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Ashwin Vasavada
Ashwin Vasavada became the project scientist for NASA’s Curiosity rover mission in January. His role is to coordinate efforts of an international team of nearly 500 scientists. (Credit: NASA / JPL-Caltech)

Three years after NASA’s Curiosity rover landed on Mars, scientists are celebrating a curious milestone: Although the six-wheeled, plutonium-powered robot has lasted a year longer than they planned for, Curiosity has been moving more slowly than they planned for.

“In one sense, we’re not as far as maybe we would have predicted before landing…. Looking in hindsight at what we’ve studied in Gale Crater, we had a very naive understanding of how things would unfold once we landed,” Ashwin Vasavada, the $2.5 billion mission’s project scientist at NASA’s Jet Propulsion Laboratory, said during a GeekWire interview.

That may sound like a bad thing, but it turned out to be very, very good. Curiosity and its handlers have been taking their time since that amazing touchdown on Aug. 5, 2012, largely because there’s more to discover than they expected. For example, a months-long detour to a place called Yellowknife Bay met one of the mission’s prime objectives: the identification of an ancient lake bed where habitable conditions existed billions of years ago.

Vasavada still ranks that find as the mission’s top achievement – but now that Curiosity is finally making its way up a 3-mile-high peak known as Aeolis Mons or Mount Sharp, he and his colleagues are filling out an even bigger picture. Curiosity is studying different elevations in the mountain’s layered bedrock – and revealing how Mars’ climate morphed from an ancient environment that was warm and wet into the cold, dry world we see today.

Vasavada said the terrain through which Curiosity has been traveling built up more than 3.5 billion years ago, during a key geological period known as the Noachian-Hesperian boundary. “That is the probably most critical time in Mars’ history, in terms of transitions, because Noachian Mars was definitely a wetter planet,” he said.

As Curiosity moves up the slopes of Mount Sharp, it’s documenting shifts in the composition of the sedimentary rock. Those shifts indicate that Mars’ water gradually became more acidic and less friendly to life. “The chemistry is slightly changing,” Vasavada said.

That’s consistent with a scenario backed up by other data, not only from Curiosity but from other Mars probes as well: The Red Planet’s atmosphere lacked the protective shield of a global magnetosphere, and so it was stripped away by solar radiation. The atmospheric conditions conducive to liquid water and habitability faded away as a result.

Lamoose rock
A fragment of silica-rich rock dubbed “Lamoose” is shown in this picture taken by the Curiosity rover’s Mars Hand Lens Imager. (Credit: NASA / JPL-Caltech / MSSS)

Did life on Mars fade away as well? Or did life ever exist there to begin with? Although Curiosity isn’t built to detect the direct signs of life directly, it’s looking for carbon-bearing chemicals that could have been left behind by ancient organisms. Some such chemicals were identified last year, but scientists couldn’t determine whether they were produced biologically.

Now the team is focusing on a promising patch of rock that has surprisingly high levels of silica. There’s a good chance that the interior of the rock may harbor ancient organic material, so scientists are using Curiosity’s percussive rock drill and its onboard chemical lab to find out what’s there.

“What’s nice is that it’s a mystery for us to solve,” Vasavada said. “It’s going to result in something new that we learn about Mars, the fact that there’s all that silica there. It’d be boring if all the drill holes had the same chemistry.”

After three years of discovery and more than seven miles of grueling travel, the rover team has had to cope with Curiosity’s worn-down wheels as well as a glitchy drill, but Vasavada is confident those signs of age won’t slow the rover down too much. “With the success of our drilling activities this week, that has gone down on the ‘worry-meter,'” he said.

So far, there’s nothing to stop Curiosity from continuing its climb up Mount Sharp – unless, of course, Vasavada and his colleagues want to stop, for science’s sake.

So what’s next? Find out at 5 p.m. PT today when Vasavada and I discuss Curiosity’s past and future on “Virtually Speaking Science,” an hourlong talk show on BlogTalkRadio. If you’ve got a Second Life avatar, come join the audience in the Exploratorium’s virtual auditorium. And if you miss the live program, never fear: You can always download the podcast from BlogTalkRadio or iTunes.

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