Newly formed craters on Mars were first discovered by Malin et al. (2006), using an imaging campaign with the Mars Global Surveyor Mars Orbiter Camera (MOC) to find 20 new impacts by manually comparing the repeat images of the same areas. These techniques have been continued with the Context Camera (CTX) on the Mars Reconnaissance Orbiter for the last ∼15 years (Daubar et al., 2013 and this work). These new craters have provided valuable new information about Mars, revealing shallow subsurface ice (
Terminal lakes are important archives of continental hydroclimate and in some cases contain important economic resources. Here we present an ~3.6 Myr lacustrine carbonate carbon and oxygen stable isotope record from a Great Basin continental drill core. We pair these measurements with bulk lithium concentrations to reveal a relationship between past climate and lithium enrichment in authigenic lacustrine clays. Further, we explore the possible effects of changing seasonality on the isotope record through the use of paired air mass trajectories and modern isotope data. Our findings show the evolution of the basin's moisture balance over million-year timescales, which we attribute to variations in precipitation seasonality as well as fluctuations in the amount of evaporation associated with changes in atmospheric moisture convergence and divergence. We observe a positive correlation between the oxygen isotope values of the lake carbonate and the bulk sediment lithium concentrations, which we argue is indicative of evapoconcentration of the lake environment and subsequent enrichment of the authigenic clays. Our results suggest a link between past hydroclimate changes and the formation of lithium rich authigenic clays feeding high lithium concentrations in this modern brine aquifer system.
<p>An increasing number of newly formed impact craters on Mars have been detected in the last 15 years. These small craters are normally identified via dark spots in lower resolution images that formed during the impact process, presumably through the removal or disturbance of bright surface material [1]. Later higher resolution images revealed single craters or crater clusters, which form when impactors fragment in the atmosphere, within those halos [1,2]. Due to this detection method, most of the new impact sites found are in dusty regions, which imposes an observational bias [3]. Newly formed clusters consist of two to thousands of individual craters and can be tightly clustered or spread out over hundreds of meters [2]. Since the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed on Mars in 2018 [4], the search for newly formed impact craters has become even more important, because identifying impacts in seismic signals could provide further constraints on both the atmospheric and solid-body effects of impact cratering process on Mars, as well as help place further constraints on the properties of the uppermost layer of the crust. As one of InSight&#8217;s mission goals is to estimate the current impact rate on Mars, the seismic detection of impacts is also crucial [4].</p> <p>The aim of this new study is to describe the properties of the complete catalog of known newly formed craters on Mars and examine correlations between different crater cluster properties. We investigated 559 crater clusters and 493 single craters detected between 2008 and 2020 using 25 cm/px HiRISE images. The locations and diameters were noted for each single crater, as well as for every individual crater within a cluster down to 1 m diameter. This was done using ArcMap (ArcGIS) software with the three-point method of the CraterTools add-in [5]. We describe the cluster characteristics, such as the number of craters within a cluster, largest crater in a cluster, cluster effective diameter, cluster dispersion, elevation of the impact sites, and the variation in sizes of craters within a cluster.</p> <p>More than half of the new impact sites form as clusters. We did not find any differences between the spatial distribution of single and crater clusters across Mars. The mapped crater clusters from this study consist of 2 to 2334 individual craters. More than half of all clusters (58%) consist of 10 craters or less. Crater clusters containing more than 100 craters are rare. With regard to the sizes of craters within crater clusters, we found that for highly populated clusters, the majority of craters are very small, and clusters with few craters have a tendency for craters that are more equal in size. Clusters having large effective diameters contain more equally sized craters. Our results show the full range of parameter spaces that are possible for cluster properties, which can help validate theoretical atmospheric fragmentation models.</p> <p><strong>References:</strong></p> <p>[1] Malin M. C. et al. (2006) Science, 314, 1573-1577.</p> <p>[2] Daubar I. J. et al. (2019) JGR, 124, 958-969.</p> <p>[3] Daubar I. J. et al. (2013) Icarus, 225, 506-516.</p> <p>[4] Banerdt B. W. et al. (2020) Nature, 13, 183-189.</p> <p>[5] Kneissl T. et al. (2011) Planet. Space Sci., 59, 1243-1254.</p>
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