Where did life exist on Mars? NASA chooses landing site for Curiosity rover

NASA scientists announced Friday that the next Mars rover will land at the foot of a towering mountain – higher than any in the continental United States – and so dramatically layered that scientists hope to read it like a novel of Martian history, discovering where and when life might have existed on the Red Planet.

The August 2012 arrival of the roving Mars Science Laboratory, nicknamed Curiosity, represents an important moment in the history of Mars science, team members suggested.

Curiosity will land on the floor of Gale crater, a tiny landing target that would have been off-limits to previous rovers. Moreover, the rover, which is much bigger and burlier than earlier rovers, is designed easily to cover distances and climb slopes that would have sent shivers down the spine of previous rover-mission managers.

The Curiosity team has even dared to dream that, one day, Curiosity might stand atop the mysterious three-mile-high mountain in the middle of Gale crater, giving its Earthbound operators a spectacular view over the Marian landscape. The crater floor is sloped, so the southern side of the mountain rises some 15,000 feet, while the northern approach – which Curiosity will likely take – reaches closer to 18,000 feet.

This mission marks a new and growing confidence among planetary scientists. While the human spaceflight program has an uncertain future, after the ending of the space shuttle program on Thursday with the landing of Atlantis, NASA probes are becoming ever-more adept at exploring previously out-of-reach realms of the solar system, from Pluto to the surface of Saturnian moons to the scorched face of Mercury.

Curiosity, in that way, represents a significant step toward breaking down the technological barriers that have prevented scientists from going where they want in our cosmic neighborhood.

“Geologists like to climb up cliffs, and scientists get to do this for the first time on Mars with this rover,” said Dawn Summer, a geologist at the University of California at Davis, who was a panelist at the announcement Friday. “There is an incredibly rich suite” of things to investigate, she adds, “and it is an incredibly beautiful place.”

Curiosity has been billed as NASA’s first astrobiology mission since Viking arrived on Mars in 1976. Its goal is not to find direct evidence of past life – no fossil-hunting here. Instead, it will look for where and when Mars might once have been habitable – a step further than the Opportunity and Spirit rovers went in seeking signatures of water in 2004.

The rocket holding Curiosity is set to launch from the Kennedy Space Center in Florida between Nov. 25 and Dec. 18 of this year, and the rover should arrive on Mars in August 2012.

The Gale crater landing site announced Friday was chosen from among 60 original candidate sites, which NASA had whittled down to four finalists by last summer. The clincher? The mountain sitting inside Gale crater is a mystery that may hold the history of water – and potentially life – on Mars.

The mount pokes above the crater rim surrounding it, suggesting that it formed after the crater did. Moreover, it shows clear signs of sedimentation – meaning that the material that formed it was carried there from somewhere else, either by wind or liquid water.

And that is its allure.

The 100-mile-wide crater might once have contained a Martian sea, scientists theorize.

Far away on the planes of Meridiani, the Opportunity rover sent to Mars in 2003 has pored over layers of Martian soil reshaped by water – but the craters which it has scoured are comparatively shallow, no more than 60 feet deep. At Gale, the entire mountain could bear testimony to the history and action of liquid water on Mars.

For geologists, this is a virtual pot of gold at the end of the nine-month flight. Sedimentary layers are laid down chronologically, with the oldest layers at the bottom. With perhaps 1,000 feet of layers to drill, prod, and analyze during the first martian year (687 Earth days), geologists think they have a virtual textbook before them in the Gale crater mountain.

“It’s like the Grand Canyon,” said John Grotzinger, Mars Science Laboratory project scientist at the Jet Propulsion Laboratory in Pasadena, Calif., at the news conference.

“You start at the bottom and go to the top, and it reads like a novel. We think that Gale is going to be a great novel to learn the environmental history” of Mars, he added.

Even from images taken by the orbiting Mars Reconnaissance Orbiter, the story looks intriguing.

• The plain on which the rover will land shows traces of an ancient fluvial fan – evidence that water might once have flowed onto the plains and spread out like the fan-shaped deltas of the Nile or the Mississippi River.
• The rocks at the base of the mountain are clays – rocks typically formed in water.
• Farther up the slope are sulfates – materials also usually formed by interaction with water.
• Higher still on the mountain lie so-called cemented fractures – a landscape that looks vaguely like bubble wrap, with rocky prominences interspersed by straight-line fractures. Dr. Grotzinger said the formations appear to be shaped by water and could include basins that collected mineral-rich water in the distant past.

And beyond is the summit. Team members were careful to stress that summiting the mountain is not a goal of the mission. Scientists are not going to push the pedal and race the rover to the summit to see the sunset. Curiosity might stay in one spot for six months, if it finds something that transforms our understanding of where life could have existed on the Red Planet.

Engineers have given the rover a warranty of two Earth years – after that, any science is a bonus. The Curiosity team would like at least to get the rover to the cemented fractures by then.

But Opportunity’s “primary mission” ran out in 2004, and it’s still trundling across Mars. So there’s hope that Curiosity could be similarly long-lived.

To this end, the science team convened a “Gale Summit Team” to see if it would even be possible to navigate the rover to the top of the mountain. It is. The team found several possible ascent routes. But when Grotzinger talked about the summit, he threw out a hypothetical timeline of 10 years.

If Curiosity were to last that long, a summit run would almost certainly be a victory lap.

Says Grotzinger, Gale crater may have an “exceptionally high diversity of many different kinds of habitable environments.”