Journal of Geophysical Research: Planets最新文献

Marius Hills, Rümker Hills, and Gardner are three prominent volcanic complexes on the lunar nearside characterized by well-preserved elevated topography, highly concentrated domes/cones, and positive gravity anomalies. Here, we perform a comparative study of the geology and geophysics of these three volcanic complexes using multi-source remote-sensing data to better understand the volcanism diversity and magmatic evolution of the lunar nearside. Uniform and precise feature extraction methods are used to explore the morphological and geochemical characteristics of the volcanic complexes and their quasi-circular small shields (domes/cones). A new generalized approach based on three-dimensional (3D) gravity forward modeling is utilized to estimate the subsurface magma intrusion volumes. The results are about 2.63–6.65 × 10⁴, 1.48–3.86 × 10⁴, and 2.75–4.22 × 10⁴ km³ for the Marius Hills, Rümker Hills, and Gardner, respectively. Together with their extrusion volumes, Marius Hills has the largest magnitude of magmatic activity and the lowest ratio of intrusive versus extrusive volumes. Taking into account their geological and geophysical diversities, we propose three magma intrusion and extrusion schematic models and suggest that potassium, rare earth elements, and phosphorus (KREEP) may serve as an important driving force for the long-term and large-magnitude volcanism in Marius Hills, while the relatively short-lived and small-scale volcanism in Rümker Hills and Gardner may not be related to KREEP. Future geochemical studies of basalt samples from the Marius Hills region may provide additional clues to the role of KREEP in lunar nearside volcanism and thermal evolution.

Nanoparticles within lunar soil grains are a primary product of space weathering. The microstructural and chemical characteristics of the nanoparticles are diverse and their formation mechanisms are still under debate. In this paper, for the first time, tadpole-shaped nanoparticles (with Fe-Ni(-S) head and Fe-Ti-O tail) were found in the impact melt glass spherule of an agglutinate in the returned Chang'e-5 lunar soil, and their possible formation mechanisms were discussed. In terms of the Fe-Ni(-S) “head” formation mechanisms, they probably produced by shock-induced dissemination. Another possibility is that the Fe-Ni(-S) heads were derived from the impact glass due to liquid immiscibility. The S degassing of FeS was contributed to nanophase Fe-Ni metal. For the Fe-Ti-O tails, they are devitrified ilmenites, nucleated as a result of the passage of the Fe nanoparticles through the melt. These nanoparticles formed though impact-induced nonequilibrium growth and recorded the movement and migration of the Fe-Ni-S nanoparticles within the melt. The tadpole-shape nanoparticles provide a new example of viscous fingering in impact melts and the associated ilmenite dendrites point to the formation of high-temperature chemical gardens in lunar impact melt.

Layered deposits are found on the plateaus surrounding the western portion of Valles Marineris, mantling the chasmata rims. These rim deposits exhibit intricate layering and are described as light-toned layered deposits (LLDs) in previous studies. Light-toned layered deposits are thought to be composed of pyroclastic ash that was emplaced during volcanic eruptions and later chemically altered. Using Shallow Radar (SHARAD) observations to map radar reflections from what appears to be the base of these deposits, we discovered two additional types of rim deposits that are contiguous with the well-known LLDs; weakly layered deposits (WLDs) that exhibit less obvious stratification and completely unstratified deposits designated as nonlayered deposits (NDs). Complementing the SHARAD data with imagery from Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) and with narrow-angle imagery from the Mars Global Surveyor Mars Observer Camera (MOC-NA), we mapped the full extent of all rim deposits and present the finished map within this study. We hypothesize that all three deposits originate from pyroclastic ashfall but experienced different degrees of modification due to the variable presence of liquid water. This hypothesis requires a source of volcanic depositional material and past aqueous environments in regions with LLDs and WLDs. We discuss the potential for several large Tharsis volcanoes and a hypothesized degraded volcano within Noctis Labyrinthus as sources of the ash, and we examine the evidence for past aqueous environments.

Impact cratering is one of the fundamental processes throughout the history of the Solar System. The formation of new impact craters on planetary bodies has been observed with repeat images from orbiting satellites. However, the time gap between images is often large enough to preclude detailed analysis of smaller-scale features such as secondary impact craters, which are often removed or buried over a short time period. Here we use a seismic event detected on Mars by the NASA InSight mission to investigate secondary cratering at a new impact crater. We strengthen the case that the seismic event that occurred on Sol 1034 (S1034a) is the result of a new impact cratering event. Using the exact timing of this event from InSight, we investigated the resulting new impact crater in orbital image data. The S1034a impact crater is approximately 9 m in diameter but is responsible for over 900 secondary impact events in the form of low albedo spots that are located at distances of up to almost 7 km from the primary crater. We suggest that the low albedo spots formed from relatively low energy ejecta, with individual ejecta block velocities less than 200 m s⁻¹. We estimate that the low albedo spots, the main evidence of secondary impact processes at this new impact event, fade within 200–300 days after formation.

Main-belt objects (MBOs) with volatile components provide important insights into the solar system's evolution and the origin of Earth's water. In this study, we employ a 3D thermophysical model to simulate the evolution of a representative ellipsoidal main-belt comet (MBC) and investigate the factors influencing its gas and dust activity. Our results highlight the important role of large obliquities in amplifying the detectability of sublimation-driven dust emission in MBCs. For the modeled ellipsoidal 133P/Elst-Pizarro, we found an obliquity of at least $��\sim �30�°�$ is likely required to sustain a dust production rate of $��\sim �$0.01 kg/s (this required obliquity increases to $��\ge �\sim �45�°�$ for a dust production rate of $��\ge �\sim �$0.1 kg/s). By exploring the influence of locations and sizes of ice-exposed surface regions, we find that both the impact-triggered and landslide-triggered ice-exposure mechanisms can lead to detectable dust and gas activities for the modeled MBC. With probable distributions of ice-exposed surface regions, our results show that MBCs' sublimation-driven activity should be predominantly detectable near perihelion, independent of the true anomaly at solstice and the activation-triggering mechanism. Moreover, we find that the landslide-triggered mechanism results in dual peaks in dust and gas emission curves. This enables potential differentiation between the two mechanisms, suggesting that monitoring of MBCs' activity at various orbital positions is important to discern the underlying activation-triggering mechanism. Our analyses provide quantitative constraints on producing the observable cometary activity in ice-containing MBOs and highlight the importance of studying the rotational evolution and structural dynamics of ice-containing MBOs in characterizing their overall population.

The collapse of large impact craters requires a temporary reduction in the resistance to shear deformation of the target rocks. One explanation for such weakening is acoustic fluidization, where impact-generated pressure fluctuations temporarily and locally relieve overburden pressure facilitating slip. A model of acoustic fluidization widely used in numerical impact simulations is the Block model. Simulations employing the Block model have successfully reproduced large-scale crater morphometry and structural deformation but fail to predict localized weakening in the rim area and require unrealistically long pressure fluctuation decay times. Here, we modify the iSALE shock physics code to implement an alternative model of acoustic fluidization, which we call the Melosh model, that accounts for regeneration and scattering of acoustic vibrations not considered by the Block model. The Melosh model of acoustic fluidization is shown to be an effective model of dynamic weakening, differing from the Block model in the style of crater collapse and peak ring formation that it promotes. While the Block model facilitates complex crater collapse by weakening rocks deep beneath the crater, the Melosh model results in shallower and more localized weakening. Inclusion of acoustic energy regeneration in the Melosh model reconciles required acoustic energy dissipation rates with those typically derived from crustal seismic wave propagation analysis.

The diversity and abundance of diagenetic textures observed in sedimentary rocks of the clay-sulfate transition recorded in the stratigraphic record of Gale crater are distinctive within the rover's traverse. This study catalogs all textures observed by the MAHLI instrument, including their abundances, morphologies, and cross-cutting relationships in order to suggest a paragenetic sequence in which multiple episodes of diagenetic fluid flow were required to form co-occurring color variations, pits, and nodules; secondary nodule populations; and two generations of Ca sulfate fracture-filling vein precipitation. Spatial heterogeneities in the abundance and diversity of these textures throughout the studied stratigraphic section loosely correlate with stratigraphic unit, suggesting that grain size and compaction controls on fluid pathways influenced their formation; these patterns are especially prevalent in the Pontours member, where primary stratigraphy is entirely overprinted by a nodular fabric, and the base of the stratigraphic section, where increased textural diversity may be influenced by the underlying less permeable clay-bearing rocks of the Glen Torridon region. Correlations between quantitative nodule abundance and subtle variations in measured bulk rock chemistry (especially MgO and SO₃ enrichment) by the Alpha Particle X-Ray Spectrometer instrument suggest that an increase in Mg sulfate upsection is linked to precipitation of pore-filling diagenetic cement. Due to a lack of sedimentological evidence for widespread evaporite or near-surface crust formation of these Mg sulfates, we propose three alternative hypotheses for subsurface groundwater-related remobilization of pre-existing sulfates and reprecipitation at depth in pore spaces.

The Mars NO and the O₂ nightglow are produced by the recombination of atoms produced on the dayside by photodissociation and transported to the nightside. These emissions are tracers of the summer to winter pole dynamics in the upper Mars atmosphere. The UV-visible (UVIS) channel of the Nadir and Occultation for MArs Discovery (NOMAD) spectrometer onboard Trace Gas Orbiter (TGO) is the first instrument able to simultaneously monitor both nightglow emissions. Observations by NOMAD/UVIS during the first part of the Martian year show that both the NO and O₂ nightglow emissions are enhanced near the southern winter pole. Their mean brightnesses are 15 and 108 kR, respectively. These nightglow emissions generally occur between 30 and 60 km, the NO emitting layer being consistently located ∼10 km higher than the O₂ nightglow layer. Numerical simulations with the Mars Planetary Climate Model (MPCM, v6.1) properly reproduce the nightglow brightness but tend to overestimate the NO peak altitude by ∼10 km. These results suggest that the atomic oxygen density is correctly predicted by the model but that the nitrogen density altitude distribution might not be properly modeled.