Periodic bedrock ridges (PBRs) are enigmatic landforms carved by wind on Mars. Although they have been demonstrated to be erosional features carved into lithified bedrock, the precise cause of the ridge and groove topography is not fully understood. Previous work has suggested that aeolian bedforms may have been required to form the periodicity, but some questions about this mechanism still remain. Can interbedform erosion lead to ridge-and-trough topography? To test this, we conducted a wind tunnel experiment simulating the proposed landscape formation mechanism. Additionally, we studied a field analog system where bedforms armored a hardened mud substrate. Results from these supplement observations of known and new PBR fields on Mars. The preponderance of evidence suggests that the topography derives from interbedform erosion: Bedforms shield the substrate directly beneath them, but abrasion deflates the exposed material between bedforms. Eventually, abrasion in the deflating troughs undercuts the shielding bedforms, causing them to winnow and narrow. This leads to remnant bedforms perched on ridges that separate the deepening troughs and ultimately the characteristic periodic ridge topography. This mechanism requires that the shielding bedforms' migration rate is slow with respect to the local rate of aeolian erosion. Examples of modern bedforms near periodic ridges on Mars suggest that the erosional features respond to the largest wavelengths in overlying bedform fields, filtering out the signal of small bedforms. Overall, the combined evidence from wind tunnel experiments, field work, and remote sensing supports the formation of PBRs via aeolian deflation between aeolian bedforms.

The distribution and origin of serpentine on Mars can provide insights into the planet's aqueous history, habitability, and past climate. In this study, we used dynamic aperture factor analysis/target transformation applied to 15,760 images from the Compact Reconnaissance Imaging Spectrometer for Mars, followed by validation with the radiance ratio method, to construct a map of Mg-serpentine deposits on Mars. Although relatively rare, Mg-serpentine was detected in diverse geomorphic settings across Noachian and Hesperian-aged terrains in the southern highlands of Mars, implying that serpentinization was active on early Mars and that multiple formation mechanisms may be needed to explain its spatial distribution. We also calculated the amount of H-2 produced during the formation of the observed deposits and conclude that serpentinization was likely more widespread on Mars than indicated by the observed distribution.

In Jezero crater, Mars, the Perseverance rover has explored the western fan and encountered loose pieces of rock separated from outcrops or “float” rocks. Comparing float rocks to in‐place outcrops can provide key insights into the crater's erosional history and the diversity of units in the Jezero watershed that Perseverance cannot visit in situ. Here, we used multispectral observations from Perseverance's Mastcam‐Z instrument to investigate the lithology and origin of float rocks found on the western Jezero fan front (sols 415–707). We identified four textural classes of float rocks (conglomerates, layered, massive, and light‐toned) and investigated their physical characteristics, spectral properties, and distribution to interpret their source and mode of transport. Likely derived from local sedimentary fan outcrops, conglomerate and layered float rocks are highly spectrally variable and altered with differing ferric and ferrous signatures. Massive float rocks are the least altered with ferrous signatures and likely derived from local outcrop sources or more distal sources (∼50–250 km) in the Jezero watershed. Massive float rocks separate into two subclasses: massive olivine and massive pyroxene, which are likely derived from the regional olivine‐carbonate‐bearing watershed unit and the crustal Noachian basement unit, respectively. The unique light‐toned float rocks have variable hydration and low Fe‐abundance, but there is no local outcrop equivalent of these rocks on the crater floor or fan front, suggesting transport into the basin from a source region outside Jezero. Perseverance found no meteorites at the western fan, implying that fan sediments may be in the youngest ages estimated from crater counts (Hesperian).

The Mars 2020 Perseverance rover landing site is located within Jezero crater, a  $\sim50~\mbox{km}$ diameter impact crater interpreted to be a Noachian-aged lake basin inside the western edge of the Isidis impact structure. Jezero hosts remnants of a fluvial delta, inlet and outlet valleys, and infill deposits containing diverse carbonate, mafic, and hydrated minerals. Prior to the launch of the Mars 2020 mission, members of the Science Team collaborated to produce a photogeologic map of the Perseverance landing site in Jezero crater. Mapping was performed at a 1:5000 digital map scale using a 25 cm/pixel High Resolution Imaging Science Experiment (HiRISE) orthoimage mosaic base map and a 1 m/pixel HiRISE stereo digital terrain model. Mapped bedrock and surficial units were distinguished by differences in relative brightness, tone, topography, surface texture, and apparent roughness. Mapped bedrock units are generally consistent with those identified in previously published mapping efforts, but this study’s map includes the distribution of surficial deposits and sub-units of the Jezero delta at a higher level of detail than previous studies. This study considers four possible unit correlations to explain the relative age relationships of major units within the map area. Unit correlations include previously published interpretations as well as those that consider more complex interfingering relationships and alternative relative age relationships. The photogeologic map presented here is the foundation for scientific hypothesis development and strategic planning for Perseverance’s exploration of Jezero crater.

The NASA Perseverance rover has been traversing the Jezero western fan, a clastic succession on the western rim of Jezero crater, containing a series of rocks deposited between ~3.6-3.8 Ga that show evidence of basinward prograding fluvial-deltaic depositional conditions.The lowest stratigraphy in the Jezero fan records a transition from igneous crater floor material to distal deltaic deposits. A transition to fluvio-deltaic and periodic debris flow deposition is recorded in the upper fan series: The Tenby formation sandstones are comparable to terrestrial meandering fluvial systems, planar-bedded coarse sandstones of the Otis Peak member overlie the Tenby formation, and a blocky unit of boulder deposits, referred to as the Boulder Unit tops the fan. To the west and north, the upper fan overlies a carbonate-bearing sandstone deposited on the crater rim: the Margin Unit. The contacts between these units have been obscured for much of the traverse, precluding detailed assessment of their stratigraphic relationships. Gnaraloo Bay, visited on Sols 959 – 1000 of the mission, is an erosional window where the upper fan intersects the Margin Unit. Erosion through three key stratigraphic elements presents an opportunity to unravel the relative timing relationships of the Jezero crater rim and upper fan. We present a stratigraphic framework built from observations in Gnaraloo Bay made from images collected with the Mastcam-Z stereo-camera system.The majority of Gnaraloo Bay is formed of shallow dipping (

The NASA Mars 2020 Perseverance Rover Mission has collected samples of rock, regolith, and atmosphere within the Noachian-aged Jezero Crater, once the site of a delta-lake system with a high potential for habitability and biosignature preservation. Between sols 109 and 1,088 of the mission, 27 sample tubes have been sealed, including witness tubes. Each sealed sample tube has been collected along with detailed documentation provided by the Perseverance instrument payload, preserving geological and environmental context. Samples representative of the stratigraphy within each of four campaigns have been collected: samples from the Crater Floor Campaign represent a suite of potentially petrogenetically related igneous rocks displaying variable degrees of aqueous alteration; samples from the Fan Front record fluvial to deltaic sediments formed by the transport and deposition of materials from the Jezero watershed; regolith samples from the Fan Front preserve material possibly representative of global dust as well as diverse, locally derived clasts; Upper Fan samples record the latest stages of aqueous activity within Jezero; and samples from the Margin Campaign preserve lacustrine, littoral, or possibly igneous processes that may have occurred early in the history of the crater. Along with anticipated samples from the older rocks within the rim of Jezero Crater, Perseverance promises to deliver a suite of samples preserving a diversity of formation environments and ages. Upon return to Earth and analysis in terrestrial laboratories, these samples would address longstanding questions pertaining to the geologic evolution of Mars, its habitability, and the potential for life outside the Earth.

Aerial platforms can explore planetary surfaces without the mobility limitations of rovers and landers. Inspired by the recent successes and challenges of NASA’s IngenuAity Mars Helicopter, the Rover-Aerial Vehicle Exploration Network project explored the operations and science value of a dual-platform rover-helicopter mission architecture coupled with simulated orbiter image data. A remote mission operations team carried out a 5 day long Mars mission simulation executed by a field team in the Rainbow Basin Natural Area near Barstow, California, USA. The simulation demonstrated the rover’s ability to collect progressively finer-scale, specifically targeted image and compositional observations with a complementary multi-instrument payload. The helicopter excelled at the collection of extensive image surveys, providing views of diverse terrains and geologic units within the exploration area otherwise inaccessible to the rover. Of the helicopter data, high-resolution, low-altitude oblique images proved to be the most useful from a science and strategic operational planning perspective. The dual-platform mission architecture had clear science advantages over the individual rover or helicopter investigations during the simulation, but sharing daily data downlink between the mission platforms presented one of the greatest operational challenges. Rover operations demanded daily “reactive” tactical planning and rapid downlink of science data to enable targeting and traverse decisions, while the helicopter was best suited to a “predictive” advanced planning timeline for operations, data volume management, and science analysis.

On Mars, phyllosilicate ("clay") minerals are often associated with older terrains, and sulfate minerals are associated with younger terrains, and this dichotomy is taken as evidence that Mars' surface dried up over time. Therefore, in situ investigation of the Mount Sharp strata in Gale crater, which record a shift from dominantly clay -bearing to sulfate -bearing minerals, as seen in visible- near -infrared orbital reflectance spectra, is a key science objective for the Mars Science Laboratory (MSL) Curiosity rover mission. Here, we present regional (orbiter -based) and in situ (rover -based) evidence for a lowangle erosional unconformity that separates the lacustrine and marginal lacustrine deposits of the Carolyn Shoemaker formation from the dominantly eolian deposits of the lower Mirador formation within the orbitally defined clay -sulfate transition region. The upsection record of wetter (Carolyn Shoemaker formation) to drier (lower Mirador formation) depositional conditions is accompanied by distinct changes in diagenesis. Clay minerals occur preferentially within the Carolyn Shoemaker formation and are absent within the lower members of the Mirador formation. At and above the proposed unconformity, strata are characterized by an increase in diagenetic nodules enriched in X-ray amorphous Mg -sulfate. Early clay formation in the Carolyn Shoemaker formation may have created a hydraulic barrier such that later migrating magnesium- and sulfur -rich fluids accumulated preferentially within the lower members of the Mirador formation. The proposed unconformity may have also acted as a fluid conduit to further promote Mg -sulfate nodule formation at the Carolyn Shoemaker-Mirador formation boundary. These results confirm an association of the clay -sulfate transition with the drying of depositional environments, but they also suggest that at least some orbital sulfate signatures within the region are not time -congruent with the environmental signals extracted from primary sedimentology. Our findings highlight that complex interactions among primary depositional environment, erosion, and diagenesis contribute to the transition in clay -sulfate orbital signatures observed in the stratigraphy of Mount Sharp.

This study uses data from the Mars Science Laboratory Curiosity rover to document the facies of the Sutton Island member of the Murray formation, interpret paleoenvironments, and establish key stratigraphic transitions at Gale crater. Two facies associations were identified: Facies Association 1 (FA1) and Facies Association 2 (FA2). Individual facies in FA1 include planar-laminated mudstone with minor intervals of planar sandstone, ripple cross-laminated sandstone, cross-stratified sandstone, and alternating laminated sandstone and mudstone. Meter-thick packages of planar-laminated mudstone in FA1 are interpreted to represent deposition in low-energy ponded environments along the lake margin. Straight- and curve-crested ripple cross-laminated facies are interpreted to represent current-influenced deposition. Cross-stratified sandstone facies consist of dm-thick sets that represent deposition in distal channels. Intercalated mm-scale mudstone and sandstone laminae represent waning flow conditions and possible channel abandonment. Facies in FA1 collectively represent deposition in a distal delta plain. FA2 is comprised of planar-laminated mudstone with minor sandstone and is interpreted to represent deposition in a lacustrine-basin setting by suspension settling linked to density flows. FA1 transitions upward into FA2, defining a rapid transgression substantial enough to facilitate the deposition of distal lake facies above delta plain facies. The abrupt transition from FA2 back to FA1 deltaic deposits is suggestive of forced regression. Facies in FA1 and FA2 are consistent with the prevalence of aqueous environments recorded in other Murray formation members and extend our understanding of the dynamic sedimentary processes that characterized ancient lacustrine systems at Gale crater. This study classifies sedimentary rock characteristics within an interval of sedimentary rock layers comprising the Sutton Island member, which is part of the Murray formation. The main goals of this study are to determine the ancient environments represented by the different sedimentary rock groups (facies) and to understand how ancient environments changed through time. Facies are grouped into two categories (associations) based on their distribution within the stratigraphy: Facies Association 1 (FA1) and Facies Association 2 (FA2). FA1 contains rocks with a range of sedimentary structures and grain sizes and formed via aqueous processes. The environment represented by FA1 is a delta plain adjacent to a lake. Facies Association 2 consists of one fine-grained facies that represents deposition in a lake basin environment. The lowermost interval of stratigraphy is comprised of FA1 (delta plain), which transitions upward into the middle interval of stratigraphy comprised FA2 (lake) and subsequently returns to FA1 in the uppermost stratigraphic interval. Transitions between facies associations represent shifts in the ancient lake shoreline that may have been caused by lake-level change. The delta plain and lake environments represented by FA1 and FA2 are consistent with facies in other members of the Murray formation. The Sutton Island member consists of two distinct facies associations that record delta plain and lacustrine environmentsThe depositional history is indicative of a rapid transgression followed by forced regressionFacies record diverse aqueous processes and expand the range of environments interpreted in the Murray formation

We use the crystallinity of hydrated silica, represented by the 1.4 mu m absorption position in orbiter spectroscopic data, as a proxy for the longevity of water-rock interaction in the Syrtis Major region. Geological maps and crater size-frequency distribution analyses are employed to contextualize mineral detections and estimate surface ages. Hydrated silica is detected within two distinct geological units: a younger "volcanic terrain" (vt) unit (similar to 2.4 Ga) and an older "highland terrain" (ht) unit (3.5-3.7 Ga). Hydrated silica in the vt unit typically has a band position <1.41 mu m, consistent with amorphous opal-A, suggesting these younger terrains have experienced limited interaction with water. In contrast, hydrated silica in the older highlands typically has a band position >1.41 mu m, indicating opal-CT, suggesting that these deposits have had more time to interact with water, while also producing accessory minerals such as kaolinite and Fe/Mg phyllosilicates.