Aug. 5, 2012 -- NASA's Mars Curiosity Rover closed in on its target today, all systems go for a landing on Mars late tonight (Monday morning at 1:31 a.m. EDT). If there's anxiety at the Jet Propulsion Laboratory in Pasadena, Calif., which controls the mission, one can understand.
Curiosity (the mission's formal name is Mars Science Laboratory) is the largest, most expensive and most ambitious Mars probe sent by the United States in a generation. It's been a decade in the making and ran up bills of $2.5 billion.
NASA is playing down expectations, but if the building blocks of life are buried in the Martian soil, Curiosity's miniature onboard chemistry laboratory is designed to pick them out.
"Can we do this? Yeah, I think we can do this. I'm confident," Doug McCuistion, head of the Mars exploration program at NASA headquarters, said Saturday. "We have the A-plus team on this. They've done everything possible to ensure success, but that risk still exists."
"We have to keep looking," said Andrew Kessler, a writer who spent three months covering the team that made the last successful landing, in 2008. "Every question leads to more understanding," said Kessler, the author of a book called "Martian Summer."
Curiosity weighed 5,293 pounds on Earth. It's the size of a small car and much, much bigger than the twin rovers Spirit and Opportunity, which landed on Mars in 2004, cradled in airbags. Curiosity is simply too big for that, so it will be lowered to the surface by a heat shield, then a parachute, then retro-rockets, and finally a rocket-powered sky crane. That's something engineers have never tried before -- and that's what makes this so scary for them.
"When people look at it, it looks crazy," says Adam Stelzner, an engineer who laid out the landing plans, in a video NASA produced about the landing. "Sometimes when we look at it, it looks crazy. It is the result of reasoned engineering thought. But it still looks crazy."
NASA says it thinks there's a 90 percent chance of a safe landing. If they're right, they say they hope Curiosity will explore for one Martian year -- about 22 months on Earth.
If Curiosity doesn't find evidence of life, scientists say it will mean very little. The half-dozen probes to land on Mars since 1976 have only explored a few square miles of the planet.
But what if it hits pay dirt? What if it really does find something? The results would probably not be conclusive, but they would be incentive for further exploration -- a tender subject at NASA because, hampered by budget cuts, it currently has no future Mars missions approved.
"If we don't ponder these things, then we're not asking ourselves the right questions," said Kessler, "and we're not looking to build bigger and better futures for ourselves."
ABC's Gina Sunseri contributed reporting for this story. Additional information from The Associated Press.