¹Yukari Yamaguchi, ¹Akiko M. Nakamura
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117005]
¹Graduate School of Science, Kobe University, 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan
Copyright Elsevier

Hypervelocity impacts play a key role in material transport among planetary bodies. To investigate how target material properties influence high-velocity ejecta, we conducted impact experiments using aluminum projectiles at velocities of about 7 km s−1, with serpentinite, dolerite, and pyrophyllite as targets. Ejecta were impacted onto polycarbonate plates and analyzed using high-speed imaging and crater measurements. Ejecta velocities ranged from 5 to 13 km s−1, with maximum fragment sizes decreasing from 100 to 7 μm as velocity increased. Ejecta with velocities exceeding twice the particle velocity existed, consistent with previous numerical simulations. No clear differences in size–velocity or ejection angle–velocity relationships were observed among the targets. The largest sizes of high-velocity ejecta in this study may suggest that near the impact point, the material may behave as if it were in a fully cracked state. The axial ratios of the craters, which are considered to reflect those of the ejecta, were approximately 0.6–0.7. Although direct extrapolation to planetary scales is not straightforward, these results provide new experimental constraints on the influence of target properties on high-velocity ejecta production, contributing to a better understanding of material transport between planetary bodies.

^1,2Sergey N. Britvin,¹Oleg S. Vereshchagin,¹Natalia S. Vlasenko,¹Maria G. Krzhizhanovskaya,³Marina A. Ivanova,¹Irina A. Volkova
American Mineralogist 111, 335-344 ink to Article [https://doi.org/10.2138/am-2025-9851]
¹Saint Petersburg State University, Universitetskaya Nab. 7/9, 199034 St. Petersburg, Russia
²Kola Science Center, Russian Academy of Sciences, Fersman Str. 14, 184209 Apatity, Russia
³Vernadsky Institute of Geochemistry of the Russian Academy of Sciences, Kosygin St. 19, Moscow 119991, Russia
Copyright: The Mineralogical Society of America

The enigma of ammonium mineral speciation in the solar system has no proven solution due to the lack of data on the real minerals serving as space ammonium carriers. We herein report on the discovery of the first ammonium mineral in meteoritic substance and show its relevance to compositional and spectral characteristics ascribed to hypothetical ammonium phases in cometary and asteroidal bodies. Chemically distant from previously inferred volatile organics or ammoniated phyllosilicates, the mineral is an aqueous metal-ammonium sulfate related to the picromerite group—a family of so-called Tutton’s salts. Nickeloan boussingaultite, (NH4)2(Mg,Ni)(SO4)2·6H2O, was discovered in Orgueil, a primitive carbonaceous chondrite closely related to (162173) Ryugu and (101955) Bennu, the C-type asteroids. The available spectroscopic, chemical, and mineralogical data signify that natural sulfates related to boussingaultite-nickelboussingaultite series perfectly fit into the role of bound ammonia carriers under conditions of cometary nuclei and carbonaceous asteroids. The potential technogenic contamination of astromaterial samples and the difficulties in electron microprobe determination of ammonium are discussed in the context of recently published reports on the discovery of lunar and asteroidal ammonium-containing minerals.

¹Jiaming Zhu, ¹Bo Wu, ²Zikang Li, ²Yiliang Li
Earth and Planetary Science Letters 680, 119904 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.119904]
¹Planetary Remote Sensing Laboratory, Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
²Department of Earth & Planetary Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong
Copyright Elsevier

The behavior of volatiles is critically important for understanding crustal fluids and the potential existence of a subsurface biosphere on Mars. However, our knowledge of the volatile cycle on Mars is limited by insufficient data from landed rovers and orbiter sensors. Halite salt crusts are widespread in the Qaidam Basin on the northern Tibetan Plateau due to strong evaporation under hyperarid climate conditions. We observed that the halite-dominated salt crust in the desiccated playa area diverts fluids percolating from depth to the surface, leading to the formation of raised polygonal rims enriched in gypsum. We drilled through the salt crust using a hand mill and measured the instantaneous gas concentrations and compositions. Beneath the halite salt crust, significantly higher concentrations of H2O, CO2, and CH4 were detected compared with levels in the atmospheric background and at the polygonal rims. The thickness of the salt crust ranges from approximately 0.3 to 1 m, with halite content primarily between 5 and 30 wt%, and is comparable in scale to the thickness (typically ❤ m) and abundance (10–25 wt%) of chloride deposits on Mars. These results suggest that similar salt crust formation should also be common in Martian crater basins subjected to long-term evaporation under hyperarid conditions. Furthermore, such salt crusts could trap deep volatiles, including potential biogenic gases, which may be detectable by gas spectrometers aboard Mars landers.

¹Claudia A. Trepmann,^1,2Fabian Dellefant,¹Lina Seybold,¹Wolfgang W. Schmahl,¹Elena Sturm,¹Daniel Weidendorfer,^1,3Sandro Jahn,¹Iuliia V. Sleptsova,¹Stuart A. Gilder
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70098]
¹Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany
²Department of Cultural and Ancient Studies, Ludwig-Maximilians-Universität München, Munich, Germany
³Mineralogical State Collection Munich (MSM), SNSB (Bavarian Natural History Collections), Munich, Germany
Published by arrangement with John Wiley & Sons

Calcite is prone to chemical and microstructural modifications, especially after having been strained at high stresses and strain rates, as during hypervelocity impact events. These modifications include precipitation from pore fluid as well as replacement of strained volumes by recrystallization. In calcite aggregates of a metagranite breccia of the Ries Bunte Breccia, shocked calcite is partly replaced by new, undeformed grains. This breccia indicates shock conditions of 10–20 GPa by the presence of planar deformation features in quartz of the metagranite. Shocked calcite shows grain orientation spread (GOS) angles of 3–10° and contains e-, f-, and r– twins, as well as a– and f-type lamellae. In contrast, the new coarse calcite grains, which are hundreds of μm in diameter, have low GOS angles (<1°), and do not contain twins. Calcite aggregates have a chemical zonation (varying Mnⁿ⁺ content), which is independent of new grains, suggestive of fast transformation. We propose that the new grains originate from sites of high crystal-plastic strain and grew by grain boundary migration driven by the reduction in strain energy, replacing previously strained grains at low stresses, that is, static recrystallization. Heating experiments on shocked calcite confirm the strain control on static recrystallization.

¹Brittany A. Cymes,²Katherine D. Burgess,^3,4Noah Jäggi,³André Galli,⁵Herbert Biber,⁵Johannes Brötzner,⁶Paul S. Szabo,⁷Andreas Nenning,⁵Friedrich Aumayr
The Planetary Science Journal 7, 6 Open Access Link to Article [DOI 10.3847/PSJ/ae2657]

¹Amentum, NASA Johnson Space Center, 2101 E. NASA Parkway, Houston, TX 77058, USA
²Materials Science and Technology Division, U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA
³Space Research and Planetary Sciences, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁴Laboratory for Astrophysics and Surface Physics, University of Virginia, 395 McCormick Road, Charlottesville, VA 22904, USA
⁵Institute of Applied Physics, TU Wien, Wiedner Hauptstraße 8-10, 1040, Vienna, Austria
⁶Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720, USA
⁷Institute of Chemical Technologies and Analytics, TU Wien, Getreidemarkt 9, 1060, Vienna, Austria

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Addi Bischoff et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70106]
¹Institut für Planetologie, University of Münster, Münster, Germany
Published by arrangement with John Wiley & Sons

On Tuesday, February 18, 2025, at 18:04:14 local time, residents of Poland observed a bright fireball registered by many Polish fireball stations belonging to the Skytinel Network established a few months before by Mateusz Żmija. Thus, the meteoroid’s orbit, atmospheric trajectory, and the strewn field were calculated, and over 70 fragments with a mass of approximately 3900 g were found near Drelów (Lublin Voivodeship, Poland; The Meteorite Bulletin Database, 2025). The samples were recovered by scientists, private searchers, and dealers, and many samples were offered immediately for collections and scientific research on the international meteorite market. Drelów is the 13th officially registered meteorite fall in Poland and is now officially classified as an L6 ordinary chondrite (S3, W0; The Meteorite Bulletin Database, 2025). Short-lived radionuclides were measured on a small sample shortly after recovery, and the results confirm that the meteorite specimen studied here derived from the bolide fireball event. The equilibrated and recrystallized type 6 character is also supported by the large plagioclase grains (An9-12; with grains >100 μm) and the homogeneous compositions of olivine (Fa24.7±0.4) and low-Ca pyroxene (Fs20.8±0.3). The olivine in Drelów is dominated by grains with planar fractures, but in the Münster samples a significant fraction of olivine shows weak mosaicism, indicating a moderately shocked S4 (C-S4) chondritic rock. Such mosaic olivine grains appear to lack in other fragments of Drelów requiring a S3 (C-S3) classification. Thus, Drelów experienced an equilibrium shock pressure close to the strength that defines the S3/S4 transition, which requires an equilibrium shock pressure of slightly above 20 GPa. The meteorite shows easily visible dark shock veins that cross-cut the bulk rock; the high-pressure phases maskelynite and wadsleyite were detected within or close to the veins. The O isotope data and the bulk chemical composition are consistent with the L-group membership. This is also confirmed by the density and the magnetic susceptibility measurements. The soluble organic compositions of Drelów are consistent with the profiles of unbrecciated L6 chondrites and comparable to Braunschweig (L6), showing molecular characteristics consistent with the complex shock and metamorphic history of the parent rock.

¹Sam Uthup, ¹J. Gregory Shellnutt
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.116985]

¹Department of Earth Science, National Taiwan Normal University, 88 Tingzhou Road Section 4, Taipei 11677, Taiwan
Copyright Elsevier

Venus is a telluric planet with similar size, composition, and mass to that of the Earth. The Venusian crust is mainly divided into lowland (~80%) and highland regions (~10%) based on their surface elevation. The lowland regions are characterized by featureless lava plains, whereas the highlands consist of crustal plateaux, tesserae terrane, and volcanic troughs. The presence of evolved silicic igneous rocks in the highland regions of the Venus has been debated. In this study, phase equilibria modelling using THERMOCALC and the basaltic compositions obtained from the Venera 14 and Vega 2 lander missions are employed to estimate partial melt compositions in both hydrous and anhydrous conditions. Hydrous partial melting of the Venera 14 composition generated tonalitic-trondhjemite-granodiorite- (TTG) melts at shallow crustal depths with 5% partial melting. The Vega 2 composition could also generate TTG like melts in hydrous conditions, but at a slightly higher-pressure (~5 kbar). However, anhydrous partial melting modelling results were unable to generate a TTG-like melts. The results of THERMOCALC modelling indicate that TTG-like melts can be generated in the crust from the basaltic compositions of Venera 14 and Vega 2 by hydrous partial melting. The implication is that the highland regions of Venus may be an ideal location to search for silicic rocks that are typical of terrestrial Archean crust.

¹Ashley Rogers,^1,2Lucy Forman,³Kai Rankenburg,^1,4Rachel Kirby,³Martin Danišík,¹Victoria Cousins,^1,2,5Gretchen K. Benedix
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70101]
¹Space Science and Technology Centre, School of Earth and Planetary Science, Curtin University, Perth, Western Australia,Australia
²Department of Minerals & Meteorites, Western Australian Museum, Perth, Western Australia, Australia
³John de Laeter Centre, Curtin University, Perth, Western Australia, Australia
⁴School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
⁵Planetary Science Institute, Tucson, Arizona, USA
Published by arrangement with John Wiley & Sons

Under the current classification scheme, ungrouped irons make up ~11% of all recognized iron meteorites. A further ~7% of iron meteorites are currently classified as simply “irons” and are yet to be fully classified. To potentially classify these meteorites, newer approaches, including either statistical modeling or advanced geochemical/petrological characterization, may be required. To approach this issue, we studied three ungrouped iron meteorites from Western Australia—Pennyweight, Prospector Pool, and Redfields. We conducted petrographical and geochemical analyses using a TESCAN Integrated Mineral Analyzer (TIMA), electron backscattered diffraction (EBSD), and laser ablation inductively coupled mass spectrometry (LA-ICP-MS). Through these analyses, the modal abundances, orientation relationships, and geochemical properties of the key metallic phases were determined. From this work, we have found that spot analyses of the kamacite and plessite are sufficient for iron meteorite classification, and these values can be used to reconstruct a “bulk” geochemical composition. Additionally, statistical data reduction (principal component analysis and t-distributed stochastic neighbor embedding) models have been used, in conjunction with the traditional logarithmic element plots, to assist with classification. Our results agree with previous studies that recommend the reclassification of Prospector Pool to the IIE group. Pennyweight may be a mesosiderite metal nodule with a metal composition closer to the IIIAB and IIE meteorites but has petrographical features similar to the IIE irons. It should remain ungrouped at this stage. Redfields is most likely a member of the IAB complex, potentially an IAB anomalous meteorite. Finally, the statistical models show a dichotomy between the IAB group and that the current iron meteorite groups seem to have more geochemical similarities than differences. Further analysis is required to assess the validity of the current classification scheme.

^1,2Lauren A. Jennings, ¹Stephan Klemme, ³Max Collinet, ²Julia Maia, ^1,2Carianna Herrera, ²Ana-Catalina Plesa
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.116986]
¹Institut für Mineralogie, Universität Münster, Corrensstraße 24, Münster 48149, Germany
²Institute of Space Research, German Aerospace Center (DLR), Berlin, Germany
³Institute of Life, Earth and Environment, Geology Department, University of Namur, Namur, Belgium
Copyright Elsevier

The mantle composition of Venus is often assumed to be similar to Earth, albeit with a lower iron content to account for the density differences between the two planets. However, it has yet to be tested whether partial melting of proposed Venusian mantle compositions can produce melts that are similar to the measured basaltic rock compositions analysed in-situ during the Venera 14 and Vega 2 missions. In this study, we used Perple_X to calculate melt compositions from several bulk mantle compositions of Venus and found they were unable to reliably produce primary melt compositions that are similar to the Venera 14 or Vega 2 basalts, regardless of the oxidation state or degree of fractional crystallisation. As such, we used an iterative approach to identify new mantle compositions for Venus that are able to produce Vega 2- and/or Venera 14-like melts over a large pressure and temperature range. We found 23 mantle compositions that are similar to the terrestrial composition of KLB-1, but have a high Al2O3 and low CaO abundance, resulting in a sub-chondritic CaO/Al2O3 and SiO2/Al2O3. We recommend two of these as new mantle compositions for Venus as they were the most successful at producing Venus-like melts. Lastly, we propose that the sub-chondritic ratios of these new mantle compositions are the result of igneous processes, such as magma ocean differentiation and Ca-rich carbonatite melt extraction, that altered the mantle composition prior to the melting that produced the basalts sampled by the Venera 14 and Vega 2 missions.

¹M.C. Benner, ^1,2T.J. Zega, ¹B.S. Prince, ³Z.E. Wilbur,^1,4,5H.C. Connolly Jr., ¹D.S. Lauretta
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2026.01.056]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
²Department of Materials Science & Engineering, University of Arizona, Tucson, AZ, USA
³Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
⁴Department of Geology, Rowan University, Glassboro, NJ, USA
⁵Department of Earth and Planetary Science, American Museum of Natural History, New York, NY, USA
Copyright Elsevier

We report the discovery of fibrous mackinawite in samples of asteroid Bennu returned by the OSIRIS-REx mission. Mackinawite occurs primarily in particles belonging to Bennu’s hummocky lithology, with fibers that range from 75 to 250 nm in length and 10 to 30 nm in width. In Bennu particles, mackinawite displays both fibrous and tabular habits and forms flower-like clusters that resemble the texture of coarse-grained phyllosilicates previously described. Energy-dispersive X-ray spectroscopy indicates an Fe/S ratio of 1, and four-dimensional scanning transmission electron microscopy reveals a tetragonal structure consistent with mackinawite. Similar to terrestrial occurrences, the activities of Fe2+ and S2– in aqueous solution are likely the main drivers of mackinawite precipitation within Bennu’s parent body. We suggest that mackinawite formed via precipitation from solution following the dissolution of accreted metal and sulfides when Fe and S activities were high enough to support mackinawite stability. Based on comparison to terrestrial Pourbaix diagrams, we hypothesize that mackinawite precipitation within Bennu’s parent body was possible at 7 < pH < 10, –0.5 < Eh < –0.15, 10–9 ≤ aFe ≤ 10–6, and temperatures up to 70°C.