Astrogeology Science Center

Abstract Consumptive use of freshwater is of concern in many estuarine ecosystems, and various frameworks have been used to prescribe environmental flows to benefit native species. However, few of these frameworks explicitly examine the potential trade‐offs between socioeconomic and conservation‐oriented values. This is exemplified in California, USA, where freshwater management has been an area of focus and controversy. Operations of numerous reservoirs and water diversion facilities distributed throughout the state, while critical for economic and public health benefits, have contributed to the decline of many native species. The endangered delta smelt ( Hypomesus transpacificus ) is endemic to the Sacramento‐San Joaquin Delta, the heart of California's complex water conveyance system. To aid recovery of delta smelt, fall‐timed freshwater pulse flows were implemented, which require water to be either released from reservoirs, or made unavailable to export for consumptive uses. Previous research has indicated that the effectiveness of the current pulse flow action could be improved by reconsidering the timing and magnitude; however, uncertainties in the predicted fish response to flow pulses may hinder decision‐making about flow management. Using a water resource planning model, different iterations of an individual‐based life cycle model, and decision analysis tools, we assessed the importance of sources of uncertainty to hypothetical flow management decisions, including uncertainty surrounding the predicted responses in delta smelt population growth rates, and variability of decision‐maker's values. We found both the choice of which (if any) flow action to take for delta smelt, and the expected value of further research, depended on how decision‐makers weight the delta smelt and water supply objectives. There was expected value of information (VOI) only if a decision‐maker weighted the delta smelt objective ≥0.59, and within this range, research to improve estimates of changes in delta smelt prey items related to flow actions could be prioritized over other sources of uncertainty to improve outcomes of decision‐making. Our study demonstrates how uncertainty, even if large, may not be equally relevant to different decision‐makers (e.g., with different agency missions), and how VOI analysis can be used to guide management in an overallocated water system such as California.

Abstract We needed to evaluate available orbital data of NASA’s Volatiles Investigating Polar Exploration Rover (VIPER) mission area in order to derive a variety of maps to help the science team identify scientifically interesting places for the rover to visit and to provide scientific context for our mission. Some of these maps also fulfilled engineering and mission design needs to enable safe and efficient landing and roving. We incorporated data from the Lunar Reconnaissance Orbiter Camera, the Lunar Orbital Laser Altimeter, the Mini-RF instrument, the Chandrayaan-2 Orbital High Resolution Camera, the Korean Pathfinder Lunar Orbiter’s Shadowcam, the Kaguya Spectral Profiler and Multiband Imager, and the Chandrayaan-1 Moon Mineralogy Mapper. We used a variety of techniques to build these maps, including stereogrammetry, shape-from-shading, ice stability depth and surface temperature calculations, and the horizon method for solar illumination and direct-to-Earth communications maps. Altogether, these maps allowed us to survey for boulders, evaluate features in permanently shadowed regions that VIPER might explore, provide mineralogic context for what VIPER’s instruments may learn, estimate the ages and radar properties of craters in the VIPER mission area, and evaluate the potential for gravity traverses with the rover. These data and techniques provided a rich set of information from which both the VIPER science team and engineering teams were able to draw in order to plan a safe landing and to plan a VIPER surface mission that will be both scientifically valuable and robust from an operational perspective.

Volatiles, such as chlorine (Cl), are important species that are easily mobilized by fluids and thus play a key role in alteration processes on Mars [1]. The first detections of Cl were made in the 1970’s by the Viking 1 & 2 X-ray fluorescence (XRF) spectrometers. The ɑ-proton x-ray spectrometer (APXS) instruments onboard the Mars Pathfinder (Sojourner), Mars Exploration rovers (Spirit & Opportunity), and the Curiosity rover continued to document Cl at their respective landing sites [2,3,4,5,6]. The Phoenix mission also detected Cl mainly in the form of soluble perchlorates and chlorides in the soil at its landing site [7]. The coexistence of soluble perchlorate and chloride salts in the soils of the Phoenix landing site is highly relevant for the redox potential point of view. The PIXL instrument onboard Perseverance produced Cl maps that show the Cl-rich regions overlapping sodium.The SuperCam instrument onboard the Perseverance rover has been collecting Laser Induced Breakdown Spectroscopy (LIBS) data along our traverse for almost 1500 sols, with an elevation increase of 700 meters from the crater floor up to the crater rim. During this time, we have obtained more than 700 Cl-bearing points in approximately 310 targets which have all been quantified. LIBS has the ability to detect Cl above 0.8 wt.% using the model developed by Wolf et al., (2025) [8]. All LIBS data collected by SuperCam were quantified and categorized by geologic unit and rock type. Results show that Jezero crater has higher average Cl concentrations in soil, rock exterior, and rock interiors compared to previous landing sites. Results also show that Cl is highest in the rock interiors on the crater floor at the lowest elevation of -2500 meters in the Máaz formation. Raman data collected in abraded patches of Máaz formation confirmed that one of the phases of Cl present on the crater floor is Na-perchlorate [9]. The presence of perchlorate salts in the pores of the rocks suggest the past presence of perchlorate-rich fluids in contact with the basaltic rocks of Máaz formation when the crater floor was covered by water. Quantified values show rock interiors on the crater floor have up to nearly 6 wt.% Cl, with an average concentration that is higher than all other geologic units including analyses on soils, rock exteriors, and rock interiors. This demonstrates a unique aqueous alteration history in Jezero crater, Mars compared to the landing sites of other rovers.

The complexity of Enceladus’ surface and the presence of young, heavily tectonized regions such as the South Polar Terrain make it a compelling exploration target for understanding icy satellite evolution and potential habitability. However, the current gap in our understanding of Enceladus’s thermal history limits our ability to constrain the longevity of its internal ocean and timescales of endogenic geologic activity. In contrast to the tectonized terrains, Enceladus’ ancient, heavily cratered surfaces preserve the earliest geologic events and preserve potential evidence of Enceladus’ thermal and geophysical history. Characterizing geologic features within the cratered terrains provides observation-based insight into the long-term evolution of the ice shell and can place constraints on the evolution of tidal stresses and heat flow affecting the surface geology.Many craters within the cratered terrains appear to have undergone viscous relaxation, where their depths are shallower than what is expected for fresh craters and can be attributed to elevated heat flow in the subsurface [1]. Global models of present-day heat flux indicate that there are spatial variations in heat flow across the ice shell [2]. However, these models are a snapshot in time and do not represent temporal variations. Observational studies of the cratered terrains have found evidence of extreme viscous relaxation in regions where modeled present-day heat flux is relatively low [3], although these correlations have not been systematically analyzed.Most, if not all, large craters on Enceladus show some degree of viscous relaxation with shallow floors and large central mounds. We present on the compilation of a global database of impact craters on Enceladus and how this data product feeds into our systematic campaign to identify signs of crater relaxation across Enceladus’ heavily cratered terrains. These data will feed into a larger effort to use the spatial distribution of relaxed craters and models of crater relaxation to gain insight into the thermal history of the cratered terrains. In comparing the distribution of relaxed craters to models of present-day heat flux, we may determine whether these models are sufficient to explain the observed relaxation states of craters and, in turn, whether there is observational evidence that Enceladus has experienced one or more past episodes of elevated heat flux.

Climate-driven forest mortality events have been extensively observed in recent decades, prompting the question of how quickly these affected forests can recover their functionality following such events. Here we assessed forest recovery in vegetation greenness (normalized difference vegetation index) and canopy water content (normalized difference infrared index) for 1,699 well-documented forest mortality events across 1,600 sites worldwide. By analysing 158,427 Landsat surface reflectance images sampled from these sites, we provided a global assessment on the time required for impacted forests to return to their pre-mortality state (recovery time). Our findings reveal a consistent decline in global forest recovery rate over the past decades indicated by both greenness and canopy water content. This decline is particularly noticeable since the 1990s. Further analysis on underlying mechanisms suggests that this reduction in global forest recovery rates is primarily associated with rising temperatures and increased water scarcity, while the escalation in the severity of forest mortality contributes only partially to this reduction. Moreover, our global-scale analysis reveals that the recovery of forest canopy water content lags significantly behind that of vegetation greenness, implying that vegetation indices based solely on greenness can overestimate post-mortality recovery rates globally. Our findings underscore the increasing vulnerability of forest ecosystems to future warming and water insufficiency, accentuating the need to prioritize forest conservation and restoration as an integral component of efforts to mitigate climate change impacts.

Abstract Solar energy is rapidly growing to decarbonize the electrical grid. Maintaining ecosystem function with solar energy generation can be promoted through construction methods that minimize negative impacts on soils and vegetation. However, the disturbance created by less‐impactful construction methods at utility‐scale solar energy (USSE) facilities and the ecosystem responses remain relatively unknown. We monitored soils and vegetation before and after the USSE build‐out to assess the short‐term impacts of construction on soils and vegetation at the Gemini Solar Project in the Mojave Desert. The facility was constructed with methods intended to be less impactful than traditional techniques. Our goal was to answer three questions: (1) What are the short‐term effects of construction on soils and vegetation? (2) Do construction effects vary by the initial plant community and soil type? and (3) Does disturbance intensity from construction affect soil and vegetation response? We found strong evidence that the construction of the Gemini facility increased bare soil and soil compaction, and decreased dark biocrust cover and soil stability in the short term. For every 1% increase in disturbance intensity, we found a 0.23% increase in bare soil cover and a 0.10% decrease in dark biocrust cover. Plant responses varied more than soil responses and depended on the initial plant community and soil type, with decreases in plant canopy cover highest in sandy soils dominated by creosote bush (Larrea tridentata) and white bursage (Ambrosia dumosa) shrubs. Synthesis and applications: Many impacts of USSE facility construction depend on the underlying vegetation and soils and the level of disturbance intensity. The use of less‐impactful construction methods, including a combination of overland travel and drive‐and‐crush examined in our study, can ameliorate negative effects relative to traditional construction practices and provide a pathway to maintain ecosystem function.

Background Wildfire simulation models are used to derive maps of burn probability (BP) based on fuels, weather, topography and ignition locations, and BP maps are key components of wildfire risk assessments. Aims Few studies have compared BP maps with real-world fires to evaluate their suitability for near-future risk assessment. Here, we evaluated a BP map for the conterminous US based on the large fire simulation model FSim. Methods We compared BP with observed wildfires from 2016 to 2022 across 128 regions representing similar fire regimes (‘pyromes’). We evaluated the distribution of burned areas across BP values, and compared burned area distributions among fire size classes. Key results Across all pyromes, mean BP was moderately correlated with observed burned area. An average of 71% of burned area occurred in higher-BP classes, vs 79% expected. BP underpredicted burned area in the Mountain West, especially for extremely large fires. Conclusions The FSim BP map was useful for estimating subsequent wildfire hazard, but may have underestimated burned areas where input data did not reflect recent climate change, vegetation change or human ignition patterns. Implications Our evaluations indicate that caution is needed when relying on simulation-based BP maps to inform management decisions. Our results also highlight potential opportunities to improve model estimates.

The frequency and severity of drought events are predicted to increase due to anthropogenic climate change, with cascading effects across forested ecosystems. Management activities such as forest thinning and prescribed burning, which are often intended to mitigate fire hazard and restore ecosystem processes, may also help promote tree resistance to drought. However, it is unclear whether these treatments remain effective during the most severe drought conditions or whether their impacts differ across environmental gradients. We used tree-ring data from a system of replicated, long-term (>20 years) experiments in the southwestern United States to evaluate the effects of forest restoration treatments (i.e., evidence-based thinning and burning) on annual growth rates (i.e., basal area increment; BAI) of ponderosa pine (Pinus ponderosa), a broadly distributed and heavily managed species in western North America. The study sites were established at the onset of the most extreme drought event in at least 1200 years and span much of the climatic niche of Rocky Mountain ponderosa pine. Across sites, tree-level BAI increased due to treatment, where trees in treated units grew 133.1% faster than trees in paired, untreated units. Likewise, trees in treated units grew an average of 85.6% faster than their pre-treatment baseline levels (1985 to ca. 2000), despite warm, dry conditions in the post-treatment period (ca. 2000-2018). Variation in the local competitive environment promoted variation in BAI, and larger trees were the fastest-growing individuals, irrespective of treatment. Tree thinning and prescribed fire altered the climatic constraints on growth, decreasing the effects of belowground moisture availability and increasing the effects of atmospheric evaporative demand over multi-year timescales. Our results illustrate that restoration treatments can enhance tree-level growth across sites spanning ponderosa pine's climatic niche, even during recent, extreme drought events. However, shifting climatic constraints, combined with predicted increases in evaporative demand in the southwestern United States, suggest that the beneficial effects of such treatments on tree growth may wane over the upcoming decades.

ABSTRACTIn addition to supplying water for agriculture, cities, and industry, the Colorado River traverses the Colorado Plateau, including several of the most unique and valued National Parks and Recreation Areas in the United States. Although the water needs of these landscapes were not considered at the time water allocations were first negotiated, these needs were recognized in subsequent legislation and policy. Management goals address a range of aquatic and riparian resources, including fine sediment (sand, silt, and clay) which, in Grand Canyon, is important for ecological, cultural, and recreational resources. Over ~30 years, stakeholders, resource managers, and scientists collectively developed operational strategies for sediment management to meet goals outlined by an adaptive management program. However, prolonged drought, or “aridification,” resulting in declining runoff and the lowest reservoir storage elevations in decades has challenged those strategies. The paradigm for sustainable sediment management relies on (1) sand accumulation on the bed of the Colorado River during periods of sediment‐rich tributary floods from summer/fall thunderstorms, and (2) dam‐released controlled (artificial) floods, referred to as High‐Flow Experiments (HFEs), to redistribute the accumulated sand to rebuild eroded bar and floodplain deposits. The management protocol, which specifies narrowly defined sand accumulation periods and HFE implementation windows, is based on implementing HFEs in late fall during the period of greatest sediment enrichment, before higher winter releases for hydropower erode the accumulated sand from the riverbed. Low dam releases associated with drought, however, have changed the pattern of sand accumulation and low reservoir elevations have prevented HFE implementation in the defined window. An alternative strategy for HFE planning and implementation was tested opportunistically in April 2023 following lower‐than‐normal winter dam releases. We present findings from this HFE indicating that sand enrichment and sandbar building equaled or exceeded that of HFEs conducted under the established management protocol. These findings show that management goals for sediment under conditions of prolonged drought may be achievable but will likely require substantial changes in dam management strategies.