Search for life: Mars rover's target crater a 'geologist's paradise'

The closer NASA's rover Curiosity gets to its final destination – Mars' Gale Crater – the more intriguing that spot looks to planetary scientists awaiting the rover's touchdown predawn Monday, EDT.

If all goes well, the one-ton, Mini Cooper-sized Curiosity is slated to spend the next 23 months looking for evidence that the desiccated planet might have been a hospitable place for at least simple forms of life.

The answer is locked up in the wedding-cake layers of rocks and minerals in Gale Crater, and especially on the crater’s three-mile-high Mt. Sharp in its center.

Mt. Sharp is far higher than any nub of a "recoil" peak that would have formed when a 10-mile-wide space rock slammed into the surface earlier in the planet’s history. It appears to have been built up from layer after layer of sediment and rock.

This apparently undisturbed layering provides researchers with a unique opportunity to make the first detailed, on-the-ground measurements that systematically trace another planet's geological and climatic evolution on extraordinary time scales.

The $2.5-billion project, formally known as the Mars Science Laboratory mission, represents "a whole new dimension of space exploration. This is the dimension of deep time," says John Grotzinger, a researcher at the California Institute of Technology in Pasadena and the mission's project scientist.

On this mission, the time periods Curiosity will probe aren't measured in hours, days, years, or even decades, but in "hundreds of millions, even to billions of years," he said during a briefing Thursday. Given the estimated age of Gale Crater, which researchers put at between 3 billion to 4 billion years old, the enormous spans of time Curiosity can cover are themselves billions of years old.

It has to do with water, a key ingredient for organic life. The crater's location on Mars and observations from orbiting satellites strongly suggest that the crater may have hosted a shallow lake at one time.

Gale Crater sports a large, sloping fan of sediment – known as an alluvial fan— that extends from the crater rim and spreads out across the crater floor. Such fans are common features on Earth, appearing at the bases of mountains where water flowing down the slopes has picked up soil and rock and carried them out onto flatter terrain.

Observations from orbiters also have found expanses of exposed rock that extend from the edge of the fan toward Mt. Sharp and remain warm well after nightfall. Lots of rock types exhibit an ability to retain heat, but one intriguing possibility is that water carried loose soil and rock onto the crater floor, where the material dried out and formed a kind of natural cement.

Once Curiosity is safely on the surface, "we can start to look for minerals that bound the particles together that tell us about the previous history of water there," Mr. Grotzinger says.

If water was there, that begins to build the case for at least one potentially habitable environment early in the planet's history, he says

Even though the ultimate destination is Mt. Sharp – a journey that will take many weeks after the initial touchdown – Curiosity's broad initial landing zone appears to present "an extraordinary opportunity for what might be a really great science discovery early on" in the mission, according to Grotzinger.

Over the past month, researchers have been building detailed maps of the crater floor in small sections, or quads. The goal is to pore over images of the floor at very fine scales to see what other interesting features the floor in the rover's landing zone might hold.

The mapping is still under way, but Grotzinger displayed one small patch of the crater floor – one on which Curiosity might well land: "No matter where we land, what we now know from studying the details of these quads is that we're going to have something exciting to do," he says.

For instance, the map segment shows a small crater some 820 feet across, comparable to craters NASA’s rover Opportunity has explored elsewhere. The crater walls sport more layering, opening a window onto the rock formations below the current floor. In addition, a low scarp perhaps three feet high also appears on this patch, comparable to scarps Opportunity’s twin, Spirit, has examined.

"What you've got here is really kind of a geologist's paradise!" Grotzinger says.