Engineering topics

Nittler, Larry R.

Publications and source records attributed to Nittler, Larry R..

18 records

DOE OSTI2020

Origin of Large Meteoritic SiC Stardust Grains in Metal-rich AGB Stars

Stardust grains that originated in ancient stars and supernovae are recovered from meteorites and carry the detailed composition of their astronomical sites of origin. We present evidence that the majority of large (μm-sized) meteoritic silicon carbide (SiC) grains formed in C-rich asymptotic giant branch (AGB) stars that were more metal-rich than the Sun. In the framework of the slow neutron captures (the s process) that occur in AGB stars, the lower-than-solar $^{88}$Sr/$^{86}$Sr isotopic ratios measured in the large SiC grains can only be accompanied by Ce/Y elemental ratios that are also lower than solar and predominately observed in metal-rich barium stars—the binary companions of AGB stars. Such an origin suggests that these large grains represent the material from high-metallicity AGB stars needed to explain the s-process nucleosynthesis variations observed in bulk meteorites. In the outflows of metal-rich, C-rich AGB stars, SiC grains are predicted to be small (≃0.2 μm); large (≃μm-sized) SiC grains can grow if the number of dust seeds is 2–3 orders of magnitude lower than the standard value of 10 -13 times the number of H atoms. We therefore predict that with increasing metallicity, the number of dust seeds might decrease, resulting in the production of larger SiC grains.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2018

Evidence Connecting Mercury's Magnesium Exosphere to Its Magnesium-Rich Surface Terrane

Mercury is surrounded by a tenuous, collisionless exosphere where the surface of the planet is directly exposed to the space environment. As a consequence, impacts and space weathering processes are expected to eject atoms and molecules from the surface into the exosphere, implying a direct link between the exospheric composition and the planet's regolith material. However, observational evidence demonstrating this link has been elusive. Here we report that exospheric magnesium, a species recently discovered and systematically measured by the Mercury Surface, Space ENvironment, GEochemistry, and Ranging mission, is enhanced when observed over a portion of the planet's surface regolith rich in magnesium. These observations confirm a direct link between Mercury's magnesium exosphere and the underlying crustal surface composition, providing strong evidence supporting theoretical arguments that impact vaporization can directly supply material to the exosphere from the regolith of a rocky, airless body.

Mercury↗

NASA NTRS2016

Stellar Origins of C-13 and N-15-Enriched Presolar SiC Grains

Extreme excesses of 13 C ( C (12 C/ 13 C<10) and 15 N ( N (14 N/ 15 N< 20) in rare presolar SiC 20) in rare presolar SiClar SiC grains have been considered diagnostic of an origin in classical novae [1], though an origin in core-collapse supernovae (CCSNe) has also been proposed [2]. We report multi-element isotopic data for 19 13 C- and 15 N-enriched presolar SiC grains(12 C/13 C<16 and 14 N/ 15 N<~150) from an acid resistant residue of the Murchison meteorite. These grains are enriched in 13 C and15 N, but with quite diverse Si isotopic signatures. Four grains with isotopic signatures. Four grains with isotopic signatures. Four grains with isotopic signatures. Four grains with isotopic signatures.

Liu, Nan↗

NASA NTRS2016

Mineralogy of the Mercurian Surface

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft orbited Mercury for four years until April 2015, revealing its structure, chemical makeup, and compositional diversity. Data from the mission have confirmed that Mercury is a compositional end-member among the terrestrial planets. The X-Ray Spectrometer (XRS) and Gamma-Ray Spectrometer (GRS) on board MESSENGER provided the first detailed geochemical analyses of Mercury's surface. These instruments have been used in conjunction with the Neutron Spectrometer and the Mercury Dual Imaging System to classify numerous geological and geochemical features on the surface of Mercury that were previously unknown. Furthermore, the data have revealed several surprising characteristics about Mercury's surface, including elevated S abundances (up to 4 wt%) and low Fe abundances (less than 2.5 wt%). The S and Fe abundances were used to quantify Mercury's highly reduced state, i.e., between 2.6 and 7.3 log10 units below the Iron-Wustite (IW) buffer. This fO2 is lower than any of the other terrestrial planets in the inner Solar System and has important consequences for the thermal and magmatic evolution of Mercury, its surface mineralogy and geochemistry, and the petrogenesis of the planet's magmas. Although MESSENGER has revealed substantial geochemical diversity across the surface of Mercury, until now, there have been only limited efforts to understand the mineralogical and petrological diversity of the planet. Here we present a systematic and comprehensive study of the potential mineralogical and petrological diversity of Mercury.

Vander Kaaden, Kathleen E.↗

NASA NTRS2014

Mercury's Weather-Beaten Surface: Understanding Mercury in the Context of Lunar and Asteroidal Space Weathering Studies

Mercury's regolith, derived from the crustal bedrock, has been altered by a set of space weathering processes. Before we can interpret crustal composition, it is necessary to understand the nature of these surface alterations. The processes that space weather the surface are the same as those that form Mercury's exosphere (micrometeoroid flux and solar wind interactions) and are moderated by the local space environment and the presence of a global magnetic field. To comprehend how space weathering acts on Mercury's regolith, an understanding is needed of how contributing processes act as an interactive system. As no direct information (e.g., from returned samples) is available about how the system of space weathering affects Mercury's regolith, we use as a basis for comparison the current understanding of these same processes on lunar and asteroidal regoliths as well as laboratory simulations. These comparisons suggest that Mercury's regolith is overturned more frequently (though the characteristic surface time for a grain is unknown even relative to the lunar case), more than an order of magnitude more melt and vapor per unit time and unit area is produced by impact processes than on the Moon (creating a higher glass content via grain coatings and agglutinates), the degree of surface irradiation is comparable to or greater than that on the Moon, and photon irradiation is up to an order of magnitude greater (creating amorphous grain rims, chemically reducing the upper layers of grains to produce nanometer scale particles of metallic iron, and depleting surface grains in volatile elements and alkali metals). The processes that chemically reduce the surface and produce nanometer-scale particles on Mercury are suggested to be more effective than similar processes on the Moon. Estimated abundances of nanometer-scale particles can account for Mercury's dark surface relative to that of the Moon without requiring macroscopic grains of opaque minerals. The presence of nanometer-scale particles may also account for Mercury's relatively featureless visible-near-infrared reflectance spectra. Characteristics of material returned from asteroid 25143 Itokawa demonstrate that this nanometer-scale material need not be pure iron, raising the possibility that the nanometer-scale material on Mercury may have a composition different from iron metal [such as (Fe,Mg)S]. The expected depletion of volatiles and particularly alkali metals from solar-wind interaction processes are inconsistent with the detection of sodium, potassium, and sulfur within the regolith. One plausible explanation invokes a larger fine fraction (grain size less than 45 micron) and more radiation-damaged grains than in the lunar surface material to create a regolith that is a more efficient reservoir for these volatiles. By this view the volatile elements detected are present not only within the grain structures, but also as adsorbates within the regolith and deposits on the surfaces of the regolith grains. The comparisons with findings from the Moon and asteroids provide a basis for predicting how compositional modifications induced by space weathering have affected Mercury's surface composition.

Weathering↗

NASA NTRS2013

MESSENGER at Mercury: Early Orbital Operations

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched in August 2004 under NASA's Discovery Program, was inserted into orbit about the planet Mercury in March 2011. MESSENGER's three flybys of Mercury in 2008-2009 marked the first spacecraft visits to the innermost planet since the Mariner 10 flybys in 1974-1975. The unprecedented orbital operations are yielding new insights into the nature and evolution of Mercury. The scientific questions that frame the MESSENGER mission led to the mission measurement objectives to be achieved by the seven payload instruments and the radio science experiment. Interweaving the full set of required orbital observations in a manner that maximizes the opportunity to satisfy all mission objectives and yet meet stringent spacecraft pointing and thermal constraints was a complex optimization problem that was solved with a software tool that simulates science observations and tracks progress toward meeting each objective. The final orbital observation plan, the outcome of that optimization process, meets all mission objectives. MESSENGER's Mercury Dual Imaging System is acquiring a global monochromatic image mosaic at better than 90% coverage and at least 250 m average resolution, a global color image mosaic at better than 90% coverage and at least 1 km average resolution, and global stereo imaging at better than 80% coverage and at least 250 m average resolution. Higher-resolution images are also being acquired of targeted areas. The elemental remote sensing instruments, including the Gamma-Ray and Neutron Spectrometer and the X-Ray Spectrometer, are being operated nearly continuously and will establish the average surface abundances of most major elements. The Visible and Infrared Spectrograph channel of MESSENGER's Mercury Atmospheric and Surface Composition Spectrometer is acquiring a global map of spectral reflectance from 300 to 1450 nm wavelength at a range of incidence and emission angles. Targeted areas have been selected for spectral coverage into the ultraviolet with the Ultraviolet and Visible Spectrometer (UVVS). MESSENGER's Mercury Laser Altimeter is acquiring topographic profiles when the slant range to Mercury's surface is less than 1800 km, encompassing latitudes from 20 deg. S to the north pole. Topography over the remainder of the southern hemisphere will be derived from stereo imaging, radio occultations, and limb profiles. MESSENGER's radio science experiment is determining Mercury's gravity field from Doppler signals acquired during frequent downlinks. MESSENGER's Magnetometer is measuring the vector magnetic field both within Mercury's magnetosphere and in Mercury's solar wind environment at an instrument sampling rate of up to 20 samples/s. The UVVS is determining the three-dimensional, time-dependent distribution of Mercury's exospheric neutral and ionic species via their emission lines. During each spacecraft orbit, the Energetic Particle Spectrometer measures energetic electrons and ions, and the Fast Imaging Plasma Spectrometer measures the energies and mass per charge of thermal plasma components, both within Mercury's magnetosphere and in Mercury's solar-wind environment. The primary mission observation sequence will continue for one Earth year, until March 2012. An extended mission, currently under discussion with NASA, would add a second year of orbital observations targeting a set of focused follow-on questions that build on observations to date and take advantage of the more active Sun expected during 2012-2013. MESSENGER's total primary mission cost, projected at $446 M in real-year dollars, is comparable to that of Mariner 10 after adjustment for inflation.

mercury↗

NASA NTRS2012

MESSENGER at Mercury: Early Orbital Operations

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched in August 2004 under NASA's Discovery Program, was inserted into orbit about the planet Mercury in March 2011. MESSENGER's three flybys of Mercury in 2008-2009 marked the first spacecraft visits to the innermost planet since the Mariner 10 flybys in 1974-1975. The unprecedented orbital operations are yielding new insights into the nature and evolution of Mercury. The scientific questions that frame the MESSENGER mission led to the mission measurement objectives to be achieved by the seven payload instruments and the radio science experiment. Interweaving the full set of required orbital observations in a manner that maximizes the opportunity to satisfy all mission objectives and yet meet stringent spacecraft pointing and thermal constraints was a complex optimization problem that was solved with a software tool that simulates science observations and tracks progress toward meeting each objective. The final orbital observation plan, the outcome of that optimization process, meets all mission objectives. MESSENGER's Mercury Dual Imaging System is acquiring a global monochromatic image mosaic at better than 90%coverage and at least 250 m average resolution, a global color image mosaic at better than 90%coverage and at least 1 km average resolution, and global stereo imaging at better than 80%coverage and at least 250 m average resolution. Higher-resolution images are also being acquired of targeted areas. The elemental remote sensing instruments, including the Gamma-Ray and Neutron Spectrometer and the X-Ray Spectrometer, are being operated nearly continuously and will establish the average surface abundances of most major elements. The Visible and Infrared Spectrograph channel of MESSENGER's Mercury Atmospheric and Surface Composition Spectrometer is acquiring a global map of spectral reflectance from 300 to 1450 nm wavelength at a range of incidence and emission angles. Targeted areas have been selected for spectral coverage into the ultraviolet with the Ultraviolet and Visible Spectrometer (UVVS). MESSENGER's Mercury Laser Altimeter is acquiring topographic profiles when the slant range to Mercury's surface is less than 1800 km, encompassing latitudes from 201S to the north pole. Topography over the remainder of the southern hemisphere will be derived from stereo imaging, radio occultations, and limb profiles. MESSENGER's radio science experiment is determining Mercury's gravity field from Doppler signals acquired during frequent downlinks. MESSENGER's Magnetometer is measuring the vector magnetic field both within Mercury's magnetosphere and in Mercury's solar wind environment at an instrument sampling rate of up to 20 samples/s. The UVVS is determining the three-dimensional, time-dependent distribution of Mercury's exospheric neutral and ionic species via their emission lines. During each spacecraft orbit, the Energetic Particle Spectrometer measures energetic electrons and ions, and the Fast Imaging Plasma Spectrometer measures the energies and mass per charge of thermal plasma components, both within Mercury's magnetosphere and in Mercury's solar-wind environment. The primary mission observation sequence will continue for one Earth year, until March 2012. An extended mission, currently under discussion with NASA, would add a second year of orbital observations targeting a set of focused follow-on questions that build on observations to date and take advantage of the more active Sun expected during 2012-2013. MESSENGER's total primary mission cost, projected at $446 M in real-year dollars, is comparable to that of Mariner 10 after adjustment for inflation.

Planetary Science↗

NASA NTRS2012

Chemical Heterogeneity on Mercury's Surface Revealed by the MESSENGER X-ray Spectrometer

We present the analysis of 205 spatially resolved measurements of the surfacecomposition of Mercury from MESSENGERs X-Ray Spectrometer. The surfacefootprints of these measurements are categorized according to geological terrain. Northernsmooth plains deposits and the plains interior to the Caloris basin differ compositionallyfrom older terrain on Mercury. The older terrain generally has higher MgSi, SSi, andCaSi ratios, and a lower AlSi ratio than the smooth plains. Mercurys surface mineralogyis likely dominated by high-Mg mafic minerals (e.g., enstatite), plagioclase feldspar, andlesser amounts of Ca, Mg, andor Fe sulfides (e.g., oldhamite). The compositionaldifference between the volcanic smooth plains and the older terrain reflects differentabundances of these minerals and points to the crystallization of the smooth plains from amore chemically evolved magma source. High-degree partial melts of enstatite chondritematerial provide a generally good compositional and mineralogical match for much ofthe surface of Mercury. An exception is Fe, for which the low surface abundance onMercury is still higher than that of melts from enstatite chondrites and may indicate anexogenous contribution from meteoroid impacts.

Chemical heterogeneity↗

NASA NTRS2011

The Effects of Surface Roughness on the NEAR XRS Elemental Results: Monte-Carlo Modeling

The objective of the NEAR-Shoemaker X-ray Gamma-Ray Spec1roscopy ("XGRS") investigation was to determine the elemental composition of the near-Earth asteroid 433 Eros. The X-ray Spectrometer (XRS) system measured the characteristic fluorescence of six major elements (Mg, Al, Si, S, Ca, Fe) in the 1-10 keV energy range excited by the interaction of solar X-rays with the upper 100 microns of the surface of 433 Eros. Various investigators, using both laboratory experiments and computer simulations have established that X-ray fluorescent line ratios can be influenced by small-scale surface roughness at high incidence or emission angles. The effect on the line ratio is specific to the geometry, excitation spectrum, and composition involved, In general, however, the effect is only substantial for ratios of lines with a significant energy difference between them: Fe/Si and Ca/Si are much more likely to be affected than AI/Si or Mg/Si. We apply a Monte-Carlo code to the specific geometry and spectrum of a major NEAR XRS solar flare observation, using an H chondrite composition as the substrate. The seventeen most abundant elements were included in the composition model, from oxygen to titanium.

Lin, Lucy F.↗

NASA NTRS2011

Origin and Evolution of Prebiotic Organic Matter as Inferred from the Tagish Lake Meteorite

The complex suite of organic materials in carbonaceous chondrite meteorites probably originally formed in the interstellar medium and/or the solar protoplanetary disk, but was subsequently modified in the meteorites' asteroidal parent bodies. The mechanisms of formation and modification are still very poorly understood. We carried out a systematic study of variations in the mineralogy, petrology, and soluble and insoluble organic matter in distinct fragments of the Tagish Lake meteorite. The variations correlate with indicators of parent body aqueous alteration and at least some molecules of pre-biotic importance formed during the alteration.

Herd, Christopher D.↗

NASA NTRS2010

MESSENGER Observations of Extreme Loading and Unloading of Mercury's Magnetic Tail

During MESSENGER's third flyby of Mercury, the magnetic field in the planet's magnetotail increased by factors of 2 to 3.5 over intervals of 2 to 3 min. Magnetospheric substorms at Earth are powered by similar tail loading, but the amplitude is approx.10 times less and typical durations are approx.1 hour. The extreme tail loading observed at Mercury implies that the relative intensity of sub storms must be much larger than at Earth. The correspondence between the duration of tail field enhancements and the characteristic time for the Dungey cycle, which describes plasma circulation through Mercury's magnetosphere. suggests that such circulation determines substorm timescale. A key aspect of tail unloading during terrestrial substorms is the acceleration of energetic charged particles, but no acceleration signatures were seen during the MESSENGER flyby.

Slavin, James A.↗

NASA NTRS2010

MESSENGER Observations of Extreme Loading and Unloading of Mercury's Magnetic Tail

During MESSENGER's third flyby of Mercury, a series of 2-3 minute long enhancements of the magnetic field in the planet's magnetotail were observed. Magnetospheric substorms at Earth are powered by similar tail loading, but the amplitude is approximately 10 times less and the durations are 1 hr. These observations of extreme loading imply that the relative intensity of substorms at Mercury must be much larger than at Earth. The correspondence between the duration of tail enhancements and the calculated approximately 2 min Dungey cycle, which describes plasma circulation through Mercury's magnetosphere, suggests that such circulation determines substorm timescale. A key aspect of tail unloading during terrestrial substorms is the acceleration of energetic charged particles. Such signatures are puzzlingly absent from the MESSENGER flyby measurements.

Slavin, James A.↗

NASA NTRS2010

MESSENGER Observations of Reconnection and Its Effects on Mercury's Magnetosphere

During MESSENGER's second and third flybys of Mercury on October 6, 2008 and September 29, 2009, respectively, southward interplanetary magnetic fields produced very intense reconnection signatures in the dayside and nightside magnetosphere and very different systemlevel responses. The IMF during the second flyby was continuously southward and the magnetosphere appeared very active with very large magnetic fields normal to the magnetopause and the generation of flux transfer events at the magnetopause and plasmoids in the tail current sheet every 30 s to 90 s. However, the strength and direction of the tail magnetic field was very stable. In contrast the third flyby experienced a variable IMF with it varying from north to south on timescales of minutes. Although the MESSENGER measurements were limited this time to the nightside magnetosphere, numerous examples of plasmoid release in the tail were detected, but they were not periodic. Rather, plasmoid release was highly correlated with the four large enhancements of the tail magnetic field (i.e. by factors > 2) with durations of approx. 2 - 3 min. The increased flaring of the magnetic field during these intervals indicates that the enhancements were caused by loading of the tail with magnetic flux transferred from the dayside magnetosphere. New analyses of the second and third flyby observations of reconnection and its system-level effects will be presented. The results will be examined in light of what is known about the response of the Earth's magnetosphere to variable versus steady southward IMF.

Slavin, James A.↗

NASA NTRS2009

Elemental Composition of 433 Eros: New Calibration of the NEAR-Shoemaker XRS Data

We present a new calibration of the elemental-abundance data for Asteroid 433 Fros taken by the X-ray spectrometer (XRS) aboard the NEAR-Shoemaker spacecraft. (NEAR is an acronym for "Near-Earth Asteroid Rendezvous,") Quintification of the asteroid surface elemental abundance ratios depends critically on accurate knowledge of the incident solar X-ray spectrum, which was monitored simultaneously with asteroid observations. Previously published results suffered from incompletely characterized systematic uncertainties due to an imperfect ground calibrations of the NEAR gas solar monitor. The solar monitor response function and associated uncertainties have now been characterized by cross-calibration of a large sample of NEAR solar monitor flight data against. contemporary broadband solar X-ray data from the Earth-orbiting GOES-8 (Geostationary Operational Environmental Satellite). The results have been used to analyze XRS spectra acquired from Eros during eight major solar flares (including three that have not previously been reported). The end product of this analysis is a revised set of Eros surface elemental abundance ratios with new error estimates that more accurately reflect the remaining uncertainties in the solar flare spectra: Mg/Si=.753 +0.078/-0.055, Al/Si=0.069 +/-0.055, S/Si=0.005+/-0.008, Ca/Si=0.060+0.023/-0.024, and Fe/Si= 1.578+0.338/-0.320. These revised abundance ratios are consitent within cited uncertainties with the results of Nittler et al. [Nittler, L.R., and 14 colleagues, 2001. Meteorit Planet. Sci 36, 1673-1695] and thus support the prior conclusions that 433 Eros has major-element composition simular to ordinary chondrites with the exception of a stong depletoin in sulfur, most likely caused by space weathering.

Lim, Lucy F.↗

NASA NTRS2003

Acquisition of a High Resolution Field Emission Scanning Electron Microscope for the Analysis of Returned Samples

This grant furnished funds to purchase a state-of-the-art scanning electron microscope (SEM) to support our analytical facilities for extraterrestrial samples. After evaluating several instruments, we purchased a JEOL 6500F thermal field emission SEM with the following analytical accessories: EDAX energy-dispersive x-ray analysis system with fully automated control of instrument and sample stage; EDAX LEXS wavelength-dispersive x-ray spectrometer for high sensitivity light-element analysis; EDAX/TSL electron backscatter diffraction (EBSD) system with software for phase identification and crystal orientation mapping; Robinson backscatter electron detector; and an in situ micro-manipulator (Kleindiek). The total price was $550,000 (with $150,000 of the purchase supported by Carnegie institution matching funds). The microscope was delivered in October 2002, and most of the analytical accessories were installed by January 2003. With the exception of the wavelength spectrometer (which has been undergoing design changes) everything is working well and the SEM is in routine use in our laboratory.

Nittler, Larry R.↗

NASA NTRS2003

Transmission Electron Microscopy of Non-Etched Presolar Silicon Carbide

Our solar system formed from nuclei produced in earlier generations of stars. Mixing in the proto-solar nebula isotopically homogenized most of this material, but some grains, called presolar grains, retain their original isotopic composition. The isotopic properties of presolar SiC grains indicate that most of the grains formed in the outflows of carbon-rich Asymptotic Giant Branch (AGB) stars. The microstructure of these presolar grains reflects the conditions of the dust formation and subsequent alteration. Early microstructural studies of SiC grains obtained by acid dissolution from meteorites show that most isotopically anomalous SiC grains have the face-centered cubic b- SiC structure. However, Daulton et al. have shown that a small fraction of sub-micron presolar SiC grains are of the hexagonal 2H polytype (a-SiC). Although the harsh chemical treatments of these grains does not alter their crystal structure, significant alteration of the surface morphology of the grains due to the acid treatments has been observed. In addition, the acid treatments may preferentially remove cracked or fissured grains, and possible sub-grains, such as graphite. By studying SiC grains isolated by physical separation and found in situ, we attempt to obtain a more complete analysis of presolar SiC microstructures, including the surface morphology, in order to address the formation and processing history of the grains. In our prior work, we reported on one in situ SiC grain (hereafter CBIS1). Here we present results from two additional grains, one in situ, and one prepared as a physical separate.

Stroud, Rhonda M.↗

NASA NTRS2002

Transmission Electron Microscopy of an In Situ Presolar Silicon Carbide Grain

We used a focused ion beam workstation to prepare ultra-thin sections of a presolar SiC grain. Our TEM studies indicate that the SiC formed by rapid vapor-phase condensation, trapping pre-existing graphite grains in random orientations. Additional information is contained in the original extended abstract.

Stroud, Rhonda M.↗

NASA NTRS1999

Bulk Compositional Trends in Meteorites: A Guide for Analysis and Interpretation of NEAR XGRS Data from Asteroid 433 EROS

The Near Earth Asteroid Rendezvous (NEAR) spacecraft is to orbit the S-class asteroid 433 Eros for about one year beginning on February 14, 2000. The X-ray/gamma-ray O, Mg, Al, Si, Fe, and K; possibly H, Ca, S, Ti, and Th) of Eros with a spatial resolution ranging from a few km for X-rays to approx. 25% of the asteroid's surface for gamma-rays. The major scientific goals for the NEAR XGRS are to relate the composition of Eros to known classes of meteorites, to assess compositional heterogeneity and to identify geological processes that have occurred on the asteroid. Comparing remote-sensing data from asteroids to laboratory data from meteorites requires that the latter be well determined and understood. How well particular classes of meteorites can be identified as analogues of Eros depends not only on the error of the XGRS measurement, but also on the spread in abundances observed among different members of a given meteorite class. To prepare for the return of XGRS data from Eros, we have compiled a large database of bulk elemental compositions of meteorites, using data from a wide variety of published and unpublished sources. Custom software was developed to easily extract statistical information and make plots of data from different meteorite classes. Here, we use the meteorite compositional database to investigate which abundances and abundance ratios, of those measureable by the NEAR XGRS, are most diagnostic for distinguishing meteorite classes and identifying geological processes that have occurred on the samples' parent asteroids.

Nittler, Larry R.↗