WinnCad Elements Blog: And the next mars rover goes to...

By Alan Boyle

Scientists have decided to point NASA's next Mars rover toward a mountain of layered minerals inside Gale Crater, after a process they compared to picking a favorite flavor of ice cream out of 30 choices. One big reason Gale won out is because it's like Neapolitan ice cream, offering a yummy combination of flavors.

Like the strawberry-vanilla-chocolate ice cream, the 3-mile-high (5-kilometer-high) mound inside Gale Crater offers multiple possibilities — intriguing geological sites at different elevations that could document a billion years of Mars' climate history, and perhaps its habitability as well.

"Gale Crater is interesting to explore because it crosses what we think is a major time boundary on Mars that’s recorded in its mineral history," Brown University's John Mustard, a planetary scientist who helped with the early stages of the selection process, said in an emailed comment. "That boundary marks a change from an early wet, hospitable environment that would have been suitable for life to a middle period where conditions may have become more hostile. We believe that at Gale Crater, we have located that boundary where life may have sprung up and where it may have been extinguished."

In a statement, NASA Administrator Charles Bolden said the Curiosity rover could shed light on Mars' future as well as its past. "Curiosity not only will return a wealth of important science data, but it will serve as a precursor mission for human exploration to the Red Planet," he said.

$2.5 billion mission to Mars

The Curiosity rover, also known as the Mars Science Laboratory, is a mobile robot as big as a Mini Cooper automobile, bristling with scientific instruments and a camera capable of taking high-definition, full-color video at a rate of more than five frames per second.

The $2.5 billion mission is due for launch from Cape Canaveral Air Force Station in Florida on an Atlas 5 rocket, as early as the day after Thanksgiving, with landing on Mars set for August 2012. The rover is designed to be lowered to the Martian surface by a rocket-powered "sky crane" system that's never been used before for interplanetary probes.

NASA expects Curiosity to operate for a "warranty period" of one full Martian year, the equivalent of two Earth years, and to rove for 13 miles (20 kilometers or more). John Grotzinger, Curiosity's mission scientist at NASA's Jet Propulsion Laboratory, estimates that it would take about two years for the radioactivity-powered rover to work its way up to the summit of Gale Crater's mountain — and he's already hoping for as much of a decade's worth of extra exploration.

After all, the Spirit and Opportunity rovers on Mars were designed to operate for 90 days — but seven and a half years after they landed, Spirit only recently gave up the ghost, and Opportunity is still going strong. "If history is a predictor of the future, we expect to have future life to go," Grotzinger said today at the Smithsonian's National Air and Space Museum in Washington, where the site selection was announced.

The 96-mile-wide (154-kilometer-wide) Gale Crater should provide a spectacular backdrop for Curiosity's cinematography. Scientists compared the terrain to the Grand Canyon and Utah's Monument Valley. The mountain inside the crater rises higher than any peak in the 48 contiguous U.S. states, but it has channels that should give Curiosity a chance to make a slow ascent to the top.

"This might be the tallest mountain anywhere in the solar system that we can climb with a rover," Grotzinger said.

How the choice was made

The selection process leading to today's announcement started five years ago, when more than 100 scientists sifted through about 30 potential landing sites. Four top candidates were selected in 2008, and earlier this year, that "Final Four" was whittled down to two: Gale Crater as well as Eberswalde Crater, which scientists believe contains the remains of an ancient river delta. (Eberswalde was the favorite of Cosmic Log readers in an unscientific poll we offered last week. Sorry, folks.)

The final recommendation was made by the Curiosity mission's science team and approved by senior NASA officials. Grotzinger said choosing from among the Final Four sites was a matter of taste, like choosing between vanilla and chocolate ice cream. "When you come down to four landing sites, that's basically what it comes down to. ... In the end, we picked the one that felt best," he said.

NASA's strategy for past Mars probes has been to "follow the water," on the assumption that areas where liquid water once flowed would be prime places to look for evidence of past habitability. In NASA's announcement, Grotzinger said that was one of the factors that made Gale Crater so attractive.

"It’s a huge crater sitting in a very low-elevation position on Mars, and we all know that water runs downhill," he said. "In terms of the total vertical profile exposed and the low elevation, Gale offers attractions similar to Mars’ famous Valles Marineris, the largest canyon in the solar system."

'Great novel' focuses on Martian past

The other keys to Gale's appeal are the minerals layered throughout the 3-mile-high mountain inside the crater.

Curiosity will be targeted to land on an alluvial fan that was apparently formed from sediments carried down the mountainside by water. Then the rover will make its way up to higher levels, where orbital observations have spotted the types of clay minerals and sulfates that are typically formed by the interaction of rock and water.

Different types of geological formations are accessible at different elevations, reflecting different epochs in Mars' history. Grotzinger said Curiosity could survey samples from a vertical range extending for hundreds of meters (yards), far more than the roughly 20 meters of vertical range sampled by the Opportunity rover. He compared the vertical variation to chapters in a book, and said Gale Crater promised to be a "great novel."

Curiosity's instruments are capable of detecting organic carbon in ground-up rock samples, and Grotzinger said the rover has "a shot at potentially discovering organic compounds." He emphasized that the instruments cannot definitively pick up the presence of life. However, confirming the presence of organic compounds on Mars would represent a significant advance in the decades-long search for evidence of life on the Red Planet.

Dawn Sumner, a geologist at the University of California at Davis, said she and her colleagues were looking forward to the adventure. "Geologists like climbing up cliffs," she said at the National Air and Space Museum, "and we get to go to those places with this rover for the first time on Mars."

For the next couple of decades, robots will be the only earthly things climbing up those cliffs, but that may not always be the case. NASA's current vision for space exploration calls for sending astronauts to Mars in the mid-2030s, and some believe the job could be done earlier. When, if ever, will humans follow in Curiosity's wheel tracks? What might they find? Feel free to add your comments below.

Mars Science Laboratory Landing Site