Opportunity finds Mars had water to host life at dawn of its history

Happy anniversary, Opportunity. After a decade of roving the Martian surface, the plucky Mars rover has discovered clay minerals that support what its high-tech cousin Curiosity found on the other side of the Red Planet: an ancient environment filled with the kind of water that’s friendly to life.

The findings published in the journal Science indicate that Curiosity’s groundbreaking discovery last year — that Mars hosts life-friendly spots that could have theoretically hosted Earth-like microbes — is no fluke, and highlights a new direction for arthritic old Opportunity.

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Combined with Curiosity’s discoveries last year, “we’ve basically found strong evidence for clays on both sides of the planet,” said Cornell University planetary scientist Steve Squyres, lead scientist for the Mars Exploration Rover program.

When Opportunity and its now-defunct twin Spirit landed on the Martian surface in January 2004, they probed the planet for past evidence of water. They found mineral and chemical signs of the liquid’s past existence in Meridiani Planum, for example, discovering blueberry shaped concretions of a mineral called hematite, thought to have formed in running water. But many of those chemical clues came in the form of sulfates, a sign of highly acidic water that would not have been friendly to life.

But since arriving at the rim of Endeavour crater, the picture has changed dramatically, Squyres said. The rover has discovered signs of clay minerals that form in the presence of low-acidity, neutral-pH water. The clay-rich rocks they studied were geographically close to the sulfate-rich rocks, but they were vastly separated in time, Squyres said; the clays came from a much deeper layer of rock that represented the earliest epoch in Martian history.

“These are some of the oldest rocks we’ve looked at — probably the oldest rocks that we’ve looked at with Opportunity,” Squyres said. This neutral-water environment existed near the dawn of Martian history, and the acidic environment came later.

“These results demonstrate that early Mars was habitable, but this does not mean that Mars was inhabited,” said Curiosity’s lead scientist, John Grotzinger, a Caltech geologist who wrote a commentary on results published in Science from both the Opportunity and Curiosity rover teams.

Because Opportunity has no way to date materials, there’s no way to say for sure exactly how old these rocks are or exactly how much older the clay-rich rocks are than the sulfate-rich rocks. But Squyres estimates that the clay-rich rocks are probably on the order of 4 billion years old, and the sulfate-rich rocks (representing the acidic, unfriendly environment) probably came a few hundred million years later. How the environment changed so quickly remains a mystery, Squyres said.

The team will continue to explore new ground in Endeavour Crater, Squyres said.

“We really felt we had a brand-new mission when we crossed the boundary from the sulfate-rich sedimentary rocks that we had been driving on for seven or eight years to the rim material of Endeavour crater and went from moderately old rocks to really old rocks,” Squyres said.

Suddenly, he said, the chemistry and mineralogy of the rocks around the rover changed. “It was like a completely new landing site. It really was like a brand-new mission.”

Mars keeps throwing the team surprises, Squyres said: They’re still puzzling over the sudden appearance of a rock shaped like a jelly doughnut.