Boulder Analysis on the Oxia Planum ExoMars 2022 Rover Landing Site: Scientific and Engineering Perspectives

The Oxia Planum region has been chosen as the landing site for the future ESA ExoMars 2022 rover for both scientific value and engineering safety (Ivanov et al., 2020). The main goal of this work is the identification and measurement of boulders located over different areas of the Oxia Planum landing region to understand the generation/degradation processes that occurred over the studied area. For the boulders manual identification and counting, we use different HiRISE images and we calculate their size-frequency distribution and spatial density. The data are well-fitted with power-law and exponential curves with shallower indices in the Amazonian units, ranging from -4.03 to -4.74 for the power-law fit and from -1.43 to -1.80 for the exponential fit, while steeper indices in the three exhumed Noachian units studied (from -5.20 to -5.57 for the power-law fit and from -1.77 to -2.13 for the exponential fit). As previously studied in the former Oxia Planum landing centre (Pajola et al., 2017), the formation of boulders in this area is related to impact processes: the Amazonian unit is between 2.4 to 48.2 times richer of boulders than the exhumed Noachian units. By comparing these results with other boulder distributions, identified on other Oxia exhumed Noachian locations, we obtain a smaller boulder spatial density. We also compare our results with those derived from other Martian landing sites, finding that, for instance, the new centre location of the ExoMars ellipse is 4.5 times less dangerous than the Pathfinder landing site. The boulder analysis is of fundamental importance from an engineering perspective, returning the safest areas where the ExoMars 2022 rover might land and traverse.