We propose that the observed enrichment of sulfur at the surface of Mercury (up to 4 wt.%) is the product of silicate sulfidation reactions with a S-rich reduced volcanogenic gas phase. Here, we present new experiments on the sulfidation behavior of olivine, diopside, and anorthite. We investigate these reaction products, and those of sulfidized glasses with Mercury compositions previously reported, by mid-IR reflectance spectroscopy. We investigate both the reacted bulk materials as powders, as well as cross-sections of the reaction products by in-situ micro-IR spectroscopy. The mid-IR spectra confirm the presence of predicted reaction products including quartz. The mid-IR reflectance of sulfide reaction products, such as CaS (oldhamite) or MgS (niningerite), is insufficient to be observed in the complex run products. However, the ESA/JAXA BepiColombo mission to Mercury will be able to test our hypothesis by investigating correlated abundances of sulfides with other reaction products such as quartz.

The lithosphere of the Moon has been deformed by tectonic processes for at least 4 billion years, resulting in a variety of tectonic surface features. Extensional large lunar graben formed during an early phase of net thermal expansion before 3.6 Ga. With the emplacement of mare basalts at ~3.9 – 4.0 Ga, faulting and folding of the mare basalts initiated, and wrinkle ridges formed. Lunar wrinkle ridges exclusively occur within the lunar maria and are thought to be the result of superisostatic loading by dense mare basalts. Since 3.6 Ga, the Moon is in a thermal state of net contraction, which led to the global formation of small lobate thrust faults called lobate scarps. Hence, lunar tectonism recorded changes in the global and regional stress fields and is, therefore, an important archive for the thermal evolution of the Moon. Here, we mapped tectonic features in the non-mascon basin Mare Tranquillitatis and classified these features according to their respective erosional states. This classification aims to give new insights into the timing of lunar tectonism and the associated stress fields. We found a wide time range of tectonic activity, ranging from ancient to recent (3.8 Ga to < 50 Ma). Early wrinkle ridge formation seems to be closely related to subsidence and flexure. For the recent and ongoing growth of wrinkle ridges and lobate scarps, global contraction with a combination of recession stresses, diurnal tidal stresses, as well as with a combination of SPA ejecta loading and true polar wander are likely.

In December 2020, Chang’e-5 returned samples from mare basalt unit Em4/P58 in northern Oceanus Procellarum. With an absolute model age of 1.21-1.53 Ga (Hiesinger et al. 2003; Qian et al., 2018, 2021a). Elevation analysis of the interior of Rima Sharp and Mairan, plus geomorphological observations suggest lava backfilling of Rima Sharp with younger lava from Rima Mairan. Analysis of the magnetic field at the surface also shows that the younger lava from the southern Mairan vents, which covered the southeastern part of Em4/P58 is unmagnetized. Our new magnetic anomaly analysis shows that Em4/P58 unit can be divided into magnetized (northwest) and unmagnetized (southeast) parts. The comprehensive analysis of magnetic anomaly and topography shows that lava from southern rille is likely to have reached the Chang’e-5 landing site. Samples returned by Chang’e-5 will help constrain the source of lava flow and the evolution of the lunar magnetic field over time.

Ceres’ regolith contains water ice that has receded in response to insolation-driven sublimation. Specially targeted, high spatial-resolution measurements of hydrogen by Dawn’s Gamma Ray and Neutron Detector reveal elevated hydrogen concentrations in and around Occator, a young, 90-km diameter, complex crater located at 19.82N where near-surface ice is not expected. The excess hydrogen is explained by impact excavation of water-rich outer crustal materials and their emplacement in the crater floor and ejecta blanket. This is supported by thermophysical models that show water ice could survive at sub-meter depths, given Occator’s relatively young age (~20 Myr). We hypothesize that the regolith can be replenished with ice from large impacts and that this process partially controls the distribution and depth of near surface ice. This is supported by results from Occator and similarities in the global distribution of hydrogen and the pattern of large craters (20-100 km diameter).