Journal of Geophysical Research: Planets最新文献

Icy satellites host topography at many length scales, from rifts and craters on the small end to equatorial-pole shell thickness differences that are comparable to these bodies' circumference. The current paradigm is that icy satellites should not host stable small-scale topography. This idea comes from previous work using a “shallow”-shell model (i.e., ice shell circumference much larger than shell thickness) with a rigid outer crust. In this limit, large-scale topography relaxes over a longer time scale than small-scale features. Here we revisit this paradigm and analyze relaxation of topography starting from the Stokes equations for viscous fluid flow. For a shell with a viscosity that decreases exponentially with depth, we show numerically that there is a regime where the larger viscosity outer crust acts as a nearly rigid boundary. In this case, the relaxation time scale depends on the wavelength. For the largest spatial scales, however, the time scale becomes independent of wavelength and the value is set by the average shell viscosity. However, the spatial scale that this transition occurs at becomes larger as the viscosity contrast increases, limiting the applicability of the scale-independent relaxation rate. These results for the relaxation of topography have implications for interpreting relaxed crater profiles, inferences of ice shell thickness from topography, and upcoming observations from missions to the outer solar system.

Earth wind, namely the particles from the Earth's magnetotail, is an important source of lunar water. Besides tailward flow incident on the lunar nearside when the Moon is in the magnetotail, there exists earthward flow bombarding the farside, affecting the distribution and preservation of lunar water. In this study, we determine the incident fluxes of both the tailward and earthward flows on the lunar surface with the ARTEMIS observations and examine their influences on the concentration and migration of lunar surface water and its reservation in the polar regions using Monte Carlo modeling. It is found that water molecules produced by the earthward flow can stay longer on the surface than those produced by the tailward flow. Our results suggest that the evolution of the Earth's magnetosphere can be inferred from Earth wind particles implanted in the soils of both the lunar nearside and farside.

Seismic determination of the Moon's crustal thickness is crucial for understanding its formation, composition, and evolution. Additionally, crustal thicknesses below seismic stations serve as anchoring points for 3D crustal thickness maps derived from gravity and topography field variations. However, strong seismic scattering inside the Moon can prevent seismic waves reflected on, or converted at, crust and upper mantle discontinuities from reaching the surface without interacting with scatterers. This study estimates Auto-Correlation Functions (ACF) of all channels of Apollo seismometers during the coda of high-signal-to-noise seismic events. As expected for a strongly scattering medium, Apollo stations S12 and S15 do not detect late arrivals in the ACF indicative of waves reflected on internal discontinuities. However, station S16 and, to a lesser extent, station S14 show stable late arrivals in the ACF. Arrivals at 14.2 and 27.1 s and at 23.9 and 50.6 s in the ACF of vertical and horizontal mid-period channels of station S16 are interpreted as $��P�$ and $��S�$ waves reflected at mid-crustal and crust-mantle interfaces. A seismic crust and upper mantle model beneath station S16 fits the arrival times of $��P�$ and $��S�$ waves with realistic seismic velocities and $��V_P�/�V_S�$ ratios ranging from 1.65 to 1.88. The crustal thickness is non-uniquely estimated at 53 km below station S16. Our results are also compatible with significant variations in the properties of the interfaces, or in strength of seismic scattering between Apollo stations.

Laboratory experiments on the behavior of rock and mineral samples under Venus conditions can yield a better understanding of gas-solid chemical weathering on the Venus surface. The Glenn Extreme Environments Rig (GEER) vessel can maintain Venus surface temperature, pressure and a nine-gas atmosphere for months. We provide an overview of the GEER Test Project Marty's Minerals Test (MMT), which ran for 60 days at 460°C, 93 bars under a 9- component Venus-relevant gas mixture. This experiment included over 90 compositionally unique chips and powders of natural samples selected to explore the pathways and relative rates of alteration of a broad range of mineral and rock types. Temperature, pressure, and gas (CO₂, N₂, SO₂, OCS) composition were monitored over the run. Rapid SO₂ depletion from the vessel gas phase occurred throughout the test, indicating sequestration of SO₂ via gas-solid reactions. A significant sink for SO₂ is the formation of iron oxide and nickel sulfide coatings on some chamber parts, which was compensated by multiple SO₂ gas injections during the run. Initial results for selected samples include the formation of secondary minerals at sample surfaces (e.g., on Na₂CO₃, natrite) and complete alteration of other samples (e.g., FeS, troilite) to oxides and sulfides. Some powdered samples consolidated to form hardened layers or chips. These observations show that some mineral phases are chemically and/or physically unstable over the timescale of the run. This test confirms that the GEER is a critical asset and reference point to support the study of gas-solid interactions at Venus conditions.

A major mission goal for the Mars Science Laboratory’s rover, Curiosity, is to investigate the transition from clay-bearing to hydrated-Mg-sulfate-bearing sedimentary strata hypothesized to record a transition from a wet to a dry paleoclimate. Alpha Particle X-ray Spectrometer (APXS) results from this region, named the Clay-Sulfate Transition (CST), indicate an overall ∼5% increase in Ca-sulfate, but Mg-sulfate enrichment is limited to diagenetic nodules. Sulfates in the CST change sharply at the contact with the overlying Mg-sulfate unit, which has ∼5% Ca-sulfate and ∼10% Mg-sulfate in the bedrock matrix. Despite this change in sulfate assemblage, and the transition from fluvial-lacustrine to drier aeolian sedimentary deposits, the bulk chemical composition of the aeolian sandstone (sulfate-free basis) effectively has the same altered basalt chemical fingerprint as the underlying fluvial-lacustrine mudstone. That is, the composition of rocks that record the transition from a wet to a dry paleoclimate is isochemical. It is remarkable that the aeolian sandstone has the same altered bulk chemical characteristics as the fluvial-lacustrine mudstone, notwithstanding very different inferred geochemical regimes. We propose a simplified model wherein older basaltic sediment was aqueously altered in a fluvial-lacustrine regime and reworked, likely during cycles of alteration, salt formation, and reworking. This process led to an averaging of the bulk chemical composition of the Mt. Sharp group sediment, resulting in the isochemical characteristics of the paleoenvironment change.

The morphology of fresh lunar craters provides important clues about how craters of different sizes form, and is used as a baseline for understanding how craters evolve over time. Topographic spectral analysis is a powerful tool for studying the morphology of lunar craters, as it can quantify the scale-dependent topographic variation of individual crater morphologic features. Furthermore, the 2D topographic power spectrum can reveal the spatial directionality of surface features, as an object with a preferred orientation in the space domain will exhibit a pattern rotated by 90$��°�$ in the wavenumber domain. In this study, we calculate the 2D power spectral densities of surface elevations of three morphologic features of fresh lunar craters, including the continuous ejecta, wall, and floor, from a subset of 104 Copernican- and Eratosthenian-aged craters larger than 1 km in diameter. The calculated power spectral density in general decreases with increasing wavenumber, indicating that the crater surface is smoother at smaller scales. We fit the obtained 2D power spectral density using a function with four parameters that characterize important topographic properties of fresh lunar craters, including how topographic variation is distributed across length scales and how the relative strength of radial or circumferential topography changes in different morphologic features. We derive the dependence on crater diameter for each of the four fit parameters for each morphologic feature, and then use the empirical fits to generate a 3D shape model for synthetic fresh lunar craters, which can be used as input when modeling lunar landscape evolution.

Noachis Terra, in Mars' southern highlands, is a region where “warm/wet” climate models of the early Martian Climate predict high rates of precipitation but which is poorly dissected by Valley Networks (VNs). We searched for Fluvial Sinuous Ridges (FSRs, or “inverted channels”) here because they (a) provide alternate evidence to VNs for flowing surface water in the form of river systems with high rates of deposition, and (b) have also been found in Arabia Terra, a similarly aged but geologically distinct region of the highlands that is also poorly dissected by VNs. Using a 6 m/pixel regional image mosaic, supported by other orbital data sets, we recorded the locations, lengths and morphological characteristics of FSRs. We find that FSRs are common across Noachis Terra, with a cumulative length greater than 15,000 km, increasing the drainage density of mapped fluvial systems in the region by 18%. FSRs can occur as isolated segments, but some systems are hundreds of kilometers in length and form branching networks. The regional abundance of FSRs suggests a distributed source of water (e.g., precipitation) and their 10–30 m relief and interconnectedness at local scales suggest they were relatively long-lived river systems. Our results, especially when taken alongside those in Arabia Terra, point toward widespread, sustained fluvial conditions in Mars’ highlands at ∼3.7 Ga, and provide important input into global climate models of this period. As Noachis Terra is a typical highland region on Mars, we suggest that FSRs are likely to be present throughout highland terrains of similar ages.

Enceladus, a moon of Saturn with a subsurface ocean containing potential hydrothermal activity, is a crucial target for habitability and life detection missions. While the Cassini mission provided important information about Enceladus, many unanswered and consequential questions remain, including its habitability, geochemical history, and whether Enceladus currently hosts life. We have developed a general science traceability matrix (STM) detailing a set of science objectives relating to its geology and habitability that can be applied to different mission architectures and concepts. This STM was designed to be broad and cover a broad science trade space for mission development; a companion paper discusses the scientific details of the STM (Rodriguez et al., 2025). In this paper, we discuss which mission architectural features would be needed to meet the STM's different science goals and observables. We identify direct access to ocean samples as an important architectural feature to fulfill measurements of habitability and life detection. We additionally propose using integrated instrument suites for life detection science objectives. We highlight opportunities for advancement in research and technology development that could enable different science objectives, including autonomy and instrument design. The results of this workshop detailed in this publication can be used as a framework for mission concept design and development. This document is designed to be used as a roadmap for the development of new technology maturation for future investigations to maximize science return.

Satellites orbiting Mars have measured crustal magnetic fields up to two orders of magnitude stronger than those on Earth. Although Mars currently lacks an active global magnetic field, this magnetization preserves a valuable record of the planet's early dynamo activity and crustal evolution. We present a high-resolution model of the crustal magnetic field of Mars, using all currently available magnetic field data collected by the MGS and MAVEN spacecraft (up to 02/2025), combined with a novel modeling approach. Notably, we incorporate recent low-altitude MAVEN data which contain short wavelength signals that were not available for previous models. We show that neural networks trained from spacecraft data can accurately predict the magnetic field at any location around Mars at orbital altitudes. These physics-informed networks use the equations of magnetostatics to enforce the conservative and solenoidal nature of the field, and are enhanced with bagging to mitigate the effect of noise in the data. Using this ensemble approach, we provide an estimate of uncertainties associated with our predictions. To demonstrate the performance of this method, we benchmark it against previous models using the same input and validation data subsets. Our model achieves an unprecedented resolution of spherical harmonics degree 139, corresponding to a spatial resolution of 153 km at the surface. Using our model to investigate small scale magnetic field signatures, we find that magnetic fields over ancient paleolakes are significantly stronger than other surface features or geological units, suggesting that serpentinization may have played a key role in magnetizing the crust.

Hydrological flows generated by meteoroid impact are still largely unexplored on Mars and may also have implications for Earth. We reconstructed the hydrological sequence initiated on Mars by a less than 3 Ma old meteoroid impact that formed the 28 km-wide Tooting crater on Amazonis Planitia, an ice-bearing region. Significant thermal and mechanical erosion were produced by the temporary rivers created by the impact on the icy terrain. Through analysis of CTX and HiRISE imagery supplemented with hydrological calculations, we inferred that the meltwater flowed approximately 80 km, eroding deeply the soil. Upon encountering an extensive (more than 100 km) impact-induced fracture line network, the water plummeted in vertical waterfalls, creating thermokarst caverns and ephemeral lakes. Secondary water springs are hypothesized to stem from the impact of ballistic ejecta blocks. Our analysis reveals that the initial hydrologic activity took a short time (hours to one day), while thermal effects were more durable but still geologically rapid. HiRISE imagery reveals slope streaks inside the emptied lacustrine basins. Lines, which emerge from a deep regolith layer, are potentially indicative of aquifer-fed water springs. The consistent origination of multiple lineae at the same stratigraphic level hints at significant subsurface re-mobilized water or ice, when heat was released from temporary warm lakes.