Paper No. 20-7
Presentation Time: 9:40 AM
LONG DISTANCE OBSERVATIONS WITH THE CHEMCAM REMOTE MICRO-IMAGER: MOUNT SHARP AND RELATED SEDIMENTARY DEPOSITS ON GALE CRATER FLOOR?
A major question for Gale Crater (age 3.6 BY), is whether some deposits in the central mound (informally Mt. Sharp) originally extended across the crater floor, prior to the deposition of Peace Vallis and other fans at 3.2 BY. Orbital images show partly eroded deposits in the vicinity of the Peace Vallis fan and as yardangs on Mt. Sharp, but their nature– aeolian, fluvial, or impact-related – is not obvious. Curiosity’s ChemCam includes a Remote Micro-Imager (RMI) to provide context for the laser pits, and to obtain high resolution long-range images from the rover perspective. Use of the RMI has been enhanced by a new autofocus algorithm using onboard analysis of RMI images. The RMI has the finest pixel scale on the rover with 19.6 μrad/pixel (1024x1024 grayscale), compared to Mastcam M100 color images (74 μrad/pixel), although ChemCam optics somewhat degrade the useful RMI resolution. The theoretical pixel scale for RMI images is ~2 cm at 1 km, and ~26 cm at 12 km, beyond which HiRISE orbital resolution (25 cm/pixel) is better. Note: resolution of geological features requires 3-5 pixels. Long distance RMI images show planar beds in eroded yardangs on Mt. Sharp. Images were also obtained of partly eroded sediments in the vicinity of, but predating the Peace Vallis fan. The RMI of these deposits near the west edge of the fan confirm the presence of eroded buttes with up to 8-10 horizontal layers (0.8–1.6 m thick), consistent with a sedimentary origin. The layered buttes rise as much as 12 meters above the surrounding deposits. The surrounding deposits embay the lower portions of the buttes and are probably a phase of the Peace Vallis fan. RMI images of blocks in this fan unit about 50-80 cm across are consistent with enhanced retention of craters previously noted for this unit. Another RMI observation just above the Peace Vallis channel shows an eroded bench, that could indicate sediments deposited prior to Peace Vallis fan or entrenched early fan deposits. Conclusions - The RMI images are clarifying the sedimentary origin of materials on Mt. Sharp and on the crater floor near the Peace Vallis fan. The sediments near the Peace Vallis fan are highly eroded, are of unknown original thickness, and may be related to deposits in Mt. Sharp. The high resolution RMI images from the rover’s perspective are a powerful tool for geological analysis at Gale Crater.