Compositional mapping with the NEAR X ray/gamma ray spectrometer
TL;DR: The X ray/gamma ray spectrometer (XGRS) instrument on board the NEAR spacecraft will map asteroid 433 Eros in the 07 keV to 10 MeV energy region as discussed by the authors.
Abstract: The X ray/gamma ray spectrometer (XGRS) instrument on board the Near Earth Asteroid Rendezvous (NEAR) spacecraft will map asteroid 433 Eros in the 07 keV to 10 MeV energy region Measurements of the discrete line X ray and gamma ray emissions in this energy domain can be used to obtain both qualitative and quantitative elemental compositions with sufficient accuracy to enable comparison to the major meteorite typies It is believed that Eros is an S-type asteroid, the most common of the near-Earth asteroids The determination of whether Eros consists of either differentiated or undifferentiated materials is an important objective of this mission Observations of Eros during the NEAR mission will contribute significantly to our understanding of the structure and composition of this asteroid The NEAR spacecraft was successfully launched on February 17, 1996 The NEAR XGRS was turned on during the week of April 7, 1996, and all detector systems operated nominally Background spectra have been obtained
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Carnegie Institution for Science1, Johns Hopkins University2, Goddard Space Flight Center3, University of Colorado Boulder4, University of Arizona5, Southwest Research Institute6, University of Michigan7, University of Maryland, College Park8, Brown University9, University of California, Santa Barbara10, Washington University in St. Louis11, Northwestern University12, Massachusetts Institute of Technology13
TL;DR: The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to fly by and orbit Mercury to address several critical questions regarding the formation and evolution of the terrestrial planets as mentioned in this paper.
391 citations
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...The -ray spectrometer detects discrete-line -ray emissions and will be used to measure galactic-cosmic-ray excited elements O, Si, S, Fe, and H and naturally radioactive elements K, Th, and U to a depth of about 10 cm (Trombka et al., 1997)....
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TL;DR: Eros is a very elongated asteroid, most of the surface of which is saturated with craters smaller than 1 kilometer in diameter, and is more bland in terms of color variations than Gaspra or Ida.
Abstract: Eros is a very elongated (34 kilometers by 11 kilometers by 11 kilometers) asteroid, most of the surface of which is saturated with craters smaller than 1 kilometer in diameter. The largest crater is 5.5 kilometers across, but there is a 10-kilometer saddle-like depression with attributes of a large degraded crater. Surface lineations, both grooves and ridges, are prominent on Eros; some probably exploit planes of weakness produced by collisions on Eros and/or its parent body. Ejecta blocks (30 to 100 meters across) are abundant but not uniformly distributed over the surface. Albedo variations are restricted to the inner walls of certain craters and may be related to downslope movement of regolith. On scales of 200 meters to 1 kilometer, Eros is more bland in terms of color variations than Gaspra or Ida. Spectra (800 to 2500 nanometers) are consistent with an ordinary chondrite composition for which the measured mean density of 2.67 ± 0.1 grams per cubic centimeter implies internal porosities ranging from about 10 to 30 percent.
267 citations
Vikram Sarabhai Space Centre1, Marshall Space Flight Center2, Southwest Research Institute3, University of Kansas4, Johns Hopkins University Applied Physics Laboratory5, University College London6, Harvard University7, University of Bergen8, Lawrence Livermore National Laboratory9, Goddard Space Flight Center10
TL;DR: In this paper, the authors present a review of the X-ray emission from the solar system bodies, excluding the Sun, and an overview of the main source mechanisms of Xray production at each object.
150 citations
Cites background from "Compositional mapping with the NEAR..."
...The overall conclusion is that Eros is broadly ‘‘primitive’’ in its chemical composition and has not experienced global differentiation into a core, mantle and crust, and that the observed departures from chondritic S/Si and Fe/Si are caused by surface effects....
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...The XRS for the XGRS functioned in 1–10 keV energy range in order to determine the elemental composition of the Eros’ surface....
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...It is interesting to note that for both Eros and Itokawa the Please cite this article as: Bhardwaj, A., et al., X-rays from solar system obj compositions derived by remote spacecraft observations in close proximity to the asteroid seem consistent with those found using Earthbased spectroscopy, which is applicable to a large number of asteroids....
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...Eros has a heavily cratered surface with one side dominated by a huge, scallop-rimmed gouge, and the opposite side by a conspicuous raised sharp-rimmed crater....
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...These early results suggest that, like Eros, asteroid Itokawa’s composition can be described as an ordinary chondrite, although occurrence of some differentiation cannot be ruled out....
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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
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.
133 citations
TL;DR: In this paper, the major element ratios determined for the S-class asteroid 433 Eros using remote-sensing x-ray fluorescence spectroscopy with the near-Earth asteroid rendezvous Shoemaker X-ray spectrometer (XRS).
Abstract: We report major element ratios determined for the S-class asteroid 433 Eros using remote- sensing x-ray fluorescence spectroscopy with the near-Earth asteroid rendezvous Shoemaker x-ray spectrometer (XRS). Data analysis techniques and systematic errors are described in detail. Data acquired during five solar flares and during two extended "quiet Sun" periods are presented; these results sample a representative portion of the asteroid's surface. Although systematic uncertainties are potentially large, the most internally consistent and plausible interpretation of the data is that Eros has primitive Mg/Si, Al/Si, Ca/Si and Fe/Si ratios, closely similar to H or R chondrites. Global differentiation of the asteroid is ruled out. The S/Si ratio is much lower than that of chondrites, probably reflecting impact-induced volatilization and/or photo- or ion-induced sputtering of sulfur at the surface of the asteroid. An alternative explanation for the low S/Si ratio is that it reflects a limited degree of melting with loss of an FeS-rich partial melt. Size-sorting processes could lead to segregation of Fe-Ni metal from silicates within the regolith of Eros; this could indicate that the Fe/Si ratios determined by the x-ray spectrometer are not representative of the bulk Eros composition.
122 citations
References
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02 Nov 1991
TL;DR: The ITS system as discussed by the authors is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-independent coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence.
Abstract: The ITS system is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-independent coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. Version 3.0 is a major upgrade of the system with important improvements in the physical model, variance reduction, I/O, and user friendliness. Improvements to the cross-section generator include the replacement of Born-approximation bremsstrahlung cross section with the results of numerical phase-shift calculations, the addition of coherent scattering and binding effects in incoherent scattering, an upgrade of collisional and radiative stopping powers, and a complete rewrite to Fortran 77 standards emphasizing Block-IF structure. Improvements in the Monte Carlo codes are also described. >
392 citations
TL;DR: A broad understanding of meteorite and asteroidal studies is needed for the most dynamic progress of both disciplines, in their common goal of understanding the origin and early evolution of the solar system.
Abstract: A broad understanding of meteorite and asteroidal studies is needed for the most dynamic progress of both disciplines, in their common goal of understanding the origin and early evolution of the solar system. Asteroid compositional investigations are currently shifting from the survey mode to focused investigations of selected targets, in pursuit of specific problems. Attention is presently given the compositional nature and diversity of asteroid taxonomic classes, as addressed by the Small Main-Belt Asteroid Spectroscopic Survey.
238 citations
01 Jan 1989
TL;DR: In this article, the spectral interpretive procedures used in the investigations of asteroid mineralogy are described, together with some still unresolved issues such as the source of ordinary chondrites.
Abstract: Information available from reflectance spectroscopy on the surface mineralogy of asteroids is discussed. Current spectral interpretive procedures used in the investigations of asteroid mineralogy are described. Present understanding of the nature and history of asteroids is discussed together with some still unresolved issues such as the source of ordinary chondrites.
162 citations
TL;DR: In this article, the orbital evolution of asteroidal fragments with diameters ranging from 10 cm to 20 km, injected into the 3:1 Kirkwood gap at 2.50 A.U., has been investigated using Monte Carlo techniques.
Abstract: The orbital evolution of asteroidal fragments with diameters ranging from 10 cm to 20 km, injected into the 3:1 Kirkwood gap at 2.50 A.U., has been investigated using Monte Carlo techniques. It is assumed that this material can become Earth-crossing on a time scale of 106 years, as a result of a chaotic zone discovered by Wisdom, associated with the 3:1 resonance. This phenomenon, as well as close encounter planetary perturbations, the v6 secular resonance, and the ablative effects of the Earth's atmosphere are included in the determination of the orbital characteristics of meteorites impacting the Earth derived by fragmentation of this asteroidal material. It is found that the predicted meteorite orbits closely match those found for observed ordinary chondrites, and the total flux is in approximate agreement with the observed fall rate of ordinary chondrites. About 10% of the predicted impacting bodies are meteorite-size bodies originating directly from the asteroid belt. The remainder are obtained by subsequent fragmentation of larger (∼1 m to 20 km diameter) Earth-crossing asteroidal fragments. The largest of these fragments are observable as Apollo-Amor objects. Thus the apparent paradox between the orbital characteristics of observed ordinary chondrites and those predicted from Apollo object sources is reconciled. Both appear to be complementary aspects of the same phenomena. No other asteroidal resonance is found to be satisfactory as a source of ordinary chondrites. These meteorites are therefore most likely to be derived from S asteroids in this limited region of the asteroidal belt, the largest of which are 11 Parthenope, 17 Thetis, and 29 Amphitrite.
138 citations
01 Jan 1988
TL;DR: The hypothesis that most meteorites are asteroid fragments generated by comparatively recent collisions in the asteroid belt runs up against spectrophotometric data indicating that asteroids with the composition of the most abundant meteorite class are either rare or absent in the asteroids as discussed by the authors.
Abstract: The hypothesis that most meteorites are asteroid fragments generated by comparatively recent collisions in the asteroid belt runs up against spectrophotometric data indicating that asteroids with the composition of the most abundant meteorite class are either rare or absent in the asteroid belt An understanding of the origin and evolution of the asteroid belt is essential to an adequate interpretation of meteoritic data; conversely, the detailed early asteroidal history preserved in the meteorites provides evidence otherwise unavailable for the earliest history of any other planetary bodies
117 citations