This mosaic, taken with the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter, shows the planned route (in yellow) of NASA's Curiosity rover from "Pahrump Hills" at the base of Mount Sharp, through the "Murray Formation," and south to the hematite ridge further up the flank of Mount Sharp. Go here for more information about the image. Image Credit: NASA/JPL-Caltech
Three weeks ago, Curiosity fulfilled one of the mission's long-term goals when she arrived at Pahrump Hills, the base of Mount Sharp in Gale Crater. The suite of minerals in the three kilometer high mountain, first identified by satellites in orbit around Mars, told us that something every interesting happened in Gale Crater a long time ago.
Three distinct sets of rock units became clear from orbit: the first appears to be composed of clay-bearing rocks, the second forms a resistant hematite-bearing ridge, and the third contains sulfate-bearing rocks. Clay-bearing units, such as this one, suggest the presence of a lot of water at one time on Mars, while the sulfate-rich rocks suggest a time of "drying-out". This interesting suite of rock units may record a significant climatic change on Mars, from the time Mars was wet to the arid environments we're familiar with today - and Curiosity is starting to learn about it from the ground up!
Curiosity drove though sandy, interconnected valleys to arrive at Pahrump Hills. Her view from the ground is providing us with more information about the rocks we first saw from orbit. The rocks exposed at the very bottom of Mount Sharp are called the Murray Formation. The Pahrump Hills site (found at the edge of where the Murray Formation is exposed at the surface) includes a very soft rock unit, believed to be a fine-grained rock like a mudstone. It has morphologically interesting features in the shallow subsurface that form dendrites and clusters. These features were likely formed by fluids that moved through the Martian mudstone a long time ago. The science team hopes to learn about the composition of these fluids and the surrounding rock by analyzing samples of the rocks with the rover's internal instruments, CheMin and SAM. Curiosity drilled 6.7 centimeters into the soft rock of Pahrump Hills, and the next step is to ensure the drill powder is safe to deliver to the internal instruments. Once this is confirmed, the SAM team will get our first taste of Mount Sharp rocks!
Curiosity completed its primary mission after one Mars year (two Earth years) of surface operations. It has now begun its extended mission. SAM will continue to play a vital role in this second phase of Curiosity's mission, providing chemical and isotopic analyses that help the rover's science team understand what's in the clay-, sulfate-, and hematite-bearing rock units, how they formed in Mount Sharp, and what those rocks can tell us about the ancient environments and climatic evolution of Gale Crater - and Mars. Like a good field geologist, we're starting from the ground up at Pahrump Hills!
To see Curiosity's route from landing to Pahrump Hills, go here.