Impact crater degradation, Oxia Planum, Mars

The main goal of the European Space Agency (ESA) and Roscosmos ExoMars rover mission is to collect samples from the near-subsurface of Mars. The rover will look for any physical or chemical evidence of ancient life in the near subsurface. This map shows the distribution of impact craters at this proposed landing site in Oxia Planum on Mars. The map records 1199 impact craters > 500 m in diameter in a 5.0° × 2.5° region around Oxia Planum. The impact craters are symbolised based on the way different aspects of their morphology have degraded since their formation. The distribution of degradation and burial morphologies of impact craters can be used to determine where burial and erosion processes have occurred. Because the formation of impact craters is well constrained, occurs instantly and with a predictable flux, future studies could use this knowledge and our dataset to constrain when these events occurred

Ancient River Channels in Arabia Terra, Mars

‘Inverted channels’ on Mars are sinuous ridges that represent ancient river systems that were buried, preserved, and then exhumed. Many inverted channels occur in Arabia Terra, one of Mars’ oldest regions (about 3.7 Gyr), but precise information about their morphologies, spatial variation, settings, and associated terrain attributes is missing. Since these channels date from a period when Mars’ environment was very different than today’s, understanding how and when they formed can help us interpret Mars’ ancient fluvial and paleo-climatic history. This thesis presents new results about the morphology, distribution, erosion-styles, and pervasive fracturing of fluvial inverted deposits in Arabia Terra. It reports the results of a regional morphological classification of fluvial ridges and concludes that many were aggradational fluvial systems, formed within the downstream portions of valley networks, or other basins and topographical lows. These locations are analogous to ‘Transfer’ and ‘Depositional’ zones in fluvial systems on Earth. Next, detailed morphostratigraphic mapping (scale 1:2000) of four Mid-Late Noachian martian inverted fluvial systems reveals the presence of long-lived (10⁴ - 10⁶ years) stable fluvial systems, where valley network incision is not preserved. The volume of alluvial material was estimated for each detailed mapping site and extrapolated to the regional survey database. At least 549-1591 km³ of fluvial-alluvial deposits are still preserved in Arabia Terra. This supports the interpretation that Arabia Terra hosted widespread fluvial activity during parts of the Noachian. Finally, extensive networks of indurated veins and infilled fractures, and “pitted channel” types were found to occur in the study area. I interpret these to have formed by groundwater flows, which demonstrate the influence of groundwater on the landscape, after the development of the inverted channel deposits. The study favours the existence of a stable hydrological cycle driven by precipitation in a warmer and wetter climate than seen today on Mars

The geology of the Nawish quadrangle of Ceres: The rim of an ancient basin

Herein we present the geology of the Nawish quadrangle, located in the equatorial region of dwarf planet Ceres, named after one of the most prominent craters of the area. Geologic mapping was based on the image mosaics and digital terrain models derived from Dawn Framing Camera data. Interpretation of geologic units was supported by supplemental data, such as the multi spectral color images from the Framing Camera, and the spectral parameters derived from the Visible and Infrared Spectrometer (VIR) data, as well as Dawn gravity data. There is not a primary feature that dominates the geology of Nawish quadrangle, but rather several terrains overlap, and their relations explain the geology of the area. Crater size frequency distributions show that Nawish quadrangle is dominated by two distinct time domains. The central and eastern part of the quadrangle is topographically elevated, which we define as cratered highlands, and contains the older domain. The western lowlands show two younger domains related to impact craters Kerwan and Dantu, including the Kerwan smooth material and Dantu ejecta. This variation of elevation within the Nawish quadrangle is more than the half of the global topographic altitude variation on Ceres. Analysis and comparison of the topography of the Nawish quadrangle with surrounding ones shows that this quadrangle is dominated by the topography of the rim sector of a large, >800 km ancient impact basin, most likely the putative Vendimia Planitia. The Nawish quadrangle thus represents a sector of Ceres which has not undergone large-scale, post-Kerwan, intermediate age-events, but rather represents a place on Ceres where a well-preserved relict of old cerean crust can be studied, together with ejecta from more recent impact events