It's easy to understand why scientists are so fascinated by Mars: it’s the most Earthlike planet in our solar system. NASA has sent several missions to investigate Mars since the 1970s. It has used satellites to survey the planet from above, and spacecraft to explore the surface. But when spacecraft land, they essentially remain in place. To enhance surface exploration, NASA has developed robotic motor vehicles called rovers.

So far, NASA has landed three rovers on Mars. Their designs and scientific equipment have varied from mission to mission. During the Mars Pathfinder mission that launched in 1996, the "microrover" Sojourner carried three instruments to examine properties of the soils, rocks, and crust and learn more about the planet’s past environmental conditions. The Mars Exploration Rover mission, launched in 2003, carried two rovers, Spirit and Opportunity. Using high-resolution panoramic cameras, microscopic imagers to see surface features close-up, and robotic arms, these rovers found lots of evidence that Mars was once a warmer place with liquid water and not just ice on its surface. For the next mission to Mars, scheduled to launch in late 2011, NASA has designed a rover, named Curiosity, for a new goal: to investigate whether Mars has—or has ever had—the ability to support life.

Over the course of one Martian year (about 23 Earth months) after landing, Curiosity will analyze and explore more than any previous Mars rover. It possesses many features used in earlier rovers but is much larger and capable of carrying more instruments—10 in all. These fall into four categories:

• Remote sensing instruments located on Curiosity’s mast will assess potential research targets.
• Contact science instruments located on the “hand” of its robotic arm will observe rocks and formations in place where they lie on the planet's surface.
• Analytical instruments inside the rover will analyze extracted samples.
• Environmental instruments located elsewhere on its body will measure environmental characteristics, such as atmospheric pressure and radiation levels.

While much of the technology behind these instruments has been applied before, Curiosity does have something novel: the ability to not only collect samples of rocks and soil but to analyze them as well. This makes Curiosity in effect a large, mobile laboratory.

As it investigates surface features near its landing site, inside Gale crater, Curiosity’s instruments will gather important information about the planet’s past conditions. Gale crater is an impact crater whose rock layers might contain evidence of a number of diverse environments that existed over millions of years. In the course of its work, Curiosity may detect forms of carbon, the chemical building blocks of life. While finding carbon compounds—known as organics—would not prove the existence of life, scientists know that life cannot exist without them.

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