Scientists considered hundreds of landing sites for Curiosity before choosing the Gale Crater, which probably formed when an asteroid or comet crashed into the planet some 3.5 billion to 4 billion years ago. From high-resolution images taken by orbiting satellites, Gale Crater's central mound, known as Mount Sharp, appears to consist of layers of sediment rising like a stack of cards 3 miles into the sky, taller than the crater's rim.
The most likely origin of the mountain is that it formed from the remains of whatever material filled up the basin long ago. How it was left standing in the middle of Gale Crater, a 96-mile- (154-km) wide bowl located near the planet's equator, is a mystery, one of many scientists hope to answer during Curiosity's two-year science mission. Regardless of how it formed, scientists consider Mount Sharp a gift of time.
Nothing like it exists on Earth, where plate tectonics, erosion and other natural phenomena constantly reshape the planet's surface.
"We have the opportunity to start in the past, rove up the surface of Mount Sharp and come through time to see how the environments have changed," said Michael Meyer, NASA's Mars exploration program scientist.
WARMER, WETTER MARTIAN PAST
A succession of previous rovers, landers and orbiting spacecraft have gathered compelling evidence that Mars, which is about half the size of Earth and 50 percent farther away from the sun, was not always the dry, acidic, cold desert that appears today. NASA's strategy since resuming Mars exploration following the 1970s-era Viking missions there has been to look for the chemical and physical fingerprints of water, which is necessary for life - at least as it has evolved on Earth.
The second ingredient in the recipe for life is carbon, which provides organic structure. Carbon will be far more difficult to detect on Mars, if it exists, because the same processes that produce rock tend to destroy organics. The planet's harsh radiation environment doesn't help either. Mars is today a radiation-rich environment that can destroy organics in a short time, so even if it was there, it may be hard to find a place where it's been preserved.