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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Irradiation history of lunar cores and the development of the regolith

Detailed studies by the nuclear particle track method of lunar core sections 70009, 70008, 60007, 60010, and 60009 indicate that the irradiation and depositional histories of individual lunar cores vary greatly. The presence of layers a few cm thick which have remained largely undisturbed for periods ranging from 1 to 100 m.y. is a common feature although the development of the regolith usually proceeds through the accumulation of smaller increments of heavily irradiated material that do not result in distinct layers. Typical accumulation rates are on the order of 1 cm/m.y.

Crozaz, G.↗
NASA NTRSDate not supplied

Particle Loading Tests on HEPA Flat Sheet Media at Sub-Ambient Pressures Using a Lunar Dust Simulant

When humans return to the moon under the NASA Artemis program, their activities on the lunar surface will inevitably lead to the intrusion of some level of lunar dust into the lander cabin. Therein the crew would be exposed to the potential hazards of lunar dust and the possibility of subsequent transfer into orbiting segments after docking. The spacecraft’s cabin filtration system will need to be effective at removing the airborne lunar dust to properly purify the breathable cabin air and minimize the spreading of the dust throughout the vehicle and orbital segments through the mission duration. The fine nature of the lunar dust will require high efficiency filtration, such as HEPA. A series of tests were performed in a specially designed recirculating sealed flow loop, for testing filter media and filter elements at the NASA Glenn Research Center. The flow loop was used to assess the performance and capacity of flat sheet filter media at representative cabin pressures using JSC-1AF lunar dust simulant and at high rates of particle loading. The pressure drop across the filter media was measured as a function of accumulated particle mass load at ambient pressure and at two sub-ambient pressures, 0.0703MPa and 0.0565MPa, and at a media velocity that was scaled relative to its pleated configuration. The challenge particle flows were generated by a custom designed particle generator that introduces dispersed particles of the lunar simulant at high concentrations. An optical particle counting instrument provided filter efficiency measurements within the sealed environment. The pressure drop was found to increase linearly with the amount of dust load on the media, for all test conditions, while the starting pressure drop was found to be lower at the lowest sub-ambient pressure case. High filter efficiency was maintained after high particle loads on the media.

Sub-ambient↗
NASA NTRS1981

Origin of Ca-Al-rich inclusions. II - Sputtering and collisions in the three-ph8se interstellar medium

The theory put forward by Clayton (1977) for the formation of the Ca-Al-rich inclusions within C3 meteorites is extended to an evolutionary history in a three-phase interstellar medium. Widespread supersonic turbulence in the hot interstellar medium is maintained by supernova shock waves, giving rise to heavy sputtering of the refractory dust. Subsequent reaccumulation with varying dust/gas ratios or varying particle sizes produces isotopically fractionated Ca-Al-rich accumulates. It is thought that the Ca-Al-rich inclusions themselves are formed by the following sequence in the solar system: (1) cold accumulation of larger-than-average Ca-Al-rich particles containing supernova condensate cores into macroscopic (approximately 1 cm) Ca-Al-rich agglomerates, probably by sedimentation; and (2) fusion of the supernova condensates into macroscopic minerals by exothermic chemical reactions that begin when the accumulate has been warmed, thereby releasing energy from the unequilibrated forms accumulated from the interstellar medium.

Clayton, D. D.↗
NASA NTRS2014

Cosmic Ray Exposure Ages of Stony Meteorites: Space Erosion or Yarkovsky?

Space erosion from dust impacts may set upper limits on the cosmic ray exposure (CRE) ages of stony meteorites. A meteoroid orbiting within the asteroid belt is bombarded by both cosmic rays and interplanetary dust particles. Galactic cosmic rays penetrate only the first few meters of the meteoroid; deeper regions are shielded. The dust particle impacts create tiny craters on the meteoroid's surface, wearing it away by space erosion (abrasion) at a particular rate. Hence a particular point inside a meteoroid accumulates cosmic ray products only until that point wears away, limiting CRE ages. The results would apply to other regolith-free surfaces in the solar system as well, so that abrasion may set upper CRE age limits which depend on the dusty environment. Calculations based on N. Divine's dust populations and on micrometeoroid cratering indicate that stony meteoroids in circular ecliptic orbits at 2 AU will record 21Ne CRE ages of approx.176 x 10(exp 6) years if dust masses are in the range 10(exp -21) - 10(exp -3) kg. This is in broad agreement with the maximum observed CRE ages of approx. 100 x 10(exp 6) years for stones. High erosion rates in the inner solar system may limit the CRE ages of Near-Earth Asteroids (NEAs) to approx. 120 x 10(exp 6) years. If abrasion should prove to be approx. 6 times quicker than found here, then space erosion may be responsible for many of the measured CRE ages of main belt stony meteorites. In that case the CRE ages may not measure the drift time to the resonances due to the Yarkovsky effects as in the standard scenario, and that for some reason Yarkovsky is ineffective.

Yarkovsky↗
NASA NTRS2009

NASA Tech Briefs, March 2009

Topics covered include: Improved Instrument for Detecting Water and Ice in Soil; Real-Time Detection of Dust Devils from Pressure Readings; Determining Surface Roughness in Urban Areas Using Lidar Data; DSN Data Visualization Suite; Hamming and Accumulator Codes Concatenated with MPSK or QAM; Wide-Angle-Scanning Reflectarray Antennas Actuated by MEMS; Biasable Subharmonic Membrane Mixer for 520 to 600 GHz; Hardware Implementation of Serially Concatenated PPM Decoder; Symbolic Processing Combined with Model-Based Reasoning; Presentation Extensions of the SOAP; Spreadsheets for Analyzing and Optimizing Space Missions; Processing Ocean Images to Detect Large Drift Nets; Alternative Packaging for Back-Illuminated Imagers; Diamond Machining of an Off-Axis Biconic Aspherical Mirror; Laser Ablation Increases PEM/Catalyst Interfacial Area; Damage Detection and Self-Repair in Inflatable/Deployable Structures; Polyimide/Glass Composite High-Temperature Insulation; Nanocomposite Strain Gauges Having Small TCRs; Quick-Connect Windowed Non-Stick Penetrator Tips for Rapid Sampling; Modeling Unsteady Cavitation and Dynamic Loads in Turbopumps; Continuous-Flow System Produces Medical-Grade Water; Discrimination of Spore-Forming Bacilli Using spoIVA; nBn Infrared Detector Containing Graded Absorption Layer; Atomic References for Measuring Small Accelerations; Ultra-Broad-Band Optical Parametric Amplifier or Oscillator; Particle-Image Velocimeter Having Large Depth of Field; Enhancing SERS by Means of Supramolecular Charge Transfer; Improving 3D Wavelet-Based Compression of Hyperspectral Images; Improved Signal Chains for Readout of CMOS Imagers; SOI CMOS Imager with Suppression of Cross-Talk; Error-Rate Bounds for Coded PPM on a Poisson Channel; Biomorphic Multi-Agent Architecture for Persistent Computing; and Using Covariance Analysis to Assess Pointing Performance.

Source record↗
DOE OSTI2022

Connecting the Radiative Influences of Aerosol upon the Mass Flux Profiles of Shallow Cumuli across the Southeast Atlantic Ocean Basin and its Boundaries (Final Report)

The Atlantic Ocean covers approximately 25% of Earth’s surface and the atmosphere above it is home to a complex array of clouds and aerosols that have important influences on regional and global weather and climate. These influences must be accurately depicted in short range, medium range, seasonal, and climate forecast models. Conditions over the tropical Atlantic are particularly complex due to continental scale plumes of dust from the Sahara Desert and smoke from agricultural burning in Africa that drift across the Atlantic Ocean basin toward the Americas. These plumes are often found meandering in the lower atmosphere above shallow tropical clouds that form above the ocean surface, presumably mingling with these clouds on occasion due to convective mixing processes. Elevated dust and smoke particles absorb incoming sunlight and substantially warm the marine atmosphere in the layer in which they are present. This warming may alter the thermal stability of the marine atmosphere and may throttle or enhance the development of clouds, change their internal structure and the rate at which they precipitate. Alternatively, it may isolate the lower atmosphere from drier layers above enabling water vapor to accumulate near the ocean surface potentially leading to the development of deeper convection. Our study was organized around the principal concept of determining the impact of African smoke and dust plumes upon cloud development at ASI and understanding how a popular shallow convection parameterization used in models responds to the presence of this aerosol. We analyzed observations collected during the US Department of Energy (DOE) Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign using the Atmospheric Radiation Measurement Program’s Mobile Facility #1 (AMF-1), which was deployed to Ascension Island (ASI) in Southeastern Atlantic for a one-year period. Ascension Island is immediately downwind from an African source of these plumes, but far enough removed to enable the lower atmosphere to have reacted to their presence. A main goal of our study was to compute radiative heating rate profiles over Ascension Island and along the trajectory from the biomass burning regions along coastal Africa to Ascension Island. To compute the radiative heating rate due to aerosols and clouds, we employed observed profiles of temperature, humidity, and clouds from LASIC alongside aerosol optical properties from the Modern-era Retrospective analysis for Research and Applications Version 2 (MERRA-2), as input for the Rapid Radiation Transfer Model (RRTM). Radiative heating was also assessed across the southeast Atlantic Ocean using an ensemble of back trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. We were successful in this effort and the resulting publication is already being cited despite its relatively short lifetime in the literature. The second part of our study involved the process-level representation of the clouds observed over the Southeastern Atlantic in models. Our initial task, upon which the balance of this portion of the study depended, was to evaluate the representativeness of the clouds observed by AMF-1. What orographic influence did Ascension Island have on the measured cloud structure? We set out to answer this question by trying to separate observations that were clearly indicative of orographic forcing from those that were representative of open ocean. The siting of AMF-1, which was 340-m above sea-level on the slope of a steep escarpment, proved demonstrably problematic for cloud process measurements. Despite considerable effort using multiple approaches including artificial intelligence (AI), we were unable to successfully compensate for the orographic forcing present at the AMF-1 site on ASI and, hence, produce process-level summaries of the convective mass flux representative of open ocean over the Southeastern Atlantic. Even though the project has officially ended, we are making a final attempt using two new types of clustering algorithm (i.e., AI) on the recommendation of a former student, who is an expert in this area. Since we have only recently begun to test these new AI schemes, the recommendations from the second part of our project outlined below are based on our experience at the time of this report.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2001

Molecular microbial diversity of a spacecraft assembly facility

In ongoing investigations to map and archive the microbial footprints in various components of the spacecraft and its accessories, we have examined the microbial populations of the Jet Propulsion Laboratory's Spacecraft Assembly Facility (JPL-SAF). Witness plates made up of spacecraft materials, some painted with spacecraft qualified paints, were exposed for approximately 7 to 9 months at JPL-SAF and examined the particulate materials collected for the incidence of total cultivable aerobic heterotrophs and heat-tolerant (80 degrees C for 15-min.) spore-formers. The results showed that the witness plates coated with spacecraft qualified paints attracted more dust particles than the non-coated stainless steel witness plates. Among the four paints tested, witness plates coated with NS43G accumulated the highest number of particles, and hence attracted more cultivable microbes. The conventional microbiological examination revealed that the JPL-SAF harbors mainly Gram-positive microbes and mostly spore-forming Bacillus species. Most of the isolated microbes were heat resistant to 80 degrees C and proliferate at 60 degrees C. The phylogenetic relationships among 23 cultivable heat-tolerant microbes were examined using a battery of morphological, physiological, molecular and chemotaxonomic characterizations. By 16S rDNA sequence analysis, the isolates fell into seven clades: Bacillus licheniformis, B. pumilus, B. cereus, B. circulans, Staphylococcus capitis, Planococcus sp. and Micrococcus lylae. In contrast to the cultivable approach, direct DNA isolation, cloning and 16S rDNA sequencing analysis revealed equal representation of both Gram-positive and Gram-negative microorganisms.

Industry↗
NASA NTRS2000

Microbiological Contamination of Spacecraft

The International Space Station (ISS) Phase1 Program resulted in seven US astronauts residing aboard the Russian Space Station Mir between March 1995 and May 1998. Collaboration between U.S. and Russian scientists consisted of collection and analyses of samples from the crewmembers and the Mir and Shuttle environments before, during, and after missions that lasted from 75 to 209 days in duration. The effects of long-duration space flight on the microbial characteristics of closed life support systems and the interactions of microbes with the spacecraft environment and crewmembers were investigated. Air samples were collected using a Russian or U.S.-supplied sampler (SAS, RCS, or Burkard,) while surface samples were collected using contact slides (Hycon) or swabs. Mir recycled condensate and stored potable water sources were analyzed using the U.S.-supplied Water Experiment Kit. In-flight analysis consisted of enumeration of levels of bacteria and fungi. Amounts of microorganisms seen in the air and on surfaces were mostly within acceptability lin1its; observed temporal fluctuations in levels of microbes probably reflect changes in environmental conditions (e.g., humidity). All Mir galley hot water samples were within the standards set for Mir and the ISS. Microbial isolates were returned to Earth for identification of bacterial and fungal isolates. Crew samples (nose, throat, skin, urine, and feces) were analyzed using methods approved for the medical evaluations of Shuttle flight crews. No significant changes in crew microbiota were found during space flight or upon return relative to preflight results. Dissemination of microbes between the crew and environment was demonstrated by D A fingerprinting. Some biodegradation of spacecraft materials was observed. Accumulation of condensate allowed for the recovery of a wide range of bacteria and fungi as well as some protozoa and dust mites.

Pierson, D. L.↗
NASA NTRS1986

Grain processes in massive star formation

Observational evidence suggests that stars greater than 100 M(solar) exist in the Galaxy and Large Magellanic Cloud (LMC), however classical star formation theory predicts stellar mass limits of only approx. 60 M(solar). A protostellar accretion flow consists of inflowing gas and dust. Grains are destroyed as they are near the central protostar creating a dust shell or cocoon. Radiation pressure acting on the grain can halt the inflow of material thereby limiting the amount of mass accumulated by the protostar. We first consider rather general constraints on the initial grain to gas ratio and mass accretion rates that permit inflow. We further constrain these results by constructing a numerical model. Radiative deceleration of grains and grain destruction processes are explicitly accounted for in an iterative solution of the radiation-hydrodynamic equations. Findings seem to suggest that star formation by spherical accretion requires rather extreme preconditioning of the grain and gas environment.

Wolfire, M. G.↗
NASA NTRS2016

Comparison of Key Absorption and Optical Properties Between Pure and Transported Anthropogenic Dust over East and Central Asia

Asian dust particulate is one of the primary aerosol constituents in the Earth-atmosphere system that exerts profound influences on environmental quality, human health, the marine biogeochemical cycle, and Earth's climate. To date, the absorptive capacity of dust aerosol generated from the Asian desert region is still an open question. In this article, we compile columnar key absorption and optical properties of mineral dust over East and Central Asian areas by utilizing the multiyear quality-assured datasets observed at 13 sites of the Aerosol Robotic Network (AERONET). We identify two types of Asian dust according to threshold criteria from previously published literature. (1) The particles with high aerosol optical depth at 440 nm (AOD(440) > or = 0.4) and a low Angstrom wavelength exponent at 440-870 nm (alpha < 0.2) are defined as Pure Dust (PDU), which decreases disturbance of other non-dust aerosols and keeps high accuracy of pure Asian dust. (2) The particles with AOD(440) > or = 0.4 and 0.2 < alpha < 0.6 are designated as Transported Anthropogenic Dust (TDU), which is mainly dominated by dust aerosol and might mix with other anthropogenic aerosol types. Our results reveal that the primary components of high AOD days are predominantly dust over East and Central Asian regions, even if their variations rely on different sources, distance from the source, emission mechanisms, and meteorological characteristics. The overall mean and standard deviation of single-scattering albedo, asymmetry factor, real part and imaginary part of complex refractive index at 550 nm for Asian PDU are 0.935 +/- 0.014, 0.742 +/- 0.008, 1.526 +/- 0.029, and 0.00226 +/- 0.00056, respectively, while corresponding values are 0.921 +/- 0.021, 0.723 +/- 0.009, 1.521 +/- 0.025, and 0.00364 +/- 0.0014 for Asian TDU. Aerosol shortwave direct radiative effects at the top of the atmosphere (TOA), at the surface (SFC), and in the atmospheric layer (ATM) for Asian PDU (alpha < 0.2) and TDU (0.2 < alpha < 0.6) computed in this study, are a factor of 2 smaller than the results of Optical Properties of Aerosols and Clouds (OPAC) mineral-accumulated (mineral-acc.) and mineral-transported (mineral-tran.) modes. Therefore, we are convinced that our results hold promise for updating and improving accuracies of Asian dust characteristics in present-day remote sensing applications and regional or global climate models.

Bi, Jianrong↗
DOE OSTI2021

An Overview of Atmospheric Features Over the Western North Atlantic Ocean and North American East Coast - Part 1: Analysis of Aerosols, Gases, and Wet Deposition Chemistry

The Western North Atlantic Ocean (WNAO) and adjoining East Coast of North America are of great importance for atmospheric research and have been extensively studied for several decades. This broad region exhibits complex meteorological features, diverse cloud types, and a wide range of conditions associated with gas and particulate species that originate from many sources regionally and from other continents. As Part 1 of a 2-part paper series, this work provides a characterization of quantities associated with atmospheric chemistry, including gases, aerosols, and wet deposition, based on satellite observations, ground-based data, model simulations, and reanalysis products. Key results include spatial and seasonal differences in composition along the North American East Coast and over the WNAO associated with varying sources of smoke and dust and meteorological drivers such as temperature, moisture, and precipitation. Spatial and seasonal variations of tropospheric carbon monoxide and ozone highlight different pathways towards accumulation of these species in the troposphere. Spatial distributions of speciated aerosol optical depth and vertical profiles of aerosol mass mixing ratios show a clear seasonal cycle highlighting the influence of both natural and anthropogenic sources in addition to the impact of intercontinental transport on their vertical profiles. Analysis of long-term climate model simulations of aerosol species and satellite observations of carbon monoxide confirm that there has been a significant decline in recent decades among anthropogenic constituents owing to regulatory activities. The results can inform current and future lines of research for the region.

Corral, Andrea↗
NASA NTRS1987

On the evolution and activity of cometary nuclei

The thermal evolution of a spherical cometary nucleus, composed initially of very cold amorphous ice and moving in comet Halley's orbit, is simulated numerically for 280 revolutions. It is found that the phase transition from amorphous to crystalline ice constitutes a major internal heat source. The transitions occur in five distinct rounds, with the phase transition front advancing into the nucleus to progressively greater depths. At the time of crystallization, the temperature of the transformed ice rises to 180 K. It is argued that gas tends to accumulate in pockets that eventually explode, forming 'volcanic calderas' and exposing gas-laden amorphous ice which may be a major source of gas and dust jets into the coma. The activity of new comets and, possibly, cometary outbursts and splits may also be explained in terms of explosive gas release following the transition from amorphous to crystalline ice.

Prialnik, Dina↗
NASA NTRS2010

Investigating Premature Ignition of Thruster Pressure Cartridges by Vibration-Induced Electrostatic Discharge

Pyrotechnic thruster pressure cartridges (TPCs) are used for aeroshell separation on a new NASA crew launch vehicle. Nondestructive evaluation (NDE) during TPC acceptance testing indicated that internal assemblies moved during shock and vibration testing due to an internal bond anomaly. This caused concerns that the launch environment might produce the same movement and release propellant grains that might be prematurely ignited through impact or through electrostatic discharge (ESD) as grains vibrated against internal surfaces. Since a new lot could not be fabricated in time, a determination had to be made as to whether the lot was acceptable to fly. This paper discusses the ESD evaluation and a separate paper addresses the impact problem. A challenge to straight forward assessment existed due to the unavailability of triboelectric data characterizing the static charging characteristics of the propellants within the TPC. The approach examined the physical limitations for charge buildup within the TPC system geometry and evaluated it for discharge under simulated vibrations used to qualify components for launch. A facsimile TPC was fabricated using SS 301 for the case and surrogate worst case materials for the propellants based on triboelectric data. System discharge behavior was evaluated by applying high voltage to the point of discharge in air and by placing worst case charge accumulations within the facsimile TPC and forcing discharge. The facsimile TPC contained simulated propellant grains and lycopodium, a well characterized indicator for static discharge in dust explosions, and was subjected to accelerations equivalent to the maximum accelerations possible during launch. The magnitude of charge generated within the facsimile TPC system was demonstrated to lie in a range of 100 to 10,000 times smaller than the spark energies measured to ignite propellant grains in industry standard discharge tests. The test apparatus, methodology, and results are described in this paper.

Woods, Stephen S.↗
NASA NTRS2022

An Overview of Atmospheric Features Over the Western North Atlantic Ocean and North American East Coast – Part 1: Analysis of Aerosols, Gases, and Wet Deposition Chemistry

The Western North Atlantic Ocean (WNAO) and adjoining East Coast of North America are of great importance for atmospheric research and have been extensively studied for several decades. This broad region exhibits complex meteorological features and a wide range of conditions associated with gas and particulate species from many sources regionally and other continents. As Part 1 of a 2‐part paper series, this work characterizes quantities associated with atmospheric chemistry, including gases, aerosols, and wet deposition, by analyzing available satellite observations, ground‐based data, model simulations, and reanalysis products. Part 2 provides insight into the atmospheric circulation, boundary layer variability, three‐dimensional cloud structure, properties, and precipitation over the WNAO domain. Key results include spatial and seasonal differences in composition along the North American East Coast and over the WNAO associated with varying sources of smoke and dust and meteorological drivers such as temperature, moisture, and precipitation. Spatial and seasonal variations of tropospheric carbon monoxide and ozone highlight different pathways towards the accumulation of these species in the troposphere. Spatial distributions of speciated aerosol optical depth and vertical profiles of aerosol mass mixing ratios show a clear seasonal cycle highlighting the influence of different sources in addition to the impact of intercontinental transport. Analysis of long‐term climate model simulations of aerosol species and satellite observations of carbon monoxide confirm that there has been a significant decline in recent decades among anthropogenic constituents owing to regulatory activities.

ACTIVATE↗
NASA NTRS1999

Surface Ages and Resurfacing Rates of the Polar Layered Deposits on Mars

The martian polar layered deposits (PLD) are probably the best source of information about the recent climate history of Mars, but their origin and the mechanisms of accumulation are still a mystery. The polar layers are sedimentary deposits that most planetary scientists believe are composed of water ice and varying amounts of wind-blown dust, but their composition is poorly constrained. Interpretation of the observed polar stratigraphy in terms of global climate changes is complicated by the significant difference in surface ages between the north and south PLD inferred from crater statistics. While no craters have been found in the north PLD, the surface of the south PLD appears to have been stable for many of the orbital/axial cycles that are thought to have induced global climate changes on Mars. Using medium-resolution Viking imagery, Plaut et al. found at least 15 impact craters in the southern layered deposits and concluded that their surface is 120 +/- 40 million years old. In contrast, Cutts et al. found no fresh impact craters larger than about 300 meters in summertime images of the north polar layered deposits. Additional information is contained in the original extended abstract.

Herkenhoff, K. E.↗
NASA NTRS2000

Large Grooves in the South Polar Layered Deposits: Insights from Spacecraft Data and Terrestrial Analogs

The Martian polar layered deposits (PLD) are probably the best source of information about the recent climate history of Mars, but their origin and the mechanisms of accumulation are still a mystery. The polar layers are sedimentary deposits that most planetary scientists believe are composed of water ice and varying amounts of wind-blown dust, although their composition is poorly constrained. Interpretation of the observed polar stratigraphy in terms of global climate changes is complicated by the significant difference in surface ages between the north and south PLD inferred from crater statistics. The study reported here was undertaken as part of the landing site selection effort for the Mars Polar Lander (MPL) and Deep Space 2 (DS2) missions that made use of all available data. We used Mariner 9, Viking, and Mars Global Surveyor images of the south PLD in the area accessible to MPL and DS2 to evaluate the topography and morphology of grooves, terraced layers, and other features. Here we report on results from grooves that appear to have been carved by strong winds. Because these features are found throughout the interior of the PLD, where MPL and DS2 were targeted to land, their topographic characteristics were judged as important input for landing site safety assessment. The characteristics of the grooves also provide constraints and insights into aeolian processes in the polar regions and the effects these have on PLD ablation. Our results indicate that these grooves do not represent landing hazards at the scale of the images (approx. 80 m/pixel). Their topography and shape do not seem correlated with south PLD layering. No Earth analog of suitable scale exists, although the grooves bear some resemblance to smaller terrestrial deflation hollows found in soft sediment and ice. Additional information is contained in original extended abstract.

Bridges, N. T.↗
NASA NTRS2019

A Kuiper Belt Source for Solar Flare Track-Rich Interplanetary Dust Particles

The presence of solar flare particle tracks in mineral grains within interplanetary dust particles (IDPs) has long been accepted as proof of their extraterrestrial origin [e.g. 1]. The 10-20 micrometers diameter IDPs released by dust producing objects in the solar system (mainly comets and asteroids) spiral in towards the Sun under the influence of Poynting-Robertson (PR) drag forces [2] and accumulate solar flare energetic particle tracks during their journey. The number of IDPs with well-constrained track density measurements is small, owing to the difficulty in the measurements and the lack of appropriatelysized crystals in which to image them. In order to use track densities as a chronometer of space exposure, the track production rate must be known. All previous work relied on track production rates determined by chemical etching techniques [e.g. 3], but tracks in IDPs are measured using TEM imaging. Here we report measurements of track densities in IDPs from both the anhydrous and hydrated IDP groups. Using the track production calibration determined from TEM observations of anorthite and olivine in lunar rock 64455 [4] we estimate space exposure times for these IDPs to constrain their parent body sources.

Keller, L. P.↗
DOE OSTI2024

Weathering Incongruence in Mountainous Mediterranean Climates Recorded by Stream Lithium Isotope Ratios

Lithium isotope ratios (δ 7 Li) of rivers are increasingly serving as a diagnostic of the balance between chemical and physical weathering contributions to overall landscape denudation rates. Here, we show that intermediate weathering intensities and highly enriched stream δ 7 Li values typically associated with lowland floodplains can also describe small upland watersheds subject to cool, wet climates. This behavior is revealed by stream δ 7 Li between +22.4 and +23.5‰ within a Critical Zone observatory located in the Cévennes region of southern France, where dilute stream solute concentrations and significant atmospheric deposition otherwise mask evidence of incongruence. The water-rock reaction pathways underlying this behavior are quantified through a multicomponent, isotope-enabled reactive transport model. Using geochemical characterization of soil profiles, bedrock, and long-term stream samples as constraints, we evolve the simulation from an initially unweathered granite to a steady state weathering profile which reflects the balance between (a) fluid infiltration and drainage and (b) bedrock uplift and soil erosion. Enriched stream δ 7 Li occurs because Li is strongly incorporated into actively precipitating secondary clay phases beyond what prior laboratory experiments have suggested. Chemical weathering incongruence is maintained despite relatively slow reaction rates and moderate clay accumulation due to a combination of two factors. First, reactive primary mineral phases persist across the weathering profile and effectively “shield” the secondary clays from resolubilization due to their greater solubility. Second, the clays accumulating in the near-surface profile are relatively mature weathering byproducts. These factors promote characteristically low total dissolved solute export from the catchment despite significant input of exogenous dust.

54 ENVIRONMENTAL SCIENCES↗