Journal of Geophysical Research: Planets最新文献

We investigate the nature of diagenetic features encountered by the Curiosity rover within Mount Sharp from sols 1900–3,049. Using Curiosity's Mars Hand Lens Imager and Mast Camera (Mastcam), we classify diagenetic features into established morphological categories and assess their spatial distribution, density, and size. Our analysis reveals variations in diagenetic feature density and morphology linked to stratigraphic boundaries and proximity to the Greenheugh Pediment unconformity, highlighting the role of diagenetic fluids in shaping these features. We find a reduction in diagenetic features at the Jura to Knockfarril Hill member boundary, a spike in feature abundance at the Knockfarril Hill to Glasgow member boundary, and a strong statistical relationship between feature abundance and vertical distance from the Greenheugh Pediment. These trends point to a dynamic history of diagenetic fluid flow, influenced by variations in porosity, permeability, and structural controls, including the presence of the Pediment.

The “light mantle” deposit at the base of South Massif in the Moon's Taurus-Littrow Valley was a primary science target for the Apollo 17 exploration. The possibility that it was a landslide triggered by ejecta from Tycho Crater is critical for establishing the age of Tycho and constraining recent lunar impact chronology; however, the mechanism of emplacement of the deposit has recently been questioned. The newly opened 73001/73002 double drive tube from Station 3 sampled 70.6 cm deep into the regolith and represents the first stratigraphic section of an extraterrestrial landslide deposit returned to Earth. Here we provide an overview of the stratigraphy of the 73001/73002 core based on top to bottom variations revealed by coordinated laboratory analyses and explore constraints on the emplacement of the light mantle deposit. Briefly, the upper ∼10 cm of 73002 contains a disturbed zone from space weathering and emplacement of ejecta from a nearby crater that excavated and ejected basaltic material. Below 10 cm is a nearly uniform unit of immature regolith. These data support a single event for the emplacement of the deposit at this location, followed by weathering and mixing of materials from nearby crater ejecta in the upper 10 cm. Slight variations in chemistry and clast components may reflect the relative stratigraphy of the South Massif slope, with material toward the bottom of 73001 originating from lower slopes and material from higher up in the core representing regolith from higher up the South Massif slopes.

The Mars 2020 rover, Perseverance, encountered a range of basaltic igneous rocks on the floor of Jezero crater, two of which are olivine cumulates, formed by accumulation of olivine crystals from basaltic magma. These olivine cumulates lie in a geomorphically distinct region, named Séítah, on the Jezero crater floor. To understand the origin of the olivine cumulates and their relationship with the adjacent basalts of the Máaz formation, we calculated the composition of the parent magma of one of the olivine cumulates, named Brac, based on chemical analyses and mineralogic interpretations from the Planetary Instrument for X-ray Lithochemistry (PIXL) instrument. Acceptable Brac/Dourbes parent magmas are olivine tholeiite basalts with SiO₂ ∼ 45%, MgO ∼ 8%, FeO_Tot ∼ 27%, Al₂O₃ ∼ 6%, and total alkali oxides of ∼2.8% weight. These compositions are similar to one of the Máaz basalts, the rock Rimplas, which is stratigraphically close to Séítah, but chemically distinct from other Máaz basalts. Rimplas could (within uncertainty) be a sample of the Brac parent magma, but it is more likely that Rimplas and Brac had a common (or similar) parent magma. Geochemical similarities between Rimplas and the other Máaz basalts thus suggest that Brac (and other olivine-rich rocks of Séítah) and the Máaz basalts could be geochemically related; they could have been cogenetic and possibly contemporaneous, or could have been derived (at different times) from similar or related mantle source(s).

Equatorial Layered Deposits (ELDs) are sedimentary landforms found at equatorial latitudes of Mars showing repetitive bedding and commonly associated with hydrous minerals. These deposits are important archives of Mars' past aqueous conditions yet in most cases their formation mechanisms are still debated and elusive. Here we provide a detailed characterization of the mineralogy and stratigraphy of three different exposures of ELDs in Meridiani Planum, where such formations are found within small impact craters and are dated back to the Noachian-Hesperian boundary. Our analysis highlights a varying degree of mixture between polyhydrated Mg sulfates and Fe/Mg phyllosilicates within the beds of all three chosen targets, with several alternating strata of sulfate-rich and phyllosilicate-rich materials. In one case, Al-phyllosilicates are also found along with their Fe/Mg counterpart. This is a much more varied mineral assemblage than previously reported for ELDs in this area. We propose a formation mechanism which explains the observed interbedding as a result of surface ponding of groundwaters, aqueous alteration of atmospherically-sourced basaltic materials and water table/pH oscillations (wet/dry cycles) leading to recurrent sulfate precipitation. Our findings show how local environments play a substantial role in recording small-scale variations of complex aqueous processes, generally not observed at regional and global scales on Mars.

Meteorite paleomagnetic studies indicate planetesimal generated magnetic fields, but spacecraft magnetic measurements have yet to identify asteroidal natural remanent magnetization (NRM). This apparent discrepancy is of particular interest in the context of the NASA Psyche mission, which will search for evidence of past magnetic activity of the metal-rich asteroid (16) Psyche. Here, we aim to test whether the NRM of meteorites inevitably drops below detectable values as specimen size increases, which could explain why asteroidal NRMs could never be detected. We focus on iron meteorites as possible analogs to (16) Psyche's constituent material. To do so, we measure the remanent magnetic field and estimate the NRM of samples of four iron meteorites with volumes between mm³ and m³. We find that their estimated NRMs decrease with increasing sample size but appear to plateau. These data are compatible with the idea that the bulk NRM of increasingly large objects becomes dominated by the fraction of this NRM produced by assemblages of magnetic minerals sharing a common magnetization direction. Moreover, all m³-sized meteorites carry NRMs that are two orders of magnitude above the detectability limit of the Psyche Magnetometer, three of which are possibly pre-terrestrial. These data, acquired on some of the largest masses of iron meteorites available on Earth, support the range of plausible NRM values for km-size regions of (16) Psyche, used to establish the spacecraft Magnetometer's performance requirements. Nevertheless, large-scale events such as brecciation of the asteroid following magnetization acquisition could always lower the asteroid's NRM below the detectability limit.

Certain spiral density waves in Saturn's rings are generated through resonances with planetary normal modes, making them valuable probes of Saturn's internal structure. Previous research has primarily focused on the rotation rates of these waves. However, other characteristics of these waves also contain valuable information about the planet's interior. In this work, we investigate the amplitudes of the waves across the C-ring by analyzing high signal-to-noise profiles derived from phase-corrected averages of occultation profiles obtained by Cassini's Visual and Infrared Mapping Spectrometer (VIMS). By fitting these wave profiles to linear density wave models, we estimate the ring's surface mass density, mass extinction coefficient, and effective kinematic viscosity at 34 locations in the C-ring, as well as the amplitude of the gravitational potential perturbations associated with 6 satellite resonances and 28 planetary normal mode resonances. Our estimates of the C-ring's mass extinction coefficient indicate that the typical particle mass density is around 0.3 g/cm³ interior to 84,000 km, but can get as low as 0.03 g/cm³ exterior to 84,000 km. We also find the ring's viscosity is reduced in the outer C-ring, which is consistent with the exceptionally high porosity of the particles in this region. Meanwhile, we find the amplitudes of Saturn's normal modes are complex functions of frequency, $���\ell ��$ and $���m��$, implying that multiple factors influence how efficiently these modes are excited. This analysis identified two primary sources of these normal-mode oscillations: a deep source located close to Saturn's core, and a shallow source residing near the surface.

Space weathering alters the surface materials of airless planetary bodies; however, the effects on moderately volatile elements in the lunar regolith are not well constrained. For the first time, we provide depth profiles for stable K and Fe isotopes in a continuous lunar regolith core, Apollo 17 double drive tube 73001/2. The top of the core is enriched in heavy K isotopes (δ⁴¹K = 3.48 ± 0.05‰) with a significant trend toward lighter K isotopes to a depth of 7 cm; while the lower 44 cm has only slight variation with an average δ⁴¹K value of 0.15 ± 0.05‰. Iron, which is more refractory, shows only minor variation; the δ⁵⁶Fe value at the top of the core is 0.16 ± 0.02‰ while the average bottom 44 cm is 0.11 ± 0.03‰. The isotopic fractionation in the top 7 cm of the core, especially the K isotopes, correlates with soil maturity as measured by ferromagnetic resonance. Kinetic fractionation from volatilization by micrometeoroid impacts is modeled in the double drive tube 73001/2 using Rayleigh fractionation and can explain the observed K and Fe isotopic fractionation. Effects from cosmogenic ⁴¹K (from decay of ⁴¹Ca) were calculated and found to be negligible in 73001/2. In future sample return missions, researchers can use heavy K isotope signatures as tracers of space weathering effects.

Satellites play a crucial role in understanding the formation and evolution of trans-Neptunian objects (TNOs). The spin–orbit evolution of satellite systems depends on their thermal histories, allowing us to constrain the rock mass fraction within TNOs based on their current spin–orbit states. In this study, we perform coupled thermal–orbital evolution calculations for two satellite systems around undifferentiated TNOs: Orcus–Vanth and Salacia–Actaea. Our results demonstrate that the current spin–orbit states of these systems are consistent with a rock mass fraction of approximately 20%–30%. Additionally, we estimate the organic mass fraction within the TNOs and find that it is comparable to the rock mass fraction. These findings suggest that the chemical composition of TNOs closely resembles that of comets.

Large dendritic valley networks observed on Mars present a paleoclimate paradox. Geologic observations of Noachian units on Mars reveal a global extent of valley networks, which are believed to have been formed through incisions made by flowing water. However, most climate models predict global surface temperatures too far below the freezing point of water to support an active hydrological system. Conflicting observations and models have led to disparate theories for the climate of early Mars. In this work, we surveyed a large region of the cratered southern highlands to identify the location, elevation, and distribution of observed valley heads. These valley head locations were compared to landscape evolution simulations in which the spatial distribution of runoff was varied. The measured valley head distributions were compared to predictions from landscape evolution models for two end-member hypotheses: (a) a warm wet climate that supported spatially distributed precipitation, and (b) surface runoff from ice cap margins, as envisioned by the Late Noachian Icy Highland model (LNIH). The observed elevation distribution in valley heads is consistent with the prediction of precipitation-fed models, and inconsistent with models in which runoff derives exclusively from a single line-source of high-elevation ice-melt. The results support the view that it is unlikely for ice caps to be the sole source of water and are consistent with the hypothesis that precipitation significantly contributed to valley network formation on ancient Mars.

The formation and evolution of rocky planets such as the Earth are marked by the heavy bombardments that dominated the first parts of the accretions. The outcomes of the large and giant impacts depend on the critical points and liquid-vapor equilibria of the constituent materials. Several determinations of the positions of the critical points have been conducted in the last few years, but they have mainly focused on systems devoid of volatiles. Here, we study, for the first time, a volatile-rich ubiquitous model mineral, phlogopite. For this, we employ ab initio molecular dynamics simulations. Its critical point is constrained in the 0.40–0.68 g/cm³ density range and 5,000–5,500 K temperature range. This shows that adding volatiles decreases the critical temperature of silicates while having a smaller effect on the critical density. The vapor phase that forms under cooling from the supercritical state is dominated by hydrogen, present in the form of H₂O, H, OH, with oxygen and various F-bearing phases coming next. Our simulations show that up to 93% of the total hydrogen is retained in the silicate melt. Our results suggest that early magma oceans must have been hydrated. In particular for the Moon's history, even if catastrophic dehydrogenation occurred during the cooling of the lunar magma ocean, the amount of water incorporated during its formation could have been sufficient to explain the amounts of water found today in the last lunar samples.