Morphology, Morphometry and Distribution of Isolated Landforms in Southern Chryse Planitia, Mars

The margin of Chryse Planitia, Mars, contains >10⁵ kilometer‐scale mesas, buttes, and plateaus (“mounds”), many of which are found in and around Oxia Planum, the ExoMars 2022 Rover landing site. Despite this, their origins and evolution are unknown. We have analyzed the morphologies and morphometries of 14,386 individual mounds to: (1) classify them based on their geomorphology; (2) constrain when they formed based on their stratigraphic and spatial relationships; and (3) develop hypotheses for their geological history. The mounds are classified as compound mounds, mesas, clustered mounds, and hills. Mound heights show that their elevations above the plains tend to a maximum height of 500 m. We interpret this as the thickness of a previously continuous layer that extended several hundred kilometers from the southern highlands into Chryse Planitia. Stratigraphy constrains the deposition of this layer to the Early‐Middle Noachian, correlatable to the phyllosilicate‐bearing strata of Mawrth Vallis, with similar layering also observable in some mounds, suggesting a genetic relationship. The mounds sometimes occur in circular arrangements, interpreted as an association with buried impact structures. We propose that the mounds formed through differential erosion after the premound layer was indurated by mineralization from groundwater in areas superposing underlying crustal weaknesses, for example, at buried crater margins. The subsequent differential erosion of this layer preferentially removed areas unaffected by this induration in the Late Noachian‐Early Hesperian leaving the mound population seen at present. These features present accessible three‐dimensional exposures of ancient layered rocks, and so are exciting targets for future study

Characterizing Rock Abundance At ExoMars Landing Site Candidates

We present preliminary work to characterize surface rock abundance at ExoMars Rover landing site candidates. A challenge in quantifying the abundance of surface rocks is using the population of large (≳1 m) rocks that are resolved in orbital images to infer the size of the smaller, unresolved rock population. This is particularly relevant for the ExoMars Rover mission, where the Landing Module’s clearance of 35 cm makes it necessary to know the probability of encountering rocks where 0.35 < D < 1 m. ‘Float rocks’ are individual fragments of rock not associated with a continuous outcrop or body of rock —e.g. transported rocks or impact debris. These can be identified in Mars Reconnaissence Orbiter HiRISE images, where the mid-afternoon local solar time, dictated by MROs’ orbit, causes float rocks to appear as bright sunlit features adjacent to strong shadows. However, the smallest features resolvable in HiRISE images occupy around 3-4 pixels, corresponding to ~1-m sized rocks. This inherently limits the ability to directly identify from orbit the small, but potentially hazardous rock population. ‘Outcrop’ is defined as continuous expanses of bedrock or surficial deposits exposed at the surface. Both float rocks and outcrop can contribute to slopes that may constitute a hazard for landed missions. We present rock counts at ExoMars Rover landing site candidates and assess approaches to constrain the morphological characteristics of Mars’ surface that are relevant to rover and lander safety