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Saponite Bearing Material Excavated During the Formation of a Recent 25‐m‐Diameter Impact Crater in Southeastern Arabia Terra on Mars.

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Title: Saponite Bearing Material Excavated During the Formation of a Recent 25‐m‐Diameter Impact Crater in Southeastern Arabia Terra on Mars.
Authors: Arvidson, R. E.1 (AUTHOR) arvidson@wunder.wustl.edu, Catalano, J. G.1 (AUTHOR), Christian, J. R.1 (AUTHOR), Fraeman, A. A.2 (AUTHOR), Hughes, M. N.1 (AUTHOR), Knight, A. L.1 (AUTHOR), McKinnon, W. B.1 (AUTHOR), Morris, R. V.3 (AUTHOR), Murchie, S. L.4 (AUTHOR), O'Sullivan, J. A.5 (AUTHOR), Politte, D. V.1 (AUTHOR), Seelos, F.4 (AUTHOR), Wolff, M. J.6 (AUTHOR), Zhou, F.1 (AUTHOR)
Source: Journal of Geophysical Research. Planets. May2026, Vol. 131 Issue 5, p1-28. 28p.
Subject Terms: *Spectrum analysis, Impact craters, Saponite, Martian craters, Analytical geochemistry, Deoxygenation
Abstract: Mars Reconnaissance Orbiter's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), Context Imager (CTX), and High Resolution Imaging Science Experiment observations were analyzed for a 25‐m‐wide impact crater and associated ejecta deposits located in the dust‐covered Arabia Terra region. The crater formed within plains nestled inside the degraded rim of a Noachian‐aged crater. Temporal image coverage constrains the impact event to between the years 2010–2012. The crater morphology and proximal and far‐ranging ejecta deposits, together with lunar analogs and impact simulations, collectively indicate a hypervelocity impact from an incoming heliocentric bolide. A CRISM along‐track oversampled observation (0.45–3.75 μm) covering the crater and its ejecta deposits was processed to retrieve surface single‐scattering albedos and surface temperatures, followed by regularization of overlapping 18‐m‐wide pixels to a projected spatial resolution of 12 m/pixel. Spatial variations in mapped temperatures show that ejecta emplacement altered the surface thermophysical properties relative to the undisturbed dusty terrain. Results show that the proximal ejecta deposit, excavated from only a few meters in depth, includes magnesium saponite with more Fe2+ than Fe3+ in the octahedral sheet. This discovery provides a rare view into the subsurface of a dusty area and indicates that aqueous alteration is more widespread than previously inferred from surface exposures amenable to mapping via orbital spectroscopy. It is also consistent with saponite formation in an anoxic environment without complete oxidation. Plain Language Summary: Impact craters are "nature's drills," exposing subsurface rocks both within the craters and across the surrounding ejecta deposits. In this study, we examine a newly formed 25‐m‐wide impact crater in the southeastern corner of Mars's Arabia Terra to identify and map the smectite clay mineral magnesium saponite within its ejecta deposits. Saponite forms only in the presence of water, and in this case, the material was excavated from just a few meters beneath an otherwise dust‐covered surface. Our analysis was made possible by coordinated observations from the Mars Reconnaissance Orbiter, including high‐resolution spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars. These data were acquired in an along‐track oversampled mode, enhancing the effective spatial resolution and enabling a detailed spectral study of this small crater and its ejecta deposits. Key Points: Ejecta deposits were analyzed for a newly formed 25‐m‐wide impact crater in the dust‐covered Arabia Terra region of MarsMagnesium saponite was excavated, offering a rare glimpse into shallow subsurface aqueous alteration beneath the regional dust mantleIron contained in the saponite octahedral sheet is predominantly Fe2+, consistent with its formation under anoxic conditions [ABSTRACT FROM AUTHOR]
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Abstract:Mars Reconnaissance Orbiter's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), Context Imager (CTX), and High Resolution Imaging Science Experiment observations were analyzed for a 25‐m‐wide impact crater and associated ejecta deposits located in the dust‐covered Arabia Terra region. The crater formed within plains nestled inside the degraded rim of a Noachian‐aged crater. Temporal image coverage constrains the impact event to between the years 2010–2012. The crater morphology and proximal and far‐ranging ejecta deposits, together with lunar analogs and impact simulations, collectively indicate a hypervelocity impact from an incoming heliocentric bolide. A CRISM along‐track oversampled observation (0.45–3.75 μm) covering the crater and its ejecta deposits was processed to retrieve surface single‐scattering albedos and surface temperatures, followed by regularization of overlapping 18‐m‐wide pixels to a projected spatial resolution of 12 m/pixel. Spatial variations in mapped temperatures show that ejecta emplacement altered the surface thermophysical properties relative to the undisturbed dusty terrain. Results show that the proximal ejecta deposit, excavated from only a few meters in depth, includes magnesium saponite with more Fe2+ than Fe3+ in the octahedral sheet. This discovery provides a rare view into the subsurface of a dusty area and indicates that aqueous alteration is more widespread than previously inferred from surface exposures amenable to mapping via orbital spectroscopy. It is also consistent with saponite formation in an anoxic environment without complete oxidation. Plain Language Summary: Impact craters are "nature's drills," exposing subsurface rocks both within the craters and across the surrounding ejecta deposits. In this study, we examine a newly formed 25‐m‐wide impact crater in the southeastern corner of Mars's Arabia Terra to identify and map the smectite clay mineral magnesium saponite within its ejecta deposits. Saponite forms only in the presence of water, and in this case, the material was excavated from just a few meters beneath an otherwise dust‐covered surface. Our analysis was made possible by coordinated observations from the Mars Reconnaissance Orbiter, including high‐resolution spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars. These data were acquired in an along‐track oversampled mode, enhancing the effective spatial resolution and enabling a detailed spectral study of this small crater and its ejecta deposits. Key Points: Ejecta deposits were analyzed for a newly formed 25‐m‐wide impact crater in the dust‐covered Arabia Terra region of MarsMagnesium saponite was excavated, offering a rare glimpse into shallow subsurface aqueous alteration beneath the regional dust mantleIron contained in the saponite octahedral sheet is predominantly Fe2+, consistent with its formation under anoxic conditions [ABSTRACT FROM AUTHOR]
ISSN:21699097
DOI:10.1029/2025JE009535