After more than two years and five miles of driving, Curiosity has finally broken ground on Mount Sharp, the mountain that sits in the middle of Mars's Gale Crater that the rover was sent to the Red Planet to explore.
Curiosity's overall science goal was always to assess the present and past habitability of Mars. Habitability in this case meaning an environment with water, a source of carbon and other vital elements, as well as an energy source—in short, the things we know life needs to thrive on Earth.
Curiosity was sent to look for these vital resources in the Gale Crater field site, which is notable for the massive mountain that sits at its centre, Mount Sharp.
Even for Mars, Mount Sharp is a really exciting place. The mountain, officially known as Aeolis Mons, has layers of exposed rocks of varying textures that not only provide a ripe sampling ground for the rover, the environment stands as a record of one of the most important transitions in Mars's planetary and climatic evolution.
These rocks might hold the clues to Mars's transition from a wet planet to a dry one, so as it samples increasingly high strata, Curiosity might find evidence of the planet's change from habitable to hostile.
Studying the diverse rock layers might also shed light on what environmental factors have affected Mars's habitability and also what factors might be at play in preserving organic carbon. Looking for organic carbon might help scientists narrow the search for fossils.
But of course, Curiosity didn't land right at the base of the mountain. It landed miles away, and getting there hasn't been easy. Hazardous terrain has taken its toll on the rover's wheels and forced a circuitous route along the Martian surface.
Even so, the mission has thus far been a success: Curiosity achieved its primary mission goal within its first year; drilling and sampling mudstones revealed ancient fresh water existed on Mars, along with the main elemental building blocks of life and a source of energy. Microbes could have existed on Mars, though this doesn't mean they did.
So with its primary science goal achieved and a recent arrival at its main target site, what's next for Curiosity?
We're into the rover's first extended mission now, EM1, and it's bringing a bit of a change. According to NASA, the next big question the rover will answer is an obvious one coming on the heels of its previous discoveries: "What geological settings and environmental conditions have been conducive to preserving evidence of carbon and other biomarkers?"
Starting at the base of Mount Sharp, Curiosity will focus on four unique geologic regions. In ascending order, the first is the basal rocks that look from orbit to have a "paintbrush" texture. The second target will be the overlying and younger hematite-bearing rocks. Next, Curiosity will look at even younger clay-bearing rocks. Finally, the last layer the rover will focus on, at least within its first extended mission, is the layer of magnesium sulfate-bearing rocks that extend to the upper reaches of the foothills.
Last week, Curiosity dug into that first layer, the basal rocks. The rover arrived at an outcrop called Pahrump Hills on September 19, a section of the mountain's basal geological unit called the Murray formation. After a test procedure described by NASA as a "mini-drill" at a target called Confidence Hills confirmed the rock was suitable for drilling, the rover finally dug in on September 24. Its hammering drill dug a little more than 2.5 inches into the outcrop to collect a sample of the powdered rock onboard instruments will eventually analyze.
Answering this extended mission question will be Curiosity's real legacy, and it will also see the rover fulfill its full potential. And it's not just a rock sampling mission now, either. Curiosity will look at the atmospheric isotope data in conjunction with data gathered by the MAVEN spacecraft, painting a more complete picture of volatile compounds in the Martian atmosphere.
There's no reason to think we won't see these goals met. Thanks to its radioisotope thermoelectric generator, Curiosity has plenty of power and is still going strong. And the team behind the rover is also getting stronger, becoming more familiar with their local environment on Mars and the intricacies of their surrogate in exploration. The primary mission might be over, but this mission on the whole is only going to get better.