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The Martian highlands contain Noachian‐aged areally‐extensive (>225 km2) bedrock exposures that have been mapped using thermal and visible imaging datasets. Given their age, crater density and impact gardening should have led to the formation of decameter scale layers of regolith that would overlie and bury these outcrops if composed of competent materials like basaltic lavas. However, many of these regions lack thick regolith layers and show clear exposures of bedrock materials with elevated thermal inertia values compared to the global average. Hypothesized reasons for the lack of regolith include: (a) relatively weaker material properties than lavas, where friable materials are comminuted and deflated during wind erosion, (b) long‐term protection from regolith development through burial and later exhumation through one or more surface processes, and (c) spatially concentrated aeolian erosion and wind energetics on well‐lithified basaltic substrates. To test the third hypothesis, we used the Mars Regional Atmospheric Modeling System to calculate wind erosive strength at 10 regions throughout the Martian highlands and compared it to their thermophysical properties by using thermal infrared data derived from the Thermal Emission Spectrometer to understand the effect that Amazonian mesoscale wind patterns may have on the exposure of bedrock. We also investigated the effect of planet obliquity, Ls of perihelion, and atmospheric mean pressure on wind erosion potential. We found no evidence for increased aeolian activity over bedrock‐containing regions relative to surrounding terrains, including at the mafic floor unit at Jezero crater (Máaz formation), supporting the first or second hypotheses for these regions. Plain Language Summary: Several regions of Mars have exposed ancient bedrock materials (>∼3.6 billion years old) that should be buried underneath thick layers of granular material (regolith) that forms due to physical breakdown of the bedrock over prolonged periods of time. However, many regions lack regolith and have ancient bedrock exposures. One possible explanation for the spatial variability in bedrock exposure is that these rock materials break down into much smaller particles than typical Martian crustal materials, that are then carried away by wind, preventing a buildup of granular material. Another possible explanation is spatial variation in modern wind erosional patterns and strength. We used an atmospheric model and compared the spatial distribution of modeled wind strengths to that of exposed bedrock within the oldest regions on Mars to assess if there is any connection between exposed bedrock and Late Amazonian (250 Mya‐present) modern‐day wind patterns. We found no correlation between wind strength and exposed bedrock in these regions suggesting that material strength is the primary control on the present day distribution of bedrock exposure in Mars' older terrains. Key Points: There is no observed relationship between simulated Late Amazonian wind patterns and the spatial bedrock exposuresFlat‐lying surfaces in craters have lower wind erosion potential (WEP) values than intercrater plains. Jezero crater floor had the lowest valuesIncreased atmospheric pressure had the strongest effect on calculated WEP values [ABSTRACT FROM AUTHOR]

Secure Children's Homes (SCH) in the UK are locked establishments for children perceived to be at serious risk and referred through welfare or youth justice systems. The UK SCH population has recently decreased, but the percentage accommodated for welfare concerns has not. It is of concern that some of the children referred to SCHs through the welfare system cannot be placed and are therefore found an alternative accommodation. This article is concerned with children from England referred to SCHs for welfare reasons particularly the process of trying to find a SCH place, the characteristics of children placed in alternative accommodations and the residences used for alternative accommodation. Findings show that two-fifths of the children, typically older males with challenging, offending, or sexually harmful behaviors were not placed in a SCH. While the children's behaviors contributed to SCH refusals, the situations were more nuanced with other contributory factors including children not meeting secure accommodation criteria, non-implementation of secure orders and children entering different secure settings. The study returns attention to the difficulty of finding an SCH place for extremely vulnerable children and raises concerns about current SCH service capacity and the unknown nature of alternative accommodations. [ABSTRACT FROM AUTHOR]

Stereotactic MR-guided Adaptive Radiation Therapy (SMART) dose painting in hypoxia shows promise in improving treatment outcomes but clinically feasible imaging and localization remains a challenge. Oxygen-enhanced (OE)-MRI is compelling for hypoxia imaging via preferential O 2 uptake and T 1 relaxation shortening in normoxic tissues, as changes in 1/T 1 (ΔR) quantifiability reflect tissue oxygenation level dependent (TOLD) contrast. While OE-MRI has been investigated at high-fields, no studies have optimized low-field TOLD T 1 detection and quantification. This work aims to establish the feasibility of clinically-efficient hypoxia imaging with TOLD T 1 contrast on a 0.35T MR-Linac by optimizing a low-field MP2RAGE sequence for time-efficient dynamic T 1 mapping and quantifying T 1 sensitivity and O 2 change detectability limits. Clinically-efficient low-field OE-MRI with dynamic volumetric acquisitions to quantify and map O 2 distributions was achieved by developing an optimized 3D MP2RAGE T 1 mapping method that maximizes signal-to-noise ratio (SNR) and temporal resolution on a 0.35T MR-Linac. High-resolution whole-brain scans were acquired in 5 healthy volunteers to evaluate image fidelity and repeatability. T 1 mapping validation was performed with a phantom containing 8 chemically-formulated inserts of known T 1 values. Mean T 1 values within a volumetric region-of-interest were compared with ground-truth to evaluate T 1 linearity with the optimized sequences. Sensitivity to T 1 changes were evaluated with a dynamic 3D protocol with 20 consecutive measurements. Two-sided 95% prediction intervals were computed to determine the T 1 and ΔR detectability margins to define the O 2 detectability limits. Whole-brain scans showed excellent T 1 concordance with literature values at 0.35T and high repeatability. 3D MP2RAGE optimization for clinically-efficient low-field OE-MRI with a GRAPPA parallel imaging approach achieved a balance of spatial resolution, SNR, and temporal resolution with a 26.6 second whole-brain 3D scan time, capable of 20 measurements within 8:52 min. Phantom scans resulted in T 1 maps with robust linear correlations (R2 = 0.983) within a clinically-relevant T 1 range. Statistical analysis reveals a median (range) T 1 detectability margin of 8.26 (3.91–16.55) ms for T 1 values 344 (180–703) ms, corresponding to a ΔR 1 of 0.028 (0.009–0.097) ms-1, which establishes high sensitivity to T 1 changes and O 2 change detectability, equivalent or superior to high-field studies. We optimized a low-field MP2RAGE sequence with the capability for dynamic 3D T 1 mapping with high sensitivity and O 2 change detectability on a 0.35T MR-Linac. This work establishes the feasibility of clinically efficient hypoxia imaging with OE-MRI TOLD T 1 contrast, enabling hypoxic tissues characterization, and contributing to novel technical advancements to biologically guided adaption and dose painting to hypoxic spatial distributions. [ABSTRACT FROM AUTHOR]

The InSight lander rests on a regolith‐covered, Hesperian to Early Amazonian lava plain in Elysium Planitia within a ∼27‐m‐diameter, degraded impact crater called Homestead hollow. The km to cm‐scale stratigraphy beneath the lander is relevant to the mission's geophysical investigations. Geologic mapping and crater statistics indicate that ∼170 m of mostly Hesperian to Early Amazonian basaltic lavas are underlain by Noachian to Early Hesperian (∼3.6 Ga) materials of possible sedimentary origin. Up to ∼140 m of this volcanic resurfacing occurred in the Early Amazonian at 1.7 Ga, accounting for removal of craters ≤700 m in diameter. Seismic data however, suggest a clastic horizon that interrupts the volcanic sequence between depths of ∼30 and ∼75 m. Meter‐scale stratigraphy beneath the lander is constrained by local and regional regolith thickness estimates that indicate up to 10–30 m of coarse‐grained, brecciated regolith that fines upwards to a ∼3 m thick loosely‐consolidated, sand‐dominated unit. The maximum depth of Homestead hollow, at ∼3 m, indicates that the crater is entirely embedded in regolith. The hollow is filled by sand‐size eolian sediments, with contributions from sand to cobble‐size slope debris, and sand to cobble‐size ejecta. Lander‐based observations indicate that the fill at Homestead hollow contains a cohesive layer down to ∼10–20 cm depth that is visible in lander rocket‐excavated pits and the HP3 mole hole. The surface of the landing site is capped by a ∼1 to 2 cm‐thick loosely granular, sand‐sized layer with a microns‐thick surficial dust horizon. Plain Language Summary: The InSight lander has geophysical instruments that are designed to determine the interior structure of Mars. Understanding the results from these instruments requires a geological analysis of materials beneath the landing site at Elysium Planitia. This study presents data that describe the vertical sequence of rocks and soils beneath the lander, as well as the geologic history. The results indicate that InSight rests on a 1.7‐billion‐year‐old lava plain that is covered in a 10–30 m thick regolith that was produced by impact cratering and modified by wind. The uppermost portion of the regolith is a ∼3 m thick horizon of sand. InSight rests on sand within a degraded impact crater. The sandy material contains a slightly cohesive horizon that is only ∼1–2 cm beneath the lander and is up to 10–20 cm thick. The sandy horizon overlies rock fragments that get progressively larger with depth. Bedrock of basaltic lava exists beneath the regolith down to a depth of ∼170 m. The bedrock is interrupted by weaker materials between depths of ∼30 and 75 m. Beneath ∼170 m, the sequence is dominated by ancient (3.7–4.1 billion years old), possibly sedimentary materials. Key Points: InSight rests on Early Amazonian basaltic lava with an up to 10–30 m thick regolith. The upper 3 m of the regolith is sand dominatedThe regolith contains a 10–20 cm thick cohesive horizon or duricrust. This horizon rests 1–2 cm beneath the landerThe upper 1–2 cm of the regolith comprises loosely‐consolidated sand to pebbles. Sand is rarely mobilized under current wind conditions [ABSTRACT FROM AUTHOR]

Rock shapes and heights around the InSight lander are examined to refine the degradation history of the 27 m‐diameter Homestead hollow. Results document decreasing average exposed rock height and increasing percentage of rocks where height comprises the short axis from outside to within the hollow and support prior models of ejecta deflation accompanied by hollow infilling. We estimate 0.3 m of deflation at the current rim that is realistic compared to rock relief, original ejecta thickness, and predicted aeolian contributions to infilling. We also find that shapes of embayed basalt rocks outside the hollow appear platy, bladed, and elongate in a triangular form factor plot, and more discoidal and bladed in an axes ratio plot. By contrast, expected shapes based on terrestrial studies of basalt rocks are mostly compact, compact platy, compact bladed, compact elongated, platy, bladed, and elongate in triangular form factor plots, and equant with lesser, but significant disc‐ and blade‐shaped rocks in axes ratio plots. We find addition of 10 cm to the heights of rocks near the hollow rim, to account for continued partial embedding in ejecta, yields the best match between observed and expected rock shapes. Exposure of small ejecta rocks in the hollow supports degradation rates of 10−4 m/Myr during most of hollow history. Results indicate that deflation from ejecta accompanied by downwind deposition in the hollow can account for the current degraded form of the crater. Our approach is a new tool for characterizing small crater degradation on regolith‐covered lava plains on Mars. Key Points: Rock heights and shapes at Homestead hollow indicate early transport of deflated ejecta sediments can account for infilling of the craterNear‐rim rock heights and shapes relative to the expected original versus remnant ejecta thickness indicates 30 cm deflation at the current rimExposure of later arriving, small ejecta rocks in the hollow supports very low estimates of degradation over most hollow history [ABSTRACT FROM AUTHOR]

Rocks around the InSight lander were measured in lander orthoimages of the near field (<10 m), in panoramas of the far field (<40 m), and in a high‐resolution orbital image around the lander (1 km2). The cumulative fractional area versus diameter size‐frequency distributions for four areas in the near field fall on exponential model curves used for estimating hazards for landing spacecraft. The rock abundance varies in the near field from 0.6% for the sand and pebble‐rich area to the east within Homestead hollow to ∼3–5% for the progressively rockier areas to the south, north, and west. The rock abundance of the entire near field is just over 3%, which falls between that at the Phoenix (2%) and Spirit (5%) landing sites. Rocks in the far field (<40 m) that could be identified in both the surface panorama and a high‐resolution orbital image fall on the same exponential model curve as the average near‐field rocks. Rocks measured in a high‐resolution orbital image (27.5 cm/pixel) within ∼500 m of the lander that includes several rocky ejecta craters fall on 4–5% exponential model curves, similar to the northern and western near‐field areas. As a result, the rock abundances observed from orbit fall on the same exponential model rock abundance curves as those viewed from the surface. These rock abundance measurements around the lander are consistent with thermal imaging estimates over larger pixel areas as well as expectations from fragmentation theory of an impacted Amazonian/Hesperian lava flow. Key Points: Rocks measured within 10 m, 40 m, and ∼500 m of the InSight lander cover 0.6–5%, ∼3%, and 4–5% cumulative fractional area of the surfaceThe rock size‐frequency distributions observed from the orbit and the surface are on similar exponential model curvesRock abundance at InSight is between the Phoenix and Spirit landing sites and is consistent with orbital thermal imaging estimates [ABSTRACT FROM AUTHOR]

We report the aeolian changes observed in situ by NASA's InSight lander during the first 400 sols of operations: Granule creep, saltation, dust removal, and the formation of dark surface tracks. Aeolian changes are infrequent and sporadic. However, on sols, when they do occur, they consistently appear between noon to 3 p.m., and are associated with the passage of convective vortices during periods of high vortex activity. Aeolian changes are more frequent at elevated locations, such as the top surfaces of rocks and lander footpads. InSight observed these changes using, for the first time, simultaneous in‐situ and orbital imaging and high‐frequency meteorological, seismological, and magnetic measurements. Seismometer measurements of ground acceleration constrain the timing and trajectory of convective vortex encounters, linking surface changes to source vortices. Magnetometer measurements show perturbations in magnetic field strength during the passage of convective vortices consistent with charged‐particle motion. Detachment of sand‐scale particles occurs when high background winds and vortex‐induced turbulence provide a peak surface friction wind speed above the classic saltation fluid threshold. However, detachment of dust‐ and granule‐scale particles also occurred when the surface friction wind speed remained below this threshold. This may be explained by local enhancement of the surface roughness and other effects described here and further studied in Part 2 (Baker et al., 2021). The lack of saltation and bright dust‐coated surfaces at the InSight landing site implies surface stability and the onset of particle motion may be suppressed by dust "cushioning." This differentiates the InSight landing site from other areas on Mars that exhibit more aeolian activity. Plain Language Summary: Aeolian activity, the movement of dust and sand by the wind, is common on Earth and has been observed on other planets, including Mars. A new Mars lander, InSight, has for the first time monitored aeolian changes by combining imaging with weather, seismic and magnetic field measurements. Sand grains are seen moving along the ground and dust is lifted from both artificial and natural surfaces. We found these changes were rare, but almost always happened in the early afternoon when tornado‐like phenomena, called convective vortices, passed by the lander, sometimes leaving dark surface trails behind. The combination of the background wind speed and the rotational wind speed within a vortex was likely to be high enough to detach particles from the surface and set them into motion. When these vortices passed by the lander, the seismometer detected the ground tilting, and there was a pulse in the magnetic field, indicating charged particles were part of these dust‐clearing events. Key Points: Aeolian activity at InSight is observed using imaging, meteorological, seismological, and magnetic field measurements for the first time on MarsInfrequent episodes of creep, dust removal, saltation, and track formation coincide with passage of convective vortices in early afternoonPaucity of observations of saltation coupled with the bright appearance of dust‐coated surfaces suggests surface stability around InSight [ABSTRACT FROM AUTHOR]

Geologic and climatic processes on modern‐day Mars are heavily influenced by aeolian surface activity, yet the relationship between atmospheric conditions and sediment mobilization is not well understood. The Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) spacecraft is uniquely able to address this issue, due to its joint imaging and continuous high‐frequency meteorological capabilities, which allow for direct comparison between surface activity and atmospheric conditions. Since landing in the volcanic plains of Elysium Planitia, InSight's camera's have recorded intermittent, small‐scale surface changes, including removal of fine material on the lander footpad, linear tracks and localized surface darkening caused by minor dust removal, and surface creep of granules, as presented in Part 1 (Charalambous et al., 2021, this issue). Surface activity is found to correlate well with the timing of abrupt pressure drops (ΔP ∼ 1–9 Pa) and transient wind gusts (v ∼ 14–31 m/s) associated with convective vortex passage. Here we identify the major erosive forces acting on surface particles during these events, including the vertical pressure gradient force at the vortex core and the drag force generated by quickly‐rotating tangential winds. Orbital and ground‐truth data suggest that aeolian activity at InSight's landing site is sporadic under modern climatic conditions. Ongoing aeolian surface modifcation is driven primarily by turbulent vortices that sporadically lift dust and redistribute coarser sediment (i.e., sand and granules) but do not aid in the development of organized aeolian bedforms. Surface erosion is localized within the path these vortices take across the surface which is controlled by seasonally‐reversing background circulation patterns. Plain Language Summary: Numerous orbiting and landed spacecraft have imaged wind‐driven ("aeolian") motion of sand and dust on Mars. However, spacecraft on the surface have generally lacked the instrumentation required to interpret the atmospheric conditions driving this motion. Here we utilize the unique opportunity provided by the NASA InSight lander's joint imaging and meteorological capabilities to closely interpret ongoing aeolian activity at the spacecraft's landing site at Elysium Planitia and similar plains regions across Mars. During the first 400 martian days (sols) of the mission, intermittent, small‐scale motion of dust and sand are observed in association with local, thermally driven vortices passing over or near the lander. In situ data are also compared to orbital images and atmospheric model predictions to obtain a more comprehensive picture of wind‐related processes across the region. Overall, aeolian surface modification at this location is found to be very limited under current climatic conditions and is likely dominated by redistribution of fine material caused by transient convective events. Key Points: NASA's InSight mission provides a chance to study aeolian transport through concurrent imaging and high‐frequency atmospheric monitoringThe surface at InSight's landing site is generally stable besides intermittent surface activity caused by convective vortex passageThe vertical pressure gradient within the vortex core and increased drag caused by rotational winds help facilitate surface erosion [ABSTRACT FROM AUTHOR]

The InSight mission landed on Mars in November 2018 and has since observed multiple convective vortices with both the high performance barometer and the low‐noise seismometer SEIS that has unprecedented sensitivity. Here, we present a new method that uses the simultaneous pressure and seismic measurements of convective vortices to place constraints on the elastic properties of the Martian subsurface and the Martian vortex properties, while also allowing a reconstruction of the convective vortex trajectories. From data filtered in the (0.02–0.3 Hz) frequency band, we estimate that the mean value of η (η = E/[1 − ν2], where E is the Young's modulus and ν is the Poisson's ratio) of the Martian ground in the region around SEIS is 239 ± 140 MPa. In addition, we suggest that the previously reported paucity of vortex seismic observations to the west of InSight may be due to the fact that the ground is harder to the west than to the east, consistent with geomorphological surface interpretations. Plain Language Summary: In 2018, the InSight mission placed a seismic instrument on the surface of Mars in order to measure the motion of the Martian ground. As on Earth, there are fluctuations of pressure in the Martian atmosphere caused by small local variations in the atmospheric weight. Whirlwinds, for example, have a lower pressure in their center and they pull up the ground (like a vacuum cleaner). Such changes in pressure deform the elastic Martian ground and the InSight seismic instrument is sensitive enough to measure these deformations. We present a new method that uses the InSight pressure and seismic measurements of whirlwinds in order to determine how hard or soft the Martian ground is. We are also able to estimate the path that the whirlwinds follow as they pass by InSight. We find that the surface material just under InSight has elastic properties similar to dense gravel, but that the whirlwinds detected by the seismic instrument are not in the same places as the whirlwinds tracks observed from space. Our results suggest that the ground is harder to the west and, consequently, that it is more difficult for whirlwinds to deform the ground and create a seismic signal in that region. Key Points: Elastic properties of the Martian subsurface can be constrained using simultaneous pressure and seismic measurements of convective vorticesOur modeling can also be used to constrain Martian convective vortex properties and to reconstruct the vortex trajectoriesThe results indicate that the Martian ground may be harder to the west of InSight, consistent with geomorphological surface interpretations [ABSTRACT FROM AUTHOR]

Knowing precisely where a spacecraft lands on Mars is important for understanding the regional and local context, setting, and the offset between the inertial and cartographic frames. For the InSight spacecraft, the payload of geophysical and environmental sensors also particularly benefits from knowing exactly where the instruments are located. A ~30 cm/pixel image acquired from orbit after landing clearly resolves the lander and the large circular solar panels. This image was carefully georeferenced to a hierarchically generated and coregistered set of decreasing resolution orthoimages and digital elevation models to the established positive east, planetocentric coordinate system. The lander is located at 4.502384°N, 135.623447°E at an elevation of −2,613.426 m with respect to the geoid in Elysium Planitia. Instrument locations (and the magnetometer orientation) are derived by transforming from Instrument Deployment Arm, spacecraft mechanical, and site frames into the cartographic frame. A viewshed created from 1.5 m above the lander and the high‐resolution orbital digital elevation model shows the lander is on a shallow regional slope down to the east that reveals crater rims on the east horizon ~400 m and 2.4 km away. A slope up to the north limits the horizon to about 50 m away where three rocks and an eolian bedform are visible on the rim of a degraded crater rim. Azimuths to rocks and craters identified in both surface panoramas and high‐resolution orbital images reveal that north in the site frame and the cartographic frame are the same (within 1°). Key Points: A carefully georeferenced high‐resolution image of the InSight lander shows it is located at 4.5024N, 135.6234E in Elysium Planitia, MarsInstrument locations are derived by transforming from spacecraft and site frames into the cartographic frameA viewshed shows the lander is on a shallow regional slope down to the east and a local slope up to the north [ABSTRACT FROM AUTHOR]

Comprehensive analysis of remote sensing data used to select the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) landing site correctly predicted the atmospheric temperature and pressure profile during entry and descent, the safe landing surface, and the geologic setting of the site. The smooth plains upon which the InSight landing site is located were accurately predicted to be generally similar to the Mars Exploration Rover Spirit landing site with relatively low rock abundance, low slopes, and a moderately dusty surface with a 3–10 m impact fragmented regolith over Hesperian to Early Amazonian basaltic lava flows. The deceleration profile and surface pressure encountered by the spacecraft during entry, descent, and landing compared well (within 1σ) of the envelope of modeled temperature profiles and the expected surface pressure. Orbital estimates of thermal inertia are similar to surface radiometer measurements, and materials at the surface are dominated by poorly consolidated sand as expected. Thin coatings of bright atmospheric dust on the surface were as indicated by orbital albedo and dust cover index measurements. Orbital estimates of rock abundance from shadow measurements in high‐resolution images and thermal differencing indicated very low rock abundance and surface counts show 1–4% area covered by rocks. Slopes at 100 to 5 m length scale measured from orbital topographic and radar data correctly indicated a surface comparably smooth and flat as the two smoothest landing sites (Opportunity and Phoenix). Thermal inertia and radar data indicated the surface would be load bearing as found. Plain Language Summary: Orbital remote sensing data were used to select the landing site for InSight and to confirm that the surface met the engineering constraints required for a safe landing and successful instrument deployment. By relating remote sensing signatures to surface characteristics at landing sites, these sites can be used as ground truth for orbital data and are essential for selecting and validating landing sites for future missions. Models of the atmosphere that included monitoring during approach by orbiting spacecraft compared well with the deceleration profile and surface pressure encountered by the spacecraft during entry, descent, and landing, and the spacecraft landed successfully. The smooth plains on which InSight landed are consistent with expectations made prior to landing. Remote sensing data indicated that the InSight landing site would be similar to the Mars Exploration Rover Spirit landing site. Both sites have relatively low rock abundance, low slopes, and a moderately dusty surface, with a 3–10 m impact fragmented regolith over Hesperian to Early Amazonian basaltic lava flows. Key Points: The atmosphere, safe surface, and geologic setting of the landing site were correctly predicted by remote sensing data before landingThe modeled atmospheric temperature profiles and surface pressure were within 1 sigma of the measured deceleration profile and surface pressureInSight's surface is similar to Spirit's with low rock abundance, low slopes, moderate dust, and is composed of impact regolith over basalt [ABSTRACT FROM AUTHOR]

While development of the Utica/Point Pleasant Shale (UPP) is extensive in Ohio (U.S.) and increasing in Pennsylvania and West Virginia, few studies report the chemistry of produced waters from UPP wells. These data have important implications for developing best management practices for handling and waste disposal, or identifying the fluid in the event of accidental spill events. Here, we evaluated the elemental and isotope chemistry of UPP produced waters from 26 wells throughout Ohio, Pennsylvania, and West Virginia to determine any unique fluid chemistries that could be used for forensic studies. Compared to the Marcellus, UPP produced waters contain higher activities of total radium (226Ra + 228Ra) and higher 228Ra/226Ra ratios. As with the Marcellus Shale, elemental ratios (Sr/Ca) and isotope ratios (87Sr/86Sr) can distinguish UPP produced waters from many conventional oil and gas formations. Sr/Ca and 87Sr/86Sr ratios can fingerprint small fractions (∼0.1%) of UPP produced water in freshwater. However, because Marcellus and UPP produced waters display similar major elemental chemistry (i.e., Na, Ca, and Cl) and overlapping ratios of Sr/Ca and 87Sr/86Sr, 228Ra/226Ra ratios may be the best tracer to distinguish these waters. [ABSTRACT FROM AUTHOR]

The InSight mission to Mars landed within Homestead hollow on an Early Amazonian lava plain. The hollow is a 27‐m‐diameter, 0.3‐m‐deep quasi‐circular depression that shares morphologic and sedimentologic characteristics to degraded impact craters. Unlike the intercrater plains outside of the hollow, the interior lacks cobbles and is dominated by loose sand, granules, and pebbles. Fresher craters near the landing site exhibit meter‐scale bedforms in their ejecta and on their floors due to sediment trapping. The sedimentology of the interior fill of Homestead hollow suggests similar trapping. The hollow falls along a morphologic continuum that requires low rates of rim degradation and fill. Crater degradation rates (rim erosion plus filling) in the landing site decline nonlinearly through time from 10−2 to 10−4 m/Myr as craters evolve to a hollow‐like form. Rim erosion rates are lower initially, at 10−3 m/Myr, but converge with degradation rates to 10−4 m/Myr. This implies that while filling plays an important role soon after crater formation, it is limited in later stages. Crater statistics indicate that the bulk of the fill occurred in the first ~50 Myr for Homestead hollow. The estimated maximum age of the hollow is ~400 to 700 Myr. This requires near‐zero fill aggradation and long‐term soil stability for the bulk of the crater's history. Fill stability manifests in Homestead hollow as a ~5‐ to 10‐cm‐thick duricrust, formed by exchanges of atmospheric water vapor with soil. The estimated degradation in the hollow requires ~2 to 3 m of sedimentary fill beneath the lander. Plain Language Summary: The Interior Exploration using Seismic Investigation, Geodesy and Heat Transport (InSight) mission to Mars landed in western Elysium Planitia. The landing site consists of a smooth, flat surface that is unique relative to the surrounding rockier plains. Observations from orbital satellite imagery indicate that InSight landed inside of an almost circular depression in the landscape. Here we evaluate the shape and form of this small circular depression and compare it against nearby degraded impact craters. We conclude that InSight landed inside a very old crater that has filled in with windblown sediment and slope debris from the crater wall. We also estimate that the crater has been sitting on the landscape, experiencing extremely slow degradation, for approximately 400 to 700 Myr. The crater origin for the depression has implications for our understanding of the materials that exist immediately beneath the lander and the results from the two geophysical instruments onboard InSight, the Seismic Experiment for Interior Structure (SEIS) and Heat Flow and Physical Properties Package (HP3). Key Points: InSight landed within a 27‐m‐diameter, 0.3‐m‐deep, degraded impact crater called Homestead hollowHomestead hollow has a maximum age of 400 to 700 Myr. Degradation rates were two orders of magnitude higher in first 50 Myr after impactHomestead hollow is filled with up to 3 m of loose infill that is composed of sand and pebbles. The hollow fill is capped by a duricrust [ABSTRACT FROM AUTHOR]