Opportunity rover finds further evidence of wet martian past.

NASA’s Mars lander Opportunity has found minerals and rock formations that help to prove that the planet was once very wet.

“Liquid water once drenched the surface of Meridiani Planum,” says Ed Weiler, NASA’s associate administrator for space science. “It would have been habitable for some time,” he says.

The flat plain of Opportunity’s landing site covers an area roughly twice the size of Lake Superior. Scientists are still unclear whether the whole area was once a giant lake, or whether the minerals they have found were simply soaked in ground water that percolated up through the rock.

The evidence comes from the analysis of a rocky outcrop called El Capitan, found near Opportunity’s landing site, says Steven Squyres, principal investigator on the project.

Opportunity first found that the dust on this rock’s surface is rich in sulphur. This confirms evidence seen by the Viking 2 lander in 1976. But Opportunity was able to use infrared measurements to go one step further, showing that much of it is in the form of sulphate ions - a key component of common salts that are usually formed in water.

“You’d need a lot of water to have the massive amounts of sulphur we see here,” says Squyres.

Upper parts of the rock were found to contain up to 40% sulphate. Lower parts of the rock were found to be rich in bromide ions, which are more soluble in water than sulphate.

This is clear evidence of an ‘evaporitic sequence’, says Benton Clark, chief space scientist at Lockheed Martin Space Systems at Denver, Colorado. As a pond of salty water evaporates, it leaves behind different minerals at different times. Less-soluble minerals precipitate out first, and more soluble minerals only appear as most of the water disappears.

Source: Nature News Service