¹Ivy Ettenborough, ¹Anna Szynkiewicz
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116384]
¹Department of Earth and Planetary Sciences, University of Tennessee, 1621 Cumberland Ave., Knoxville, TN 37996, USA
Copyright Elsevier

Secondary sulfate minerals are common throughout the sedimentary deposits of Mount Sharp, located within Gale crater on Mars. However, the source of sulfate (SO42−) and past climatic conditions during their formation are not well understood. Therefore, we investigated the δ34S, δ18O, and δ2H of gypsum veins and other Mg- and Ca- sulfates forming as salt crusts and cement within the shallow sediments of the Rio Puerco watershed in central New Mexico. The δ34S values of vein gypsum and acid-soluble SO42− (cement) varied over the same range (₋33.3 to ₋12.9 ‰ and ₋34.6 to ₋12.1 ‰, respectively), which was similar to the δ34S of bedrock sulfide minerals (₋37.4 to ₋5.9 ‰). This implies that sulfide oxidation is the main source of SO42− in the Rio Puerco aqueous system. The measured δ18O values of SO42− (₋8.9 to +3.1 ‰) as well as δ18O and δ2H values of gypsum hydration water (₋8.9 to +0.6 ‰, and ₋112 to ₋82 ‰, respectively) overlapped with the isotope composition of local meteoric precipitation, suggesting that sulfide oxidation to SO42− and gypsum formation have occurred under semi-arid climate conditions. The isotope results suggest the top-down infiltration of meteoric water leads to leaching of SO42−, Mg+, and Ca2+ from bedrock sulfide weathering followed by abundant formation of Mg- and Ca-sulfates in surface deposits and gypsum veins with depth. Because of spatial and mineralogical similarities in the secondary Mg- and Ca-sulfate mineral occurrences, we hypothesize that chemical weathering of sulfide minerals could have been the main source of SO42− in the aqueous system of Gale crater.

^1,2A. Morbidelli, ³T. Kleine, ⁴F. Nimmo
Earth and Planetary Science Letters 650, 119120 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.119120]
¹Collège de France, CNRS, PSL Univ., Sorbonne Univ., Paris, 75014, France
²Observatoire de la Côte d’Azur, Université Cote d’Azur, CNRS, Laboratoire Lagrange, Boulevard de l’Observatoire, 06304 Cedex 4 Nice, France
³Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁴Dept. Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz CA 95060, USA
Copyright Elsevier

The dominant accretion process leading to the formation of the terrestrial planets of the Solar System is a subject of intense scientific debate. Two radically different scenarios have been proposed. The classic scenario starts from a disk of planetesimals which, by mutual collisions, produce a set of Moon to Mars-mass planetary embryos. After the removal of gas from the disk, the embryos experience mutual giant impacts which, together with the accretion of additional planetesimals, lead to the formation of the terrestrial planets on a timescale of tens of millions of years. In the alternative, pebble accretion scenario, the terrestrial planets grow by accreting sunward-drifting mm-cm sized particles from the outer disk. The planets all form within the lifetime of the disk, with the sole exception of Earth, which undergoes a single post-disk giant impact with Theia (a fifth protoplanet formed by pebble accretion itself) to form the Moon. To distinguish between these two scenarios, we revisit all available constraints: compositional (in terms of nucleosynthetic isotope anomalies and chemical composition), dynamical and chronological. We find that the pebble accretion scenario is unable to match these constraints in a self-consistent manner, unlike the classic scenario.