The thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here, we show that observations of tidally-driven diurnal surface displacements can constrain the mean ice shell thickness. Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite-element model of Enceladus to calculate diurnal tidal displacements for a range of mean crustal thickness values in the presence of such structural heterogeneities. Consistent with results from prior studies, we find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing ---such as Tiger Stripes on Enceladus---their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of mean crustal thickness that assume spherical symmetry a priori can deviate from the true value by as much as ~41% when structural heterogeneities are present. Additionally, we show that crustal heterogeneites near the South Pole produce differences of up to 35% between Love numbers evaluated at different spherical harmonic orders. A ~41% range in estimates of mean crustal thickness from Love numbers is smaller than that found with approaches relying on static gravity and topography (~250%) or analyzing diurnal libration amplitudes (~ 85%) to infer mean crustal thickness at Enceladus. As such, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring mean crustal thickness.

During the first 2934 sols of the Curiosity rover’s mission 33,468 passive visible/near-infrared reflectance spectra were taken of the surface by the mast-mounted ChemCam instrument on a range of target types. ChemCam spectra of bedrock targets from the Murray and Carolyn Shoemaker formations on Mt. Sharp were investigated using principal component analysis (PCA) and various spectral parameters including the band depth at 535 nm and the slope between 840 nm and 750 nm. Four endmember spectra were identified. Passive spectra were compared to Laser Induced Breakdown Spectroscopy (LIBS) data to search for correlations between spectral properties and elemental abundances. The correlation coefficient between FeOT reported by LIBS and BD535 from passive spectra was used to search for regions where iron may have been added to the bedrock through oxidation of ferrous-bearing fluids, but no correlations were found. Rocks in the Blunts Point-Sutton Island transition that have unique spectral properties compared to surrounding rocks, that is flat near-infrared (NIR) slopes and weak 535 nm absorptions, are associated with higher Mn and Mg in the LIBS spectra of bedrock. Additionally, calcium-sulfate cements, previously identified by Ca and S enrichments in the LIBS spectra of bedrock, were also shown to be associated with spectral trends seen in Blunts Point. A shift towards steeper near-infrared slope is seen in the Hutton interval, indicative of changing depositional conditions or increased diagenesis.

MarsWRF, the general circulation model of Mars, is one of the most commonly used models to study the dust cycle in the Martian atmosphere. It has been widely used to study the mechanisms of dust storms and their effects on the Martian atmosphere. To better understand the ability of MarsWRF to simulate the dust cycle on Mars, this study assesses the current dust lifting schemes in the model, specifically the convective lifting and wind stress schemes. It is found that, by tuning lifting efficiency, the model with the convective lifting scheme can generally reproduce the seasonal variation of the mid-level atmospheric temperature (T15) but cannot reproduce the observed spatial distribution of dust devils, which exhibits non-homogeneous (uniform) distribution in the northern (southern) hemisphere. The model with the wind stress lifting scheme can generally capture the observed magnitude of T15 and column dust optical depth (CDOD) with properly tuned lifting efficiency and threshold drag velocity. There is a discrepancy in the assessment of modeling seasonal variations of dust with T15 and CDOD, which may be partly due to the observational uncertainties related to T15 and CDOD and the empirical modeling methods of Martian dust optical properties and radiative effect. For the spatial distribution of dust, there are significant simulation biases regardless of the tuning, which may be caused by the biases in the dust lifting process and large-scale atmospheric circulation. The analysis highlights that dust lifting schemes need further improvement to better represent the dust cycle and their impacts on Mars.

Comets are active geological worlds with primitive surfaces that have been shaped to varying degrees by sublimation-driven sediment transport processes. Rosetta’s rendezvous with comet 67P/Churyumov-Gerasimenko (67P) in 2014 provided data with the necessary spatial and temporal resolutions to observe how micro-gravity worlds evolve. Rosetta’s observations have thus far revealed that the majority of changes to the surface occurred within 67P’s smooth terrains, vast sedimentary deposits that blanket a significant fraction of the nucleus. Understanding the global context of these changes, and therefore the sediment transport pathways that govern the evolution of 67P’s surface requires a thorough description of their changing morphologies, and an evaluation of existing global-scale spatial and temporal trends. Accordingly, we present a time-resolved synthesis of erosion and deposition activity on comet 67P as it passed through its August 13, 2015 perihelion from September, 2014 to August, 2016. Our mapping results indicate that, around perihelion, sediment is globally redistributed inter-regionally from 67P’s more active south to the north. Equally important, however, are local, topographically-influenced sediment transport processes, with large volumes of sediment moving intra-regionally over sub-kilometer scales. We also show evidence for regions of near-zero net erosion/deposition between approximately 30–60° latitude, which may act as terminal sedimentary sinks, with remobilization of these materials hindered by multiple factors. This work provides a complete mapping of the sediment transport processes and pathways across 67P observed by the Rosetta misison, and represents a critical step toward understanding the global landscape evolution of cometary surfaces.

Although deuterium (D) on Mars has received substantial attention, the deuterated ionosphere remains relatively unstudied. This means that we also know very little about non-thermal D escape from Mars, since it is primarily driven by excess energy imparted to atoms produced in ion-neutral reactions. Most D escape from Mars is expected to be non-thermal, highlighting a gap in our understanding of water loss from Mars. In this work, we set out to fill this knowledge gap. To accomplish our goals, we use an upgraded 1D photochemical model that fully couples ions and neutrals and does not assume photochemical equilibrium. To our knowledge, such a model has not been applied to Mars previously. We model the atmosphere during solar minimum, mean, and maximum, and find that the deuterated ionosphere behaves similarly to the H-bearing ionosphere, but that non-thermal escape on the order of 8000-9000 cm-2s-1 dominates atomic D loss under all solar conditions. The total fractionation factor, f, is 0.04–0.07, and integrated water loss is 147–158 m GEL. This is still less than geomorphological estimates. Deuterated ions at Mars are likely difficult to measure with current techniques due to low densities and mass degeneracies with more abundant H ions. Future missions wishing to measure the deuterated ionosphere in situ will need to develop innovative techniques to do so.

The Jovian moon Io features hundreds of paterae, broad depressions often filled with lava. The largest such example, Loki Patera, features a large, polygonal, and fractured island in its center. This island may reflect the fragmentation of the upper Ionian lithosphere by a shallow magma body, facilitated by a great number of shallow extensional structures. We propose a model for the Ionian lithosphere in which the upper portion is heavily deformed by joints, normal faults, and graben resulting from combined tidal, subsidence, and thermal stresses, and a lower portion rife with major thrust faults formed by horizontal compression of deeper crustal levels from the continued burial of surface units. Some of those thrusts may be reactivated normal faults. An extensionally fractured upper lithosphere accounts for the Loki Patera island, for observations of more than 175 paterae with straight edges, for the fact that almost 95% of Io’s surface is covered with volcanic flow and plains units, and for widespread instances of mass wasting within Io’s gigantic mountain blocks. Additional, high-resolution image and topographic data are required to test this hypothesized model for the moon’s lithosphere.

Using the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere Volatile and Evolution spacecraft (MAVEN) we analyzed data from Mars Year (MY) 32, 34, and 35 to examine the He bulge during the northern winter solstice (Ls ~180-240) specifically focusing on the effects from the planet encircling dust event (PEDE-2018). He collects on the dawn/nightside winter polar hemisphere of the terrestrial planets (Earth, Mars, and Venus). The seasonal migration of the Martian He bulge has been observed and modeled (Elrod et al., 2017, Gupta et al., 2021). The MAVEN orbit precesses around Mars allowing for a variety of latitude and local time observations throughout the Martian year. MY32, 34 and 35 had the best possible opportunities to observe the He bulge during northern winter (Ls ~180-240). NGIMS observations during MY 32 and MY 35 revealed a He bulge on the nightside to dawn in alignment with modeling and previous publications. However, in MY 34, during the PEDE, the He bulge was not present indicating the PEDE directly impacted upper atmospheric circulation. Updates in modeling indicate changes in circulation and winds can cause He to shift further north and dawn-ward than MAVEN was able to observe. The temperature increases in the thermosphere on the nightside during the dust storm along with changes in gravity waves and eddy diffusion occurring during this event could account for this circulation change.