Curiosity has started on the long trek to Aeolis Mons, which NASA unofficially refers to as “Mount Sharp”. With some eight kilometres (5 miles) between the rover an its initial destination among the lower slopes of the mound, the drive is liable to take several months to complete. Nevertheless, the drive marks the start of the core part of the mission.
The journey started on July 4th, when Curiosity departed the sedimentary rock target NASA had dubbed “Shaler” within the “Glenelg” region of Gale Crater between “Yellowknife Bay”, where the rover had been carrying out drilling and other tasks, and the landing zone at Bradbury Landing. “Shaler” had actually been passed b the rover on its way to “Yellowknife Bay” and had, along with another location in “Glenelg” which had been dubbed “Point Lake”, been identified as a “target of interest” for the rover as it backtracked through “Glenelg” in order to start the long trip to “Mount Sharp”.
Point Lake first caught the interest of Curiosity’s science team in October and November of 2012. It caught the attention of mission scientists for two reasons: it forms a small cliff, and geologists love cliffs because they offer a sense of how a rock unit differs from bottom to top; plus images captured by the rover as it passed relatively close to the outcrop while en route to “Yellowknife Bay” revealed it to be full of holes. Why holes form in rocks can be due to diverse mechanisms, and Identifying which mechanism in particular is responsible can provide a greater understanding about the rock and its history.
The rover returned to “Point Lake” on Sol 301 / 302 (June 11th and 12th, 2013) and captured a further series of images using the Mastcam systems, some of which were then put together to create a mosaic.
The mosaic clearly shows that the upper and lower portions of the outcrop differ in composition, with the upper part having more holes while being more resistant to weathering. The holes themselves range in size from about that of a garden pea through to some larger than a golf ball’s diameter. Some additionally have raised rims, as if the material immediately around a hole is slightly more resistant than material farther from the hole. A number of smaller rock fragments towards the right-hand end of the mosaic look as if they might have fallen out of some of the holes, and some of these exhibit colour banding suggestive of material which could have coated the interior of a hole.
The science tem are still studying the images captured by the Mastcam system and by the rover’s Mars Hand Lens Imager (MAHLI), mounted on the turret at the end of Curiosity’s robot arm. Taken from a distance of just 4cm, the MAHLI images reveal pebble-like deposits within many of the holes covering “Point Lake”, and which have made the identification of the processes responsible for forming the holes somewhat harder, as both sedimentary and igneous processes could account for the “pebbles”.
Following the stop at “Point Lake”, Curiosity continued retracing its route back through “Glenelg”, reaching the vicinity of “Shaler” around Sol 313, where it remained for several days taking further images and manoeuvring in the area immediately adjacent to the rock formation. Then on July 4th, the rover started on the drive to “Mount Sharp” in earnest, initially travelling back towards “Rocknest”, which it visited in September 2012, prior to skirting around it in a drive of some 36 metres (118 feet) between July 5th and July 8th (Sol 327).