The elemental composition of asteroid 433 Eros: Results of the NEAR-Shoemaker X-ray spectrometer
Cornell University1, Max Planck Society2, University of Arizona3, Los Alamos National Laboratory4, National Museum of Natural History5, Smithsonian Astrophysical Observatory6, Computer Sciences Corporation7, University of California, San Diego8, The Catholic University of America9, Goddard Space Flight Center10, Johns Hopkins University Applied Physics Laboratory11
22 Sep 2000-Science (American Association for the Advancement of Science)-Vol. 289, Iss: 5487, pp 2101-2105
TL;DR: Major element composition ratios for regions of the asteroid 433 Eros imaged during two solar flares and quiet sun conditions during the period of May to July 2000 are reported.
Abstract: We report major element composition ratios for regions of the asteroid 433 Eros imaged during two solar flares and quiet sun conditions during the period of May to July 2000. Low aluminum abundances for all regions argue against global differentiation of Eros. Magnesium/silicon, aluminum/silicon, calcium/silicon, and iron/silicon ratios are best interpreted as a relatively primitive, chondritic composition. Marked depletions in sulfur and possible aluminum and calcium depletions, relative to ordinary chondrites, may represent signatures of limited partial melting or impact volatilization.
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TL;DR: X-ray fluorescence spectra obtained by the MESSENGENGER spacecraft orbiting Mercury indicate that the planet's surface differs in composition from those of other terrestrial planets as discussed by the authors, and this observation, together with a low surface Fe abundance, supports the view that Mercury formed from highly reduced precursor materials, perhaps akin to enstatite chondrite meteorites or anhydrous cometary dust particles.
Abstract: X-ray fluorescence spectra obtained by the MESSENGER spacecraft orbiting Mercury indicate that the planet's surface differs in composition from those of other terrestrial planets Relatively high Mg/Si and low Al/Si and Ca/Si ratios rule out a lunarlike feldspar-rich crust The sulfur abundance is at least 10 times higher than that of the silicate portion of Earth or the Moon, and this observation, together with a low surface Fe abundance, supports the view that Mercury formed from highly reduced precursor materials, perhaps akin to enstatite chondrite meteorites or anhydrous cometary dust particles Low Fe and Ti abundances do not support the proposal that opaque oxides of these elements contribute substantially to Mercury's low and variable surface reflectance
396 citations
TL;DR: Observations by transmission electron microscopy of olivine samples subjected to pulse laser irradiation find nanophase iron particles similar to those observed in the rims of space-weathered lunar regolith grains, and support the idea that ordinary chondrites came from S-type asteroids, and thereby provides some constraints on the surface exposure ages of those asteroids.
Abstract: ‘Space weathering’ is the term applied to the darkening and reddening of planetary surface materials with time, along with the changes to the depths of absorption bands in their optical spectra. It has been invoked to explain the mismatched spectra of lunar rocks and regolith, and between those of asteroids and meteorites1,2,3,4,5,6. The formation of nanophase iron particles on regolith grains as a result of micrometeorite impacts or irradiation by the solar wind has been proposed as the main cause of the change in the optical properties7,8. But laboratory simulations9,10,11,12,13,14 have not revealed the presence of these particles, although nano-second-pulse laser irradiation did reproduce the optical changes12. Here we report observations by transmission electron microscopy of olivine samples subjected to pulse laser irradiation. We find within the amorphous vapour-deposited rims of olivine grains nanophase iron particles similar to those observed in the rims of space-weathered lunar regolith grains15,16. Reduction by hydrogen atoms implanted by the solar wind is therefore not necessary to form the particles. Moreover, the results support the idea that ordinary chondrites came from S-type asteroids5, and thereby provides some constraints on the surface exposure ages of those asteroids.
364 citations
Cites methods from "The elemental composition of astero..."
...Furthermore, recent measurement by an X-ray spectrometer on board the NEAR-Shoemaker spacecraft showed that S-type asteroid 433 Eros has an elemental composition close to unfractionated ordinary chondrite...
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TL;DR: In this article, the authors present new visible and near-infrared spectroscopic measurements for 252 near-Earth and Mars-crossing (MC) objects observed from 1994 through 2002 as a complement to the Small Main Belt Asteroid Spectroscopic Survey (SMASS), combined with previously published SMASS results, have an internally consistent data set of more than 400 of these objects for investigating trends related to size, orbits, and dynamical history.
360 citations
University of Arizona1, Los Alamos National Laboratory2, Space Research Institute3, Computer Sciences Corporation4, University of New Mexico5, Cornell University6, The Catholic University of America7, Goddard Space Flight Center8, University of California, San Diego9, University of Hawaii at Manoa10, California Institute of Technology11, Max Planck Society12
TL;DR: The Mars Odyssey Gamma-Ray Spectrometer (MOGRS) is a suite of three different instruments, a gamma subsystem (GS), a neutron spectrometer, and a high-energy neutron detector, working together to collect data that will permit the mapping of elemental concentrations on the surface of Mars.
Abstract: The Mars Odyssey Gamma-Ray Spectrometer is a suite of three different instruments, a gamma subsystem (GS), a neutron spectrometer, and a high-energy neutron detector, working together to collect data that will permit the mapping of elemental concentrations on the surface of Mars. The instruments are complimentary in that the neutron instruments have greater sensitivity to low amounts of hydrogen, but their signals saturate as the hydrogen content gets high. The hydrogen signal in the GS, on the other hand, does not saturate at high hydrogen contents and is sensitive to small differences in hydrogen content even when hydrogen is very abundant. The hydrogen signal in the neutron instruments and the GS have a different dependence on depth, and thus by combining both data sets we can infer not only the amount of hydrogen, but constrain its distribution with depth. In addition to hydrogen, the GS determines the abundances of several other elements. The instruments, the basis of the technique, and the data processing requirements are described as are some expected applications of the data to scientific problems.
292 citations
Cites methods from "The elemental composition of astero..."
...Most recently, a gamma-ray spectrometer was flown to the asteroid Eros as part of the Near Earth Asteroid Rendezvous (NEAR) mission (Trombka et al., 2000)....
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University of Arizona1, University of Hawaii at Manoa2, Computer Sciences Corporation3, University of New Mexico4, The Catholic University of America5, California Institute of Technology6, Cornell University7, California Polytechnic State University8, University of California, San Diego9, Max Planck Society10, Centre national de la recherche scientifique11, Goddard Space Flight Center12
TL;DR: The Gamma Ray Spectrometer (GRS) on board the 2001 Mars Odyssey Mission for ±∼45° latitudes was used to determine the concentrations of H, Si, Cl, K, Fe, and Th.
Abstract: [1] We report maps of the concentrations of H, Si, Cl, K, Fe, and Th as determined by the Gamma Ray Spectrometer (GRS) on board the 2001 Mars Odyssey Mission for ±∼45° latitudes. The procedures by which the spectra are processed to yield quantitative concentrations are described in detail. The concentrations of elements determined over the locations of the various Mars landers generally agree well with the lander values except for Fe, although the mean of the GRS Fe data agrees well with that of Martian meteorites. The water-equivalent concentration of hydrogen by mass varies from about 1.5% to 7.5% (by mass) with the most enriched areas being near Apollinaris Patera and Arabia Terra. Cl shows a distribution similar to H over the surface except that the Cl content over Medusae Fossae is much greater than elsewhere. The map of Fe shows enrichment in the northern lowlands versus the southern highlands. Silicon shows only very modest variation over the surface with mass fractions ranging from 19% to 22% over most of the planet, though a significant depletion in Si is noted in a region west of Tharsis Montes and Olympus Mons where the Si content is as low as 18%. K and Th show a very similar pattern with depletions associated with young volcanic deposits and enrichments associated with the TES Surface Type-2 material. It is noted that there appears to be no evidence of significant globally distributed thick dust deposits of uniform composition.
283 citations
References
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TL;DR: In this article, the atomic scattering factors for all angles of coherent scattering and at the higher photon energies are obtained from these tabulated forward-scattering values by adding a simple angle-dependent form-factor correction.
5,470 citations
TL;DR: The spectrum of radiation emitted by a hot optically thin plasma with abundances and equilibrium ionization balance appropriate to interstellar conditions has been calculated in this article for wavelengths shorter than 200 A.
Abstract: The spectrum of radiation emitted by a hot optically thin plasma with abundances and equilibrium ionization balance appropriate to interstellar conditions has been calculated. The results at wavelengths shorter than 200 A are discussed for material in the electron-temperature range from 160,000 to 100 million K.
1,378 citations
TL;DR: In this article, a study has been made of some 350 chemical analyses of stone meteorites available in the literature, and criteria have been applied in an attempt to select those which are more reliable.
492 citations
TL;DR: In this paper, a detailed description of the procedure used for computing color temperature and emission measure from GOES X-ray data, including a table of constants for SMS and GOES sensors that are necessary for reducing the archived data from these satellites.
Abstract: GOES (Geostationary Operational Environmental Satellite) X-ray sensors observe the Sun continuously in two broadband soft X-ray channels. These data are collected in real time and are used operationally to detect the onset and the intensity of solar flares. For these purposes it is usually sufficient to monitor only the soft channel (1–8 A). The second, harder channel (0.5–4 A) provides additional information on the state of the coronal plasma. The dual X-ray measurement data are archived and made available to external users for basic research. The GOES X-ray sensors operate on the ion-chamber principle: measured ion-chamber electric current is proportional to the net ionization rate caused by incident X-ray flux on encapsulated noble gases. The ratio of the outputs of the two channels in electric current, therefore, is uniquely a function of the color temperature of the emitting plasma, and the magnitude of each of the currents is proportional to a quantity, known as the emission measure, that convolves the volume and the density of the emitting plasma. This paper provides a detailed description of the procedure used for computing color temperature and emission measure from GOES X-ray data, including a table of constants for SMS and GOES X-ray sensors that are necessary for reducing the archived data from these satellites. Temperature and theoretical current tables were constructed, for individual GOES sensors, from laboratory calibrations of instrument responses and from synthetic solar X-ray spectra generated by two models of solar thermal X-ray emission: Raymond-Smith and Mewe-Alkemade. Example tables are shown and others are available on request. Errors that may be incurred from the use of GOES X-ray data in the computation of flare temperatures and emission measures may be classified under four major groups: instrumentinduced errors, including errors of calibration and random measurement errors; environmentally induced errors, due primarily to the ambient energetic electron background; solar influences, including the consequences of the isothermal assumption and the single-source assumption; and uncertainties in the modelled solar synthetic spectrum. These error sources are discussed separately, and a rough estimation of the collective error is made where this is quantitatively feasible. Finally, temperatures and emission measures are computed from GOES data and are compared with those derived from SMM andHinotori soft X-ray spectrometer data and from broadband photometric data from the PROGNOZ satellite.
234 citations
Book•
01 Jan 1969
TL;DR: In this paper, the authors discuss all of the usual practical difficulties experienced in the application of x-ray fluorescence spectrometry, and illustrate the specific points by worked examples where possible.
Abstract: Worthwhile treatment which discusses all of the usual practical difficulties experienced in the application of x-ray fluorescence spectrometry. Purely theoretical data is purposely kept minimal. Specific points are illustrated by worked examples where possible. Chapter references. For those training to be x-ray spectroscopists as well as more experienced workers in the field. Contents: Physics of x-rays. Dispersion. Detection. Pulse height selection. Counting statistics. Matrix effects. Quantative analysis. Sample preparation. Trace analysis. Appendices. Index. -- AATA
189 citations
"The elemental composition of astero..." refers methods in this paper
...R. Jenkins and J. DeVries, Practical X-ray Spectrome- try (Springer-Verlag, New York, 1967)....
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...We used an analytic model, similar to that described by Jenkins and DeVries (20), to predict fluorescent and scattered x-ray spectra for any assumed elemental composition, incident solar spectrum, and observational geometry (21)....
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...We used an analytic model, similar to that described by Jenkins and DeVries (20), to predict fluorescent and scattered x-ray spectra for any assumed elemental composition, incident solar spectrum, and observational geometry (21)....
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