Mars Science Laboratory Research Articles

Adaptive entry guidance for the Tianwen-1 mission

To meet the requirements of the Tianwen-1 mission, adaptive entry guidance for entry vehicles, with low lift-to-drag ratios, limited control authority, and large initial state bias, was presented. Typically, the entry guidance law is divided into four distinct phases: trim angle-of-attack phase, range control phase, heading alignment phase, and trim-wing deployment phase. In the range control phase, the predictor—corrector guidance algorithm is improved by planning an on-board trajectory based on the Mars Science Laboratory (MSL) entry guidance algorithm. The nominal trajectory was designed and described using a combination of the downrange value and other states, such as drag acceleration and altitude rate. For a large initial state bias, the nominal downrange value was modified onboard by weighing the landing accuracy, control authority, and parachute deployment altitude. The biggest advantage of this approach is that it allows the successful correction of altitude errors and the avoidance of control saturation. An overview of the optimal trajectory design process, including a discussion of the design of the initial flight path angle, relevant event trigger, and transition conditions between the four phases, was also presented. Finally, telemetry data analysis and post-flight assessment results were used to illustrate the adaptive guidance law, create good conditions for subsequent parachute reduction and power reduction processes, and gauge the success of the mission.

Thermal Inertia at the MSL and InSight Mission Sites on Mars

For planetary surface materials, thermal inertia is the critical property that governs the surface’s daily thermal response and controls diurnal and seasonal surface temperature variations. Here we use the ground measurements made by the MSL Curiosity rover and the InSight lander to determine the thermal inertia of two sites on Mars. This study compares the variation of thermal inertia during and after the Large Dust Storm (LDS) of Martian Year (MY) 34. To determine surface thermal inertia, we derive a simple approximation (using energy balance), which utilizes surface albedo, surface energy flux, and diurnal change in the surface temperature. The average thermal inertia in MY34 is about 39.2%, 3.7%, and 3.4% higher than MY35 average thermal inertia for the MSL, InSight (FOV1), and InSight (FOV2), respectively. Notably, the thermal inertia at the InSight (FOV1) is consistently lower by about 20 J·m^–2·s^–1/2·K^–1 than the InSight (FOV2) site for all scenarios, indicating variation in the region’s surface composition. The best-fit surface albedo in MY34 (determined using the KRC model) are about 0.08, 0.05, and 0.03 higher than MY35 surface albedo for the MSL, InSight (FOV1), and InSight (FOV2), respectively. An increase in both surface albedo and thermal inertia during the LDS indicates that the underlying surface is both more thermally resistant and more reflective than the overlying loose dust.

Constraints on Emission Source Locations of Methane Detected by Mars Science Laboratory

AbstractThe Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) Curiosity rover has detected both methane spikes and variable background methane abundance in recent years in Gale Crater, Mars. While methane spikes have been attributed to a hypothetical local or regional source emission, the background measurements acquired during the nighttime were postulated to represent the global methane abundance on Mars. However, recent high‐accuracy observations by instruments on the Trace Gas Orbiter (TGO) in several locations around the planet have not detected methane at all, apparently contradicting the SAM measurements. This paper analyzes the constraints that TGO and MSL impose on the hypothetical location of the emission source of methane responsible for the levels detected by SAM. The numerical simulations presented here indicate that not only the spikes but also the background measurements performed by MSL must result from localized emissions, specifically in the northwest interior of Gale Crater. Other simulated emission source locations at a greater distance from MSL, even if still within Gale Crater, are difficult to reconcile with current observations by MSL and TGO. Confirming previous studies, these results therefore point either to an improbable scenario, in which the rover has landed close to one of only a few localized emission sources on Mars, or to a problematic scenario, in which an unknown loss mechanism must be invoked that is able to destroy methane orders of magnitude faster than predicted by standard gas chemistry or to a weighted action between both scenarios.

Clustering Supported Classification of ChemCam Data From Gale Crater, Mars

AbstractThe Chemistry and Camera (ChemCam) instrument on board the Mars Science Laboratory (MSL) rover Curiosity has collected a very large and unique data set of in‐situ spectra and images of Mars since landing in August 2012. More than 800,000 single shot laser‐induced breakdown spectroscopy (LIBS) spectra measured on more than 2,500 individual targets were returned so far by ChemCam. Such a data set is ideally suited for the application of statistical methods for the recognition of patterns that are difficult to observe by humans. In this work, we develop an approach relying on the feature extraction method Non‐Negative Matrix Factorization (NMF) and the repetition of k‐means clustering to classify ChemCam spectra. A strong consistency of the clustering results among the repetitions were found, which allowed us to identify six clusters representing the dominant compositions measured by ChemCam in Gale crater so far. By tracking clusters across the rover traverse from landing to sol 2756, we are able to provide a chemostratigraphic overview of the Gale crater from the ChemCam perspective. Transitions between major geologic groups (such as the Bradbury and the Mt. Sharp groups) are identifiable demonstrating that they are compositionally distinct, consistent with previous work. Compositional differences between their members also appear in the results. Furthermore, a first approach in which a random forest classifier was trained and validated with the obtained cluster assignments, reveals promising results for predicting cluster memberships of new ChemCam LIBS data acquired after sol 2756.

Long-Distance 3D Reconstructions Using Photogrammetry with Curiosity’s ChemCam Remote Micro-Imager in Gale Crater (Mars)

The Mars Science Laboratory rover Curiosity landed in Gale crater (Mars) in August 2012. It has since been studying the lower part of the 5 km-high sedimentary pile that composes Gale’s central mound, Aeolis Mons. To assess the sedimentary record, the MSL team mainly uses a suite of imagers onboard the rover, providing various pixel sizes and fields of view from close to long-range observations. For this latter, we notably use the Remote Micro Imager (RMI), a subsystem of the ChemCam instrument that acts as 700 mm-focal length telescope, providing the smallest angular pixel size of the set of cameras on the Remote Sensing Mast. The RMI allows observations of remote outcrops up to a few kilometers away from the rover. As retrieving 3D information is critical to characterize the structures of the sedimentary deposits, we describe in this work an experiment aiming at computing for the first time with RMI Digital Outcrop Models of these distant outcrops. We show that Structure-from-Motion photogrammetry can successfully be applied to suitable sets of individual RMI frames to reconstruct the 3D shape and relief of these distant outcrops. These results show that a dedicated set of observations can be envisaged to characterize the most interesting geological features surrounding the rover.

A three-dimensional atmospheric dispersion model for Mars

Atmospheric local-to-regional dispersion models are widely used on Earth to predict and study the effects of chemical species emitted into the atmosphere and to contextualize sparse data acquired at particular locations and/or times. However, to date, no local-to-regional dispersion models for Mars have been developed; only mesoscale/microscale meteorological models have some dispersion and chemical capabilities, but they do not offer the versatility of a dedicated atmospheric dispersion model when studying the dispersion of chemical species in the atmosphere, as it is performed on Earth. Here, a new three-dimensional local-to-regional-scale Eulerian atmospheric dispersion model for Mars (DISVERMAR) that can simulate emissions to the Martian atmosphere from particular locations or regions including chemical loss and predefined deposition rates, is presented. The model can deal with topography and non-uniform grids. As a case study, the model is applied to the simulation of methane spikes as detected by NASA’s Mars Science Laboratory (MSL); this choice is made given the strong interest in and controversy regarding the detection and variability of this chemical species on Mars.

Early diagenesis at and below Vera Rubin ridge, Gale crater, Mars

AbstractData returned by NASA’s Mars Science Laboratory Curiosity rover showed evidence for abundant secondary materials, including Fe‐oxides, phyllosilicates, and an amorphous component on and below Vera Rubin ridge in the Murray formation. We used equilibrium thermochemical modeling to test the hypothesis that altered sediments were deposited as detrital igneous grains and subsequently underwent diagenesis. Chemical compositions of the Murray formations’ altered components were calculated using data returned by the chemistry and mineralogy X‐ray diffraction instrument and the alpha particle X‐ray spectrometer on board Curiosity. Reaction of these alteration compositions with a CO2‐poor and oxidizing dilute aqueous solution was modeled at 25–100 °C, with 10–50% Fe3+/Fetot of the host rock. The modeled alteration assemblages included abundant phyllosilicates and Fe‐oxides at water‐to‐rock ratios >100. Modeled alteration abundances were directly comparable to observed abundances of hematite and clay minerals at a water‐to‐rock ratio of 10,000, for system temperatures of 50–100 °C with fluid pH ranging from 7.9 to 9.3. Modeling results suggest that the hematite–clay mineral assemblage is primarily the result of enhanced groundwater flow compared to the Sheepbed mudstone observed at Yellowknife Bay, and underwent further, localized alteration to produce the mineralogy observed by Curiosity.

Merging Perspectives on Secondary Minerals on Mars: A Review of Ancient Water-Rock Interactions in Gale Crater Inferred from Orbital and In-Situ Observations

Phyllosilicates, sulfates, and Fe oxides are the most prevalent secondary minerals detected on Mars from orbit and the surface, including in the Mars Science Laboratory Curiosity rover’s field site at Gale crater. These records of aqueous activity have been investigated in detail in Gale crater, where Curiosity’s X-ray diffractometer allows for direct observation and detailed characterization of mineral structure and abundance. This capability provides critical ground truthing to better understand how to interpret Martian mineralogy inferred from orbital datasets. Curiosity is about to leave behind phyllosilicate-rich strata for more sulfate-rich terrains, while the Mars 2020 Perseverance rover is in its early exploration of ancient sedimentary strata in Jezero crater. It is thus an appropriate time to review Gale crater’s mineral distribution from multiple perspectives, utilizing the range of chemical, mineralogical, and spectral measurements provided by orbital and in situ observations. This review compares orbital predictions of composition in Gale crater with higher fidelity (but more spatially restricted) in situ measurements by Curiosity, and we synthesize how this information contributes to our understanding of water-rock interaction in Gale crater. In the context of combining these disparate spatial scales, we also discuss implications for the larger understanding of martian surface evolution and the need for a wide range of data types and scales to properly reconstruct ancient geologic processes using remote methods.

The Surface Energy Budget at Gale Crater During the First 2500 Sols of the Mars Science Laboratory Mission

AbstractWe use in situ environmental measurements by the Mars Science Laboratory (MSL) mission to obtain the surface energy budget (SEB) across Curiosity's traverse during the first 2500 sols of the mission. This includes values of the downwelling shortwave solar radiation, the upwelling solar radiation reflected by the surface, the downwelling longwave radiation from the atmosphere, the upwelling longwave radiation emitted by the surface, the sensible heat flux associated with turbulent motions, and the latent heat flux associated with water phase changes. We then analyze their temporal variation on different timescales and relate this to the mechanisms causing these variations. Through its Rover Environmental Monitoring Station, MSL allows for a more accurate determination of the SEB than its predecessors on Mars. Moreover, the unprecedented duration, cadence, and frequency of MSL environmental observations allow for analyses of the SEB from diurnal to interannual timescales. The results presented in this article can be used to evaluate the consistency with predictions from atmospheric numerical models, to validate aerosol radiative properties under a range of dust conditions, to understand the energy available for solar‐powered missions, and to enable comparisons with measurements of the SEB by the Perseverance rover at Jezero crater.

The ultraviolet radiation environment and shielding in pit craters and cave skylights on Mars

Caves and their entrances have been proposed as habitable environments and regions that could have preserved evidence of life, mostly due to their natural shielding from the damaging ionizing and non-ionizing radiation present on the surface. However, no studies to date have quantitatively determined the shielding offered by these voids on Mars. This paper describes the ultraviolet (UV) radiation environment in such environments by means of extensive radiative transfer (RT) model simulations applied to representative void geometries on Mars. The spatial and temporal characterization of the radiation field inside each void geometry is also performed. The RT model was previously tested against in situ Mars Science Laboratory UV observations on the Martian surface; the model showed excellent performance in terms of predicting the UV irradiances. The results presented here strongly suggest that pit craters and cave skylights are effectively shielded from the damaging UV radiation found on the Martian surface. In particular, locations on the floors of pit craters and skylights without cavernous spaces strongly attenuate UV irradiance at latitudes higher than ~45°; observing in several cases irradiances of the order of ~2% of those values found on the surface. Numerical simulations of cave entrances show a reduction even more than two orders of magnitude in UV radiation, both in the maximum instantaneous and cumulative doses, throughout the year and at any location of the planet. The attenuated UV irradiance in cavernous spaces remains stable in a 10 Myr timescale, while at the same time the photosynthetically active radiation is higher than the minimum required for Earth-like phototrophs. The intermediate radiation environment between the damaging radiation on the surface and the permanent darkness of a hypothetical cave offered by voids on Mars may represent favorable environments for habitability without constraining the type of energy source for potential as-yet unknown Martian organisms.

A Review of the Phyllosilicates in Gale Crater as Detected by the CheMin Instrument on the Mars Science Laboratory, Curiosity Rover

Curiosity, the Mars Science Laboratory (MSL) rover, landed on Mars in August 2012 to investigate the ~3.5-billion-year-old (Ga) fluvio-lacustrine sedimentary deposits of Aeolis Mons (informally known as Mount Sharp) and the surrounding plains (Aeolis Palus) in Gale crater. After nearly nine years, Curiosity has traversed over 25 km, and the Chemistry and Mineralogy (CheMin) X-ray diffraction instrument on-board Curiosity has analyzed 30 drilled rock and three scooped soil samples to date. The principal strategic goal of the mission is to assess the habitability of Mars in its ancient past. Phyllosilicates are common in ancient Martian terrains dating to ~3.5–4 Ga and were detected from orbit in some of the lower strata of Mount Sharp. Phyllosilicates on Earth are important for harboring and preserving organics. On Mars, phyllosilicates are significant for exploration as they are hypothesized to be a marker for potential habitable environments. CheMin data demonstrate that ancient fluvio-lacustrine rocks in Gale crater contain up to ~35 wt. % phyllosilicates. Phyllosilicates are key indicators of past fluid–rock interactions, and variation in the structure and composition of phyllosilicates in Gale crater suggest changes in past aqueous environments that may have been habitable to microbial life with a variety of possible energy sources.

Natural Radiation Shielding on Mars Measured With the MSL/RAD Instrument

AbstractProtecting astronauts from the effects of space radiation remains one major stepping stone for the exploration of Mars. Long‐term exposure to radiation can lead to severe health effects and affects allowable mission duration. Mission designs for Mars include the use of radiation shelters that provide additional mass to surround the astronauts. This leads to incoming radiation losing energy through ionization processes. This is important during solar energetic particle events when solar protons can reach the surface with high intensities. Additionally, shelters provide a long‐term reduction of the exposure to galactic cosmic rays. As mass is an important time and cost factor in space travel, using natural sheltering already on Mars is a desirable option. One candidate is to use subterranean lava tubes that provide shelter from the radiation from above. Other options include craters, cliff walls, or rock overhangs. Here, we present the first in situ measurements of radiation sheltering by natural environments on the surface of Mars. The data were acquired with the Radiation Assessment Detector (RAD) on board the Curiosity rover in Gale crater on Mars. We show measurements from when Curiosity was parked close to Butte M12 in the Murray Buttes formation, which blocked out 19% of the surrounding sky view. During this time, from Mars Science Laboratory (MSL) sol 1456–1467, we find a decrease of 4% in the expected dose rate, and a decrease of 7.5% in the neutral particle environment. This proof of principle is an important step to validate plans to use natural sheltering on Mars.

Making an Onboard Reference Map From MRO/CTX Imagery for Mars 2020 Lander Vision System

AbstractThe Mars 2020 rover, Perseverance, landed in Jezero crater (18.4663°N, 77.4298°E) on February 18, 2021 to collect samples from Mars that could be returned to Earth by a future Mars Sample Return campaign. While providing a rich sampling opportunity, Jezero also contains numerous landing hazards including scarps, canyons, mesas, dune fields, rock fields, and smaller craters. The Mars 2020 onboard inertial navigation system, which is the same as that used by the Mars Science Laboratory (MSL), only provides a very coarse inertially propagated position, which can have error as large as 3.2 km. The Lander Vision System (LVS) was added to Mars 2020 to reduce this position knowledge error to less than 40 m with respect to an on‐board reference map of the landing area. LVS uses a reference map on board to compare with the descent images for lander localization during the terminal stage of Entry, Descent and Landing (EDL). Because the reference map is used directly during EDL, it is critical that it have as little spatial and photometric error as possible. Photometrically, it should resemble as much as possible the real descent images to allow reliable terrain matching. Spatially, it should match as faithfully as possible the real, underlying terrain and contribute minimal error to the final localization solution. On February 18, 2021, the LVS reference map passed its ultimate test. The LVS system executed Terrain Relative Navigation (TRN) flawlessly based on the LVS reference map. In addition to its use for TRN, the local hazard map is also registered to the LVS reference map so that the safe target selection (STS) system can select a safe and reachable landing site. The final error between the site targeted by the STS system and the real landing site is estimated at only 5 m. The exceptional performance of LVS indicates that the reference map met mission requirements with comfortable margin. LVS on Mars 2020 represents the first ever use of a reference map during spacecraft EDL. This breakthrough will have profound implications for future lander missions and the scope of scientific inquiry they are able to address. In this paper, we will describe the necessary precursor steps to building the Jezero Crater LVS map, including the methodology to dejitter Context Imager (CTX) images, improve the CTX sensor model, as well as the process used to validate the LVS map accuracy.

Alien Aeolian Bedforms: A Comparative Sedimentary Analysis of the Dingo Gap Bedform and Hidden Valley Ripple Traverses, Gale Crater, Mars

AbstractAt the end of January 2014 (Sols 528–540), the Mars Science Laboratory rover Curiosity approached the valley opening known as Dingo Gap. Spanning this gap was an unusual bedform with a maximum height of 1.34 m and a maximum width of ∼8 m. Curiosity encountered, imaged, and successfully traversed this atypical bedform. In August of 2014, Curiosity began to traverse a field of ripples in Hidden Valley, but was forced to abort the attempt due to high wheel slip. The Hidden Valley ripples are ∼1/6 of the height of the Dingo Gap bedform, and yet posed a serious hazard to the rover. Here, we present a sedimentological analysis of the Dingo Gap bedform and the Hidden Valley ripples and discuss how their differences may have impacted rover traversability. The Dingo Gap and Hidden Valley bedforms are morphologically similar to many commonly observed bedforms on Mars that have few clear analogs on Earth, and Curiosity's encounters provide a framework for studying these bedforms in detail. Furthermore, the rover tracks across the bedforms have persisted for >5 Earth years, even through a global dust storm. The longevity of the tracks demonstrates that on multi‐year timescales (a) sediment transport on some Martian bedforms is inactive or slow enough that areas disturbed by the rover are not resurfaced, and (b) the rate of dust deposition on the Martian surface, even after a global dust storm, is too low to create an optically thick layer.

Nitrogen Fixation at Early Mars.

The Mars Science Laboratory (MSL) recently discovered nitrates in Gale Crater (e.g., Stern et al., 2015; Sutter et al., 2017). One possible mechanism for ancient nitrate deposition on Mars is through HNOx formation and rain out in the atmosphere, for which lightning-induced NO is likely the fundamental source. This study investigates nitrogen (N2) fixation in early Mars' atmosphere, with implications for early Mars' habitability. We consider a 1 bar atmosphere of background CO2, with abundance of N2, hydrogen, and methane varied from 1% to 10% to explore a swath of potential early Mars climates. We derive lightning-induced thermochemical equilibrium fluxes of NO and HCN by coupling the lightning-rate parametrization from the study of Romps et al. (2014) with chemical equilibrium with applications, and we use a Geant4 simulation platform to estimate the effect of solar energetic particle events. These fluxes are used as input into KINETICS, the Caltech/JPL coupled photochemistry and transport code, which models the chemistry of 50 species linked by 495 reactions to derive rain-out fluxes of HNOx and HCN. We compute equilibrium concentrations of cyanide and nitrate in a putative northern ocean at early Mars, assuming hydrothermal vent circulation and photoreduction act as the dominant loss mechanisms. We find average oceanic concentrations of ∼0.1-2 nM nitrate and ∼0.01-2 mM cyanide. HCN is critical for protein synthesis at concentrations >0.01 M (e.g., Holm and Neubeck, 2009), and our result is astrobiologically significant if secondary local concentration mechanisms occurred. Nitrates may act as high-potential electron acceptors for early metabolisms, although the minimum concentration required is unknown. Our study derives concentrations that will be useful for future laboratory studies to investigate the habitability at early Mars. The aqueous nitrate concentrations correspond to surface nitrate precipitates of ∼1-8 × 10-4 wt % that may have formed after the evaporation of surface waters, and these values roughly agree with recent MSL measurements.

Gravity Wave Observations by the Mars Science Laboratory REMS Pressure Sensor and Comparison With Mesoscale Atmospheric Modeling With MarsWRF

AbstractSurface pressure measurements on Mars have revealed a wide variety of atmospheric phenomena. The Mars Science Laboratory Rover Environmental Monitoring Station pressure sensor data set is now the longest duration record of surface pressure on Mars. We use the first 2580 Martian sols, nearly 4 Mars years, of measurements to identify atmospheric pressure waves with periods of tens of minutes to hours using wavelet analysis on residual pressure after the tidal harmonics are removed. We find these waves have a clear diurnal cycle with strongest activity in the early morning and late evening and a seasonal cycle with the strongest waves in the second half of the martian year (Ls = 180–360°). The strongest such waves of the entire mission occurred during the Mars Year 34 global dust storm. Comparable atmospheric waves are identified using atmospheric modeling with the MarsWRF general circulation model in a “nested” high spatial resolution mode. With the support of the modeling, we find these waves best fit the expected properties of inertia‐gravity waves with horizontal wavelengths of O(100s) of km.

FURTHER ADVENTURES IN MARS DTM QUALITY: SMOOTHING ERRORS, SHARPENING DETAILS

Abstract. We have used high-precision, high-resolution digital terrain models (DTMs) of the NASA Mars Science Laboratory and Mars 2020 rover landing sites based on mosaicked images from the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (MRO HiRISE) camera as a reference data set to evaluate DTMs based on Mars Express High Resolution Stereo Camera (MEX HRSC) images. The Next Generation Automatic Terrain Extraction (NGATE) matcher in the SOCET SET/GXP® commercial photogram- metric system produces DTMs with relatively good (small) horizontal resolution but high error, and results are terrain dependent, with poorer resolution and smaller errors on smoother surfaces. Multiple approaches to smoothing the NGATE DTMs give very similar tradeoffs between resolution and error. Smoothing the NGATE DTMs with a 5x5 lowpass filter is near optimal in terms of both combined resolution-error performance and local slope estimation, but smoothing with a single pass of an area-based matcher, which has been the standard approach for generating planetary DTMs at the U.S. Geological Survey to date results in similar errors and only slightly worse resolution. DTMs from the HRSC team processing pipeline fall within this same trade space but are less sensitive to terrain roughness. DTMs produced with the Ames Stereo Pipeline also fall in this space at resolutions intermediate between NGATE and the team pipeline. Although DTM resolution and error each vary by a factor of 2, the product of resolution and error is much more consistent, varying by ≤20% across multiple image sets and matching algorithms. Refinement of the stereo DTM by photoclinometry can yield significant quantitative improvement in resolution and some improvement in error (improving their product by as much as a factor of 2), provided that albedo variations over distances smaller than the stereo DTM resolution are not too severe.

Long lasting habitable periods in Gale crater constrained by glauconitic clays.

In situ investigations by the Mars Science Laboratory, Curiosity rover, have confirmed the presence of an ancient lake in Gale crater for up to 10 million years. The lake was filled with sediments that eventually converted to a compacted sandstone. However, it remains unclear whether the infilling of the lake was the result of background sedimentation processes or represents punctual flooding events in a largely isolated lake. Here we used the XRD data obtained with the Chemistry and Mineralogy instrument (CheMin), on board the Curiosity rover, to characterize the degree of disorder of clay minerals in the Murray formation (MF) at Gale crater. Our analysis shows that they are structurally and compositionally related to glauconitic clays, which are a sensitive proxy of quiescent conditions in liquid bodies for extended periods of time. Such results provide evidence of long periods of extremely low sedimentation in an ancient brackish lake on Mars, signature of an aqueous regime with slow evaporation at low temperatures. More in general, the identification of lacustrine glauconitic clays on Mars provides a key parameter in the characterization of aqueous Martian paleoenvironments that may once have harbored life.

The hydrology and climate of Mars during the sedimentary infilling of Gale crater

Gale crater's central sedimentary mound (Aeolis Mons or, informally, Mount Sharp) preserves one of the best records of early Martian climatic, hydrologic, and sedimentary history. Mount Sharp's sediment sequence is broadly consistent with a transition from wetter surface conditions with lakes and fluvial activity, to groundwater influenced sediment cementation under dryer conditions, to a period of anhydrous sediment accumulation and erosion dominated by aeolian processes. However, surface conditions alone do not provide a direct constraint on the climate evolution. We use models of the hydrological evolution of the crater, evaluated against constraints on the local depositional environment from both satellite observations and ground-based observations by the Mars Science Laboratory on the Curiosity rover to shed light on the evolution of the climate at Gale crater. The results show that the local depositional environment is influenced by both climate and the state of crater infill. The overall trend in the stratigraphic sequence, recording a transition from wet to dry environments within Gale crater, could have formed under a dominantly arid climate with changes in sediment properties exposed along the edge of Mount Sharp resulting from both lateral and vertical changes in depositional environment due to a decrease in the accommodation space and changing basin geometry as the crater filled with sediment. Alternatively, the sedimentary sequence within Gale crater could be explained by a changing climate, with lake formation during the waning period of a wetter epoch followed by secular drying to account for the observed phyllosilicate to sulfate transition. In either scenario, short-term climate changes are required to explain local changes in facies and mineralogy. A later shift to much dryer conditions is required to explain the aeolian erosion of the mound, followed by renewed arid to semiarid conditions to explain the later-stage lakes. Hydrological modeling constrains the early climate at Gale crater to have been between arid and semiarid, largely consistent with geomorphological and geochemical constraints on the climate at the Noachian–Hesperian boundary.

CME Magnetic Structure and IMF Preconditioning Affecting SEP Transport

AbstractCoronal mass ejections (CMEs) and solar energetic particles (SEPs) are two phenomena that can cause severe space weather effects throughout the heliosphere. The evolution of CMEs, especially in terms of their magnetic structure, and the configuration of the interplanetary magnetic field (IMF) that influences the transport of SEPs are currently areas of active research. These two aspects are not necessarily independent of each other, especially during solar maximum when multiple eruptive events can occur close in time. Accordingly, we present the analysis of a CME that erupted on May 11, 2012 (SOL2012‐05‐11) and an SEP event following an eruption that took place on May 17, 2012 (SOL2012‐05‐17). After observing the May 11 CME using remote‐sensing data from three viewpoints, we evaluate its propagation through interplanetary space using several models. Then, we analyze in‐situ measurements from five predicted impact locations (Venus, Earth, the Spitzer Space Telescope, the Mars Science Laboratory en route to Mars, and Mars) in order to search for CME signatures. We find that all in‐situ locations detect signatures of an SEP event, which we trace back to the May 17 eruption. These findings suggest that the May 11 CME provided a direct magnetic connectivity for the efficient transport of SEPs. We discuss the space weather implications of CME evolution, regarding in particular its magnetic structure, and CME‐driven IMF preconditioning that facilitates SEP transport. Finally, this work remarks the importance of using data from multiple spacecraft, even those that do not include space weather research as their primary objective.