Curiosity’s “Spyglass” Megamosaic of Mount Sharp

A quick introduction, since I'm not a regular author of Curiosity's blog: since the rover's landing, I’ve been involved in the processing of ChemCam’s images at France's University of Nantes. I'm always eager when new data come down, and the images we've collected here as a video are a real treat.

The recent “Housedon Hill” imaging campaign planned by the team during a two-month period while staying at the “Mary Anning” drill site broke a record, being the largest mosaic obtained so far with ChemCam’s Remote Micro-Imager (RMI). RMI was originally designed to document the tiny areas analyzed by ChemCam’s laser-induced breakdown spectroscopy (LIBS) technique on rocks only a few meters from the rover. During Curiosity’s first year on Mars, it was recognized that, thanks to its powerful optics, RMI could also go from a microscope to a telescope and play a significant role as a long-distance reconnaissance tool. It gives a typical circular “spyglass” black and white picture of a small region. So RMI complements other cameras quite nicely, thanks to its very long focal length. When stitched together, RMI mosaics reveal details of the landscape several kilometers from the rover, and provides pictures that are very complementary to orbital observations, giving a more human-like, ground-based perspective.

From July to October of 2020, Curiosity stayed parked at the same place to perform various rock sampling analyses. This rare opportunity of staying at the same location for a long time was used by the team to target very distant areas of interest, building an ever-growing RMI mosaic between September 9 and October 23 (sols 2878 and 2921) that eventually became 216 overlapping images. When stitched into a 46947x7260 pixel panorama, it covers over 50 degrees of azimuth along the horizon, from the bottom layers of “Mount Sharp” on the right to the edge of “Vera Rubin Ridge” on the left. The insets show how the high resolution achieved by RMI reveals various geologic landforms, such as a field of sand ripples near Vera Rubin Ridge, and an impressive variety of layered units. These features all highlight Gale crater’s complex geologic history. Mount Sharp has a prominent “marker bed," a distinct single layer that can be traced almost all along its base, extending over tens of kilometers. It appears in this mosaic as a dark layer that marks a key change in the formation of the mountain’s slopes.

By stretching the contrast of the image in the middle of the panorama above the foreground, one can even recognize features corresponding to blocky rocks that rolled partway down from Gale’s crater wall way off in the distance. When measured using imagery from the Mars Reconnaissance Orbiter’s Context Camera (CTX), these blocks are 59 kilometers from the rover – a record distance for a ChemCam/RMI observation. This is the equivalent of seeing Baltimore’s downtown buildings from Washington DC’s city center. This indicates that despite the dust in the atmosphere, which varies significantly across seasons, the sky at this time was clear enough to perform such very distant imaging.

Stéphane Le Mouélic, Remote Sensing specialist at LPG/CNRS, Nantes, France