The flux of meteoroids reaching the Earth is continuous, ranging from microscopic grains to occasional metre and decametre scale bodies. The smallest ones fully ablate in the upper atmosphere, whereas sufficiently large or strong objects survive entry and deposit fragments on the ground as meteorites. Predicting where these fragments land, and reconstructing the atmospheric trajectory and fragmentation sequence that produced them, is central both to hazard assessment and to the recovery of freshly fallen material. The accuracy of such predictions, however, remains limited by poorly constrained fragmentation processes and by sparse, heterogeneous observational coverage of individual events. Traditional strewn field simulations rely on detailed fireball data and event-specific assumptions on fragment masses, aerodynamics, and breakup. These approaches are effective for well-instrumented events, but their applicability degrades rapidly when observations are sparse, often resulting in huge uncertainties. We present an ab initio framework predicting strewn fields of near-Earth asteroids directly from pre-impact orbital solutions. It propagates luminous trajectory and dark flight using a physics-based translational dynamics model and realistic atmospheric conditions, without requiring fireball triangulation or event-specific tuning. Validation against recent asteroid falls with recovered meteorites shows agreement with observations, with nominal solutions reproducing fall locations within 100-200 m. The new method has been integrated into the ESA Aegis pipeline, which now enables hours-ahead computation of impact locations, supporting recovery efforts, minimizing contamination, and, where warranted by object size and predicted ground hazard, civil-protection decision making.
Stellar occultations have revealed two rings around the dwarf planet Quaoar outside the Roche limit. Simulations suggest that the rings are sustained by large velocity dispersions. We present the first analytical, first-principles theory that extends the Roche limit to describe planetary rings with large velocity dispersion. The underlying principle is an analogy between a liquid/gas phase transition and the moon/ring transition: just as high temperatures can boil a liquid under pressure, high velocity dispersions can stabilize ring systems beyond the Roche limit. We employ statistical mechanics to derive a modification to the Roche limit that treats rings with nonzero velocity dispersion. We demonstrate the new model's consistency with previous simulations of Quaoar's outermost ring. We also note that dense regions of the ring experience negative pressure, which would cause them to shrink over time if the assumptions of the model continue to hold. This could help explain the rings' azimuthal asymmetry.
Paracelsus C is a pre-Nectarian highland crater located within the South Pole–Aitken ejecta field. Apollo 15 panoramic photography revealed two unusual high-contrast features on the crater floor that were later resolved in Lunar Reconnaissance Orbiter Camera (LROC) imagery as two elongated high-relief structures together with a smaller nearby feature. Morphometric analyses using co-registered LROC images, QuickMap terrain products, and Lunar Orbiter Laser Altimeter (LOLA) data indicate that the two largest features are approximately 61 × 20.5 × 10.4 m and 44 × 22 × 10.2 m in size and exhibit peak slopes of 42–52°, exceeding typical slopes observed in degraded lunar highland terrains. Synthetic terrain visualizations derived from shape-from-shading reconstruction reveal textural and geometric characteristics consistent with several possible origins, including ejecta blocks, bedrock exposures, or impact-melt remnants. Regional compositional products derived from Kaguya data indicate relatively elevated olivine abundance in the vicinity of one feature, although the available datasets do not spatially resolve the individual structures. Meter-scale morphologic features are preserved in terrain exhibiting relatively low OMAT values consistent with mature surface materials. Topographic diffusion modeling suggests characteristic smoothing timescales of order 10–20 My for reconstructed meter-scale relief under published lunar diffusivities. The combined observations indicate unusually well-preserved topography whose origin remains uncertain and warrant further investigation using higher-resolution topographic, compositional, and imaging data.
Asteroid physical parameter inversion is a challenging problem prone to local optima, but massive sampling used to improve accuracy is computationally expensive. To address these issues, we propose a curvature-guided probe-diffuse inversion approach (CG-PDIA) that operates with sparse samples. We identify that the core challenge lies in the existence of a solution subspace where the chi-square value remains nearly constant despite significant errors in the asteroid physical parameters. We define this as the low-sensitivity subspace and its orthogonal complement as the high-sensitivity subspace. To formalize this insight, we present and demonstrate two theorems: the curvature irreducibility theorem, which justifies the necessity of introducing curvature, and the chi-square constraint theorem, which validates the feasibility of exploiting the low-sensitivity subspace. The CG-PDIA operates in two sequential stages. In the probe stage, the Levenberg-Marquardt (LM) algorithm acts as a probe to locate a promising point in the parameter space, yielding a probed parameter vector. In the subsequent diffuse stage, guided by curvature analysis, the low-sensitivity subspace is constructed. The high-sensitivity components of the probed vector are maintained, while sparse samples generated by diffusing the probed vector within the low-sensitivity subspace serve as initial points. These sparse samples are then further refined by the LM algorithm to obtain the final asteroid physical parameter estimates. Simulation results demonstrate that the proposed CG-PDIA achieves a 60% higher estimation accuracy while requiring only 2.30% of the computation time compared to the traditional LM method alone.
Circumplanetary disks are open, dynamic systems sustained by a meridional circulation that draws gas and dust from the parent nebula along nearly polar streamlines, and ultimately returns some of this material through a viscously driven, in-plane outflow. In such a disk, the water ice line acts as a site of solid-mass accumulation: inward-drifting icy solids sublimate interior to the ice line, the resulting vapor is advected outward by the gas, and recondensation beyond the ice line resets the material to a small Stokes number. The operation of this drift-mediated loop requires the fragmentation-limited Stokes number of the mass-dominant icy aggregates to exceed the equilibrium Stokes number at which the radial drift of solids reverses. Because the former scales inversely with the Shakura-Sunyaev viscosity parameter α while the latter is directly proportional to it, this requirement yields a compact upper bound on the vigor of turbulence in the satellite-forming region. Adopting an actively heated, steady-state circumjovian disk truncated at the tidal radius, we find a marginal bound of α≲ 10^-3 for an icy-particle fragmentation threshold of v_f≃1 m s^-1 - appropriate for cold ice with sticking properties similar to silicate dust. This bound scales linearly with v_f, reaching α≲5×10^-3 for more adhesive, warm ice (v_f≃5 m s^-1). The bound carries no explicit dependence on the disk's mass flux, and is set entirely by the local thermal state, pressure gradient, and geometry of the circumjovian nebula.
High-precision mass-independent Ru isotope data for iron meteorites reveal that in three-isotope diagrams including the p-process Ru nuclides 96Ru or 98Ru, non‑carbonaceous (NC) meteorites plot along an s-process mixing line, while the carbonaceous (CC) type irons plot as a cluster off the NC-line. As previously observed for Mo, this offset can be accounted for by an r-process excess in CC over NC materials. As a highly siderophile element, Ru in the bulk silicate Earth (BSE) is thought to predominantly derive from the late veneer, making the Ru isotope dichotomy a powerful genetic tracer of Earth's late accretionary epoch. The BSE and the isotopically anomalous Itsaq Gneiss Complex as defined in prior studies plot on the NC-line defined in this study, suggesting a predominantly NC late veneer that may have evolved over time from more s-process-enriched to more s-process-depleted compositions. However, more precise 96Ru and 98Ru measurements of the BSE's composition are needed to more reliably determine the genetic heritage of the late veneer and to quantify as to whether it contains CC material.
We investigate the thermal structure of the Venusian middle atmosphere between 45 and 80 km using radio occultation (RO) measurements from Venus Express and Akatsuki spanning 2006-2024. Retrieved temperature profiles are compared with climatological predictions from the Venus-GRAM and the Venus Climate Database (VCD). Systematic deviations exceeding 10 K are observed between the RO temperatures and model climatologies, particularly at high latitudes in both hemispheres. The long-term dataset further reveals a possible decadal-scale temporal variability in temperatures across the low-to-mid latitude regions. This variability becomes less coherent at higher altitudes. A combination of post-stratification and bootstrap analysis on the temperature anomalies indicates that the observed temporal variability at low-to-mid and polar latitudes is not readily explained by the latitudinal sampling bias quantified using the adopted analysis, while the trends at mid-to-high latitudes are affected by sparse and uneven RO sounding. Sensitivity tests using modified cloud albedo inputs in VCD simulations show that adjusting cloud radiative forcing partially reconciles the discrepancies, especially at the lower altitudes, below 60 km. However, above the cloud top, at the lower latitudes, the divergence from the observations increases significantly, thereby failing to provide a general reconciliation between VCD and RO. These results highlight the need for updated empirical climatologies incorporating recent RO measurements and for improved physical parameterizations in Venus general circulation models to better capture the global variability in the planet's middle atmosphere.
In lunar exploration missions, obtaining high-resolution optical imagery data from lunar orbiter cameras is crucial for both scientific research and engineering tasks. However, due to the limitations of satellite design, such as onboard storage capacity and downlink bandwidth constraints, satellite imagery typically needs to be compressed onboard prior to transmission. Before satellite launch, it is essential to test the parameters related to onboard compression, and the construction of compression test datasets plays a vital role in this procedure. In this study, a high-resolution optical imagery dataset specifically designed for lunar scenes is constructed to evaluate the onboard compression quality of lunar orbiter images. The dataset considers the information on lunar scenarios, including lunar time phase, illumination conditions and topography characteristics. We performed a quality assessment on the dataset. The results indicate that as the compression ratio increases, the image quality degrades significantly. Based on objective metrics, when the compression ratio is around 4, the change in image quality is relatively small. Furthermore, under the same compression ratio, a higher the solar incidence angle leads to a more significant degradation in compressed image quality.
We measured reflectance spectra (250–2500 nm) of a 200 mg aliquot (sample id OREX-800029-0) of aggregate (unsorted) regolith particles returned from asteroid Bennu by the OSIRIS-REx mission). Our measurements include spots centered on small (<0.5 mm), medium (0.5–1 mm), and large particles (1–2 mm), as well as spots dominated by larger individual particles, including angular, hummocky, and mottled examples. The ultraviolet (UV) spectra (250–450 nm) are characterized by low reflectance (<3%), slightly red spectral slopes, absorption features near 270 and 320 nm attributable to Fe2+-O charge transfers, and Fe3+-associated absorption features, respectively. The 450–2500 nm region spectra are of low reflectance (<3% at 550 nm), red-sloped, and exhibit variable but weak absorption features, the most ubiquitous being a broad region of absorption in the 1000 nm region (<~2%), attributable to magnetite and Fe2+-bearing phyllosilicates. The low albedo, weak absorption features, and red-sloped spectra can be attributed to the presence of carbonaceous components. Overall, we confirm the spectral similarities between Bennu aggregate material and powders of the rare CI1 chondrite meteorites. The spectra we measured are generally red-sloped, in contrast to the blue-sloped global-average spectra measured by ground-based telescopes and the OSIRIS-REx spacecraft. This difference is consistent with Bennu's boulder-dominated surface and limited fine-grained dust, in combination with compositional contributions from optically efficient minor phases.
Swift heavy ion irradiation of pure CH3CN ice was investigated to evaluate the influence of the initial ice morphology on its radiolytic evolution under astrophysically relevant conditions. Two deposition protocols were compared: (i) CH3CN ice deposited and irradiated at 50 K, and (ii) CH3CN ice deposited at 130 K, subsequently cooled to 10 K prior to irradiation, thereby preserving the structural organization established during deposition. In situ FTIR spectroscopy revealed efficient destruction of CH3CN and the formation of HCN, HC3N, CH3NC, NH3, and imine-like compounds. The thermally organized ice exhibited a distinct infrared spectral evolution, enhanced destruction, and differences in the stabilization of daughter species compared with the amorphous ice. Destruction cross sections of (2.85±0.52)×10−12 and (4.65±0.43)×10−12 cm2 were determined for the amorphous and thermally organized ices, respectively. These results demonstrate that the thermal history of CH3CN ice, through its influence on the initial ice morphology, strongly affects radical diffusion, recombination, and product formation during irradiation. The present measurements provide benchmark radiochemical data for acetonitrile and establish a basis for future investigations of more realistic nitrile-bearing astrophysical ice analogues relevant to Titan and other outer Solar System environments.
Io and Europa, the innermost Galilean satellites characterized by the highest rock fraction, may have accreted in a similar environment within the circumjovian planetary disk from building blocks of comparable composition. In this study, the interior structure and composition of Io and Europa are modeled through a joint analysis using a MCMC scheme constrained on the mass, radius and Moment-of-Inertia factor retrieved during the Galileo mission. Density profiles are calculated using state-of-the-art equations of state for a large range of Fe/Si and Mg/Si ratios. We show that Io and Europa can have Fe/Si and Mg/Si ratios comparable to the solar composition and carbonaceous chondrites only if a low-density component here taken as graphite is considered. The graphite content in Io’s and Europa’s refractory interior is estimated between 3–8 wt% and 1–22 wt%, respectively, which can exceed up to a factor five the typical carbon content in carbonaceous chondrites. The amount of graphite within Europa is anti-correlated with the thickness of the hydrosphere and positively correlated with the radius of the metallic core. A hydrosphere thickness larger than 130-140 km would either suggest a completely undifferentiated rocky core or a partially differentiated interior with a small (R< 550 km) metallic core and low carbon fractions. Thinner hydrospheres (<125 km) would be indicator of a differentiated interior into a metallic core (R> 550 km) and a rocky mantle containing more than 5 wt% of graphite. Thermal metamorphism of the accreted carbonaceous matter in Europa leads to its graphitization and the release of water in proportions that can be sufficient to entirely form its present-day hydrosphere. Thermal degradation of carbonaceous matter may thus be a major contributor to the water and volatile budget of Europa. Future gravimetric, altimetric and magnetic measurements by Europa Clipper will refine the Moment-of-Inertia factor and determine the hydrosphere thickness. Such information are crucial to determine carbon content and differentiation state of Europa and hence the thermo-chemical evolution of Europa and the habitability of its subsurface ocean. The SUDA dust analyzer on board Europa Clipper will also provide constraints on the composition of Europa’s ice grains and volcanic dust ejected by Io, thus allowing testing of the potential contribution of carbon to their bulk composition.
Dust accumulation poses a critical yet under-quantified risk to lunar rover navigation by degrading perception and mobility in fine-grained regolith. Here, we present an integrated analogue-driven framework combining terrestrial experiments, high-fidelity rover simulations, and long-term data from the Chang'e-3 and Chang'e-4 missions to quantify dust-induced navigation fragility. Our approach links environmental disturbance, perception degradation, and navigation performance through a four-component model capturing instantaneous degradation, cumulative effects of traverse distance, terrain-dependent amplification, and nonlinear dust–vision–navigation coupling. Results demonstrate that navigation failure risk correlates more strongly with cumulative distance than mission duration, with intermediate dust levels posing the greatest challenge due to delayed adaptive responses. Model predictions closely match mission observations, validating cross-domain transferability. This framework provides a scalable tool for predicting mobility constraints and guiding design and operational strategies for future lunar exploration.
This study investigates the response of lunar breccia minerals and selected reference materials to accelerated Ga+ ion irradiation using focused ion beam (FIB) processing combined with Raman spectroscopy. Anorthite and pyroxene bearing clasts from Apollo 15 breccias 15405 and 15445 were examined alongside monocrystalline silicon, magnetite, and pyrite to evaluate mineral specific structural modifications induced by heavy ion exposure. Samples were characterized by Raman spectroscopy before and after irradiation with 30 keV Ga+ ions at four beam currents (0.43, 0.79, 2.5, and 9.3 nA). Silicate phases exhibited band broadening, peak shifts, and partial amorphization consistent with increasing lattice disorder. Monocrystalline silicon showed progressive damage of the crystalline structure, while magnetite and pyrite displayed enhanced structural disorder and modifications of Fe-bearing spectral features. At the highest irradiation conditions, Ga implantation and local heating may have contributed to the observed changes. Based on published SRIM-derived displacement estimates, the maximum Ga+ fluence applied in this study corresponds to approximately 105–106 years of natural solar wind exposure in terms of cumulative atomic displacement damage. This estimate is intended only as an approximate comparison between laboratory irradiation and natural space weathering. Although Ga+ FIB irradiation does not directly reproduce natural solar wind conditions, it provides an accelerated approach for assessing the relative susceptibility of planetary materials to heavy ion induced structural degradation and offers implications for future spectroscopic and paleomagnetic investigations of lunar samples.
The Zhurong rover was part of the first integrated Chinese mission to Mars. It landed in May 2021 in Utopia Planitia, a region that might have hosted in the distant past a marine to oceanic basin. 3D shape of rocks and their internal structures provide critical information to assess their origin, which is particularly helpful to decipher the original depositional settings in the case of sedimentary rocks. In this work, we assess the feasibility of reconstruction of Digital Outcrop Models of various areas of interest explored by the rover using a Structure-from-Motion photogrammetric chain and publicly available image data. These images were acquired by two distinct instruments with varying optical parameters and resolution: the NaTeCam and MSCam. For the first time, we managed to integrate these multi-scale image data into single 3D outcrop models to improve rendering quality and scientific return. We also propose large-scale outcrop models based solely on multiple, georeferenced acquisition stations and no further internal or external data. We demonstrate that a simple, accessible pipeline can be applied to these data and produce readily usable 3D product for current and future scientific studies, including within a Virtual Reality environment. 3D outcrop models can be used to provide accurate measurement of small-scale geomorphic features, but also to investigate surface properties, such as small, circular deflations (hollow impact craters) that are not clearly visible in raw images.
Small, undifferentiated objects in the Kuiper Belt and Oort Cloud are some of the solar system’s most primitive bodies; their structures and compositions may retain unique information about processes that occurred during the period of planetesimal formation. These objects are extremely difficult to observe in-situ, but gravitational perturbations result in a small subset entering the inner solar system as comets. Before this population can be reliably used to gain insight into the process of planetesimal formation, however, the type and degree of alteration experienced by these objects between formation and present-day observation must be understood. Previous research suggested that KBOs should rapidly lose their most volatile materials, which is seemingly at odds with observations of the highly volatile CO outgassing from dynamically new comets. This apparent discrepancy necessitates a re-examination of the long-term evolution of these bodies. We have therefore developed a new thermophysical evolution model for small, porous, and volatile-rich objects. We explore a wide range of potential interior structures and compositions, in accordance with the large uncertainties suggested by experiments and observations. We find that, although most of our simulated objects lost their CO on short (≪1 Gyr) timescales, some late-accreting (>3 Myrs after CAI formation) objects retained substantial CO inventories until the present day. These results suggest that, while hypervolatile outgassing from comets may in most cases result from secondary processes or trapping within more refractory ices, modern hypervolatile gas fluxes from some objects may provide insight into conditions in the earliest era of our solar system.
