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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Lunar and Planetary Science XXXV: Lunar Rocks from Outer Space

The following topics were discussed: Mineralogy and Petrology of Unbrecciated Lunar Basaltic Meteorite LAP 02205; LAP02205 Lunar Meteorite: Lunar Mare Basalt with Similarities to the Apollo 12 Ilmenite Basalt; Mineral Chemistry of LaPaz Ice Field 02205 - A New Lunar Basalt; Petrography of Lunar Meteorite LAP 02205, a New Low-Ti Basalt Possibly Launch Paired with NWA 032; KREEP-rich Basaltic Magmatism: Diversity of Composition and Consistency of Age; Mineralogy of Yamato 983885 Lunar Polymict Breccia with Alkali-rich and Mg-rich Rocks; Ar-Ar Studies of Dhofar Clast-rich Feldspathic Highland Meteorites: 025, 026, 280, 303; Can Granulite Metamorphic Conditions Reset 40Ar-39Ar Ages in Lunar Rocks? [#1009] A Ferroan Gabbronorite Clast in Lunar Meteorite ALHA81005: Major and Trace Element Composition, and Origin; Petrography of Lunar Meteorite PCA02007, a New Feldspathic Regolith Breccia; and Troilite Formed by Sulfurization: A Crystal Structure of Synthetic Analogue

Source record↗
NASA NTRS2009

The Lunar Regolith as a Remote Sensing Target for the Lunar Reconnaissance Orbiter (LRO)

Of the 6 instruments and one technology demonstration aboard the LRO, only CRaTER does not measure some kind of interaction of particles with the lunar regolith. LEND detects neutron fluence that contains information about the number density of protons in the upper regolith. To infer the presence of protons, the PI must assume a model that characterizes the surface as a collection of atoms. Thus, LEND does not sense the regolith as a structure. LROC, LOLA, and LAMP sense reflected photons whose wavelength is much shorter than the median particle size in the regolith. The photons interact with electrons, either in atomic shells or in chemical bonds. These interactions occur within a nanometer or so of the surface of a particle. Thus, the particles are macroscopic objects and models of the reflection process invoke ray-tracing optics. DIVINER senses photons that have been emitted by surface particles through thermal phonon processes. The wavelengths detected by the instrument are of the same order as the median particle size, and the photons contain information on particle dimensions as well as the molecular bonds in the constituent compounds. The Mini-RF synthetic aperture radar generates and detects photons of a few centimeters wavelength that interact with the regolith as a dielectric, the dielectric properties of the particulate component being described through effective medium theory. However, the interaction with rocks (macroscopic objects of interest to geologists) can be characterized using Fresnel or Mie models of electromagnetic properties.

Mendell, Wendell W.↗
NASA NTRS2004

Effect of Palagonite Dust Deposition on the Automated Detection of Carbonate Vis/NIR Spectra

Currently Mars missions can collect more data than can be returned. Future rovers of increased mission lifetime will benefit from onboard autonomous data processing systems to guide the selection, measurement and return of scientifically important data. One approach is to train a neural net to recognize spectral reflectance characteristics of minerals of interest. We have developed a carbonate detector using a neural net algorithm trained on 10,000 synthetic Vis/NIR (350-2500 nm) spectra. The detector was able to correctly identify carbonates in the spectra of 30 carbonate and noncarbonate field samples with 100% success. However, Martian dust coatings strongly affect the spectral characteristics of surface rocks potentially masking the underlying substrate rock. In this experiment, we measure Vis/NIR spectra of calcite coated with different thicknesses of palagonite dust and evaluate the performance of the carbonate detector.

Gilmore, Martha S.↗
NASA NTRSDate not supplied

Characterization of Fluorescence Signals in Synthetic Anorthite

In-situ resource utilization (ISRU) is a key capability to enable a long term presence on the Moon and other planetary bodies. For example, efforts have been underway to develop processes to utilize the lunar regolith to produce building materials and extract useful resources. In processes that utilize the regolith directly to produce construction materials, such as in various sintering methods, characterizing the composition of the regolith is important as the composition can affect the optimal process parame-ters. In processes that involve extracting resources such as iron, oxygen, hydrogen, etc., identifying areas with higher abundance of a particular resource will be critical since different regions of the Moon exhibit differing regolith composition. To this end, Ra-man is one technique that can rapidly characterize the mineralogy of rock samples. This technique has al-ready been deployed on Mars to detect various miner-als including olivine, carbonates, phosphates, etc. Besides characterizing the mineralogy, Raman spectra often contain unwanted fluorescence signals that can mask Raman peaks. In some cases, the fluorescence signals are narrow enough to aid in the identification of specific elements in soils. In this work, we explore fluorescence peaks in a synthetic anorthite sample, which are at the same position as Ruby fluorescence peaks attributed to chromium. These fluorescence peaks, as well as similar fluorescence peaks attributed to other elements, could have important implications for ISRU and the mining of critical resources as has been previously described.

Raman Spectroscopy↗
NASA NTRS2019

Saponite Dissolution Experiments and Implications for Mars

Recent work suggests that the mineralogical sequence of the Murray formation at Gale crater may have resulted from diagenetic alteration after sedimentation, or deposition in a stratified lake with oxic surface and anoxic bottom waters. Fe-containing clay minerals are common both at Gale crater, and throughout the Noachian-aged terrains on Mars. These clay minerals are primarily ferric (Fe3+), and previous work suggests that these ferric clay minerals may result from alteration of ferrous (Fe2+) smectites that were oxidized after deposition. The detection of trioctahedral smectites at Gale crater by CheMin suggests Fe2+ smectite was also deposited during the early Hesperian. However, due to their sensitivity to oxygen, Fe2+ smectites are difficult to analyze on Earth and very few saponite dissolution rates exist in the literature. To the best of our knowledge, no experiments have measured the dissolution rates of ferrous saponites under oxidizing and reducing conditions. In order to better understand the characteristics of water-rock interaction at Gale crater, particularly the oxidation state, we report our results to date on ongoing syntheses of ferrous and magnesium saponites and dissolution experiments of natural saponite under ambient conditions. Future experiments will include the dissolution of synthetic ferric, ferrous, and magnesium saponites under oxidizing and anoxic conditions at a range of pH values.

Luu, N. C.↗
DOE OSTI2022

Impact of Concurrent Solubilization and Fines Migration on Fracture Aperture Growth in Shales during Acidized Brine Injection

Acidic hydraulic fracturing fluid chemically and physically alters shale rock fabric during injection and shut-in, creating a “reaction-altered zone” along the fracture faces. To better characterize the variable thickness and composition of this reaction-altered zone under advective flow, we take a coupled experimental and modeling approach. A fluidic cell, with six fiducial markers, is first fabricated to keep the rock sample in place during the core floods and to allow image alignment of acquired images. Then, we conduct a series of reactive core floods in a clay-rich siliceous Wolfcamp shale sample with 10 wt % carbonate, using a synthetic fracturing fluid under no confining stress and at room temperature. High-resolution computed tomography (CT) scans are periodically conducted to observe the spatial alteration of the fracture network. We then perform scanning electron microscopy (SEM-EDS) on the two orthogonal surfaces (fracture surface and freshly cut profile face) to generate high-resolution elemental maps that show the change in mineralogy, both with distance along a given flow path along a fracture surface and with depth from the fracture surface into the shale matrix. These results are contrasted against a two-dimensional (2D) advection-diffusion reaction model developed previously for batch reactions between shale and synthetic fracturing fluids. The model simulates the geochemical interaction occurring at the fracture/matrix interface and penetrating into the shale matrix during the reactive core flood. Both model and experimental results show that the acidic brine is neutralized during the core flood, corresponding to an increase in fracture aperture as a function of fluid volume injected with the greatest change near the inlet. SEM-EDS scans reveal significant dissolution of carbonates on the fracture surface without pyrite oxidation. The reactive transport model indicates that carbonate depletion into the shale interior should be observable, yet SEM-EDS shows no discernible loss of carbonate in the orthogonal profile face. The combination of these observations suggests an additional fracture evolution mechanism in the reactive system, i.e., fines migration. We show that fines migration enhances the access of fracturing fluid to the matrix resulting in a more pronounced fracture widening. Finally, we conclude that coupled mineral dissolution and fines migration govern fracture aperture growth during acidized brine injection. In this work, we effectively show the underlying risk of relying solely on models that do not include an important (transport) process that can alter the system significantly and propose a combined chemomechanical mechanism for fracture evolution appropriate for this shale mineralogy.

58 GEOSCIENCES↗
NASA NTRS1987

Mussel Glue

A mytilus edilus, a common blue ocean mussel is attaching itself to the underside of a wet glass in a laboratory. It secretes a glue like substance in the form of multiple threads which attach to surfaces such as shells, rocks, piers and ships. This natural super glue hardens within minutes and tightly affixes to its selected platform even in the roughest seas. Its superior adhesive properties suggest many practical applications. One company, Bio-Polymers, Inc., has developed a synthetic mussel glue for the commercial market.

Source record↗
NASA NTRS2001

Evolution of the Earth and Origin of Life: The Role of Gas/Fluid Interactions with Rocks

The work under the Cooperative Agreement will be centered on questions of the evolution of Life on the early Earth and possibly on Mars. It is still hotly debated whether the essential organic molecules were delivered to the early Earth from space (by comets, meteorites or interplanetary dust particles) or were generated in situ on Earth. Prior work that has shown that the matrix of igneous minerals is a medium in which progenitors of organic molecules assemble from H2O, C02 and N2 incorporated as minority "impurities" in minerals of igneous rocks during crystallization from H2O/CO2/N2-laden magmas. The underlying processes involve a redox. conversion whereby C, H, and N become chemically reduced, while 0 becomes oxidized to the peroxy state. During Year 02 the work will be divided into three tasks. Task 1: After carboxylic (fatty) acids and N-bearing compounds have been identified, other extractable organic molecules including lipids, oily substances and amino acids will be studied. Dedicated lipid analysis will be combined with gas chromatographic-mass spectroscopic (GCMS) analysis of organic compounds extracted from minerals and rocks. Task 2: Using infrared (IR) spectroscopy, C-H entities that are indicators for the organic progenitors in mineral matrices will be studied. A preliminary heating experiment with MgO single crystals has shown that the C-H entities can be pyrolyzed, causing the IR bands to disappear, but at room temperature the IR bands reappear in a matter of days to weeks. This work will be expanded, both by studying synthetic MgO crystals and olivine crystals from the Earth's upper mantle. The C-H bands will be compared to the published "organic" IR feature of dust in the interstellar medium (ISM) and interplanetary dust particles (IDP). Task 3: A paradox marks the evolution of early Life: Oxygen is highly toxic to primitive life, yet early organisms "learned" to detoxify reactive oxygen species, to utilize oxygen, and even produce it. Why would organisms on the early anaerobic Earth be under evolutionary pressure to evolve defenses against reactive oxygen species? Minerals in igneous rocks are now known to contain peroxy. When such minerals weather, the peroxy hydrolyzes to H2O2. The hypothesis will be tested whether organisms living in intimate contact with rock surfaces are subjected to a constant trickle of H202 and thus under stress to develop strategies to either detoxify the reactive oxygen species or repair the molecular damage that they cause. Understanding these processes is central to the Astrobiology mission. It opens new avenues toward understanding the evolution of early life on Earth, and the potential for aerobic life elsewhere. This Cooperative Agreement also has a strong educational and public outreach component involving high school, undergraduate students, and high school teachers.

Freund, Friedemann↗
DOE OSTI2022

Geochemical Modeling of Celestite (SrSO 4 ) Precipitation and Reactive Transport in Shales

Celestite (SrSO 4 ) precipitation is a prevalent example of secondary sulfate mineral scaling issues in hydraulic fracturing systems, particularly in basins where large concentrations of naturally occurring strontium are present. Herein, we present a validated and flexible geochemical model capable of predicting celestite formation under such unconventional environments. Simulations were built using CrunchFlow and guided by experimental data derived from batch reactors. These data allowed the constraint of key kinetic and thermodynamic parameters for celestite precipitation under relevant synthetic hydraulic fracturing fluid conditions. Effects of ionic strength, saturation index, and the presence of additives were considered in the combined experimental and modeling construction. This geochemical model was then expanded into a more complex system where interactions between hydraulic fracturing fluids and shale rocks were allowed to occur subject to diffusive transport. We find that the carbonate content of a given shale and the presence of persulfate breaker in the system strongly impact the location and extent of celestite formation. The results of this study provide a novel multicomponent reactive transport model that may be used to guide future experimental design in the pursuit of celestite and other sulfate mineral scale mitigation under extreme conditions typical of hydraulic fracturing in shale formations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Seismic Imaging of the Mw 7.1 Ridgecrest Earthquake Rupture Zone From Data Recorded by Dense Linear Arrays

Abstract We analyze seismograms recorded by four arrays (B1–B4) with 100 m station spacing and apertures of 4–8 km that cross the surface rupture of the 2019 Mw 7.1 Ridgecrest earthquake. The arrays extend from B1 in the northwest to B4 in the southeast of the surface rupture. Delay times between P wave arrivals associated with ∼1,200 local earthquakes and four teleseismic events are used to estimate local velocity variations beneath the arrays. Both teleseismic and local P waves travel faster on the northeast than the southwest side of the fault beneath arrays B1 and B4, but the velocity contrast is less reliably resolved at arrays B2 and B3. We identify several 1–2 km wide low‐velocity zones with much slower inner cores that amplify S waveforms, inferred as damage zones, beneath each array. The damage zones at arrays B2 and B4 also generate fault‐zone head and trapped waves. An automated detector, based on peak ground velocities and durations of high‐amplitude waves, identifies candidate fault‐zone trapped waves (FZTWs) in a localized zone for ∼600 earthquakes at array B4. Synthetic waveform modeling of averaged FZTWs, generated by ∼30 events with high‐quality signals, indicates that the trapping structure at array B4 has a width of ∼300 m, depth of 3–5 km, S wave velocity reduction of ∼20% with respect to the surrounding rock, Q ‐value of ∼30, and S wave velocity contrast of ∼4% across the fault (faster on the northeast side). The results show complex fault‐zone internal structures (velocity contrasts and low‐velocity zones) that vary along fault strike.

Qiu, Hongrui↗
DOE OSTI2020

The transformation of diamond to graphite: Experiments reveal the presence of an intermediate linear carbon phase

Natural diamonds that have been partially replaced by graphite have been observed to occur in natural rocks. While the graphite-to-diamond phase transition has been extensively studied the opposite of this (diamond to graphite) remains poorly understood. We performed high-pressure and temperature hydrous and anhydrous experiments up to 1.0 GPa and 1300 °C using Amplex premium virgin synthetic diamonds (20–40 μm size) as the starting material mixed with Mg(OH) 2 as a source of H 2 O for the hydrous experiments. The experiments revealed that the diamond-to-graphite transformation at P = 1.0 GPa and T = 1300 °C was triggered by the presence of H 2 O and was accomplished through a three-stage process. Stage 1: diamond reacts with a supercritical H 2 O producing an intermediate 200–500 nm size “globular carbon” phase. This phase is a linear carbon chain; i.e. a polyyne or carbyne. Stage 2: the linear carbon chains are unstable and highly reactive, and they decompose by zigzagging and cross-linking to form sp 2 -hybridized structures. Stage 3: normal, disordered, and onion-like graphite is produced by the decomposition of the sp-hybridized carbon chains which are re-organized into sp 2 bonds. Our experiments show that there is no direct transformation from sp 3 C-bonds into sp 2 C-bonds. Our hydrous high-pressure and high-temperature experiments show that the diamond-to-graphite transformation requires an intermediate metastable phase of a linear hydrocarbon. This process also provides a simple mechanism for the substitution of other elements into the graphite structure (e.g. H, S, O).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Deep Learning At Depth: Estimating subsurface parameters from geophysical monitoring data

Geophysical imaging techniques are a non-invasive way to image the subsurface and understand both subsurface solid (rock/soil) and fluid property distributions and their evolution in time. Inversions of the geophysical data, such as Electrical Resistance Tomography (ERT) data, are solved to estimate the subsurface property distributions, such as conductivity, and many inversion techniques smooth out sharp gradients in rock or fluid property distributions. Sharp gradients in subsurface properties tend to be present in situations with complex subsurface structures, which are common in many subsurface applications. We have successfully demonstrated that it is possible to inform, or constrain, inversions with neural networks trained on synthetic data with complex subsurface structures. Initial results suggest this process may be optimizable to yield property distributions that better represent the true property distributions than the same inversion process without the neural network constraint. Future work would optimize the neural network performance for this application and then apply the synthetic-data trained neural network to real data to understand the utility and performance of this technique for real data sets.

47 OTHER INSTRUMENTATION↗
NASA NTRS1982

Combined use of remote sensing and seismic observations to infer geologically recent crustal deformation, active faulting, and stress fields

Characteristic traits for earthquakes associated with strike-slip motion in Central California and the Salton Sea area, as revealed in ground based studies and LANDSAT imagery, were compared. The mapped lineaments are found to be oriented in several dominant directions. One direction is the same as the trend of the San Andreas fault. The other directions differ from area to area and may reflect the stresses of earlier geologic processes. The pattern of lineament orientations is significantly LANDSAT MSS data, SEASAT synthetic aperture radar data, and magnetic field data from the South Mountain area west of Gettysburg, Pennsylvania were registered to match each other in spatial position and merged. Pattern recognition techniques were applied to the composite data set to determine its utility in recognizing different rock types and structures in vegetated terrain around South Mountain. With the use of a texture algorithm to enhance geologic features, a classification of the entire area was made. A test of the correlation between SAR tone and texture, LANDSAT tone and texture, and magnetic field data revealed no tone or texture measures linking any two of the original data sets.

Alexander, S. S.↗
NASA NTRS1992

Multi-spectral analysis of ice sheets using co-registered SAR and TM imagery

Landsat Thematic Mapper and airborne Synthetic Aperture Radar (SAR) imagery acquired over an area of south-western Greenland are coregistered and analyzed. Significant corrections to the SAR data were required to account for range-darkening, non-square pixel dimensions, speckle, and relief distortion. In one area, exposed rock was available for use as co-registration control, while in another area it was absent and supraglacial lakes and streams were used. The coregistered scenes highlight many differences between the optical and radar signatures of ice sheets.

Vornberger, P. L.↗
NASA NTRS2010

Discovery of Carbonate-Rich Outcrops in the Gusev Crater Columbia Hills by the MER Rover Spirit

The chemical composition, global abundance, distribution, and formation pathways of carbonates are central to understanding aqueous processes, climate, and habitability of early Mars. The Mars Exploration Rover (MER) Spirit analyzed a series of olivine-rich outcrops while descending from the summit region of Husband Hill into the Inner Basin of the Columbia Hills of Gusev Crater to the eastern edge of the El Dorado ripple field in late 2005. Reanalysis of Spirit s mineralogical data from the Moessbauer Spectrometer (MB) and the Miniature Thermal Emission Spectrometer (Mini-TES) and chemical data from the Alpha Particle X-Ray Spectrometer (APXS) in 2010, coupled with new laboratory data for carbonate-bearing samples, lead to identification of carbonate in one of the outcrops (Comanche) [Morris, R.V., et al., Science, 329, 421-424]. The carbonate is rich in magnesium and iron (Mc62Sd25Cc11Rh2, assuming all Ca and Mn is associated with the carbonate) and is a major component of the Comanche outcrops (16 to 34 wt.%). The mineralogical, chemical, and abundance data are constrained in multiple, mutually consistent ways by the MER analyses. For example, a low-Ca carbonate is required by the MB and APXS data and is consistent with Mini-TES data. Three spectral features attributable to fundamental infrared vibrational modes of low-Ca carbonate are present in the Mini-TES spectra of Comanche outcrops. The average composition of Comanche carbonate approximates the average composition of the carbonate globules in Martian meteorite ALH 84001. Analogy with ALH 84001, terrestrial, and synthetic carbonate globules suggests that Comanche carbonate precipitated from aqueous solutions under hydrothermal conditions at near neutral pH in association with volcanic activity during the Noachian era. Comanche outcrop morphology suggests they are remnants of a larger carbonate-bearing formation that evolved in ultramafic rock and then preferentially eroded by a combination of aeolian abrasion and chemical decomposition by exposure to acid-sulfate vapors/solutions. The high carbonate concentration in the Comanche outcrops supports climate models involving a CO2 greenhouse gas on a wet and warm early Mars and subsequent sequestering of at least part of that atmosphere in carbonate minerals.

Morris, Richard V.↗
DOE OSTI2022

RAPID UNSEPARATED RARE EARTH ELEMENT ANALYSES BY ISOTOPE DILUTION MULTICOLLECTOR INDUCTIVELY COUPLED MASS SPECTROMETRY (ID-MC-ICP-MS)

We present a method for analyzing rare earth elements (REEs) by isotope dilution without separation of individual elements. Utilizing a Nu Plasma 2 multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) equipped with an Aridus II desolvation nebulizer, sample introduction tuning parameters (torch position, gas flows) were investigated and used to minimize oxide formation (e.g., NdO/Nd <0.05%) and remove the need to analyze the REEs as separated “cuts.” Ratios for spike/sample isotopes in mixed synthetic standards containing varying amounts of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb were measured accurately within 1% of IUPAC values. La and Lu in the standards were more than 2% off from expected values due to more demanding interference corrections. A USGS BCR-2 rock standard was also processed with flux fusion, iron coprecipitation and a single column pass bulk separation followed by analysis. The concentrations for Ce, Nd, Sm, Eu, Dy, Er, and Yb fell within 2% of consensus values. A United States Geological Survey (USGS) BIR-1A rock standard was also processed in triplicate by hydrofluoric and nitric acid digestion, yielding rare earth concentrations within 3% of consensus values with 0.3% relative standard deviation (n=3). This demonstrates the ability to produce high quality REE patterns of comparable quality to traditional methods involving labor and time intensive REE separation, with sample preparation and analytical times that are comparable to analyses against isotope dilution by single-collector ICP-MS.

Shen, Steve D.↗
DOE OSTI2023

Compaction of crushed salt for safe containment – a summary of the KOMPASS projects

Abstract. For the underground disposal of high-level nuclear waste in rock salt formations, the safety concept includes the backfilling of open cavities with crushed salt. For the prognosis of the sealing function of the backfill for the safe containment of the radioactive waste, it is crucial to have a comprehensive process understanding of the crushed-salt compaction behavior. The crushed-salt compaction process is influenced by internal properties (e.g., grain size, mineralogy, and moisture content) and boundary conditions (e.g., temperature, stress state, and compaction rate) and, therefore, involves several coupled thermal–hydro–mechanical (THM) processes (Hansen et al., 2014; Kröhn et al., 2017). With the paradigm shift from the limited release of radionuclides to safe containment due to the German Repository Site Selection Act passed in 2017, the importance of crushed salt as geotechnical barrier has increased, with a focus on the evolution of its hydraulic properties. Based on the knowledge gaps in the current process understanding, the “Compaction of crushed salt for safe containment” (KOMPASS) projects were initiated to improve the scientific basis behind using crushed salt for the long-term isolation of high-level nuclear waste within rock salt repositories. The efforts to improve the prediction of crushed-salt compaction begun during the first phase of the KOMPASS projects (Czaikowski et al., 2020) and were followed up in a second phase ending in June 2023. The primary achievements of the projects are as follows (Czaikowski et al., 2020; Friedenberg et al., 2022): specification of the KOMPASS reference material, an easily available and reproducible synthetic crushed-salt material, for generic investigations; development of pre-compaction methods and successful production of samples in the short term and under in situ loading conditions; formulation of an extended laboratory program addressing the isolated investigation of known relevant factors influencing the compaction behavior of crushed salt (Düsterloh et al., 2022); execution of long-term compaction tests addressing isotropic and deviatoric load changes, temperature, and compaction state; construction of a backfill body using the KOMPASS reference material in the Sondershausen mine through collaboration with the SAVER (Entwicklung eines salzgrusbasierten Versatzkonzepts unter der Option Rückholbarkeit) project (Schaarschmidt and Friedenberg, 2022); advancement of the tools for microstructure investigation methods (Svensson and Laurich, 2022); generation (first stages) of a microphysical process list combining literature research with our own findings; benchmarking of long-term compaction test for model development and optimization of various existing models as well as the development of new models; application of a virtual demonstrator (2D model representing a backfilled drift in rock salt) for the visualization of developments and the quantification of the models (Rabbel, 2022). In summary, the KOMPASS projects contributed to the reduction of uncertainties and the strengthening of the safety case for using crushed salt within rock salt repositories.

Friedenberg, Larissa↗
NASA NTRS2006

Radar Probing of Planetary Regoliths: An Example from the Northern Rim of Imbrium Basin

Imaging radar measurements at long wavelengths (e.g., >30 cm) allow deep (up to tens of meters) probing of the physical structure and dielectric properties of planetary regoliths. We illustrate a potential application for a Mars orbital synthetic aperture radar (SAR) using new Earth-based 70-cm wavelength radar data for the Moon. The terrae on the northern margin of Mare Imbrium, the Montes Jura region, have diffuse radar backscatter echoes that are 2-4 times weaker at 3.8-cm, 70-cm, and 7.5-m wavelengths than most other lunar nearside terrae. Possible geologic explanations are (1) a pyroclastic deposit associated with sinuous rilles in this region, (2) buried mare basalt or a zone of mixed highland/basaltic debris (cryptomaria), or (3) layers of ejecta associated with the Iridum and Plato impacts that have fewer meter-sized rocks than typical highlands regolith. While radar data at 3.8-cm to 7.5-m wavelengths suggest significant differences between the Montes Jura region and typical highlands, the surface geochemistry and rock abundance inferred from Clementine UV-VIS data and eclipse thermal images are consistent with other lunar terrae. There is no evidence for enhanced iron abundance, expected for basaltic pyroclastic deposits, near the source vents of the sinuous rilles radial to Plato. The regions of low 70-cm radar return are consistent with overlapping concentric ''haloes'' about Iridum and Plato and do not occur referentially in topographically low areas, as is observed for radar-mapped cryptomaria. Thus we suggest that the extensive radar-dark area associated with the Montes Jura region is due to overlapping, rock-poor ejecta deposits from Iridum and Plato craters. Comparison of the radial extent of low-radar-return crater haloes with a model for ejecta thickness shows that these rock-poor layers are detected by 70-cm radar where they are on the order of 10 m and thicker. A SAR in orbit about Mars could use similar deep probing to reveal the nature of crater - and basin-related deposits.

Iridum crater↗