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NASA's latest and largest rover celebrates its first anniversary on Mars today. One year ago, Curiosity came to a gentle landing in Gale Crater. Ever since, it's been chugging around what appears from orbit to be the mouth of an ancient river system. It's looking for signs that the environment on Mars might once have been suitable for life.
NPR's Joe Palca has this report on the rover's first-year accomplishments.
JOE PALCA, BYLINE: Curiosity started its first year on Mars with a picture-perfect landing, except for one tiny problem that only turned up when engineers analyzed the data the rover recorded on the way to the surface.
ADAM STELTZNER: We found that we landed more slowly than we anticipated.
PALCA: Adam Steltzner led the team at NASA's Jet Propulsion Laboratory that designed Curiosity's landing system. Steltzner says the error wasn't large.
STELTZNER: One or two inches a second more slowly than we anticipated but maybe it's a mark of how sharp our pencil was that that's a big deal for us.
PALCA: So they were determined to figure out what went wrong. Now they think they have.
STELTZNER: We've concluded that there was a gravity anomaly where we landed.
PALCA: Meaning the tug of gravity at the landing site in Gale Crater was slightly, slightly, slightly smaller than other places around the planet because of the density of the underlying rock. Steltzner says, in retrospect, finding an anomaly isn't all that surprising. He's chagrined the landing team didn't consider the possibility.
STELTZNER: And that's sort of where pride cometh before a fall, right? We felt that we knew something that clearly we didn't know well enough.
PALCA: Scientists aren't complaining about the problem - not at all. They've got a new robotic geologist working perfectly on Mars. Ashwin Vasavada is deputy project scientist for Curiosity. He says the rover has found clear signals that a river did once flow at the bottom of Gale Crater. The most compelling data come from a mineral analysis of a rock the rover drilled into.
ASHWIN VASVADA: The minerals that were present in this drilled sample were the kind that form only in the presence of water. And, in fact, form in the presence of water that's friendly to life.
PALCA: That would be water that's not too acidic and contains chemicals that most life forms need to thrive. That's not to say there was life on Mars, it's just conditions don't to rule it out.
Although they are pleased with their results, Vasavada admits scientists have had their frustrations with the rover.
VASVADA: For me, the last year has been a mix. You know, it really has honestly taken us longer to do things than we had hoped.
PALCA: That's because Curiosity is an incredibly complicated machine. Learning to operate it on Mars has required patience. And unlike the two smaller rovers, Spirit and Opportunity, which were only supposed to last a few months, Curiosity is supposed to last at least two years, so the pressure to do things fast just isn't there.
VASVADA: But on the other hand, at this point in the mission, we have already accomplished our primary goal of finding a habitable environment on the surface of Mars. And so, from that perspective it was unexpectedly wonderful.
PALCA: So how are you going to keep the press interested if you've already found what you're looking for?
PALCA: Come on.
VASVADA: Yeah, well, we're going to climb a mountain. I mean, that's going to be awesome.
PALCA: The mountain is Mount Sharp, about five miles from the landing site. Actually, the rover will only make it to the foothills of Mount Sharp. But Vasavada says scientists are expecting to see to rock formations there that will not only reveal how much water was in Gale Crater but when in Martian history it was there.
Joe Palca, NPR News. Transcript provided by NPR, Copyright NPR.