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Grotzinger describes evidence of Mars water

Rocks on Mars' surface were once "soaked in water," NASA announced yesterday in a press conference laying out the latest findings from the Opportunity rover mission.

MIT's Professor John Grotzinger, a member of NASA's science team for the Mars robotic investigations, led reporters on a "geologic field trip" at the press conference, showing images from a rock outcropping on the surface of the planet while he described the mineral and textural evidence of the one-time presence of liquid water.

"Our observations fit together in a very specific way to make a strong case for the presence of water," said Grotzinger, a professor in the Department of Earth, Atmospheric and Planetary Sciences.

He outlined the geologic evidence in three categories.

Spherical shapes "like tiny beach balls or blueberries" about a millimeter or two in diameter indicate that fluids once flowed through the rock. The "blueberries" also could have formed from a volcanic eruption or the impact of a meteorite hitting Mars and melting the surface. But the random occurrence of the spherules rather than a concentration in a particular layer is strong evidence that the shapes resulted from the crystallization of minerals.

Disc-shaped indentations called "vugs" about a centimeter long are consistent with those left by gypsum (calcium sulfate) after it has dissolved in fluid. "You need fluid to bring the ions together to form the minerals that once filled the vugs, and a second fluid event to dissolve them," Grotzinger said.

The third and most compelling piece of evidence is minerological. "And this is the most exciting. The minerology of this rock shows unequivocally the presence of a mineral called jarosite, an iron-sulfate hydrate. The only way to get that mineral is to precipitate it in the presence of water," he said.

"The bottom line is that all the textural and mineral evidence add up to the fact that this rock was significantly influenced by water that, at the very least, circulated through the rock and then precipitated in an evaporative-type environment," said Grotzinger in a telephone interview. "Evidence from the rock reflects interaction with water. We don't know yet whether or not the formation of the rock took place in water. But we have one tantalizing piece of evidence [the jarosite] that suggests the rock was created in a body of water. We'll know in a week to 10 days if it was formed in flowing water."
Grotzinger will speak at MIT today (March 3) at 1 p.m. in Room 26-100 on "A Watery Origin for the Ancient Rocks at the Opportunity Landing Site, Meridiani Planum, Mars."

Grotzinger is a geologist and director of the Earth Resources Lab at MIT. He is spending this term at NASA's Jet Propulsion Lab in Pasadena, Calif., as head of long-term planning for the science team for the Mars rover mission.

"Every day something new comes in and we're just jumping up and down like kids," he said.

A version of this article appeared in MIT Tech Talk on March 3, 2004.

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