Mars Rover Peers at Edge of Ancient Seashore

WASHINGTON (Reuters) - NASA (news - web sites)'s Mars rover Opportunity is sending data back to Earth from an ancient martian seashore, scientists reported on Tuesday.

"We think Opportunity is now parked on what was once the shoreline of a salty sea on Mars," said Steve Squyres, principal investigator for the science payload on Opportunity and its twin Mars exploration Rover, Spirit.

On March 2, astronomers announced that the Red Planet was "drenched with water" at some point. But the rovers' analysis of Mars rocks has now produced the first concrete evidence that liquid water might actually have flowed on planet's surface.

"If you have an interest in searching for fossils on Mars, this is the first place to go," said Ed Weiler, NASA's associate administrator for space science.

In a presentation titled "Opportunity hits the beach," Squyers and other Mars rover scientists stressed that the rocks they observed are at the side of a crater that shows sedimentary rock. Instead of being merely drenched, these rocks were formed by flowing water, the researchers said.

Squyers said the amount of water indicated by these rocks represents the difference between "water you can draw from a well, and water you can swim in."

"This was a habitable environment on Mars, a salt flat," Squyers said. But when asked whether he expected to see evidence that Earth-type life had existed at the site, he said, "I don't expect to see microbial fossils and I certainly don't expect to see dinosaur tracks.

Scientists do not yet know how big the body of water might have been, how deep, or when or how it formed.

Even so, this finding is a bull's-eye for the rover team, whose mission was to investigate areas believed to have been covered with water long ago. If there was water, theorists believe, there might have been life on the Red Planet.

"We're back on Mars. It's great to be there and even better to know that in due course, human explorers will follow," NASA Administrator Sean O'Keefe told the briefing.

Asked whether this discovery would affect the pacing of the Bush administration's plan to send humans to Mars someday, O'Keefe replied, "It certainly would have an impact."

Opportunity has been roving across the seemingly barren martian surface since January and is now working with rocks once covered by rippling saltwater, the scientists said.

Opportunity's controllers plan to send the rover across a plain toward a thicker exposure of rocks in the wall of a crater to search for more evidence of standing water.

So far, scientists point to patterns in some finely layered rocks indicating they were shaped by ripples of water at least 2 inches (5 cm) deep and possibly much deeper. The water flowed at a speed of 4 to 20 inches (10 to 50 cm) per second, according to John Grotzinger, a member of the science team.

The patterns come in distinctive smile-shaped curves characteristic of water's impact on rock, rather than wind erosion, he said.

Opportunity's current location might have been a salt flat when these rocks were forming, and might have been occasionally covered by shallow water and sometimes dry. On Earth, this type of environment can have water currents that produce the ripples seen in the Mars rocks.

JPL News Press Release

Standing Body of Water Left Its Mark in Mars Rocks
March 23, 2004

NASA's Opportunity rover has demonstrated some rocks on Mars probably formed as deposits at the bottom of a body of gently flowing saltwater.

"We think Opportunity is parked on what was once the shoreline of a salty sea on Mars," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the science payload on Opportunity and its twin Mars Exploration Rover, Spirit.

Clues gathered so far do not tell how long or how long ago liquid water covered the area. To gather more evidence, the rover's controllers plan to send Opportunity out across a plain toward a thicker exposure of rocks in the wall of a crater.

NASA's Associate Administrator for Space Science Dr. Ed Weiler said, "This dramatic confirmation of standing water in Mars' history builds on a progression of discoveries about that most Earthlike of alien planets. This result gives us impetus to expand our ambitious program of exploring Mars to learn whether microbes have ever lived there and, ultimately, whether we can."

"Bedding patterns in some finely layered rocks indicate the sand-sized grains of sediment that eventually bonded together were shaped into ripples by water at least five centimeters (two inches) deep, possibly much deeper, and flowing at a speed of 10 to 50 centimeters (four to 20 inches) per second," said Dr. John Grotzinger, rover science-team member from the Massachusetts Institute of Technology, Cambridge, Mass.

In telltale patterns, called crossbedding and festooning, some layers within a rock lie at angles to the main layers. Festooned layers have smile-shaped curves produced by shifting of the loose sediments' rippled shapes under a current of water.

"Ripples that formed in wind look different than ripples formed in water," Grotzinger said. "Some patterns seen in the outcrop that Opportunity has been examining might have resulted from wind, but others are reliable evidence of water flow."

According to Grotzinger, the environment at the time the rocks were forming could have been a salt flat, or playa, sometimes covered by shallow water and sometimes dry. Such environments on Earth, either at the edge of oceans or in desert basins, can have currents of water that produce the type of ripples seen in the Mars rocks.

A second line of evidence, findings of chlorine and bromine in the rocks, also suggests this type of environment. Rover scientists presented some of that news three weeks ago as evidence the rocks had at least soaked in mineral-rich water, possibly underground water, after they formed. Increased assurance of the bromine findings strengthens the case that rock-forming particles precipitated from surface water as salt concentrations climbed past saturation while water was evaporating.

Dr. James Garvin, lead scientist for Mars and lunar exploration at NASA Headquarters, Washington, said, "Many features on the surface of Mars that orbiting spacecraft have revealed to us in the past three decades look like signs of liquid water, but we have never before had this definitive class of evidence from the martian rocks themselves. We planned the Mars Exploration Rover Project to look for evidence like this, and it is succeeding better than we had any right to hope. Someday we must collect these rocks and bring them back to terrestrial laboratories to read their records for clues to the biological potential of Mars."

Squyres said, "The particular type of rock Opportunity is finding, with evaporite sediments from standing water, offers excellent capability for preserving evidence of any biochemical or biological material that may have been in the water."

Engineers at NASA's Jet Propulsion Laboratory, Pasadena, Calif., expect Opportunity and Spirit to operate several months longer than their initial three-month prime missions on Mars. To analyze hints of crossbedding, mission controllers programmed Opportunity to move its robotic arm more than 200 times in one day, taking 152 microscope pictures of layering in a rock called "Last Chance."

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for NASA's Office of Space Science, Washington. Images and additional information about the project are available on the Internet at http://www.nasa.gov, http://marsrovers.jpl.nasa.gov and http://athena.cornell.edu .

Twin Dimples Intrigue Scientists

This image from the Mars Exploration Rover Opportunity is part of the first set of pictures that was returned to Earth after the rover exited "Eagle Crater." Scientists are busy analyzing Opportunity's new view of the plains of Meridiani Planum. The plentiful ripples are a clear indication that wind is the primary geologic process currently in effect on the plains. On the left of the image are two depressions -- each about a meter (about 3.3 feet) across -- that feature bright spots in their centers. One possibility is that the bright material is similar in composition to the rocks in Eagle Crater's outcrop and the surrounding darker material is what's referred to as "lag deposit," or erosional remnants that are much harder and more difficult to wear away. These twin dimples might be revealing pieces of a larger outcrop that lies beneath. The depression closest to Opportunity is whimsically referred to as "Homeplate" and the one behind it as "First Base." The rover's panoramic camera is set to take detailed images of the depressions today, on Opportunity's 58th sol. The backshell and parachute that helped protect the rover and deliver it safely to the surface of Mars are also visible near the horizon, in the center of the image. This image was taken by the rover's navigation camera.

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