A multibillion-dollar gamble, a most scary landing and possibly learning whether Mars once could have supported life - briefly, that's what's at stake in NASA's Mars Curiosity mission, set to touch down early Monday. Mars is a difficult place to get to - only about a third of the 44 missions there have succeeded. Curiosity is the most ambitious and complex Mars mission ever conceived, writes Marc Kaufman, author of "First Contact: Scientific Breakthroughs in the Hunt for Life Beyond Earth." Soon, we'll know whether Curiosity's creators were brilliant and far-seeing - or reaching too far.
1. All the chips are riding on this
In this stripped-down economic time, the $2.5 billion mission could become the last of its kind if something goes wrong. Or it could send back such compelling information and pictures that the public demands more Mars exploration, and Congress and the White House have to respond. Before you bet, know that only six of more than a dozen spacecraft that have reached Mars landed successfully and completed their missions. All six were American. Will Curiosity be the seventh?
2. The scariest seven minutes
Why worry about Curiosity's arrival? The descent module is set to go from 13,200 mph to 0 in 6 1/2 minutes. How will the several stages survive that landing? NASA has meticulously planned but noted that on this entry -- as well as other systems on the mission -- it is using innovations tested separately before, but never together. For instance, an untried "sky crane" maneuver is supposed to drop the rover, gently, the last 60 feet from a "descent module" hovering like a helicopter.
3. Is NASA looking for Martians?
No. Nor tiny moving animals or insects. The missions wants to see if the planet 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.
4. 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 did not 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.
5. Why has it taken more than 35 years for NASA to come back?
The Viking findings were fascinating, but they made clear that NASA did not have the knowledge or 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 is generally described as the most sophisticated instrument ever sent to another planet.
6. Curiosity will be the largest object made by humans to land on Mars.
The rover is roughly three times heavier than the twin rovers Spirit and Opportunity, which landed on Mars in 2004. It's twice as large. It carries 10 instruments (the previous twins had five each), and the Curiosity instruments together weigh 165 pounds compared with 11 pounds for Spirit and Opportunity. Curiosity's heavier weight prompted the high-risk, high-stakes landing.
7. The mission won't "follow the water" but will "follow the carbon"
The water-on-Mars issue is settled. The Curiosity landing site, Gale Crater, is known to have been covered in water billions of years ago because of the presence of clays and minerals which can only be formed in the presence of water. Satellites that orbit Mars have sent back images that clearly show dried river beds, large dried deltas and even tantalizing glimpses of what might be liquid water running down cliffs during summer. The next question: Does Mars have the carbon-based organics needed for life?
8. 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 in the negative-100-degree nights. Previous Mars rovers used solar power; Curiosity was 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 as many other NASA programs are being cut?
9. The rover can climb mountains
While the Spirit and Opportunity rovers went into small craters and up gentle slopes, Curiosity was designed for tougher things. It will touch down in Gale Crater's flatlands, but its real destination is Mount Sharp, which sits in the middle of the crater and rises three miles high. Named after planetary scientist Robert Sharp, the mountain has exposed rock faces that can be "read" to learn about the planet's history.
10. We'll know how much radiation hits Mars. Too much for humans?
A detector will register high-energy atomic and subatomic particles reaching Mars from the sun, distant supernovas and other sources. The radiation they create could be harmful to any microbes near the surface of Mars or to astronauts on a future Mars mission.
11. 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 (JPL) speak of Curiosity's rudimentary "thinking," akin to a robot. 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 JPL 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 decision-making surprises.