Journal of Geophysical Research: Planets最新文献

We investigated the regolith parent rock (“protolith”) properties of Mare Tranquillitatis and Marius Hills on the Moon, utilizing lunar pit craters (“lua”) to contextualize observations of rock abundance and crater degradation. We discovered a significant difference in underlying materials: the region around the Tranquillitatis lua is characterized by a competent, dense, solidified basalt, whereas the region around the Marius Hills lua exhibits a more friable protolith, indicative of porous or vesicular volcanic deposits. These distinct protoliths directly influence rock evolution, with the Marius Hills region demonstrating higher initial rock excavation but also more rapid degradation of rocky ejecta and interiors, while the Mare Tranquillitatis region produces larger, more persistent blocks that resist fragmentation for longer periods. Consequently, the competent protolith of Mare Tranquillitatis makes its lua an ideal candidate for future lunar exploration missions, offering superior geotechnical integrity for potential subsurface habitats and enhanced protection from surface radiation and impact bombardment.

Venus' atmosphere layers between 80 and 130 km mark the transition between the superrotation and the day-to-night circulation regimes. Accurately modeling this layer is essential to better understand the planet's atmospheric dynamics. However, this region remains poorly constrained by observations, and its variability is not yet fully captured by current 3D models. Here we use the latest version of the Venus Planetary Climate Model (V-PCM), a ground-to-thermosphere global circulation model, to investigate possible scenarios relevant to future EnVision observations above the cloud tops. We focus on current data-model biases and provide a tentative interpretation of their origin. Benchmark simulations by Martinez et al. (2024, https://doi.org/10.1016/j.icarus.2024.116035) overestimate the nightside $��O_2�$ airglow emission by a factor of two and place the emission peak 5–7 km higher than observed. Furthermore, the emission distribution is not centered around midnight, but shifted to LT = 4h, likely due to a strong ($��\sim �$100 m/s) zonal wind component below 105 km. We performed sensitivity tests on unconstrained parameters (e.g., gravity wave drag and eddy diffusion) to evaluate their impact on the dynamical structures. Results show that reducing non-orographic gravity wave forcing below 105 km weakens that superrotation wind component, and recenter the emission around midnight. However, the altitude bias appears linked to insufficient vertical transport in the model. These findings underline the need for future space missions capable of continuously monitoring mesospheric gravity waves and $��O_2�$ nightglow to better constrain their spatial and temporal variability and improve the representation of key dynamical processes in Venus' upper atmosphere.

NASA's InSight mission has provided an unprecedented snapshot of Mars' seismicity, despite data analysis challenges arising from low signal-to-noise ratios (SNR) and single-station constraints. High frequency (HF) events—the most common type—were initially assumed to propagate through shallow crustal layers. However, several impacts that occurred late in the mission provided independent distance constraints, indicating that HF event energy must have propagated through the mantle. We analyzed the full HF data set using an extended catalog and denoised waveforms derived with deep learning (DL) techniques. Using a DL ensemble, we picked phase arrivals on denoised envelopes and estimated SNR-dependent pick timing uncertainties based on the removed noise. We computed distances consistent with mantle paths using the latest Mars interior models, while the back azimuth remained inconclusive due to local resonance dominating the HF bandwidth. We compared and grouped HF recordings by their similarity and investigated how attenuation properties shape their envelopes. Additionally, we re-calibrated and assigned magnitudes for the extended catalog. Overall, we (re-)located 1,430 HF events clustered between epicentral distances of around 1,600–3,600 km, but without constraints on the back azimuth, their source region remains speculative. Based on spatiotemporal similarities, we attributed a subset of 1,357 events to a common source region and labeled them as swarm events. The analysis of envelope shape confirms and extends previous results of stratified attenuation properties. Swarm events, with magnitudes between 1.5 and 2.5, are cumulatively equivalent to a single magnitude 4 event and show a high $��b�$-value and clear seasonal trends in seismicity.

Traveling waves in the Martian atmospheres play a crucial role in determining the weather and climate, particularly at mid-to-high latitudes. Previous observations have shown that these waves become prominent from early autumn to late winter in the northern hemisphere, influencing the dust cycle. However, their impact on the transport of dust and water ice clouds has not been studied quantitatively. Investigating the interaction between traveling waves and transport of such substances provides deeper insights into the climatology of Mars. In this study, we utilize data taken by the Mars Climate Sounder (MCS) onboard the Mars Reconnaissance Orbiter. Observations reveal eastward-propagating waves during the northern autumn and winter, identified as Rossby waves. The results show that waves with a zonal wavenumber of 1 become prominent during this period and in this region. Moreover, there is a correlation among the periodic variations in temperature, dust, and water ice. The amplitudes of the temperature, dust, and water ice variations are roughly consistent with each other, suggesting that the variations are all driven by the meridional advection associated with the traveling waves. These findings suggest that traveling waves play a significant role in the transport of dust and water ice clouds on Mars.

Understanding the sources of hydration on Vesta's surface provides insights into water origins in the inner solar system. We estimated the hydration content across Vesta's surface using new calibrated Dawn VIR data. High content of hydration (up to 1,000 ppm) was observed in previously identified carbonaceous chondrite (CC)-rich regions. CC-poor areas consistently showed around 100 ppm of solar wind-induced hydration with no latitudinal dependence, likely due to Vesta's low surface temperatures and high axial tilt. Despite receiving less solar wind flux, Vesta's low-latitude surfaces exhibit higher hydration content than the Moon's, attributed to better hydration retention at lower temperatures (e.g., <∼280 K). At high latitudes (>∼80°) where the maximum daytime temperatures are less than ∼280 K, the Moon can effectively retain around four to five times hydration as that on Vesta, which is in great accordance with the greater solar wind fluence received by the Moon at its heliocentric distance. Our study suggested that the formation of water by solar wind implantation is ubiquitous on airless bodies in the solar system and that the retention of solar wind water is dominantly controlled by surface temperatures of these bodies.

Surface observations of Saturn's moon Titan revealed features characterized as dissected, elevated plateaus with high valley density known as labyrinth terrains. Of this terrain class, a subtype referred to as radial labyrinth is described as dome-shaped uplifts with radial channel patterns. Uplift of these radial labyrinths has previously been explained as cryomagmatic intrusions at the brittle–ductile transition zone. Here we propose an alternative hypothesis that crustal heterogeneities in Titan's upper clathrate crust introduce density differentials due to ethane-methane substitution, as ethane-rich liquids percolate into methane clathrate, inducing solid state flow and generating domal topography. This mechanism is analogous to salt tectonics on Earth and has similarly been evoked for dome formation on the dwarf planet Ceres. We show that the elevation and width of the observed radial labyrinths are consistent with domal uplift driven by a hydraulic head within the uppermost portion of Titan's crust, given a plausible set of elastic parameters for clathrate hydrates. Additionally, the insulating effect of clathrate, combined with partial mixing with water-ice, allows for sufficiently low viscosity for geologic flow on a relevant timescale: uplift of the domes could have occurred within the last billion years.

Pitted cones have been studied on Earth for at least two millennia, and they are often linked to an origin that requires H₂O in some form. Identified on Mars half a century ago, pitted cones have been studied on the red planet with remote sensing data, and different formation models have been proposed based on terrestrial examples. In this work, we examine pitted cones on Mars that formed in patterns along the perimeter of circles, but have heretofore not been detailed in the literature. Pitted cones in these circular macrostructures are found in large quantities only in a small, ∼7,000 km² region of Elysium Planitia, which has been dated to <10 Myr. We propose that these circular macrostructures follow the rims of buried impact craters, and that sediment-laden H₂O and/or steam breached the surface where the most recent resurfacing is thinnest and therefore weakest, tracing these buried crater rims. Such a formation method is a mud volcano. Mud volcanoes typically require subsurface volatiles such as H₂O and a buried heat source or tectonic triggering, both of which are non-controversial in Elysium's recent past. If our preferred interpretation is correct, this work would bolster the case for extremely recent and potentially shallow water in this region of Mars.

Analysis of space weathering features in lunar regolith using transmission electron microscopy (TEM) allows researchers to characterize the surface exposure timescale of individual grains from the Moon. TEM analysis of regolith grains from Apollo 17 scoop samples, collected from five different locations in the Taurus-Littrow Valley (TLV), each with unique surface exposure histories, was conducted. Results show that the extent of space weathering in both mature and immature soil is significant and demonstrate that non-agglutinitic grains in the samples have almost all experienced exposure to interplanetary space on the lunar surface. Solar energetic particle (SEP) track density derived exposure age distributions, when compared to observations from lunar core samples and regolith development models, suggest evidence of varying degrees of regolith mixing and overturn on the surface of the Moon. Exposure age distributions may be indicative of mixing of mature and immature regolith. Median exposure ages for mature soils saturate between 2.0 and 3.0 Ma while mean values will continue to increase with continued exposure on the lunar surface. The saturation of median exposure ages for individual grains may be attributed to high rates of reworking on the top millimeter of regolith. Recent analysis of LROC reflectance images found that the TLV light mantle could form from reoccurring landslide events. Maximum SEP exposure ages for particles in light mantle soils appear to indicate the relative landslide depositional order. Together, these observations can be used to interpret the mixing and depositional histories of geologic units in the TLV.

Siderophile elements tend to transfer from the magma ocean to the metallic core during core formation in Vesta, but kinetic barriers may prevent equilibrium partitioning. To evaluate the kinetic effect requires knowledge of siderophile element diffusivity in silicate melts, which has yet to be experimentally determined in vestan melts. We have performed diffusion experiments for Ga, Mo and W at 0.5–1 GPa and 1,573–1,873 K in synthesized eucritic and diogenitic melts. The diffusivities of Ga, Mo and W in two vestan melts with distinct melt depolymerization are found to be similar and are 2–3 orders of magnitude higher than those in rhyolitic melts. The modeling results reveal that Ga, Mo and W are enriched into the core to the extent that equilibrium partitioning allows, whereas some highly siderophile elements (HSEs) may maintain a disequilibrium state. However, this disequilibrium does not dramatically affect HSE abundances. The significant variability in HSE abundances in Vesta is mostly due to the brecciation effects and contamination from impactors or metals.

Periodic high-resolution imagery of Io is essential for understanding its surface evolution, from volcanic eruptions to tectonic deformation to large-scale mass wasting. Juno flybys in 2023 and 2024 obtained imagery of the surface with the JunoCam imager at 1.8 km/pixel spatial resolution, comparable to global observations from the Galileo spacecraft (1996–2001). Areas of Io's north pole were imaged for the first time, with low emission (46°–61°), high incidence angle conditions revealing several-kilometers-tall mountains. We are unable to identify detailed changes in Io's mountain features due to the limited overlap in the high-resolution coverage between the Galileo and Juno data sets. However, the improved lighting conditions in the JunoCam imagery allow us to refine our understanding of previously mapped features, including an extension of the rifting relationships previously proposed at Shamshu Patera. Cocytus Montes, a newly identified trio of mountains centered at 60°N 330°W, exhibit intermediate erosional stages with morphologies grading from sharp ridges to eroded hummocks along their slopes, providing a new perspective on the pace and processes of erosion on Io. We present a regional geologic map of this region, and examine the relationships between mountain units and the underlying layered plains which connect them on a raised plateau. Unique crustal blocks strewn across the plateau have sparse analogs elsewhere on Io, and prompt questions about the erosional mechanisms that may have emplaced them. We propose several formation mechanisms and conclude that while we cannot definitively determine which is responsible, regolith creep-modified cliff collapse is the most likely.