Abstract Intra‐tessera plains are radar‐dark plains deposits that occur within tesserae. Their emplacement mechanism(s) and composition are poorly constrained, though they are hypothesized to be basaltic lava flows. Here, we map intra‐tessera plains within 16 different tesserae spanning various latitudes and elevations. Intra‐tessera plains have three dominant geologic units (regional plains, shield plains, and smooth plains) which we compare with morphologically similar lowland plains, and plains that overlap with known parabolic ejecta deposits, to better constrain the ability of these ejecta to modify surface signatures in synthetic aperture radar data. We examine the Magellan radar backscatter, emissivity, and altimetry data of all mapped intra‐tessera plains, lowland plains, and parabolic ejecta study regions. Our results support the observation that parabolic ejecta deposits modify the backscatter coefficients of intra‐tessera plains and lowland plains by smoothing these materials, while variations in the radar properties caused by differences in plains geologic units are minimal. Conversely, there are clear differences in the backscatter coefficients and emissivity of high‐ and low‐elevation intra‐tessera and lowland plains. Our mapped intra‐tessera plains follow six different elevation–emissivity patterns. Regardless of which pattern is observed, intra‐tessera plains mimic the radar behavior of the tesserae in which they occur. This parallel behavior suggests that the same processes are affecting both terrains, placing constraints on proposed high reflectivity formation mechanisms. While multiple hypotheses remain plausible, our data are most consistent with the atmospheric deposition of metallic frost.
Abstract Hypervelocity impacts from micrometeorites or asteroids are a dominant long‐term geological process that modifies the mineralogical and elemental components of surface regolith on the Moon and other airless planetary bodies. However, the pathways by which impacts drive elemental redistribution on the Moon remain poorly understood. Here, we report the discovery of thousands of chromite (FeCr 2 O 4 ) nanoparticles deposited on a space‐weathered olivine fragment from Chang'e−5 lunar regolith. These chromite nanoparticles display morphological and textural characteristics consistent with vapor‐phase condensation rather than magmatic crystallization. We therefore propose that the deposited chromite nanoparticles formed via localized vaporization of Cr, Fe, and O from lunar regolith during hypervelocity impacts, followed by rapid condensation and deposition. This study provides direct mineralogical evidence for impact‐driven Cr‐Fe‐O vaporization and deposition, offering new insights into the elemental cycling and regolith evolution on the Moon and other airless bodies.
Abstract Oxidation state of magma ocean is one of the most important factors, which influence its nature and dynamics. Since iron is the most abundant redox‐sensitive element, understanding the effect of ferrous (Fe 2+ ) and ferric (Fe 3+ ) iron on the physical properties and structure of peridotite melts are fundamental to discuss geophysical and geochemical evolutions of magma ocean. In this study, we investigate the viscosity of Fe 3+ ‐bearing peridotitic melts under Ar gas environment by utilizing an electrostatic levitation furnace at the International Space Station. The results show strong increase of the viscosity of the Fe 3+ ‐bearing peridotitic melts with increasing iron content, which is in contrast to previous reports of lower viscosities of iron‐abundant peridotitic melts than iron‐poor peridotitic melts under reduced environment. Our structural investigations show that Fe 3+ causes polymerization of melt structure with increasing iron content, while Fe 2+ ‐dominant peridotitic melts under reduced environment show almost no change in the melt structure. These results indicate that polymerization of melt structure by Fe 3+ strongly increases the viscosity of peridotitic melt, while simple replacement of Mg 2+ with Fe 2+ decreases the viscosity of peridotitic melt. Since deep magma ocean is considered to be enriched in Fe 3+ , due to disproportionation reaction to form metallic iron and Fe 3+ at high pressures, strong increase of the viscosity of peridotitic melt by the formation of Fe 3+ would be important to discuss nature and dynamics of magmas at deep planetary interiors, such as formation and stability of the basal magma ocean at the core‐mantle boundary in Mars.
Abstract Atmospheric tides drive large‐scale variability in the Martian ionosphere, but their effect on ionospheric composition remains unclear. Using measurements from the Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we examine tidal signatures in the major ions and , with emphasis on species‐dependent behavior and chemical coupling. Harmonic analysis of zonal wavenumbers 1–3 reveals strong tidal amplitudes, up to ∼30%, between 150 and 200 km, with clear dependence on altitude, spatial scale, and season. Similar variability in the ion ratio suggests that tides may influence ionospheric composition beyond simple vertical displacements. The observed correspondence between tidal variations in the neutral O/ ratio and in / is consistent with a chemically mediated coupling, in which tide‐driven neutral composition changes may alter the balance between and . Minor ions also display species‐ and season‐dependent tidal responses, indicating that chemical and dynamical factors likely contribute to their variability. Overall, atmospheric tides influence the Martian ionosphere through coupled dynamical and photochemical processes, highlighting the key role of chemistry in ionosphere‐thermosphere coupling.
Abstract With its extreme geological activity, Io represents an archetype for tidally heated exoplanets/moons and provides insight into early stages of terrestrial planet evolution. Decades of ground‐based observations and multiple space missions have refined our understanding of Io, yet it remains debated where inside Io the tidal heating takes place. Here, we synthesize several independent data sets in a Bayesian approach to provide an updated view of Io's interior. Tidal response data constrain the bulk mechanical properties of the silicate envelope but do not resolve the radial profile. We propose adding constraints based on the observed distribution of volcanic activity, thereby introducing sensitivity to the radial viscosity profile. The combined observations are consistent with the majority of the dissipation occurring in a low‐viscosity asthenosphere approximately 200 km thick, with a maximum viscosity of Pa s, which is also valid under a more conservative estimate of spatially uniform heat flux. This low viscosity implies either enhanced viscous dissipation under Io's conditions due to poorly understood rheological laws, an asthenosphere near the disaggregation threshold, corresponding to a melt fraction of , or a combination of both. Together, these results provide a coherent interior structure and thermal state that can be used in future Io studies.
Abstract In this paper we report the discovery, in the Gilf Kebir Plateau of southwest Egypt, of the first natural occurrence of Diamond‐Like‐Carbon, of microdiamonds, and new ultra‐high T (≥1300°C) silicates, phosphates in boulders and pebbles of a mullite and magnetite melt rock. We also report, in the regolith of the Libyan Desert Glass (LDG) strewn field, comparable mullite‐magnetite pebbles and, in paleosols, Diamond‐Like‐Carbon, N‐rich amorphous carbon, aliphatic hydrocarbons, moissanite, and metallic spherules and grains of native Ti. These findings point to a ∼350 km, south to north strewnfield of melt rocks and their related disaggregated debris formed by the impact of a carbonaceous meteorite in the Jebel Uweinat, near the Egypt‐Sudan border. At the northern end of their fluvial depository, the reworked debris co‐mingled with the LDG strewnfield, likely originated from a second impact in the Gilf Kebir. The date of the diamonds‐forming mullite impact melt is undetermined but tentatively linked to the 29 Ma event of the LDG, because disordered carbon + aliphatic compounds were found in a glass and in the, extraterrestrial (extrasolar) “Hypatia” from the same areas. The latter is considered as relic of the original, parent impactor.
Abstract Aluminum phyllosilicates occur in 1–10s of km 2 exposures of Noachian (∼3.7 Ga) rock across Mars and typically appear stratigraphically above Fe/Mg‐phyllosilicates. These units have been proposed to represent pedogenic basalt weathering sequences. We examine Al‐phyllosilicates in the Nili Fossae region, combining mineral maps generated from imaging spectroscopy with digital elevation models and high‐resolution imagery to determine mineral assemblages, their geologic relationships, and their history of formation. We find that the Al‐phyllosilicate is dominantly kaolinite and lacks associated Fe oxide. The Al‐phyllosilicates typically have a distinct texture relative to Fe/Mg‐phyllosilicate units, indicating an unconformity, and two different protoliths rather than formation as a pedogenic weathering sequence. Layers in some kaolinite deposits and their preferential association with sedimentary basins suggest reworked sedimentary material. The most plausible source is an Al/Si‐enriched (non‐basaltic) airfall volcanic deposit. We detect sparse jarosite closely associated with kaolinite but not Fe/Mg‐phyllosilicate. We interpret that the jarosite, which is metastable under present surface conditions, formed from reaction between Fe‐enriched fluids and S that is found sufficiently only within the kaolinite‐bearing protolith. Collectively, these observations suggest less intense near‐surface oxidative weathering than the basalt pedogenesis hypothesis, namely, an upper bound of several million cumulative years of aqueous activity in Nili Fossae that largely ended after the formation of jarosite. Detection of Al‐phyllosilicate‐bearing float rocks in nearby Jezero Crater by the Perseverance Rover shows that sample return has potential to conclusively determine processes and environmental conditions forming Nili Fossae's distinctive Al‐phyllosilicates.
Abstract The Moon's crust exhibits strong magnetic anomalies that likely record ancient magnetic fields produced by a core dynamo. Lunar materials have low magnetic susceptibility, but impactor material with high susceptibility may record the Moon's ancient dynamo. Some magnetic anomalies are antipodal to lunar basins and it is hypothesized that impact ejecta accumulates at the basin antipode and records the ancient lunar magnetic field. Previous impact simulations, which ignored the rotation of the Moon, support this hypothesis. Here, we reevaluate the deposition of antipodal ejecta by considering the rotation of the Moon. Assuming that the rotational period of the Moon is the same as the current day, we find that the rotation of the Moon does not strongly affect the deposition of the antipodal ejecta if impacts occur near the poles. In contrast, rotation has a considerable effect on antipodal deposits for impacts occurring near the equator. An eastward impact at a 45° incidence angle results in almost no antipodal ejecta, however, an eastward impact with a 30° incidence angle accumulates more antipodal ejecta than the non‐rotating case. It is hard to determine the impactor's direction and location, for basins without an ellipsoidal shape and/or an asymmetric ejecta blanket. Nevertheless, our work demonstrates that care must be taken in interpreting the magnetic anomalies antipodal to lunar basins and that the effect of rotation should not be ignored.
Abstract China plans to launch its Tianwen‐3 Mars sample return mission in 2028. Within the designated candidate landing zone, this study characterizes a geologically and compositionally diverse region (26°N–30°N, 28°W–36°W) shaped by the interplay of fluvial, periglacial, tectonic, and volatile‐related processes. Through integrated geomorphological, mineralogical, and thermophysical analyses, we identify several key features, including widespread olivine exposures within crater floors, walls, and ejecta; conical landforms potentially associated with subsurface sediment mobilization, possibly involving mud‐volcanic processes; erosion‐resistant mesa units; and polygonal terrains consistent with contractional cracking associated with volatile loss. The spatial arrangement and stratigraphic relationships among coarse‐grained residual units, ridge systems, trough networks, and elevated mesas indicate a prolonged and multi‐stage geomorphic evolution involving resurfacing, structural deformation, and erosion. Crater size–frequency distribution measurements suggest that a major resurfacing event occurred during the Middle Amazonian, approximately 600–800 million years ago, representing one of the latest resurfacing phases in the region. Collectively, geomorphological, mineralogical, and thermophysical evidence indicates a history of volatile redistribution, structural modification, and subsurface material exposure relevant to understanding the geological evolution and subsurface habitability potential of northern Chryse Planitia. Given its geomorphic diversity, exposed stratigraphy, and evidence of subsurface processes, this region represents a scientifically valuable target for future exploration, including the Tianwen‐3 mission.
Abstract Deep‐space exploration requires reliable mechanical constraints for lunar materials; however, the scarcity of samples limits destructive macroscale testing. Here, we combine automated mineralogical analysis and nanoindentation to investigate the mineral‐scale mechanical behavior of two Chang'e‐5 regolith particles and a Laâyoune 002 feldspathic breccia comparison sample. Rather than treating these materials as bulk proxies for all mare and highland regolith regions, we compare analogous mineral domains using an identical testing protocol. Minerals in the Chang'e‐5 particles generally show lower elastic modulus and hardness, greater indentation depth and creep displacement, and higher plastic work ratios than analogous minerals measured in the interior polished section of Laâyoune 002. The strongest contrast occurs in ilmenite, where more plastic, energy‐dissipative deformation is observed. These measured contrasts document micromechanical differences among analogous minerals in the analyzed lunar samples. Their interpretation considers lithology, mineral chemistry, local microstructure, and impact history, with regolith processes and space‐weathering overprint as plausible contributors to the Chang'e‐5 response. First‐order homogenization of the analyzed particle‐scale assemblages yields equivalent elastic moduli of about 54 GPa for the Chang'e‐5 assemblage and about 78 GPa for the Laâyoune 002 assemblage. These results provide mineral‐resolved mechanical constraints for interpreting lunar material evolution and for designing better simulants, experiments, and multiscale engineering assessments.
Abstract Mars lacks subduction‐driven plate tectonics, and the reason for this is poorly known. Here, we investigate whether early water on Mars inhibited long‐term sustained subduction by lowering the crustal density during metamorphism. We use numerical and thermodynamic modeling to estimate the subduction potential of the variably hydrated Martian crust. Our reference model, representative of the Hesperian (3.7–3.0 Ga) to early Amazonian (3.0–∼2.0 Ga), shows that hydration stabilized low‐density hydrous assemblages, driving the density contrast toward values that hindered subduction. In dry scenarios, subduction is predicted along cool Martian geotherms, contrasting with the lack of subduction‐driven tectonics on Mars. However, our wet models show that subduction was suppressed by minimal hydration (>0.45 wt% H 2 O). We propose that the presence of water early in Mars history explains the lack of subduction‐driven plate tectonics. Our conclusions remain valid even when accounting for variations in crustal thickness between the northern and southern hemispheres as currently observed, as well as for the presence of a lithosphere comparable in thickness to the crust, as inferred for the Noachian (4.1–3.7 Ga). Our work reconciles Mars's tectonic quiescence with its hydrologically active past.
Abstract Planetary studies of compressional structures are fundamental for understanding the tectonics and thermal evolution of planetary bodies. Compressional features are commonly characterized by their morphology, which in turn is strongly dependent on the spatial resolution of topographic data. Low‐resolution data may lose important morphological characteristics that are directly linked to their structural architecture. Although the influence of data resolution in the analysis of surface structures is widely recognized, a systematic and comparative quantification of shortening over‐ or underestimation across different morphologies and resolutions is still lacking, and the amount of these deviations remains quantitatively poorly constrained. In this work, I assess the effect of data resolution on the morphological and structural analysis of five compressional ridges with different sizes and geometries on Mars using four digital elevation models with different resolutions: Mars Orbiter Laser Altimeter (∼463 m/px), High‐Resolution Stereo Camera (∼75–∼100 m/px), CTX (∼6 m/px), and HiRISE (∼0.3 m/px). Additional applications to one example on Venus and one on Mercury are used to evaluate transferability to other planetary bodies. The results quantitatively demonstrate how morphological characterization and structural analysis can be affected by significant local deviations depending on the size of the analyzed structures and the type of topographic data. By applying a harmonic index to ridge width and relief on Mars, I identify a threshold range of approximately ∼175–275 m. Below it, low‐resolution data become unreliable, whereas above it, they can provide an overall reliable characterization. Based on the current available data sets, this threshold appears valid on Mars and potentially on Venus, but apparently not on Mercury.
Abstract Thermal tides on Venus have been extensively studied near the cloud tops, where their three‐dimensional structure and contribution to the atmospheric momentum budget have been characterized from temperature and wind fields. However, their downward propagation and influence within the deep atmosphere remain uncertain, and their behavior in the deep atmosphere, particularly near the surface, remains poorly constrained. Using the LMD Venus Planetary Climate Model, we investigate the near‐surface thermal tides and their governing timescales. The simulations show that these tides are generated by heat transfer from the surface to the planetary boundary layer and produce a diurnal pressure response with a phase lag of about corresponding to a radiative adjustment timescale of about 10 Earth days. In addition, a 35‐day oscillation appears within the stably stratified 10–20 km layer, consistent with a planetary‐scale internal gravity wave. These results suggest that coherent oscillations beyond the diurnal tide can develop in the deep atmosphere, with the surface pressure variability dominated by a superposition of three modes: the diurnal and semidiurnal tides and the 35‐day oscillation. Together, these components account for about 70 of the total surface pressure variance, with potential implications for gravity measurements by forthcoming missions such as VERITAS and EnVision.
Abstract Meteorites serve as an exceptional source of insight into our planet and the Solar System. Most meteorite fragments were recovered hundreds to thousands of years after their fall, and therefore exhibit varying degrees of terrestrial weathering, which has altered or completely removed weather‐sensitive mineral phases. This study focuses on two aubrites—NWA 14582 and Ribbeck—examining the differences in their mineral composition. The NWA 14582 was collected in a desert long after its fall and has undergone significantly greater shock metamorphic alteration than the Ribbeck meteorite. The alterations are evidenced by the structural changes in its enstatite and diopside, along with the absence of feldspars, which have transformed into maskelynite. The Ribbeck meteorite, recovered shortly after its descent, revealed several mineral phases not present in NWA 14582. Electron microprobe investigations confirmed that minerals such as troilite, daubréelite, schreibersite, and kamacite exhibit resistance to weathering. Conversely, the observed minerals, such as heideite, caswellsilverite, oldhamite, pentlandite, and alabandite, appear to be particularly susceptible to terrestrial weathering processes. Our observations further indicate that the climate at the fall site can have a substantial impact on the preservation of primary mineral phases and the formation of secondary weathering products. We additionally report a Cu‐based iodide in an early sample preparation that was not preserved in subsequently prepared mounts, as well as a rare Al–Cu–Zn alloy in Ribbeck. Further microchemical and isotopic analyses are required to determine the provenance of these phases.
Abstract Enstatite chondrites record highly reducing conditions in the early solar nebula, yet the origin of their abundant sulfides remains unclear. Niningerite (MgS) and oldhamite (CaS) are ubiquitous in EH3 enstatite chondrites and distinguish them from other chondrite groups. To investigate sulfide formation, we conducted sulfidation experiments under ultra‐reducing conditions using evacuated silica‐glass tubes to reproduce extremely low oxygen pressure environments. Experiments at 1,200–1,420°C and IW−5 to −6 with pyrrhotite–troilite buffers examined reactions of Mg‐ and Ca‐bearing silicates with sulfur‐rich gas. Niningerite formed from forsterite–enstatite, and oldhamite from diopside, producing granular niningerite surrounding olivine and enstatite and granular oldhamite associated with diopside, coexisting with cristobalite and enstatite. Mg–Fe compositions of synthetic niningerite are included in those in EH3 chondrites. In the experiments, niningerite and oldhamite did not form within the coexisting Fe‐S reservoir, whereas natural EH3 meteorites show enrichment of these sulfides in metal‐sulfide nodules, a key discrepancy with natural EH3 textures. This suggests that the precursors of chondrules and metal nodules—aggregates of chondrules and metal nodules—underwent melting and segregation events, during which niningerite and oldhamite preferentially partitioned into the metal nodules. These multi‐stage high‐temperature processes provide new constraints on the physicochemical environment of sulfide formation in the inner solar nebula.
Abstract The Martian ionosphere hosts complex current systems driven both by solar wind interactions and neutral wind dynamo processes. While the global patterns of these current systems have been statistically examined, their detailed structures and orientations remain poorly constrained. Using magnetic field observations from NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft during the Deep Dip 2 campaign, we resolve the horizontal components of dayside ionospheric currents over regions without strong Crustal Magnetic Fields (CMF). The currents are most prominent between 130 and 150 km altitude, with peak magnitudes of ∼1 μA/m 2 , and are oriented counterclockwise from, and roughly perpendicular to, the draped Interplanetary Magnetic Field in the horizontal plane when viewed from above. Theoretically calculated neutral wind‐driven dynamo currents show significant discrepancies from the derived currents, likely reflecting uncertainties in neutral winds and conductivities. In contrast, simulated magnetohydrodynamic (MHD) ionospheric currents, which are purely solar wind‐induced in the model, share similar features with the derived currents. We conclude that, for the four cases examined here, which were sampled in near‐subsolar regions with weak CMF, the derived ionospheric currents are more consistent with a solar wind‐induced origin, whereas neutral wind‐driven dynamo currents may play only a minor role under these conditions.
Abstract Previous studies that investigated the effects of magmatism on the interior dynamics, in particular for Earth‐sized planets, suggest that magmatism leads to more efficient mantle cooling. However, the extent to which different magmatic styles influence the thermal evolution of planets, and in particular smaller rocky bodies, has not yet been systematically investigated. Using geodynamic models, we compare the evolution of Mercury‐, Mars‐, the Moon‐, and Venus‐like bodies under “fully intrusive” and “fully extrusive” magmatism. For all planets, fully intrusive cases result in hotter and thinner lithospheres and, at the same time, colder deep mantles and core‐mantle boundaries compared to fully extrusive cases. During planetary evolution, intrusive models generate more melt and at shallower depths than extrusive models, thereby potentially leading to different melt compositions. While the global average temperature of the entire silicate interior is lower on Venus in the intrusive scenario compared to the extrusive scenario, the opposite is true for smaller bodies. This can be explained not only by their smaller size and lower temperatures, which allow for less melt production than on Venus, but also by their lithospheric regimes with lower mobility due to colder lithospheric temperatures. For large planets such as Venus, when an intrusive magmatism dominates, which promotes lithospheric recycling, cold recycled material leads to higher cooling efficiency than in the extrusive case. The release of latent heat due to the crystallization of intruded melt can further amplify lithospheric recycling for large bodies, while for smaller planets this generally leads to slower cooling.
Abstract The presence of water ice in permanently shadowed regions (PSRs) of lunar poles has been widely confirmed by remote sensing. However, its vertical retention within the regolith remains controversial due to the lack of in situ measurements. In this work, we build a small‐scale vacuum‐cryogenic experimental platform and study the vertical retention pattern of water ice in lunar regolith. A simulated heat flux is applied beneath a thick lunar soil layer under the vacuum‐cryogenic conditions. The transient concentration of water vapor released into the vacuum chamber is monitored, and the final vertical distribution of water content in the lunar regolith after a cryogenic cycle is demonstrated. The results show that water ice at the surface of lunar regolith is prone to release into the vacuum, while below a certain depth beneath the surface, water ice is driven by heat flux from the bottom and migrates upward. Then, water ice accumulates in a middle layer where the concentration is independent of the magnitude of the heat flux applied to the same sample. The initial water content in the lunar regolith simulants has a limited influence on the thermodynamics pattern of water retention. The present results give important implications for the retention of water ice in PSRs on the moon: the heat input from the lunar interior drives water ice to migrate upward, and then water ice is retained in the middle layer at the maximum abundance, since this layer provides balanced temperature and local pressure to preserve the water ice.
Impact-generated crater rays are well-documented on the Moon, with most appearing as high-albedo streaks extending radially from a crater's center. On Mars, however, crater rays are significantly rarer and discernible only through thermal imaging due to their lower thermal inertia compared to surrounding terrain. This study presents the first comparative analysis between the lengths of Martian and lunar crater rays, including lunar albedo rays and cold spots, which are ray-like thermal anomalies associated with many of the youngest lunar craters. Our findings indicate that both Martian crater rays and lunar cold spots extend significantly farther than lunar albedo rays, with lengths an order of magnitude greater for craters of equivalent diameter. Furthermore, we propose a connection between the formation mechanisms of Martian crater rays and lunar cold spots based on their thermal properties. By integrating thermal rays into existing ejecta models, we refine the understanding of crater-ray formation and suggest that Martian crater rays and lunar cold spots may share a similar formation mechanism via secondary cratering processes. Advancing knowledge of these features has implications for impact dynamics and surface evolution across planetary bodies.
Abstract Jupiter's moon Europa stands out for its potential to harbor life beneath an icy shell that probably overlies a global ocean, yet the shell's thickness and thermal state remain poorly constrained. Impact craters offer a window into Europa's interior because their shapes and post‐impact evolution reflect subsurface mechanical properties and thermal gradients. Tegid crater, spanning roughly 30 km in diameter, features a uniquely flattened dome in its center. To explore how this morphology arose, we used finite element simulations that incorporate remnant impact heat, to assess the influence of post‐impact viscoelastic relaxation on the final morphology of Tegid. Our results indicate that, for a high heat flux of 60 mW m −2 , relaxation is pronounced but does not fully account for the dome's height or unusually flattened appearance. For heat fluxes of 40 mW m −2 , relaxation is not pronounced and does not sufficiently explain Tegid's topographic height. These findings suggest that additional mechanisms might be involved that account for Tegid's observed topography. By integrating crater morphology studies with thermal and mechanical modeling, we can gain critical insights into the thickness and rheology of Europa's ice shell, which has implications for habitability.
