Michael Joseph Poston

This study examines lunar regolith space weathering as a function of wavelength, terrain type, and latitude using multiple datasets to quantify global and regional trends in surface reflectance and emission. Distinguishing space-weathering effects from bulk compositional controls is essential for interpreting spatial spectral variability and for identifying anomalous surface units. A statistically significant decrease in weathering with increasing latitude is observed in mare regions at all wavelengths analyzed, although the strength of the trend varies with wavelength. The strongest correlation occurs in the far-ultraviolet, consistent with its high sensitivity to space-weathering products such as submicroscopic iron. In the maria, the latitudinal dependence is well described by an equator-anchored cosine function, supporting a solar-zenith-controlled weathering process. Highlands terrains also exhibit statistically significant latitude-dependent behavior in ultraviolet and near-infrared observations, but the pattern is less monotonic and includes structured spatial variability, indicating a more complex interplay among weathering state, composition, and local geologic context. These results show that latitude-dependent space-weathering gradients are globally important but are also modulated regionally, including by longitude. Such gradients may bias spectral interpretations of regolith composition, particularly when applying commonly used compositional algorithms across terrains or spatial scales without accounting for maturity effects. Although terrain-specific approaches for maria and highlands have been proposed, the implications of latitude-dependent weathering have not yet been fully incorporated into compositional modeling or reconciled with interpretations based on optical maturity.

Building on our previous studies of the far‐ultraviolet (FUV) reflectance of Apollo soil 10084 and lunar soil simulants JSC‐1A and LMS‐1 (Gimar et al., 2022, https://doi.org/10.1029/2022je007508 ; Raut et al., 2018, https://doi.org/10.1029/2018je005567 ), we present new FUV results for Apollo soils 68501 and 71061. Heavily weathered soils (68501, 10084)–enriched in submicroscopic Fe, agglutinates, and sub‐micron scale roughness as revealed by our electron microscopy investigations–are darker in the FUV and predominantly backscatter incident light. In contrast, the relatively less weathered subsurface 71061 soil is approximately twice as bright, exhibits forward scattering, and presents a steeper blue spectral slope between 130 and 160 nm compared to the weathered soils. Differences in either primary composition or mineralogy appear to have little to no effect on the FUV albedo or scattering behavior of these soils since the reflectance of high‐Ti mare 10084 and low‐Ti highland 68501 are nearly indistinguishable within error. Further investigation of additional Apollo‐era soils across various maturity indices is needed to fully characterize the influence of space weathering on lunar soil FUV spectrophotometric response.

The Peregrine Ion Trap Mass Spectrometer (PITMS) was a mass spectrometer designed to measure lunar gases. PITMS flew on the first flight of Astrobotic’s Peregrine lander via the Commercial Lunar Payload Services (CLPS) program in 2024 January. After launch, the lander suffered a propulsion system anomaly that prevented the mission from reaching the Moon, but PITMS collected 80 high-quality spectra while in cislunar space. PITMS observed abundant outgassing products from the Peregrine lander, including water, MON-25 oxidizer from the propulsion system leak, and traces of combustion products. PITMS data help constrain the nature of the propulsion system failure: oxidizer molecular ratios show that the leak released molecules rapidly enough for them to fully dissociate, and the high observed abundances imply that the oxidizer traveled within the lander surfaces rather than jetting into space. The amount of water offgassed by the spacecraft is substantially more than other planetary spacecraft, so the PITMS results suggest that instruments flying in the CLPS paradigm need to consider lander cleanliness. Though not successful in measuring the native lunar exosphere, the PITMS results showcase the capabilities of a mass spectrometer on board a lunar lander, along with lessons in pragmatism and flexibility that would enable such an instrument to ultimately be successful in the CLPS initiative.

The role played by transient impact-induced endogenous brines in the formation of geomorphic features has been proposed on airless worlds such as Europa, Vesta, and Ceres, as well as on worlds with thin atmospheres such as Mars. After liquefaction, the hypothesized brines flow in a debris-flow-like process, incising curvilinear gullies and constructing lobate deposits within newly formed craters. Here we investigate what parameters (if any) could enable liquid to be transiently present for a sufficient time (∼tens of minutes) under postimpact transient atmospheric pressures (10⁻⁴–10⁻⁵ torr) to form curvilinear gullies and lobate deposits, as have been seen on Vesta and more tentatively Ceres. We report that water likely vacuum-freezes too quickly, while NaCl brine enables flow longevity. We also find that frozen lid formation facilitates longer liquid lifetimes, as with lava in terrestrial lava tubes and model predictions for cryovolcanic flows on Europa. This work provides additional contributions to the growing body of literature that investigates the role of transient brines in sculpting the surfaces of airless worlds.

The Kieffer model is a widely accepted explanation for seasonal modification of the Martian surface by CO₂ ice sublimation and the formation of a “zoo” of intriguing surface features. However, the lack of in situ observations and empirical laboratory measurements of Martian winter conditions hampers model validation and refinement. We present the first experiments to investigate all three main stages of the Kieffer model within a single experiment: (i) CO₂ condensation on a thick layer of Mars regolith simulant; (ii) sublimation of CO₂ ice and plume, spot, and halo formation; and (iii) the resultant formation of surface features. We find that the full Kieffer model is supported on the laboratory scale as (i) CO₂ diffuses into the regolith pore spaces and forms a thin overlying conformal layer of translucent ice. When a buried heater is activated, (ii) a plume and dark spot develop as dust is ejected with pressurized gas, and the falling dust creates a bright halo. During plume activity, (iii) thermal stress cracks form in a network similar in morphology to certain types of spiders, dendritic troughs, furrows, and patterned ground in the Martian high south polar latitudes. These cracks appear to form owing to sublimation of CO₂ within the substrate, instead of surface scouring. We discuss the potential for this process to be an alternative formation mechanism for “cracked” spider-like morphologies on Mars. Leveraging our laboratory observations, we also provide guidance for future laboratory or in situ investigations of the three stages of the Kieffer model.

Nighttime Lyman Alpha Mapping Project (LAMP) observations are used to investigate condensed volatiles at the south polar region of the Moon. This study incorporates LAMP data from the first ∼7 years of the mission and Diviner annual maximum temperatures to search for volatile signatures associated with H₂O, NH₃, and CO₂. Other stable potential species, for example, SO₂ and H₂S, are not identifiable with the ultraviolet ratio‐temperature techniques and are not directly addressed in this study. We confidently detect a ∼20% increase in normalized Off‐band (175–190 nm) to On‐band (148–162 nm) albedo ratios (consistent with condensed surface volatiles) at temperatures below ∼115 K. Elevated normalized ratios extend to temperatures capable of supporting pure aforementioned ices over geologically long time scales. Although ∼115 K is consistent with H₂O lifetimes of ∼1‐Myr, the presence of CO₂ and NH₃ are not uniquely delineated by the data trends with temperature. Future spectral modeling to appropriately identify the composition and abundance of these condensed volatiles remains necessary. Normalized albedo ratios are further analyzed for candidate species via maximum temperatures to inform the likelihood of ice signatures: H₂O (70 K < T ≤ 115 K), NH₃ + H₂O (60 K < T ≤ 70 K), and CO₂ + NH₃ + H₂O (T ≤ 60 K). We compare normalized albedo ratios across seven regions of interest (ROI), including Faustini, Shoemaker, Haworth, Cabeus, Amundsen, Nobile, and an unnamed region. Such comparisons allow for characterization of relative abundances of volatiles across the ROI important for their utilization in future crewed and robotic missions to the Moon.

The ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument aboard the Rosetta mission revolutionized our understanding of cometary material composition. One of Rosetta’s key findings is the complexity of the composition of comet 67P/Churyumov-Gerasimenko. Here, we used ROSINA data to analyze dust particles that were volatilized during a dust event in September 2016 and report the detection of large organosulfur species and an increase in the abundances of sulfurous species previously detected in the coma. Our data support the presence of complex sulfur-bearing organics on the surface of the comet. In addition, we conducted laboratory simulations that show that this material may have formed from chemical reactions that were initiated by the irradiation of mixed ices containing H ₂ S. Our findings highlight the importance of sulfur chemistry in cometary and precometary materials and the possibility of characterizing organosulfur materials in other comets and small icy bodies using the James Webb Space Telescope.