Mars rover: Scientists target huge crater in the search for signs of life (+video)

If you're hunting for places where Mars once might have hosted life, it's tough to beat Gale Crater – a 96-mile-wide dent in the Martian crust and the target for NASA's Mars Science Laboratory mission.

Early Monday morning, the mission's one-ton, Mini Cooper-sized, $2.5 billion rover named Curiosity is slated to touch down inside the crater in what scientists say will be the most pinpoint, harrowing landing ever attempted on the Martian surface.

[Editor's note: The original version of this story gave the incorrect weight for the Curiosity rover.] 

While the risks are high – NASA refers to the landing as “seven minutes of terror” – so is the potential payback as the Mars Science Laboratory team tries to answer the question: Did Mars ever have the conditions that would have allowed life to emerge?

The answer is intimately tied to the presence of water on the Martian surface early in the planet's history. Water is essential for life to gain and maintain a foothold on any planet, researchers say.

The Gale Crater straddles the boundary between the planet's southern, crater-pocked highlands and the smoother northern lowlands, according to John Grotzinger, a planetary scientist at the California Institute of Technology in Pasadena, Calif., and the mission's project scientist.

Since water flows downhill, "we think billions of years ago water flowed across that surface ... and there's Gale Crater, a little bowl capturing any water that may have been present there," he said during a recent prelanding briefing. "Gale is one of the lowest places on Mars. And if you don't know anything else in advance, that's where you want to go to find evidence of water."

But Gale Crater speaks to more than Mars' early history. It also speaks to billions of years of climatic change that have swept the Martian surface.

And it presents its own mystery: How did an enormous mountain higher than Washington’s Mount Rainier, whose base fills much of the northern half of the crater floor, form?

It's as though a cosmic kindergartner filled a bowl with soil, then changed his mind and started to empty it again around the edges – leaving a central summit and exposing rock formations at its base that the rover will analyze.

"When it comes right down to it, we don't know much about the crater and the rocks inside it," says Ralph Milliken, a planetary scientist at Brown University in Providence, R.I., and a member of the Mars Science Laboratory's science team.

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