Crater statistics and Geological history of Oxia Planum, landing site for ExoMars2022

Oxia Planum is the chosen landing site for the ExoMars2022 rover that launches between August and October 2022. The nominal mission is one Mars year, and the goal is to look for signs of past or present life on Mars. The rover has many on board instruments, among them a drill that can extract samples at a maximum depth of two meters. The samples can be studied at an onboard analytical laboratory to determine the mineralogy and chemistry. By analyzing CTX (6 m/pixel), HiRISE (25 cm/pixel) and THEMIS (100 m/pixel) images, the Oxia Planum landing ellipse was mapped and crater counting was performed, and ages was obtained by the Craterstats 2 software. On the basis of these crater counts, the emplacement history was reconstructed. The landing site area (Oxia Planum) is located near at the transition between the heavily cratered (old) highlands of Mars, and the adjacent lowland plains. Several features, such as incisions in the highlands and possible delta fans, suggest that water has played a role in modifying the terrain. The formation of the dichotomy happened at an early stage, followed by the basement units within the map area. Based on the morphology and crater statistics, I have identified several stages of formation of the dark rough unit, which could be relics of volcanic activity. Using crater statistic results, the oldest identified unit was emplaced at 3.96 Ga. The clay formed at least as early as 3.75 Ga. At some point after this, the region was covered by a unit, for later to be eroded away, leaving the rounded buttes. The dark rough unit formed last, flowing around some of the rounded buttes. The last fluvial activity happened 3.64-3.79 Ga, creating large channels and smaller rivers. Inverted rivers were also formed. Then formed the fan shaped deltas, as a result of the deposition of sediments at the channel mouth. The deltas strongly indicates that a large ocean once covered Oxia Planum, which may also have covered the northern lowlands of Mars. A dark rough unit also formed after this. The here derived timeline indicates several periods of burial and erosion. Lastly, locations that could be of interest for the rover is presented. For best possible preservation of biosignatures, it need to be buried in clay and preferably quickly covered by a dark rough unit. These locations should be close to a delta, since the accumulation and preservation of organic matter here would be the strongest.