Gale Crater forms a large natural repository for a lot of Martian geologic history. This ancient impact scar has a diameter of about 150 kilometers (90 miles) and lies close to where the cratered highlands drop off onto the northern lowlands in Elysium. Based on its size and state of preservation, scientists estimate Gale formed 3.8 to 3.5 billion years ago.
What draws scientific interest most is a big mound of layered debris filling about a third of the crater's floor. Wrapping around the crater's central peak, visible at lower right in the image, the mound stands about 5.5 km (3.4 mi) higher than the northern crater floor and about 4.5 km (2.8 mi) above the southern floor. The mound's highest parts even rise somewhat higher than Gale's southern rim.
This false-color image was taken by the Thermal Emission Imaging System (THEMIS), a multi-wavelength camera on NASA's Mars Odyssey orbiter. The view combines a daytime photo taken at visible wavelengths with a nighttime infrared image. The bluish-white tones mark areas with fine-grain materials (sand, dust) thickly covering the surface, while redder tints indicate locations where harder, rockier material lies exposed.
Gale Crater was a candidate landing site for the 2003 Mars Exploration Rover mission (Spirit and Opportunity). It now figures as one of several prospective sites for NASA's Mars Science Laboratory (MSL) mission, which will send a bigger and more powerful rover to Mars in 2009.
The MSL rover will carry a much more sophisticated instrument package than Spirit and Opportunity and have the capability to drive tens of kilometers from wherever it lands.