Mars is a difficult place to get to — only about a third of the 44 missions there have succeeded. Curiosity is considered to be the most ambitious and complex Mars mission ever conceived.
1. What is NASA looking for?
The mission will try to determine whether Mars has the carbon-based compounds that are the building blocks of life. It will also look for habitats that might once have supported life. But it is not a "life-detection" mission like the Viking landers' before it.
2. Curiosity is continuing what the Viking landers started in 1976.
The Viking landers were the first to successfully land on Mars, and their goal was to determine whether the planet could support life. The official conclusion? No, it could not. Each Viking landed on a cold, desert plain, and both failed to find organic material. No organics, no life, the thinking went. Yet one experiment, which added a radioactive tracer to nutrients deposited into a Viking-scooped soil sample, did get positive results. The experiment's principal investigator, Gilbert Levin, is still fighting to convince NASA and other scientists that the experiment did succeed — and life was present. Some accept his findings; most do not.
3. Why has it taken more than 35 years for NASA to make a return visit?
The Viking findings were fascinating, but they made clear that NASA did not have the knowledge or the equipment to rigorously search for life or its building blocks on Mars. The field of astrobiology — more generally, the search for life beyond Earth — went into eclipse for decades but was rejuvenated by a series of discoveries beginning in the mid-1990s. Now astrobiology is central to what NASA does. The Curiosity instrument that will do the heavy lifting in searching for organics is the gold-plated Sample Analysis on Mars, and it is generally described as the most sophisticated instrument ever sent to another planet.
4. Curiosity should keep on ticking.
Although the rover's mission is scheduled for two years, NASA officials say its nuclear battery easily could last for a decade, powering movement of the one-ton rover and keeping it warm during the negative-100-degree nights. Previous Mars rovers used solar power; Curiosity is too big for that. A significant threat to a longer mission is financial: Will Congress and a future White House want to pay for Curiosity while many other NASA programs are being cut?
5. Curiosity can think for itself. Sort of.
Previous Mars rovers have decided how to avoid a rock in their way or steer clear of a steep decline. But some at the Jet Propulsion Laboratory speak of Curiosity's rudimentary "thinking," akin to a robot's. Curiosity does not have what is formally considered artificial intelligence, but it can gather data and make decisions in a new way. Some of the rover drivers at the laboratory even worry that although they will know Curiosity's moves, they won't necessarily know how it decided to do them. The rover isn't about to go rogue, but it could provide some real decisionmaking surprises.