Journal of Geophysical Research: Planets最新文献

Strong magnetic fields have been measured from orbit around Mars over parts of the ancient southern highlands crust and on the surface at the InSight landing site. The geological processes that are responsible for generating strong magnetization within the crust remain poorly understood. One possibility is that intense aqueous alteration of crustal materials, through the process of serpentinization, could have produced magnetite that was magnetized in the presence of a global core-generated magnetic field. Here, we test this idea with geophysical and geochemical models. We first determine the magnetizations required to account for the observed magnetic field strengths and then estimate the amount of magnetite necessary to account for these magnetizations. For the strongest orbital magnetic field strengths, about 7 wt% magnetite is required if the magnetic layer is 10 km thick. For the surface field strength observed at the InSight landing site, 0.4–1.1 wt% magnetite is required if the magnetic layer corresponds to one or more of the three crustal layers observed in the InSight seismic data (with thicknesses from 8 to 39 km). We then investigate the minerals that are produced by aqueous alteration for various possible crustal compositions and water-to-rock ratios using a thermodynamic model. Magnetite abundances up to 6 wt% can be generated for dunitic compositions that could account for the strongest magnetic anomalies. For more representative basaltic starting compositions, however, more than 0.4 wt% can only be generated when using high water-to-rock ratios, which could account for the weaker magnetizations beneath the InSight landing site.

Mars' north polar ice cap features troughs that cut into the ice, exposing subsurface layers of different brightness and topographic expression. Specifically, these layers represent two different stratum types: lower albedo (higher dust content) marker beds, which protrude out of the wall topographically, and higher albedo (i.e., icier) interbeds, which are recessed compared to the marker beds. Here, we investigate the role of local-scale processes by performing a detailed geomorphic characterization of variability in these strata across two sites, using a novel approach to calculating true layer protrusion which utilizes data from high-resolution Digital Terrain Models. We measure protrusions of the order of meters but find lateral variations within a single trough exposure, suggesting a role for local-scale processes in the evolution of the layers. We find that the topographic relief of protruding marker beds decreases as a function of decreasing trough slope and brightness (a proxy for dust cover/content). We also observe the presence of an insulative allochthonous dust veneer present on discrete sections of the trough wall, which we suspect plays an important role in modulating ice loss from the trough walls. A companion paper (Bramson et al., 2025, https://doi.org/10.1029/2024JE008360) models the contribution of insolation-induced sublimation to present a new framework, and potential timescales for the development of the marker bed protrusion observed here.

Troughs carved into Mars' polar ice cap expose layers of different brightness and topography. These layers can be divided into two strata types: darker, higher dust content marker beds and brighter, lower dust content interbeds. In a companion paper (Pascuzzo et al., 2025, https://doi.org/10.1029/2024JE008377), we measure the topographic protrusion of the marker beds and interbeds. Here, we investigate processes and factors that contribute to the evolution of these layers to gain insight into the sublimation rates and timescales for active trough wall retreat, specifically the development of observed layer topography. We perform thermal modeling and ice sublimation calculations to explain the topography and its lateral variations. We use our results to develop a novel sublimation-based framework for the development of marker bed protrusion. Our results suggest that marker beds can develop the observed meter-scale protrusions in thousands of years via cyclical bursts of differential sublimation modulated by lag production and removal. We find that marker bed topography can easily be formed within a single period of high insolation driven by Mars' axial precession. If the present-day topographic signatures of exposed trough strata are driven strictly by the differential sublimation and lag processes proposed here, our results suggest that ice retreat may have occurred ∼60–125 kya, with the topographic relief forming in 1–20 kyr. These results also lead us to suggest that thick insulative allochthonous dust veneers (such as that observed in Pascuzzo et al. (2025, https://doi.org/10.1029/2024JE008377)) may play an important role in forcing hiatuses in trough wall retreat during high insolation periods.

Understanding the interior structures of icy moons will be crucial in untangling narratives of formation and evolution, both within our solar system and beyond it. Seismology is a proven and unparalleled methodology for investigating the deep interiors of planetary bodies but has never been deployed on an icy moon. To improve future mission design, we conduct seismic simulations for Saturn's icy moon Enceladus which account for the unique seismic responses of icy ocean worlds. We discover that even with high surface temperatures at the south pole and 3D ice thickness models, seismic amplitudes are two orders of magnitude higher than the self-noise of mission-candidate instrumentation. We compare the effects of a 2D and 3D ice shell to determine the detail of seismic inversion for ice shell properties and how this varies with source and receiver location. We also compare the travel time differences caused by ice shell variation with potential effects from the uncertain core structure and discover that these two sources of travel time perturbation have similar magnitudes but could be distinguished through careful inversion strategy. We investigate varied source types to represent focal mechanisms likely to be present at the south pole of Enceladus. We finally make recommendations supporting landing sites between 20 and 30$��°�$ from the south pole that should enable observation of a wide range of seismic phases, including core-transmitted phases that could constrain core velocities.

Based on the temperature and dust opacity data from the Mars Reconnaissance Orbiter/Mars Climate Sounder and the OpenMars reanalysis, we report an extremely strong quasi-20-sol wave (Q20SW) during the global dust storm (GDS) in Mars Year (MY) 34. After the onset of the GDS in MY34, the amplitude of the Q20SW reaches approximately 12 K in temperature, which is the strongest from MY29 to MY35. By analyzing the Eliassen-Palm fluxes of the Q20SW and their divergences, we conclude that the Q20SW is enhanced due to the unseasonal temperature increase caused by the GDS. Moreover, we find a strong eastward propagating oscillation with a period of 12–16 sols and a wavenumber of 1 exists in the dust opacity after the commencement of the GDS. This indicates that the strong Q20SW could also modulate the dust variation in the middle latitudes during the GDS.

Pluto's surface displays a wide variety of geologic units from smooth plains to extremely rugged mountainous expanses. These terrains range in age from young, actively resurfaced regions (no observable craters even in the highest-resolution New Horizons images) to old, heavily cratered, eroded regions. Here we expand upon the crater data analysis and the independent crater data set used in the production of a 1:7M scale geologic map of Pluto that is to be published by the United States Geologic Survey (USGS). We present both relative ages based on crater spatial density (number of craters in a given size bin per km²) and quantitative ages (e.g., 2 Ga) using the estimated impactor flux onto Pluto. The techniques presented here were developed specifically for the information available from a USGS geologic map, where smaller craters are mapped as points only (no specific diameter information per crater). We developed a new type of visualization, called a distributed R-plot, to understand the relative ages of the geologic units. The uncertainties in the current knowledge of the Kuiper belt populations and impactor flux at Pluto propagate to large uncertainties in the estimated quantitative ages (∼a factor of two). However, both relative and quantitative ages from crater analysis are valuable tools in developing the sequence of geologic events. Pluto has large areas of crater-free young terrains (13 units making up ∼27% of mapped higher-resolution surface area) with widely varying morphologies, indicating a variety of resurfacing mechanisms, both exogenic and endogenic, likely active in Pluto's recent past or present.

The dynamic pressure of solar wind, which is determined by both solar wind density and velocity, is a crucial factor influencing the Martian plasma environment. In this study, we employ a multifluid magnetohydrodynamic (MHD) model to investigate the distinct effects of variations in solar wind velocity and density on boundary layers and the ion escape process. The simulation results indicate that, when the solar wind dynamic pressure is held constant, an increase in solar wind density leads to a significant expansion of the bow shock (BS) and a slight contraction of the magnetic pile-up boundary. Under conditions of elevated solar wind density, the electric fields that typically inhibit solar wind penetration weaken, allowing a greater number of solar wind protons to traverse the BS. This results in enhanced energy inputs, leading to increased thermal and magnetic pressures. Consequently, the tailward ion escape flux rises substantially due to the increased planetary ion density associated with the higher solar wind proton density. Furthermore, under these conditions, the magnetic field lines exhibit greater piling-up, with the interplanetary magnetic field penetrating to lower altitudes within the ionosphere, thereby creating additional tailward transport channels for planetary ions. Additionally, as solar wind density increases, the current sheet shifts toward the dawn side, resulting in a more pronounced asymmetry structure.

Planets and stars are able to generate coherent large-scale magnetic fields by helical convective motions in their interiors. This process, known as hydromagnetic dynamo, involves nonlinear interaction between the flow and the magnetic field. Nonlinearity facilitates existence of bi-stable dynamo branches: a weak field branch where the magnetic field is not strong enough to enter into the leading order force balance in the momentum equation at large flow scales, and a strong field branch where the field enters into this balance. The transition between the two with enhancement of convection can be either subcritical or supercritical, depending on the strength of magnetic induction. In both cases, it is accompanied by topological changes in velocity field across the system; however, it is yet unclear how these changes are produced. In this work, we analyze transitions between the weak and strong dynamo regimes using a data-driven approach, separating different physical effects induced by dynamically active flow scales. Using Dynamic Mode Decomposition, we decompose the dynamo data from direct numerical simulations into different components (modes), identify the ones relevant for transition, and estimate relative magnitudes of their contributions Lorentz force and induction term. Our results suggest that subcritical transition to a strong dynamo is facilitated by a subharmonic instability, allowing for a more efficient mode of convection, and provide a modal basis for reduced-order models of this transition.

The distribution of KREEP—potassium (K), rare earth elements (REE), and phosphorus (P)—in the lunar crust is an important clue to deciphering the geochemical and thermal evolution of the Moon. Surface measurements of thorium abundance taken by the Lunar Prospector Gamma Ray Spectrometer (LP GRS) instrument have shown that KREEP is concentrated on the lunar nearside surface, mirroring the hemispheric asymmetry observed in the distribution of maria, crustal thickness, and topography. However, the overall lateral and vertical distribution of KREEP within the crust is poorly constrained, leaving uncertainty in estimates of bulk crustal thorium abundance and in the history and evolution of KREEP. In this study, we compared the overall lateral and vertical distribution of lunar KREEP in the upper crust by determining the thorium abundance of material excavated by complex impact craters. We find that the distribution of KREEP on the nearside is consistent with a layer of high-Thorium ejecta from the Imbrium impact mixing with underlying low-Th (<1 ppm) crustal material, suggesting the excavation of a sub-crustal KREEP reservoir with thorium abundances as high as 45–120 ppm by the Imbrium-forming impact. Imbrium ejecta alone does not explain the distribution of thorium on the lunar farside, particularly around the South Pole Aitken basin, suggesting other sources for farside thorium enrichments. Furthermore, our results refute the existence of a large-scale Thorium-enriched layer in the upper 16 km of the farside crust.