A little over two years after landing, Curiosity has reached a milestone. NASA recently announced that the rover has arrived at the base of Mount Sharp, a 3.4-mile-high mountain that Curiosity has been heading towards since July of 2013. The initial landing was in Gale Crater, and the total journey has been around 9km or 5.5 miles — a number that becomes more impressive if you consider that Curiosity was designed to travel a maximum of 660 feet per day and navigate difficult terrain on its six wheels. The Spirit rover traveled only 4.8 miles over its lifespan, although the still-active Opportunity rover has logged about 25 miles since 2003. Curiosity's path was rerouted earlier this year after scientists found that sharp rocks were poking holes in its wheels. Curiosity was previously set to drill for samples in a rock called "Bonanza King," but last month, NASA scientists decided the terrain was too unstable and kept pushing towards Mount Sharp. In general, it's been tasked with determining whether Mars could once have supported life and (more speculatively) whether life actually existed there. In mid-2013, it drilled samples that showed a once-wet area could have supported microbes. Now, it's going to begin climbing Mount Sharp's lower slopes, with the goal of collecting samples from different layers of sediment that could offer more insight into the past of Mars — and, to some extent, the future of Earth.