"For the entire Curiosity team, the big moment is yet to come," said science writer Marc Kaufman, the author of "Mars Up Close," a book about the $2.5 billion mission.
That big moment has everything to do with the 3-mile-high (5-kilometer-high) mountain that Curiosity is just now nearing — known as Aeolis Mons or Mount Sharp. The mountain's layers of rock appear to record billions of years' worth of the planet's geological history, and could reveal the presence of organic carbons.
Would that prove life existed on ancient Mars, or perhaps exists even today? No. But it would mark a major advance in the centuries-old debate about life's chances beyond Earth.
Space.com contributor Rod Pyle, who tells the tale of the rover mission and the team behind it in a book titled "Curiosity," admits that NASA's latest Red Planet quest seems a bit schizophrenic at the two-year mark.
"NASA keeps saying this is not a mission to look for life on Mars, but this is an astrobiology mission," he told NBC News. "The big tipping point for this one is that it's actually looking for habitable environments."
Kaufman, who was visiting NASA's Jet Propulsion Laboratory when that glitch cropped up in late February 2013, said the mission team downplayed the seriousness of the anomaly at the time. The behind-the-scenes sentiment was much scarier. "It was, 'We're sweating buckets, and we may be doomed,'" Kaufman recalled.
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Fortunately, Curiosity's handlers averted doom and went on to achieve marvels. That's the overarching theme of Kaufman's "Mars Up Close" as well as Pyle's "Curiosity" — and it's the message of the mission's motto as well: "Dare Mighty Things."
The Planetary Society's Emily Lakdawalla, who is working on her own book about Curiosity's mission, said she'll be on the watch for those times when Curiosity interrupts its trek to study sites of scientific interest along the way to Mount Sharp, especially if the robot fires up the drill that's mounted on its robotic arm. "Drilling always tells you that they think it's worthwhile to invest the time it takes to drill," she told NBC News.
Once Curiosity gets to Mount Sharp, geologists hope to use the rover's instruments to trace the changes recorded in the rocks, ranging from an age when it was warmer, wetter and more Earthlike, more than 3 billion years ago ... through a volcanically active transition period ... to the cold, dry environment we see today. That kind of wide-ranging geological record just isn't available on Earth, because Mother Nature erased it long ago.
"When we go study Mars, we're trying to understand ourselves."
"In a way, when we go study Mars, we're trying to understand ourselves," Lakdawalla said. "We're trying to understand how our own planet worked when it was young."
Because the rover is powered by plutonium, it could theoretically keep going for more than a decade — that is, if its wheels don't give out. Those wheel treads have gotten pretty chewed up in the past few months, but Kaufman said mission team members have told him the going should get easier as Curiosity approaches Mount Sharp.
"If they take the precautionary steps they have in place, they say the wheels will not be what ends the mission," he said.
With luck, Curiosity will still be in business when NASA's next Mars rover arrives. That robot, scheduled for launch in 2020, will be built with Curiosity's basic design. But its array of instruments — and its purpose — will be significantly different.
Then what? NASA says it wants to send astronauts to Mars and its moons by the 2030s, and private ventures such as Mars One and Inspiration Mars say they want to do it sooner. It's fitting that the foreword for Kaufman's book is written by SpaceX's founder, Elon Musk, who has repeatedly said he wants to die on Mars. ("Just not on impact," the 43-year-old billionaire adds.)
"I am talking about people settling on Mars and making life multiplanetary. ... When I think of going to Mars, I think of building greenhouses packed with rehydratable nutrients," Musk writes. "I think of an iron-ore refinery. I think of a pizza joint."
Others think about answering one of the biggest questions surrounding our existence: Are we alone? Or did life get its start elsewhere in the universe? Is it even possible that Earth's life came from Mars? "I personally think that would be the greatest scientific discovery of all time," Kaufman said. "That's the prize. Who knows what the greatest discovery of all time is worth?"
At its heart, the decades-long effort to explore Mars touches something deep in the human spirit, something that's hard to put a price tag on.
"We do it in part just because we're curious," Lakdawalla said, "and so 'Curiosity' is a good name."
Marc Kaufman is the moderator for a panel about the Curiosity mission, presented at National Geographic's Grosvenor Auditorium at 7:30 p.m. ET Tuesday and webcast via NatGeoSpace.com. Kaufman may also join in Wednesday's "Virtually Speaking Science" event.