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Impact craters that form on every planetary body provide a record of planetary surface evolution. On heavily cratered surfaces, new craters that form often overlap antecedent craters, but it is unknown how the presence of antecedent craters alters impact crater formation. We use overlapping complex crater pairs on the lunar surface to constrain this process and find that crater rims are systematically lower where they intersect antecedent crater basins. The rim morphology of the new crater depends on the depth of the antecedent crater and the degree of overlap between the craters. Our observations suggest that new craters do not always obliterate underlying topography and that transient rim collapse is altered by antecedent topography. This study represents the first formalization of the influence of antecedent topography on rim morphology and provides process insight into a common impact scenario relevant to the geology of potential Artemis landing sites. Craters form on the surface of many planetary bodies and help us to understand many qualities of the surface including, critically, the age of the surface. On older surfaces with many craters, new craters that form often overlap and partially destroy older craters, though we don't know if or how the presence of the older crater changes the processes that create the new crater. Looking at large Lunar craters, we can determine that the presence of an older crater causes the rim of the new crater to be asymmetric: lower where it forms within the older crater basin. The difference in height between the new crater rim inside and outside the old crater depends on both the depth of the older crater, and where the new crater forms relative to the older crater. From this we can interpret that the presence of the older crater alters the way the new crater forms, leading to an uneven collapse of early rim materials. Overlapping complex crater rims are lower inside the antecedent basins compared to outsideDeeper antecedent basins and more significant crater overlap tend to create larger differences in rim heightChanges in the impact crater formation process, mainly during transient rim collapse, influence the shape of overlapping crater rims Overlapping complex crater rims are lower inside the antecedent basins compared to outside Deeper antecedent basins and more significant crater overlap tend to create larger differences in rim height Changes in the impact crater formation process, mainly during transient rim collapse, influence the shape of overlapping crater rims

The Eridania Basin system, located in the martian southern highlands, may have hosted long‐lived lacustrine hydrothermalism. Despite its multi‐basin scale and suggested longevity that should pervasively alter the landscape, evidence for consistent compositional signatures of lacustrine hydrothermalism across varying spatial scales is poorly known. Here we synthesize orbital data sets (derived from the Gamma Ray Spectrometer, GRS; Thermal Emission Spectrometer, TES; and Compact Reconnaissance Imaging Spectrometer for Mars, CRISM) to characterize the composition of Eridania's landscape from regional to outcrop scales. The bulk geochemistry representing decimeter depths is broadly on par with mafic igneous compositions seen elsewhere on Mars. The landscape‐scale mineralogy of Eridania suggests a compositional distinction between Eridania's northernmost basin and the remaining basins. Meanwhile, chloride mapping and analyses of amorphous silica and acid‐altered clay phases at the outcrop scale both show that mineralogical evidence for hydrothermal alteration and putative lacustrine activity is broadly limited to the northernmost basin, and that most other amorphous silica in Eridania is consistent with low‐to‐minimal water/rock weathering. This suggests either limited regional hydrothermalism or extensive mafic resurfacing occurred in Eridania, the latter of which is consistent with previous studies. Our findings collectively suggest that Eridania underwent local crystal hydrothermal alteration, perhaps confined to the northernmost basin, while much of the remainder of the Eridania's basins either experienced low‐temperature weathering or extensive resurfacing to at least meter scale depths by later volcanism. This supports prior inferences of spatially and temporally limited surface hydrology on Mars and extensive volcanic resurfacing of basins, as in the Gusev Crater. Eridania Basin is a system of semi‐circular depressions in the Southern Highlands of Mars that is suggested to have once held a vast lake. This lake is inferred to have hosted hydrothermal activity for hundreds of millions of years. Such a long‐lived system should have led to mineralogical and geochemical signatures on large regional scales. Analysis of regional, local, and outcrop‐scale data—using orbital gamma ray, thermal, and near infrared spectra, respectively—indicates that the geochemistry of Eridania is consistent with relatively unaltered volcanic material, while mineralogical data suggest that aqueous activity and weathering may have been confined to a smaller region than previously thought. Materials indicating hydrothermal activities, such as chlorides and altered clays, are confined to the northernmost part of the basin system, while silica formed under low temperatures is found in the southern regions of Eridania. We propose that any hydrothermal activity in a lake setting was limited to the northernmost basin of Eridania, and that it may have been less long‐lived than previously anticipated. Evidence for ancient lakes may have also been obscured by volcanism. Across regional to outcrop scales, Eridania Basin landscapes present compositions consistent with mafic resurfacingEridania's northern basin experienced a distinct, possibly longer‐lived aqueous alteration than the southern basinsA smaller watershed for Eridania, or a volcaniclastic cap, may help explain the limited evidence for lacustrine alteration in the Gusev Crater Across regional to outcrop scales, Eridania Basin landscapes present compositions consistent with mafic resurfacing Eridania's northern basin experienced a distinct, possibly longer‐lived aqueous alteration than the southern basins A smaller watershed for Eridania, or a volcaniclastic cap, may help explain the limited evidence for lacustrine alteration in the Gusev Crater

The Greater Thaumasia region consists of three chemical provinces that include Syria, Solis, and Thaumasia Planae, the Corprates Rise, part of the Thaumasia Highlands, and the transition zone northwest of the Argyre basin. Chemical signatures obtained from the Mars Odyssey Gamma Ray Spectrometer suggest low abundances of K and Th to the west, with low H abundances and high Si abundances to the east, relative to the bulk Martian crust at midlatitudes. These observations are confirmed and quantified with a modified box and whisker analysis that simultaneously captures the degree of deviation and significance of the regionally anomalous chemistry. Motivated by regionally unique chemistry, as well as its diverse geological history, we characterize Greater Thaumasia in terms of chemistry, mineralogy, and mapped geology to determine how such complementary data record the evolution of this region. Our observations are inconsistent with a proposed salt‐lubricated landslide origin, particularly given the lack of chemical or mineralogical signatures to support near‐surface salt deposits that should arise over geological timescales. Our observations instead support magmatic processes, such as mantle evolution over geological time, which may impart the Si‐enriched signature of the eastern portion of Greater Thaumasia as well as the K and Th depletion of the southeastern flank of Syria Planum. While the observed trend of decreasing K and Th from Noachian to Hesperian lavas is inconsistent with previous models of Martian mantle evolution, we see an increase in Ca content at the Noachian‐Hesperian boundary, consistent with predictions from thermodynamic modeling. The Greater Thaumasia region is chemically distinct from average crust and shows changes in K, Th, and H2O associated with changes in ageFormation of Thaumasia Planum in a salt‐lubricated landslide is not supported, no evidence for regional aqueous alteration or salt diapirsChemical trends partially consistent with existing models for mantle evolution, this may reflect regional igneous or aqueous processes

The Martian critical zone, especially its soil‐atmosphere interface, may host an active halogen cycle affecting habitability, as inferred from halogen trends observed in situ at Gusev and Meridiani, along with oxychlorine species detected in situ. However, the sinks and sources of the Martian halogen cycle remain poorly constrained, especially for Br, including the broader geographic significance of halogen volatility in soils. Here, we statistically analyze Br, Cl, and S distribution and associated cations in the soils of Gale Crater and compare the results with soils of Gusev Crater and Meridiani Planum. We further place the overall in situ soil trends in the framework of terrestrial natural evaporative halides and Mars‐analog evaporative experiments. We observe three lines of evidence that support preferential volatilization of Br versus Cl and S in Martian soils: (a) Unlike Cl and S, Br abundance decreases from subsurface to surface. (b) Br and Cl abundances correlate strongly at the relatively dust‐free and freshly exposed surface of the active Bagnold dunes, but Br‐Cl correlations weaken and Br concentrations decrease in less mobile surface soil. (c) Laboratory experiments show preferential Br loss over Cl and S under ultraviolet (UV) irradiation, consistent with the observed Br loss relative to Cl in Martian soil samples. Overall, these findings generally suggest that soil serves as a source for volatilized halogens. Specifically, soil‐atmosphere multiphase reaction pathways constitute a crucial component missing from purely gas‐phase photochemical models of the halogen cycle. Soil records the complexity of processes at the Martian surface and is a key component of the critical zone that sustains interactions between the atmosphere and crust of Mars. Previous in situ explorations of the Mars landing site at Gusev Crater and Meridiani Planum showed that Br demonstrates a preferential loss into the atmosphere among volatile elements Br, Cl, and S in the topsoil samples. Here, we examine and demonstrate that Br volatilization observed at Gusev and Meridiani is also present in Gale Crater soils, indicating ubiquitous volatilization via soil‐atmosphere processes on Mars. We further place the in situ soil trends of Martian Br and Cl in the framework of natural evaporative halides on Earth and Mars‐analog evaporative experiments. The framework we construct shows that the Br and Cl variations in Mars soils are consistent with halide salts mixed with halogen ‐low or ‐free components (e.g., basaltic phases) and subsequent volatilization of Br over Cl. Our findings indicate a chemically active top layer on the Martian surface, challenging the preservation of any biological matter even in deeper soil horizons. Br loss relative to Cl and S from soils at Gale, Gusev, and Meridiani suggests ubiquitous Br volatilization via soil‐atmosphere processesBr and Cl vary in Mars soils from halide salts mixed with halogen ‐low or ‐free components and preferential volatilization of Br over ClSoil‐atmosphere multiphase reaction pathways are a key component missing from purely gas‐phase photochemical models of the halogen cycle Br loss relative to Cl and S from soils at Gale, Gusev, and Meridiani suggests ubiquitous Br volatilization via soil‐atmosphere processes Br and Cl vary in Mars soils from halide salts mixed with halogen ‐low or ‐free components and preferential volatilization of Br over Cl Soil‐atmosphere multiphase reaction pathways are a key component missing from purely gas‐phase photochemical models of the halogen cycle