer spectrometer also found evidence of jarosite, a hydrated iron sulfate, in the outcropping. Jarosite, which needs water to be created, is a rare mineral also found on Earth.

The results should give impetus to the development of future Mars missions, in particular, plans to return samples to Earth, said James B. Garvin, NASA's lead scientist for Mars and lunar exploration.

"What an amazing time to be alive doing science on Mars," he said. "The President gave us a challenge to go explore, and here we are, exploring."

Meanwhile, halfway across the Red Planet, the rover Spirit continued grinding away at a rock named Humphrey. Spirit is gradually heading toward the rim of a crater named Bonneville, where it will examine the terrain inside.

+ Mar Exploration Rovers Images Archive


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