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Mars Rover Sends NASA Cascade of Water Evidence

Posted on: Wednesday, 3 March 2004, 06:00 CST

Mar. 3--The Martian plain where the rover Opportunity landed was once soaked with water, NASA scientists said Tuesday, offering the most compelling evidence yet that the planet once had areas capable of supporting life.

Neither Opportunity nor its twin rover, Spirit, has found any hint that life ever existed on Mars. But experts and NASA officials said pinpointing where water once flowed is crucial for deciding where to send future robotic missions and perhaps eventually human explorers.

The finding marked the first direct evidence that the Martian surface was once warmer and awash in liquid water--an epoch that most scientists believe ended billions of years ago. Coming just five weeks after Opportunity landed in a small crater, the discovery thrilled NASA scientists.

"The purpose of this mission was to go to Mars and see whether or not it once had habitable environments," said Steve Squyres, principal investigator for the mission. "We believe at this place on Mars, for some period in time, it was a habitable environment."

The evidence that Mars once had surface water has been mounting for decades, but it was based entirely on photos and chemical readings taken by probes in orbit around Mars. Those missions found signs of ancient water channels and basins, and water in the form of ice at the planet's North Pole.

Opportunity's landing site was chosen because orbital probes scanning the area detected hematite, an iron-bearing mineral usually linked with water.

The new findings are based on data from an outcrop of bedrock near the rover's landing site, the first such outcrop a Mars probe has ever seen.

Detailed analysis of that rock revealed several minerals and tiny formations that on Earth typically form in water. Researchers said the water that caused those features likely was as salty as the Dead Sea and persisted long enough for many minerals to percolate through the rock.

Jim Garvin, lead scientist for exploration of the moon and Mars at NASA, called the results from the six-wheeled rover "stunning."

"What an amazing time to be alive, doing science on Mars," Garvin said.

Soon after it landed in January, Opportunity returned photos of the outcrop and tiny stone spheres that mission scientists dubbed "blueberries." The BB-size spheres are embedded in the outcrop and litter the floor of the crater.

At first, the origin of the blueberries was unclear--experts thought they might have formed from flying lava that solidified as spheres in midair.

But a closer look with Opportunity's onboard microscope and drilling tool indicated the blueberries had formed in water. Mission scientists believe water seeping through the outcrop left behind minerals that filled spaces in the rock, eventually forming nearly perfect little spheres.

The scientists also found curious penny-size slits in the outcrop. Evidence suggested the holes once contained crystals that formed when the rock was filled with water; they then dissolved, leaving small voids.

Some of the best evidence for water came from Opportunity's chemical analysis tools. One instrument detected jarosite, a rare mineral that on Earth tends to form in hot springs.

"This is a mineral that you've got to have water around in order to make it," said Squyres, the principal investigator.

More analysis showed that parts of the outcrop had high concentrations of salts, including one similar to common Epsom salt. Such salts accounted for 40 percent of the outcrop in some places.

"This is an astounding amount of salt," said rover science team member Benton C. Clark III. "The only way you can form such large concentrations of salt on Earth normally is to dissolve it in water and have the water evaporate."

Independent experts have not yet assessed the data from Opportunity, and even some rover scientists said Tuesday that they are just now seeing the latest results. Thanasis Economou, a rover specialist from the University of Chicago, said mission experts at the Jet Propulsion Laboratory in California are not unanimous that the results show the effects of water.

"Not everyone agrees with that interpretation yet," said Economou, who said he is still studying the data. "We have to make certain we are right."

Scientists cannot yet pinpoint when the water existed, or for how long. It's also unclear whether the water was a standing lake or groundwater seeping through the rocks.

Photos from orbit have not revealed shorelines or other signs of an ancient basin where Opportunity landed--an area called Meridiani Planum. One of the next tasks for Opportunity is to study the outcrop more closely for signs of crossbedding, a characteristic of rock that forms beneath the waves of a standing body of water.

Whether the water was on the surface or just below, experts said the area could have supported life as it exists on Earth. As long as liquid water is present, many forms of bacteria and other organisms can survive in conditions approaching those on Mars.

The next, far more difficult step for future missions will be to analyze Martian rocks for fossils or other signs of past life. Squyres said the rocks in the region around Opportunity may be a good place to look for such clues.

As the minerals form, "they can trap evidence of [life] and preserve it very well for a long period of time," Squyres said. "So these are very, very interesting rocks."

Searching for signs of life is a prime reason for sending humans to Mars--a long-term goal that President Bush outlined in January.

But experts said that first they would need to send robotic missions capable of returning samples of Martian rocks for more intensive study on Earth. NASA officials said they want to launch such a mission within the next decade--and the region around Opportunity offers an inviting target.

"Now we finally have an example of the stuff we really want to bring back here to Earth," said Garvin, the lead scientist for moon and Mars exploration. "We have a way to imagine what a Mars sample-return mission might look like."

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