¹Alison R. Santos, ²Mikhail Yu. Zolotov, ¹Martha S. Gilmore, ³Craig Motil, ³Kyle Phillips, ⁴Valerie Tu
Journal of Geophysical Research: Planets, 131, e2025JE009457
Open Access Link to Article [DOI: 10.1029/2025JE009457]
¹Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
³NASA Glenn Research Center, Cleveland, OH, USA
⁴Texas State University, Amentum JETSII Contract at NASA Johnson Space Center, Houston, TX, USA

Published by arrangement with John Wiley & Sons

Investigations of the venusian surface suggest chemical alteration (weathering) of rocks in contact with a hot, high-pressure atmosphere. This alteration was anticipated based on mineral stability considerations and has been supported by laboratory experiments conducted under Venus surface conditions. Here, we exposed iron-bearing samples (oxides, sulfides, iron-metal) to a simulated venusian environment (93 bars, 733 K, and a 9-gas mixture) for 60 days at the NASA Glenn Extreme Environments Rig (GEER). Iron metal, pyrrhotite, and troilite were altered to pyrite and magnetite. Some magnetite formed at the expense of hematite. Neither magnetite nor pyrite was altered. Measured concentrations of CO₂, SO₂, and OCS during the run suggest rapid OCS-SO₂ equilibration and drawdown of sulfur-bearing gases through reactions with the vessel and sample materials. The observed alteration assemblages and the gas composition in the vessel suggest experimental gas-phase fugacities (fO₂, fS₂, fSO₂, fOCS, fCO, fCO₂) in the vicinity of the magnetite-pyrite phase boundary and within the uncertainty of the magnetite-hematite boundary. Fugacities (log₁₀fO₂ of −22.5 to −21.5; log₁₀fS₂ of −5.4 to −4.6) and mineralogy in the Fe-O-S system are consistent with observation-based models for the near-surface conditions on Venus. This experiment supports both gas-phase chemical equilibrium and equilibration between gases and minerals in the Fe-O-S system on the surface of Venus, as proposed six decades ago.

¹Sang Woo Kim, ^1,2Kyeong Ja Kim
Journal of Geophysical Research: Planets, 131, e2026JE009892 Link to Article [DOI: 10.1029/2026JE009892]
¹Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, Republic of Korea
²University of Science and Technology (UST), Daejeon, Republic of Korea

Published by arrangement with John Wiley & Sons

The Dynamic Albedo of Neutrons (DAN) instrument on the Curiosity rover has mapped subsurface hydrogen along an extensively analyzed 27-km segment of its traverse in Gale Crater, revealing water-equivalent hydrogen (WEH) of 1–6 wt%. Neutron die-away measurements alone, however, cannot determine whether this hydrogen resides in adsorbed water, hydrated minerals, or ice. Here we use Geant4 Monte Carlo simulations (1⁢08$$ source neutrons per configuration) to quantify what a pulsed neutron generator with time-resolved prompt gamma-ray neutron activation analysis (PGNAA) adds to neutron-only measurements, for eight representative Martian regolith compositions under idealized detection. The model reproduces the established first-order sensitivity of the epithermal die-away constant to WEH (𝜏epi =57$$–77 𝜇$$s for WEH =15$$–1 wt%; power-law 𝑅2 =0.87$$)—an internal benchmark. The central experiment holds WEH fixed at 3 wt% across six compositionally distinct host endmembers: 𝜏epi$$ compresses to 61.4–67.0 µs, whereas simultaneously measured PGNAA ratios (Fe/Cl, apparent Si/Ca, Fe/H) provide complementary elemental constraints: for every host pair, at least one of the three ratios gives ≥7.6⁢𝜎$$ separation under the present idealized uncertainties. In a native-WEH benchmark, 27 of 28 pairs are separated at >5𝜎$$ by 𝜏epi$$ alone, driven largely by the broad assigned WEH range. Fe (Si) capture-to-inelastic ratios decrease monotonically by 36% (44%) for a 20 cm dry overburden, giving model-dependent depth information. These results define the information content of pulse-synchronized neutron–gamma-ray packages and modeling priorities for future Mars, Titan, and lunar volatile payloads.

¹Scott A. Sandford (>10)
Meteoritics & Planetary Science (in Press)
Open Access Link to Article [DOI: 10.1111/maps.70221]
¹NASA Ames Research Center, Moffett Field, California, USA

Published by arrangement with John Wiley & Sons

Regolith samples from the carbonaceous asteroid Bennu were stowed and delivered to Earth in the OSIRIS-REx spacecraft’s Sample Return Capsule (SRC). We applied multiple analytical techniques to study the components of the post-flight SRC, with a focus on assessing the conditions and any contaminants to which the Bennu samples were exposed. Examination of the passive temperature sensors placed inside the SRC, in combination with thermal modeling results, indicate that the samples were not heated above the 75°C limit imposed by OSIRIS-REx mission requirements. The sample canister air filter was found to contain Bennu particulates that had escaped from the sample collector, as well as a range of contaminants likely associated with the original filter component materials. No indications of terrestrial soils were found in the filter. Isotopic analyses of organic compounds and noble gases trapped in the filter show values consistent with terrestrial origins, and there are no indications of trapped asteroidal volatiles. Organic compounds found in the flight filter that were not present in a non-flight control filter include aromatic hydrocarbons, alkylated aromatic hydrocarbons, phenolic-related compounds, aliphatic hydrocarbons, and alcohols. The abundances of these organic compounds typically decrease from outer layers of the filter toward the canister interior, suggesting that they are external contaminants. We conclude that the majority of these organic compounds are chemical byproducts associated with outgassing of the SRC heatshield and backshell following the ablation portion of SRC atmospheric entry. Overall, our findings show that the OSIRIS-REx SRC performed excellently in containerizing the asteroidal samples obtained at Bennu, delivering them safely to the ground at the UTTR, and preventing most, though perhaps not all, external contaminants from reaching them. We discuss lessons learned from the flight and recovery of the OSIRIS-REx SRC that can benefit future sample return missions.