Journal of Geophysical Research: Planets最新文献

Impact craters can be used to track water activity on Mars because their formation can expose subsurface material (hydrated pre-impact) as well as create an environment for water to leave a mineralogical signature of its presence (post-impact). This work uses the iSALE shock physics code to simulate impact-induced heating and bedrock displacement in complex impact craters on Mars. In conjunction with an updated global groundwater model for Mars, we determine how, and if impact-induced hydrothermal alteration can be distinguished from pre-impact alteration. We examine the effects of impactor size and speed, bedrock porosity, and bedrock thermal gradient on hydrothermal conditions within impact craters. Bedrock heating was used to define the levels of hydrothermal conditions that could form within a crater. Our simulation results suggest that: (a) the central uplift is unlikely to preserve pre-impact alteration products because of the level of heating it suffers during crater formation, and (b) impact-induced heating is not sufficient to create hydrothermal conditions within the excavated proximal ejecta, suggesting that any hydrothermal signatures within the ejecta blanket are associated with the pre-cratering geological processes. We used the groundwater model depths to constrain when pre-impact alteration could occur. Finally, we outlined how our thermal anomaly size and geometry measurements, groundwater depths, and excavation depths can be used to assess the overall probability that an observed hydrothermal alteration product was formed pre- or post-impact.

We investigate spatiotemporal characteristics of helium (He) bulges using data from the Neutral Gas and Ion Mass Spectrometer aboard NASA's Mars Atmosphere and Volatile EvolutioN Mission and numerical simulations from the Mars Planetary Climate Model (MarsPCM). During equinoxes, we observed a He bulge at equatorial latitudes in addition to the mid-to-high latitude bulges reported in previous studies. This bulge is consistent with MarsPCM simulations. In addition, MarsPCM predicts a He bulge with larger latitudinal and poleward extents than previous studies suggest, persisting throughout the Martian year (MY) under nominal dust conditions. During equinoxes, the bulges span 85°N–90°S latitudes on the nightside. During solstices, the southern winter bulge is more dynamic between 0 and 8 hr local time (LT), and the northern one between 18 and 24 hr LT. Seasonal migration of He bulges occurs around solar longitudes (L_s) ∼ 50° and ∼183°, transitioning toward the winter hemisphere. We compare MarsPCM simulations using “climatology” and specific “MY 34” dust scenarios, alongside Mars Global Ionosphere Thermosphere Model (MGITM) simulations, to examine the impact of “MY 34” Global Dust Storm (GDS) during its pre-storm (L_s ∼ 184°), peak (L_s ∼ 207°), and decay (L_s ∼ 240°) phases. Simulations indicate that the He bulge became most distorted during the storm's peak while remaining on the dayside. These distortions likely result from enhanced damping of meridional circulation at polar latitudes, contributing to the suppression of He bulges during high-dust seasons.

Investigating the stability of hydrated minerals is integral for examining the preservation of rocks for potential Mars Sample Return and has major implications for models that use rover-based observations to quantify Mars' global water budget. The Mars 2020 Perseverance rover produces abrasion patches to investigate fresh rock surfaces at Jezero crater, Mars. However, due to operational constraints, the full analysis process typically takes several martian days (sols), and freshly exposed hydrated minerals may dehydrate upon atmospheric exposure between abrasion patch creation and their analyses. To assess the potential for short-term dehydration, the SuperCam instrument conducted the first in situ rover-based dehydration experiment on rock exposures of the “Bright Angel formation.” The SuperCam and SHERLOC rover instruments indicated that the primary mineral hydration phases were Fe-hydroxides, Ca-sulfates such as bassanite (mixed with anhydrite), with possible minor contributions from non-interlayer-water phyllosilicates (e.g., hydroxyl-bearing only). The experiment involved a four-sol sequence of observations on the Steamboat Mountain abrasion patch, beginning just 22 min after abrasion. Dehydration was assessed by tracking changes in the 1.93 μm H₂O absorption feature, which is sensitive to structural, absorbed, and adsorbed water. No significant changes in hydration were observed over the 93 hr, suggesting that the exposed minerals were already in a low hydration state and/or exhibit high stability under current martian surface conditions. These findings imply bulk rocks with low hydration and high stability minerals may not dehydrate upon exposure to the modern martian atmosphere on short time scales, consistent with predictions from laboratory simulations of Mars-like environments.

The concentration of volcanic material and Heat-Producing Elements (HPE) on the lunar nearside surface suggests an asymmetry of interior properties and thermal history between the two hemispheres. However, the distribution of HPE beneath the surface and the processes that led to their potential enrichment on the nearside remain poorly understood. Here, we use a 3D geodynamic model to infer the interior distribution of HPE based on surface heat flux estimates. We explore the consequences of a putative HPE-rich unit underneath the Procellarum region on the lateral variations of the present-day surface heat flux. Assuming a circular geometry and 1.6 km average thickness, we explore various sizes, locations, and enrichments of the HPE-rich unit, including the complete absence of such an anomaly, and select successful scenarios based on models that match the Apollo heat flux measurements. Scenarios with either a homogeneous HPE distribution in the mantle or a globally uniform HPE-rich layer lead to surface heat fluxes inconsistent with Apollo data. Conversely, a HPE anomaly beneath the nearside, extending at least to the Apollo 15 landing site and at most encircling the entire mare region, including Apollo 17 landing site, can match both measurements. The required Th concentration within the anomaly ranges from 23 to 50 ppm, assuming a 1.6 km thickness. Finally, we predict heat flux ranges of 7–12 mW/$��m^2�$ and 8–14 mW/$��m^2�$ for the upcoming Blue Ghost Mission 1 and APEX®1.0 heat flux measurements.

Jupiter's equatorial atmosphere is covered by dense hazes that extend from the main cloud level to the lower stratosphere. These hazes are variable in optical depth and brightness, although the causes of these variations are unknown. James Webb Space Telescope (JWST) observations of the equatorial hazes in 2022 in near-infrared wavelengths sensitive to the lower stratosphere (50–300 mbar) showed a narrow stratospheric jet at the equator that increases in velocity with altitude. Hubble Space Telescope (HST) observations of Jupiter centered at the strong methane absorption band at 890 nm are sensitive to hazes around 200–400 mbar, close to the lowest region observed by JWST. Here we used HST observations in the FQ889N filter obtained between 2015 and 2024 to study the variability of the zonal winds and haze brightness at the upper tropospheric levels. We find significant variability in both zonal winds and brightness at the equator. In most years, equatorial winds in the methane absorption band are similar to winds measured in visible wavelengths, but in 2019–2022 we obtain winds with values comparable to those measured by the JWST at the narrow central equatorial jet. A concurrent brightness increase during this period hints at the possibility of a change in the altitude of the hazes, which may indicate a vertically sheared jet detectable on images at 890 nm when the hazes are located high. Wind and brightness variations do not follow regular oscillations making less probable a direct relationship with Jupiter's Equatorial Stratospheric Oscillation.

Plasma depletion and electron energy flux depletion are key phenomena that contribute to the understanding of plasma escape in the Martian ionosphere. Based on electron energy flux and ion measurements obtained from the Mars Atmosphere and Volatile Evolution spacecraft from 1 October 2014 to 31 December 2023, this study analyzes the climatic characteristics of plasma depletion and electron energy flux depletion in the Martian ionosphere. The observations reveal that the plasma depletion and electron energy flux depletion are frequently observed in regions with Martian crustal magnetic fields. Electron energy flux depletion occurs approximately 2–5 times more often than the plasma depletion. In terms of the distribution of altitude of the two depletions, the observations show that the electron energy flux depletions mainly occur below 200 km, while the plasma depletions dominate 200–350 km. Additionally, the two types of depletion both exhibit variations with the local time, which shows a higher occurrence rate at night than during the day. Plasma depletion exhibits minimal seasonal variability, whereas electron energy flux depletion displays a pronounced seasonal pattern with peak occurrences near mid-season and reduced activity at the beginning and end. Moreover, simultaneous plasma and electron energy flux depletions occur both at day and night, with a higher frequency at night concentrated over Martian crustal magnetic field regions. Several mechanisms that could contribute to the formation of the depletion are analyzed and discussed.

Building on our previous studies of the far-ultraviolet (FUV) reflectance of Apollo soil 10084 and lunar soil simulants JSC-1A and LMS-1 (Gimar et al., 2022, https://doi.org/10.1029/2022je007508; Raut et al., 2018, https://doi.org/10.1029/2018je005567), we present new FUV results for Apollo soils 68501 and 71061. Heavily weathered soils (68501, 10084)–enriched in submicroscopic Fe, agglutinates, and sub-micron scale roughness as revealed by our electron microscopy investigations–are darker in the FUV and predominantly backscatter incident light. In contrast, the relatively less weathered subsurface 71061 soil is approximately twice as bright, exhibits forward scattering, and presents a steeper blue spectral slope between 130 and 160 nm compared to the weathered soils. Differences in either primary composition or mineralogy appear to have little to no effect on the FUV albedo or scattering behavior of these soils since the reflectance of high-Ti mare 10084 and low-Ti highland 68501 are nearly indistinguishable within error. Further investigation of additional Apollo-era soils across various maturity indices is needed to fully characterize the influence of space weathering on lunar soil FUV spectrophotometric response.

Although no rovers are currently capable of directly measuring rock density and strength, these properties are highly valuable to better understand the types of rocks that are being investigated by a rover, as well as the conditions on Mars during and after rock formation. Here, we use engineering data collected by the corer on the Perseverance rover to infer rock density and strength (unconfined compressive strength, or UCS) by comparing drill data for martian rocks to drill data for well-characterized analog materials that were cored using the same equipment on Earth. We calculate the energy expended by the drill to core each rock and find discrete correlations between both energy and measured rock density, as well as energy and strength of the analog materials. These correlations are then used to calculate likely values for density and strength of the rocks cored on Mars. Potential homogeneity of the martian samples is also indicated by changes in the drill response during coring. Overall, we find a wide range of UCS and density for the martian rocks. Endmembers are consistent with rover team interpretation as igneous (high strength and density) and sedimentary (low strength and density) lithologies. The extraordinarily low strength and density of the sedimentary materials are further consistent with greater porosity resulting from generally sparse cementation on Mars. The majority of rocks interpreted as igneous by team members, however, were also substantially weaker and less dense than expected based on their composition and texture, suggesting that interpretations may need refinement.

Nakhlites, clinopyroxene-rich rocks, are the largest single-origin suite of samples from Mars. Despite extensive study to discern their petrogenetic histories, nakhlite emplacement mechanisms and environments are not well-constrained, and it is unknown whether they represent intrusive or extrusive igneous rocks, or a combination. Here, we use X-ray computed microtomography (XCT) and three-dimensional (3D) quantitative textural analyses (e.g., 2D–3D modal abundances, crystal size distributions [CSDs], and petrofabrics) to place additional constraints on nakhlite formation and emplacement. Modal abundances between and within the nakhlites are variable on both a 2D and 3D basis, highlighting the significance of XCT and 3D analyses when studying these samples. All nakhlites in our study have similar crystallization conditions and histories based on 3D CSDs. Cumulus phases (=olivine and pyroxene) crystallized from magma(s) with high nucleation densities, likely related to effective undercooling, and subsequently underwent a period of magma storage. The CSD profiles record evidence for magma recharge events. Pyroxene long-axis orientations in the nakhlites studied here exhibit a magmatic foliation, which likely developed during crystal settling and accumulation in low-to-no flow settings, such as magma chambers, shallow intrusions (e.g., sills and dikes), lava lake or pond infills, or thick lava flows. We also show that the pyroxenitic layer of Theo's Flow (Canada) may not be an appropriate terrestrial analog for the nakhlites due to differences in emplacement mechanisms and conditions. Our findings suggest that lava flows may be less prevalent in the martian meteorite collection, while intrusive bodies and rocks may be more common than initially thought.

Cooling fractures found within impact melt deposits have been manually mapped within several craters on the Moon and Mercury, as their distribution can indicate which heat-loss processes were most significant in the periods after impact. However, due to the discovery of melt deposits in Lunar impact craters with sub-km diameters, it is unlikely that the complete mapping of these impact melt fractures (IMFs) on the Moon will be achievable without automation. As such, we have trained a DeepLabV3 semantic segmentation deep convolutional neural network, called IMFMapper, to detect IMFs within Lunar Reconnaissance Orbiter Narrow Angle Camera (LROC NAC) satellite imagery. As a means of maximizing the size of the training data set, “weak” pixel-level labels were generated by buffering line annotations. In testing upon the IMFs found within Ohm crater, IMFMapper achieved an average $��F_1�$-score of 69.3%. IMFMapper has also been deployed to map IMFs within the previously surveyed Crookes crater, where we have found new candidate melt deposits within the crater's western and southern walls. In addition, IMFMapper has produced the first map of IMFs within Schomberger A crater, in which IMFs may act as permanently shadowed regions due to the crater's proximity to the Lunar South Pole. The successful mapping of IMFs in Schomberger A also signifies IMFMapper's robustness to extreme solar incidence angles. We also demonstrate that IMFMapper could be implemented for automated mapping of IMFs on Mercury upon the commencement of BepiColombo's science operations.