Landing Site Selection
The final landing site selection for the Mars Science Laboratory Curiosity rover is Gale Crater. The Curiosity rover landed at the foot of a layered mountain within this massive crater. The portion of the crater where Curiosity landed has an alluvial fan likely formed by water-carried sediments. The layers at the base of the mountain contain clays and sulfates, both known to form in water. Curiosity will go beyond the "follow-the-water" strategy of recent Mars exploration. The rover's science payload can identify other ingredients of life, such as the carbon-based building blocks of biology called organic compounds.
This landing site selection was made in June 2011 and it marked the end of a process that began in June 2006, when Mars scientists from around the world attended a workshop and compiled a list of 100 potential landing sites. Using the most powerful cameras and spectrographic instruments ever sent to the red planet, Mars Reconnaissance Orbiter has been collecting data to help scientists evaluate each potential landing site in greater detail. Four candidates were down selected in 2008. An abundance of targeted images enabled thorough analysis of the safety concerns and scientific attractions of each site.
Narrowing Down Landing Sites
The mission team progressively narrowed the field of landing sites.
The ideal landing site will have clear evidence of a past or present habitable environment. The site will have a favorable geologic record, such as layers of rock that are preserved and exposed at the surface, making them accessible to exploration, as well as evidence of past water. The ideal landing site will also have the elements essential to life as we know it, all located within a relatively smooth, safe landing area. Mobility, of course, will be essential for reaching areas such as cliffs that may contain many layers of rocks telling the story of past environments on Mars. That is why the Mars Science Laboratory rover will be able to travel at least 20 kilometers (12 1/2 miles) from its landing site.
In the interest of planetary protection, NASA may choose to exclude sites from exploration that are believed to be likely sites of any possible microbial life that might be present. Planetary protection is essential to preserve our ability to study other worlds as they exist in their natural states and to avoid introducing Earth life in a way that would obscure our ability to find life elsewhere.
More at NASA's Planetary Protection Site