24 research outputs found
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The Missing Craters and Basin Rings Beneath the Lunar Maria
Evidence for a population of craters buried beneath the nearside lunar maria has been found in the gravity data returned from the Gravity Recovery and Interior Laboratory mission. Although the total population of buried and visible craters within maria is comparable to the crater population in non-mare regions at large diameters, a deficit was observed for craters less than ∼90 km in diameter. This deficit is surprising because the data can resolve craters down to 10 km in diameter. Similarly, the Imbrium basin only has a partially exposed ring system, with individual ring widths of up to ∼100 km, but where those rings should be buried beneath the mare surface, we find the gravitational signature mostly non-existent. In this study, we test a series of mechanisms and scenarios that may explain the observed deficits in the buried crater populations by comparing localized Bouguer gravity power spectra and recovered crater size-frequency distributions from models of a simulated volcanically flooded cratered surface to the observed data. Our results indicate that the observed crater deficit and missing rings of Imbrium are best explained by a smoothing of the pre-mare surface. We represent this smoothing as a diffusional process, as might occur with thermomechanical erosion during the earliest stages of the mare eruptions. The removal of the missing craters and Imbrium rings was a massive and unprecedented event that sheds light on the early evolution of the mare region, possibly supporting high temperature voluminous floods of lava early during mare formation. © 2023. American Geophysical Union. All Rights Reserved.6 month embargo; first published 13 December 2023This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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A South Pole-Aitken impact origin of the lunar compositional asymmetry
The formation of the largest and most ancient lunar impact basin, South Pole-Aitken (SPA), was a defining event in the Moon's evolution. Using numerical simulations, we show that widespread mantle heating from the SPA impact can catalyze the formation of the long-lived nearside-farside lunar asymmetry in incompatible elements and surface volcanic deposits, which has remained unexplained since its discovery in the Apollo era. The impact-induced heat drives hemisphere-scale mantle convection, which would sequester Th- and Ti-rich lunar magma ocean cumulates in the nearside hemisphere within a few hundred million years if they remain immediately beneath the lunar crust at the time of the SPA impact. A warm initial upper mantle facilitates generation of a pronounced compositional asymmetry consistent with the observed lunar asymmetry. © 2022 The Authors.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]