NASA's Mars Research Articles

Neutral Composition and Horizontal Variations of the Martian Upper Atmosphere From MAVEN NGIMS

AbstractUsing data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS), we investigate the horizontal variations in composition of the Martian upper atmosphere. We focus on ratios of Ar, N2, O, He, and H2 to CO2 and their variation with local time, latitude, season, and temperature. These are the first direct measurements of H2 in the upper atmosphere, a species important for the delivery of H to this region because H and H2 escape to space. The NGIMS data nominally cover an altitude range of ∼150–300 km, from near the mesopause to above the exobase. The ratios to CO2 of He and H2 are larger toward the poles and on the nightside of the planet, where the atmosphere is colder and downwelling leads to the enrichment of these lighter species. For example, the H2 to CO2 ratio, at a CO2 density of 1 × 108 cm−3, is observed to increase by a factor of 2.8 from 52.5°S to 72.5°S and by a factor of 5.5 from 3 p.m. to 3 a.m. around the equator. We observe seasonal variation of the Ar to CO2 ratio due to deposition and sublimation of CO2 at the polar ice caps. Finally, we find good agreement between the Ar and N2 to CO2 ratios obtained by the Viking Lander Upper Atmospheric Mass Spectrometers and those obtained by NGIMS, and significant disagreement between the N2 to CO2 ratios obtained by the Imaging Ultraviolet Spectrograph on MAVEN and those obtained by NGIMS.

Orbital and In-Situ Investigation of Periodic Bedrock Ridges in Glen Torridon, Gale Crater, Mars.

Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover, contains a diverse and extensive record of aeolian deposition and erosion. This study focuses on a series of regularly spaced, curvilinear, and sometimes branching bedrock ridges that occur within the Glen Torridon region on the lower northwest flank of Aeolis Mons, the central mound within Gale crater. During Curiosity's exploration of Glen Torridon between sols ∼2300–3080, the rover drove through this field of ridges, providing the opportunity for in situ observation of these features. This study uses orbiter and rover data to characterize ridge morphology, spatial distribution, compositional and material properties, and association with other aeolian features in the area. Based on these observations, we find that the Glen Torridon ridges are consistent with an origin as wind‐eroded bedrock ridges, carved during the exhumation of Mount Sharp. Erosional features like the Glen Torridon ridges observed elsewhere on Mars, termed periodic bedrock ridges (PBRs), have been interpreted to form transverse to the dominant wind direction. The size and morphology of the Glen Torridon PBRs are consistent with transverse formative winds, but the orientation of nearby aeolian bedforms and bedrock erosional features raise the possibility of PBR formation by a net northeasterly wind regime. Although several formation models for the Glen Torridon PBRs are still under consideration, and questions persist about the nature of PBR‐forming paleowinds, the presence of PBRs at this site provides important constraints on the depositional and erosional history of Gale crater.

The Origins of Long‐Term Variability in Martian Upper Atmospheric Densities

AbstractWe quantify and interpret the long‐term variability of dayside Martian upper thermosphere and lower exosphere densities within 180–275 km altitudes. Atmospheric CO2, N2, O, and Ar densities are from NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) observations during the time period of 2015–2020 near solar minimum. These neutral measurements, together with contemporaneous solar irradiance measurements at Mars, enable disentanglement of the orbital effect (due to the annual Sun‐Mars distance change with solar longitude) and the solar extreme ultraviolet (EUV) effect in atmospheric density variations. The relative importance of these two effects, which is obtained using a statistical method of Dominance Analysis, reveals the competition between the indirect effect of solar infrared (via the upward coupling from the middle atmosphere) and the direct effect of solar EUV (due to local heating). Our results show that, unlike the orbital effect which is relatively constant at low altitudes and then decreases with increasing altitude, the solar EUV effect nearly monotonically increases. These two effects are comparable at high altitudes (about 240/270/205 km for CO2/N2/O). This analysis is extended to include long‐term exospheric mass density estimates near 400 km from Mars Global Surveyor and Mars Odyssey data, with a focus on representative solar cycle phases of solar minimum and maximum. It is found that near 400 km, the orbital effect is always a key driver regardless of the solar cycle phase, while the solar EUV effect plays a minor role during solar minimum and is greatly enhanced and slightly exceeds the orbital effect during solar maximum.

Discrete Aurora on the Nightside of Mars: Occurrence Location and Probability

AbstractThis paper represents the first attempt to predict the occurrence location and probability of discrete electron aurora on the nightside of Mars. We run a 3‐D time‐dependent magnetohydrodynamic model to characterize the spatial and temporal dynamics of magnetic field and plasma distributions over the course of one planetary rotation. We perform eight simulation cases under solar minimum quiet‐solar‐wind conditions (four equinox/solstice seasons, each with two interplanetary magnetic field polarities) and in an actual interplanetary coronal mass ejection (ICME) case to assess quiet and space weather situations, respectively. The occurrence of detectable discrete aurora is subject to the combination of the probabilities that (a) the ionosphere is magnetically connected with high altitudes through open field lines and (b) precipitating energy fluxes of >30 eV electrons exceed 0.1 erg/cm2/s. Our results show that during quiet solar activity, discrete aurora occurs likely on small‐scale patches embedded inside strong crustal magnetic field regions (with a magnitude greater than 50 nT at 150 km), and the overall chance across the globe is ∼0.77%. The higher probability over strong crustal field regions is attributed to the stronger magnetic field convergence. Modeling shows the occurrence probability dramatically increases during the ICME event, particularly by more than an order of magnitude in weak crustal field regions. Our model results reasonably agree with NASA Mars Atmosphere and Volatile EvolutioN and Mars Express observations. Our study suggests that nightside discrete electron aurora is not caused by the direct entry of magnetosheath plasma in a cusp‐like process but due to the recycling of nightside magnetospheric electrons.

Dehydration rate of the glycine‐MgSO4·5H2O complex and the stability of glycine expelled from the complex by in situ Raman spectroscopy under Mars‐relevant conditions

AbstractIn this work, we studied the dehydration process of the glycine‐MgSO4·5H2O complex under Mars‐relevant conditions (99% CO2 and 0.6% H2O under ultra violet (UV) irradiation exposure at 7‐mbar pressure and high vacuum conditions: 8 × 10−5 and 5 × 10−5 mbar) by in situ Raman spectroscopy inside a planetary atmosphere and surface chamber (PASC). This work provides quality Raman spectra taken under simulated planetary conditions (to be integrated in a database), as Raman spectroscopy forms part of the current and upcoming NASA and ESA Mars planetary missions. The results demonstrate that Raman spectroscopy can be used to calculate rates of dehydration of the glycine‐MgSO4·5H2O compound to study the chemical stability with respect to photodecomposition (1) of metal‐bound glycine molecules forming the complex and (2) glycine expelled from the complex, both under Mars‐simulated conditions; finally, Raman spectroscopy can also be used to quantify intermolecular interactions in terms of local pressures. Importantly, advanced detection of water molecules as part of a complex with astrobiological interest under planetary conditions plays a crucial role in planetary missions.

Subpixel-Scale Topography Retrieval of Mars Using Single-Image DTM Estimation and Super-Resolution Restoration

We propose using coupled deep learning based super-resolution restoration (SRR) and single-image digital terrain model (DTM) estimation (SDE) methods to produce subpixel-scale topography from single-view ESA Trace Gas Orbiter Colour and Stereo Surface Imaging System (CaSSIS) and NASA Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) images. We present qualitative and quantitative assessments of the resultant 2 m/pixel CaSSIS SRR DTM mosaic over the ESA and Roscosmos Rosalind Franklin ExoMars rover’s (RFEXM22) planned landing site at Oxia Planum. Quantitative evaluation shows SRR improves the effective resolution of the resultant CaSSIS DTM by a factor of 4 or more, while achieving a fairly good height accuracy measured by root mean squared error (1.876 m) and structural similarity (0.607), compared to the ultra-high-resolution HiRISE SRR DTMs at 12.5 cm/pixel. We make available, along with this paper, the resultant CaSSIS SRR image and SRR DTM mosaics, as well as HiRISE full-strip SRR images and SRR DTMs, to support landing site characterisation and future rover engineering for the RFEXM22.

Quick Clusters: A GPU-Parallel Partitioning for Efficient Path Tracing of Unstructured Volumetric Grids.

We propose a simple yet effective method for clustering finite elements to improve preprocessing times and rendering performance of unstructured volumetric grids without requiring auxiliary connectivity data. Rather than building bounding volume hierarchies (BVHs) over individual elements, we sort elements along with a Hilbert curve and aggregate neighboring elements together, improving BVH memory consumption by over an order of magnitude. Then to further reduce memory consumption, we cluster the mesh on the fly into sub-meshes with smaller indices using a series of efficient parallel mesh re-indexing operations. These clusters are then passed to a highly optimized ray tracing API for point containment queries and ray-cluster intersection testing. Each cluster is assigned a maximum extinction value for adaptive sampling, which we rasterize into non-overlapping view-aligned bins allocated along the ray. These maximum extinction bins are then used to guide the placement of samples along the ray during visualization, reducing the number of samples required by multiple orders of magnitude (depending on the dataset), thereby improving overall visualization interactivity. Using our approach, we improve rendering performance over a competitive baseline on the NASA Mars Lander dataset from 6× (1 frame per second (fps) and 1.0 M rays per second (rps) up to now 6 fps and 12.4 M rps, now including volumetric shadows) while simultaneously reducing memory consumption by 3×(33 GB down to 11 GB) and avoiding any offline preprocessing steps, enabling high-quality interactive visualization on consumer graphics cards. Then by utilizing the full 48 GB of an RTX 8000, we improve the performance of Lander by 17 × (1 fps up to 17 fps, 1.0 M rps up to 35.6 M rps).

Study of the Stability of Gly·MgSO4·5H2O under Simulated Martian Conditions by In Situ Raman Spectroscopy.

Identification of spectroscopic fingerprints that correspond to relevant molecules/minerals in a Mars-like environment is a crucial search in astrobiology. Therefore, we studied the stability of Gly·MgSO4·5H2O under Mars-like surface conditions and compared it to the behavior of epsomite and glycine. Gly·MgSO4·5H2O has been identified as a molecule of astrobiological interest since an amino acid and water molecules, which are essential for life, are part of its structure. Furthermore, this compound may form by the interaction of sulfate minerals with glycine-bearing aqueous solutions, and both could be present on Mars. The main analyses were performed by using in situ Raman spectroscopy, a ground-breaking technique for NASA and ESA Mars planetary missions. We have integrated a Raman spectrometer in a Planetary Atmosphere and Surfaces Chamber (PASC) and have identified the processing of molecules exposed to a simulated martian atmosphere, UV irradiation, and temperature. Our results show that pressure is critical to provoke amorphization of Gly·MgSO4·5H2O, and the release of glycine from the compound; the stabilization effect at low temperature and stability of Gly·MgSO4·5H2O is greater than to glycine and epsomite. The strategy employed here allows us to evaluate the effect of diverse simulated martian environmental conditions on molecular preservation by using Raman spectroscopy.

Pre-landing plans for Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) science operations

The Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) is a technology demonstration on the NASA Mars 2020 Perseverance rover. MOXIE is capable of producing 6–10 g/h of oxygen via solid oxide electrolysis of atmospheric carbon dioxide. The Mars 2020 mission has allocated MOXIE a minimum of ten oxygen-producing runs, each with approximately 1 h of oxygen production. Before landing, operations were planned to meet MOXIE's five success criteria. Run structure, constraints, and thorough definition and validation processes were defined. Before producing oxygen for the first time, several checkouts were planned to verify functionality of MOXIE's major subsystems. MOXIE's first oxygen-producing run was planned to produce up to 6 g/h of oxygen for approximately 1 h and measure a conservative range of current and voltage at two inlet mass flow rates. The remaining oxygen-producing runs were planned to measure performance using the largest permissible range of current, voltage and inlet mass flow rate for a wide range of atmospheric densities. Runs were designed to be flexible, allowing modification as operational knowledge accumulates throughout the mission. Validation of runs using models and hardware has demonstrated that MOXIE is ready for surface operations.

Limitations of applying grain weight similitude in aeolian studies with NASA Mars Wind Tunnel

• Mathematical analysis shows error in Mars wind tunnel experiments. • Algebraic and numerical methods provide error evaluation of a NASA tunnel. • Weight, inertia, and drag provide an adequate account of saltation. The Mars Surface Wind Tunnel at NASA Ames Research Center is used to simulate windblown (aeolian) movement of sand and dust on the martian surface. Because objects weigh less on Mars, the tunnel employs lighter sand in the form of crushed walnut shell to compensate for Earth’s higher gravity. The tunnel is thus operated on the principle of ‘grain-weight similitude’. This approach enables successful replication of transport thresholds but it leads to major discrepancies for other aspects of grain behavior.

Large Area High-Resolution 3D Mapping of Oxia Planum: The Landing Site for the ExoMars Rosalind Franklin Rover

We demonstrate an end-to-end application of the in-house deep learning-based surface modelling system, called MADNet, to produce three large area 3D mapping products from single images taken from the ESA Mars Express’s High Resolution Stereo Camera (HRSC), the NASA Mars Reconnaissance Orbiter’s Context Camera (CTX), and the High Resolution Imaging Science Experiment (HiRISE) imaging data over the ExoMars 2022 Rosalind Franklin rover’s landing site at Oxia Planum on Mars. MADNet takes a single orbital optical image as input, provides pixelwise height predictions, and uses a separate coarse Digital Terrain Model (DTM) as reference, to produce a DTM product from the given input image. Initially, we demonstrate the resultant 25 m/pixel HRSC DTM mosaic covering an area of 197 km × 182 km, providing fine-scale details to the 50 m/pixel HRSC MC-11 level-5 DTM mosaic. Secondly, we demonstrate the resultant 12 m/pixel CTX MADNet DTM mosaic covering a 114 km × 117 km area, showing much more detail in comparison to photogrammetric DTMs produced using the open source in-house developed CASP-GO system. Finally, we demonstrate the resultant 50 cm/pixel HiRISE MADNet DTM mosaic, produced for the first time, covering a 74.3 km × 86.3 km area of the 3-sigma landing ellipse and partially the ExoMars team’s geological characterisation area. The resultant MADNet HiRISE DTM mosaic shows fine-scale details superior to existing Planetary Data System (PDS) HiRISE DTMs and covers a larger area that is considered difficult for existing photogrammetry and photoclinometry pipelines to achieve, especially given the current limitations of stereo HiRISE coverage. All of the resultant DTM mosaics are co-aligned with each other, and ultimately with the Mars Global Surveyor’s Mars Orbiter Laser Altimeter (MOLA) DTM, providing high spatial and vertical congruence. In this paper, technical details are presented, issues that arose are discussed, along with a visual evaluation and quantitative assessments of the resultant DTM mosaic products.

Synthetic topography from the decameter to the centimeter scale on Mars for scientific and rover operations of the ESA-Roscosmos ExoMars mission

The ESA-Roscosmos ExoMars platform and rover mission will have complex interactions with the martian surface. In order to plan and perform landing, roving and scientific operations, the morphological characteristics of the terrain surrounding the rover need to be characterized from the decameter to the centimeter spatial scale. The smallest possible features currently identifiable are typically >0.75 ​m in size, corresponding to three times the ground sampling resolution of the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO). We have developed a synthetic topography with a ground sampling resolution of 0.01 ​m by integrating 1) a modeled topography of small-scale topographic features (e.g., rocks) into 2) a 0.25 ​m resolution digital elevation model (DTM) built by applying stereo and shape-from-shading techniques to HiRISE data. The modeled topography of small-scale topographic features is based on the extrapolation of the abundance and spatial distribution pattern of geological features measurable in HiRISE data. We determined that the cumulative fractional area covered by relief, i.e., float blocks and ridged outcrops, over the entire Oxia Planum landing site spans the range 0–30% with a mean abundance of relief of 7 ​± ​5%. The synthetic topography can be used for highly realistic environment simulations and rover drive planning. Artificial rover camera images produced with the synthetic topography incorporate orbital-based geomorphological units and can be used for improved planning and analyses of actual rover images.

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.

Assessment of AEC Students’ Performance Using BIM-into-VR

Building Information Modeling (BIM) and Virtual reality (VR) have attracted growing attention within the architecture, engineering, and construction (AEC) industry in recent years. Integration of BIM and VR technology can develop workflow efficiency through enhanced common understanding and prepare students in architecture and engineering programs to become leaders of the AEC industry. However, the current shortage of AEC professionals trained in BIM and VR is still a barrier to collaborative working practice in this industry. This paper reviews previous work on the BIM, VR, and BIM-into-VR in AEC education/training to bridge this gap. It also presents an advanced framework to clarify creating and using the BIM model into VR workflow in the AEC industry through the integrated definition function (IDEF0) model. The authors further evaluated the BIM-into-VR applications in literature and real-life by surveying students’ learning performance in terms of eight characteristics relevant to the VR environment and students’ performance within two projects, one involving the “NASA Mars Habitat Project” and the other involving the “Norris Center Project” at Northwestern University. The results confirmed that BIM-into-VR usability and efficiency in improving students’ main learning performance characteristics: Learnability, Interoperability, Visualization, Real-world, Interaction, Creativity, Motivation, and Comfort. This study addresses the advantages of using BIM-into-VR in AEC programs. It also offers suggestions to AEC educators and students in implementing BIM-into-VR in different courses and creating a roadmap for their future as professionals in the AEC industry.

Listening for the Landing: Seismic Detections of Perseverance's Arrival at Mars With InSight

AbstractThe entry, descent, and landing (EDL) sequence of NASA's Mars 2020 Perseverance Rover will act as a seismic source of known temporal and spatial localization. We evaluate whether the signals produced by this event will be detectable by the InSight lander (3,452 km away), comparing expected signal amplitudes to noise levels at the instrument. Modeling is undertaken to predict the propagation of the acoustic signal (purely in the atmosphere), the seismoacoustic signal (atmosphere‐to‐ground coupled), and the elastodynamic seismic signal (in the ground only). Our results suggest that the acoustic and seismoacoustic signals, produced by the atmospheric shock wave from the EDL, are unlikely to be detectable due to the pattern of winds in the martian atmosphere and the weak air‐to‐ground coupling, respectively. However, the elastodynamic seismic signal produced by the impact of the spacecraft's cruise balance masses on the surface may be detected by InSight. The upper and lower bounds on predicted ground velocity at InSight are 2.0 × 10−14 and 1.3 × 10−10 m s−1. The upper value is above the noise floor at the time of landing 40% of the time on average. The large range of possible values reflects uncertainties in the current understanding of impact‐generated seismic waves and their subsequent propagation and attenuation through Mars. Uncertainty in the detectability also stems from the indeterminate instrument noise level at the time of this future event. A positive detection would be of enormous value in constraining the seismic properties of Mars, and in improving our understanding of impact‐generated seismic waves.

Impact of the 2018 Mars Global Dust Storm on the Ionospheric Peak: A Study Using a Photochemical Model

AbstractWe report the impact of the 2018 Mars global dust storm on the ionosphere, in particular, its peak altitude during the onset and growth phases of the event. A one‐dimensional photochemical model is applied to estimate the ionospheric electron densities below 200 km using the measurements of in situ neutral densities and ionizing solar radiation by the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Our model results show that while the peak density of the ionosphere on the dawn side during the dust storm is hardly impacted, the altitude of the peak layer may be lifted by ∼10 km. The simulation results support the MAVEN radio occultation observations that there is a time delay in the response of the ionospheric peak altitude in the southern hemisphere (SH), compared with the northern hemisphere (NH) during the dust storm development. Although the 2018 global dust storm developed in the northern Martian mid‐latitudes on 1 June and developed into a global dust event on 17 June, our study suggests that the impact on the ionospheric peak altitude near the equatorial and southern mid‐latitudes became important only after 22 June. This suggests that there was a time‐lag of about 3 weeks in the response of the Martian upper atmosphere of the SH to the dust storm that originated in the NH.

A Comodulation Analysis of Atmospheric Energy Injection Into the Ground Motion at InSight, Mars

AbstractSeismic observations involve signals that can be easily masked by noise injection. For the NASA Mars lander InSight, the atmosphere is a significant noise contributor, impeding the identification of seismic events for two‐thirds of a Martian day. While the noise is below that seen at even the quietest sites on Earth, the amplitude of seismic signals on Mars is also considerably lower, requiring an understanding and quantification of environmental injection at unprecedented levels. Mars’ ground and atmosphere are a continuously coupled seismic system, and although atmospheric functions are of distinct origins, the superposition of these noise contributions is poorly understood, making separation a challenging task. We present a novel method for partitioning the observed signal into seismic and environmental contributions. Atmospheric pressure and wind fluctuations are shown to exhibit temporal cross‐frequency coupling across multiple bands, injecting noise that is neither random nor coherent. We investigate this through comodulation, quantifying the synchrony of the seismic motion, wind and pressure signals. By working in the time‐frequency domain, we discriminate between the different origins of underlying processes and determine the site's environmental sensitivity. Our method aims to create a virtual vault at InSight's landing site on Mars, shielding the seismometers with effective postprocessing in lieu of a physical vault. This allows us to describe the environmental and seismic signals over a sequence of sols, to quantify the wind and pressure injection and estimate the seismic content of possible marsquakes with a signal‐to‐noise ratio that can be quantified in terms of environmental independence. Finally, we exploit the relationship between the comodulated signals to identify their sources.

A New Martian Crater Chronology: Implications for Jezero Crater

Abstract Crater chronologies are a fundamental tool to assess the relative and absolute ages of planetary surfaces when direct radiometric dating is not available. Martian crater chronologies are derived from lunar crater spatial densities on terrains with known radiometric ages, and thus they critically depend on the Moon-to-Mars extrapolation. This extrapolation requires knowledge of the time evolution of the impact flux, including contributions from various impactor populations, factors that are not trivially connected to the dynamical evolution of the early Solar System. In this paper, we will present a new Martian crater chronology based on current dynamical models, and consider the main sources of uncertainties (e.g., impactor size–frequency distribution; dynamical models with late and early instabilities, etc.). The resulting “envelope” of Martian crater chronologies significantly differs from previous chronologies. The new Martian crater chronology is discussed using two interesting applications: Jezero crater’s dark terrain (relevant to the NASA Mars 2020 mission) and the southern heavily cratered highlands. Our results indicate that Jezero’s dark terrain may have formed ∼3.1 Ga, i.e., up to 0.5 Gyr older than previously thought. In addition, available crater chronologies (including our own) overestimate the number of craters larger than 150 km on the southern highlands, suggesting either that large craters have been efficiently erased over Martian history or that dynamical models need further refinement. Further, our chronology constrains the age of Isidis basin to be 4.05–4.2 Ga and that of the Borealis basin to be 4.35–4.40 Ga; these are predictions that can be tested with future sample and return missions.

Dust Storm‐Enhanced Gravity Wave Activity in the Martian Thermosphere Observed by MAVEN and Implication for Atmospheric Escape

AbstractLower atmospheric global dust storms affect the small‐ and large‐scale weather and variability of the whole Martian atmosphere. Analysis of the CO2 density data from the Neutral Gas and Ion Mass Spectrometer instrument on board NASA's Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft show a remarkable increase of gravity wave (GW)‐induced density fluctuations in the thermosphere during the 2018 major dust storm with distinct latitude and local time variability. The mean thermospheric GW activity increases by a factor of two during the storm event. The magnitude of relative density perturbations is around 20% on average and 40% locally. One and a half months later, the GW activity gradually decreases. Enhanced temperature disturbances in the Martian thermosphere can facilitate atmospheric escape. For the first time, we estimate observationally that, for a 20% and 40% GW‐induced disturbances, the net increase of Jeans escape flux of hydrogen is a factor of 1.3 and 2, respectively.

Morphological and Spectral Diversity of the Clay-Bearing Unit at the ExoMars Landing Site Oxia Planum.

The European Space Agency and Roscosmos' ExoMars rover mission, which is planned to land in the Oxia Planum region, will be dedicated to exobiology studies at the surface and subsurface of Mars. Oxia Planum is a clay-bearing site that has preserved evidence of long-term interaction with water during the Noachian era. Fe/Mg-rich phyllosilicates have previously been shown to occur extensively throughout the landing area. Here, we analyze data from the High Resolution Imaging Science Experiment (HiRISE) and from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instruments onboard NASA's Mars Reconnaissance Orbiter and the Colour and Stereo Surface Imaging System (CaSSIS) onboard ESA's Trace Gas Orbiter to characterize, at a high spatial resolution, the morphological and spectral variability of Oxia Planum's surface deposits. Two main types of bedrocks are identified within the clay-bearing, fractured unit observed throughout the landing site: (1) an orange type in HiRISE correlated with the strongest detections of secondary minerals (dominated by Fe/Mg-rich clay minerals) with, in some locations, an additional spectral absorption near 2.5 μm, suggesting the mixture with an additional mineral, plausibly carbonate or another type of clay mineral; (2) a more bluish bedrock associated with weaker detections of secondary minerals, which exhibits at certain locations a ∼1 μm broad absorption feature consistent with olivine. Coanalysis of the same terrains with the recently acquired CaSSIS images confirms the variability in the color and spectral properties of the fractured unit. Of interest for the ExoMars mission, both types of bedrocks are extensively outcropping in the Oxia Planum region, and the one corresponding to the most intense spectral signals of clay minerals (the primary scientific target) is well exposed within the landing area, including near its center.