The X-Ray Spectrometer on the MESSENGER Spacecraft
TL;DR: The X-Ray Spectrometer (XRS) onboard the MESSENGER spacecraft has been used to measure the surface elemental composition of the terrestrial planets by observing the Kα lines for the elements Mg, Al, Si, S, Ca, Ti and Fe as discussed by the authors.
Abstract: NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission will further the understanding of the formation of the planets by examining the least studied of the terrestrial planets, Mercury. During the one-year orbital phase (beginning in 2011) and three earlier flybys (2008 and 2009), the X-Ray Spectrometer (XRS) onboard the MESSENGER spacecraft will measure the surface elemental composition. XRS will measure the characteristic X-ray emissions induced on the surface of Mercury by the incident solar flux. The Kα lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected. The 12° field-of-view of the instrument will allow a spatial resolution that ranges from 42 km at periapsis to 3200 km at apoapsis due to the spacecraft’s highly elliptical orbit. XRS will provide elemental composition measurements covering the majority of Mercury’s surface, as well as potential high-spatial-resolution measurements of features of interest. This paper summarizes XRS’s science objectives, technical design, calibration, and mission observation strategy.
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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: The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched on August 3, 2004, is nearing the halfway point on its voyage to become the first probe to orbit the planet Mercury.
Abstract: The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched on August 3, 2004, is nearing the halfway point on its voyage to become the first probe to orbit the planet Mercury. The mission, spacecraft, and payload are designed to answer six fundamental questions regarding the innermost planet: (1) What planetary formational processes led to Mercury’s high ratio of metal to silicate? (2) What is the geological history of Mercury? (3) What are the nature and origin of Mercury’s magnetic field? (4) What are the structure and state of Mercury’s core? (5) What are the radar-reflective materials at Mercury’s poles? (6) What are the important volatile species and their sources and sinks near Mercury? The mission has focused to date on commissioning the spacecraft and science payload as well as planning for flyby and orbital operations. The second Venus flyby (June 2007) will complete final rehearsals for the Mercury flyby operations in January and October 2008 and September 2009. Those flybys will provide opportunities to image the hemisphere of the planet not seen by Mariner 10, obtain high-resolution spectral observations with which to map surface mineralogy and assay the exosphere, and carry out an exploration of the magnetic field and energetic particle distribution in the near-Mercury environment. The orbital phase, beginning on March 18, 2011, is a one-year-long, near-polar-orbital observational campaign that will address all mission goals. The orbital phase will complete global imaging, yield detailed surface compositional and topographic data over the northern hemisphere, determine the geometry of Mercury’s internal magnetic field and magnetosphere, ascertain the radius and physical state of Mercury’s outer core, assess the nature of Mercury’s polar deposits, and inventory exospheric neutrals and magnetospheric charged particle species over a range of dynamic conditions. Answering the questions that have guided the MESSENGER mission will expand our understanding of the formation and evolution of the terrestrial planets as a family.
317 citations
Cites background or methods from "The X-Ray Spectrometer on the MESSE..."
...XRS is an improved version of the Near Earth Asteroid Rendezvous (NEAR) Shoemaker X-ray spectrometer to measure the atomic surface abundances of Mg, Al, Si, Ca, Ti, and Fe by solar-induced X-ray fluorescence (Schlemm et al. 2007)....
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...Detailed descriptions of each instrument can be found in companion papers in this volume (Anderson et al. 2007; Andrews et al. 2007; Cavanaugh et al. 2007; Goldsten et al. 2007; Hawkins et al. 2007; McClintock and Lankton 2007; Schlemm et al. 2007)....
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...…(Anderson et al. 2007; Andrews et al. 2007; Cavanaugh et al. 2007; Goldsten et al. 2007; Hawkins et al. 2007; McClintock and Lankton 2007; Schlemm et al. 2007), and radio science (Srinivasan et al. 2007), as well as more expansive summaries of the principal scientific issues to be…...
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...GRNS and XRS will build up observations that will yield global maps of elemental composition at resolutions that will vary with latitude, species, and (for XRS) the intensity of the solar X-ray flux (Goldsten et al. 2007; Schlemm et al. 2007)....
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TL;DR: In this paper, the authors investigated coronal hard X-ray and microwave emissions in the partially disk-occulted solar flare of 2007 December 31, using the STEREO mission to provide EUV images of the flare site at different viewing angles.
Abstract: The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph (NoRH) are used to investigate coronal hard X-ray and microwave emissions in the partially disk-occulted solar flare of 2007 December 31 The STEREO mission provides EUV images of the flare site at different viewing angles, establishing a two-ribbon flare geometry and occultation heights of the RHESSI and NoRH observations of {approx}16 Mm and {approx}25 Mm, respectively Despite the occultation, intense hard X-ray emission up to {approx}80 keV occurs during the impulsive phase from a coronal source that is also seen in microwaves The hard X-ray and microwave source during the impulsive phase is located {approx}6 Mm above thermal flare loops seen later at the soft X-ray peak time, similar in location to the above-the-loop-top source in the Masuda flare A single non-thermal electron population with a power-law distribution (with spectral index of {approx}37 from {approx}16 keV up to the MeV range) radiating in both bremsstrahlung and gyrosynchrotron emission can explain the observed hard X-ray and microwave spectrum, respectively This clearly establishes the non-thermal nature of the above-the-loop-top source The large hard X-ray intensity requires a very large number (>5 x 10{sup 35} above 16 keV for themore » derived upper limit of the ambient density of {approx}8 x 10{sup 9} cm{sup -3}) of suprathermal electrons to be present in this above-the-loop-top source This is of the same order of magnitude as the number of ambient thermal electrons We show that collisional losses of these accelerated electrons would heat all ambient electrons to superhot temperatures (tens of keV) within seconds Hence, the standard scenario, with hard X-rays produced by a beam comprising the tail of a dominant thermal core plasma, does not work Instead, all electrons in the above-the-loop-top source seem to be accelerated, suggesting that the above-the-loop-top source is itself the electron acceleration region« less
271 citations
TL;DR: The Gamma-Ray and Neutron Spectrometer (GRNS) was developed as part of the science payload for NASA's Discovery Program mission to the planet Mercury as mentioned in this paper, which was successfully launched more than six years before entering Mercury orbit to begin a one-year investigation.
Abstract: A Gamma-Ray and Neutron Spectrometer (GRNS) instrument has been developed as part of the science payload for NASA’s Discovery Program mission to the planet Mercury. Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) launched successfully in 2004 and will journey more than six years before entering Mercury orbit to begin a one-year investigation. The GRNS instrument forms part of the geochemistry investigation and will yield maps of the elemental composition of the planet surface. Major elements include H, O, Na, Mg, Si, Ca, Ti, Fe, K, and Th. The Gamma-Ray Spectrometer (GRS) portion detects gamma-ray emissions in the 0.1- to 10-MeV energy range and achieves an energy resolution of 3.5 keV full-width at half-maximum for 60Co (1332 keV). It is the first interplanetary use of a mechanically cooled Ge detector. Special construction techniques provide the necessary thermal isolation to maintain the sensor’s encapsulated detector at cryogenic temperatures (90 K) despite the intense thermal environment. Given the mission constraints, the GRS sensor is necessarily body-mounted to the spacecraft, but the outer housing is equipped with an anticoincidence shield to reduce the background from charged particles. The Neutron Spectrometer (NS) sensor consists of a sandwich of three scintillation detectors working in concert to measure the flux of ejected neutrons in three energy ranges from thermal to ∼7 MeV. The NS is particularly sensitive to H content and will help resolve the composition of Mercury’s polar deposits. This paper provides an overview of the Gamma-Ray and Neutron Spectrometer and describes its science and measurement objectives, the design and operation of the instrument, the ground calibration effort, and a look at some early in-flight data.
190 citations
Goddard Space Flight Center1, Johns Hopkins University Applied Physics Laboratory2, University of Colorado Boulder3, University of Maryland, College Park4, University of Michigan5, Academy of Athens6, Carnegie Institution for Science7, University of California, Los Angeles8, The Catholic University of America9, Academy of Sciences of the Czech Republic10
TL;DR: The magnetic field showed reconnection signatures in the form of flux transfer events, azimuthal rotations consistent with Kelvin-Helmholtz waves along the magnetopause, and extensive ultralow-frequency wave activity.
Abstract: Observations by MESSENGER show that Mercury's magnetosphere is immersed in a comet-like cloud of planetary ions. The most abundant, Na+, is broadly distributed but exhibits flux maxima in the magnetosheath, where the local plasma flow speed is high, and near the spacecraft's closest approach, where atmospheric density should peak. The magnetic field showed reconnection signatures in the form of flux transfer events, azimuthal rotations consistent with Kelvin-Helmholtz waves along the magnetopause, and extensive ultralow-frequency wave activity. Two outbound current sheet boundaries were observed, across which the magnetic field decreased in a manner suggestive of a double magnetopause. The separation of these current layers, comparable to the gyro-radius of a Na+ pickup ion entering the magnetosphere after being accelerated in the magnetosheath, may indicate a planetary ion boundary layer.
186 citations
References
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Book•
01 Jan 1979
TL;DR: In this paper, the authors present a detailed analysis of the effect of different types of detectors on the performance of the detection of neutrons and their effect on the detection efficiency and error prediction.
Abstract: Chapter 1 Radiation Sources. I. Units And Definitions. II. Fast Electron Sources. III. Heavy Charged Particle Sources. IV. Sources Of Electromagnetic Radiation. V. Neutron Sources. Chapter 2 Radiation Interactions. I. Interaction Of Heavy Charged Particles. II. Interaction Of Fast Electrons. III. Interaction Of Gamma Rays. IV. Interaction Of Neutrons. V. Radiation Exposure And Dose. Chapter 3 Counting Statistics And Error Prediction. I. Characterization Of Data. II. Statistical Models. III. Applications Of Statistical Models. IV. Error Propagation. V. Optimization Of Counting Experiments. VI. Limits Of Detectability. VII. Distribution Of Time Intervals. Chapter 4 General Properties Of Radiation Detectors. I. Simplified Detector Model. II. Modes Of Detector Operation. III. Pulse Height Spectra. IV. Counting Curves And Plateaus. V. Energy Resolution. VI. Detection Efficiency. VII. Dead Time. Chapter 5 Ionization Chambers. I. The Ionization Process In Gases. II. Charge Migration And Collection. III. Design And Operation Of Dc Ion Chambers. IV. Radiation Dose Measurement With Ion Chambers. V. Applications Of Dc Ion Chambers. VI. Pulse Mode Operation. Chapter 6 Proportional Counters. I. Gas Multiplication. II. Design Features Of Proportional Counters. III. Proportional Counter Performance. IV. Detection Efficiency And Counting Curves. V. Variants Of The Proportional Counter Design. VI. Micropattern Gas Detectors. Chapter 7 Geiger-Mueller Counters. I. The Geiger Discharge. II. Fill Gases. III. Quenching. IV. Time Behavior. V. The Geiger Counting Plateau. VI. Design Features. VII. Counting Efficiency. VIII. Time-To-First-Count Method. IX. G-M Survey Meters. Chapter 8 Scintillation Detector Principles. I. Organic Scintillators. II. Inorganic Scintillators. III. Light Collection And Scintillator Mounting. Chapter 9 Photomultiplier Tubes And Photodiodes. I. Introduction. II. The Photocathode. III. Electron Multiplication. IV. Photomultiplier Tube Characteristics. V. Ancillary Equipment Required With Photomultiplier Tubes. VI. Photodiodes As Substitutes For Photomultiplier Tubes. VII. Scintillation Pulse Shape Analysis. VIII. Hybrid Photomultiplier Tubes. IX. Position-Sensing Photomultiplier Tubes. X. Photoionization Detectors. Chapter 10 Radiation Spectroscopy With Scintillators. I. General Considerations In Gamma-Ray Spectroscopy. II. Gamma-Ray Interactions. III. Predicted Response Functions. IV. Properties Of Scintillation Gamma-Ray Spectrometers. V. Response Of Scintillation Detectors To Neutrons. VI. Electron Spectroscopy With Scintillators. VII. Specialized Detector Configurations Based On Scintillation. Chapter 11 Semiconductor Diode Detectors. I. Semiconductor Properties. II. The Action Of Ionizing Radiation In Semiconductors. III. Semiconductors As Radiation Detectors. IV. Semiconductor Detector Configurations. V. Operational Characteristics. VI. Applications Of Silicon Diode Detectors. Chapter 12 Germanium Gamma-Ray Detectors. I. General Considerations. II. Configurations Of Germanium Detectors. III. Germanium Detector Operational Characteristics. IV. Gamma-Ray Spectroscopy With Germanium Detectors. Chapter 13 Other Solid-State Detectors. I. Lithium-Drifted Silicon Detectors. II. Semiconductor Materials Other Than Silicon Or Germanium. III. Avalanche Detectors. IV. Photoconductive Detectors. V. Position-Sensitive Semiconductor Detectors. Chapter 14 Slow Neutron Detection Methods. I. Nuclear Reactions Of Interest In Neutron Detection. II. Detectors Based On The Boron Reaction. III. Detectors Based On Other Conversion Reactions. IV. Reactor Instrumentation. Chapter 15 Fast Neutron Detection And Spectroscopy. I. Counters Based On Neutron Moderation. II. Detectors Based On Fast Neutron-Induced Reactions. III. Detectors That Utilize Fast Neutron Scattering. Chapter 16 Pulse Processing. I. Overview Of Pulse Processing. II. Device Impedances. III. Coaxial Cables. IV. Linear And Logic Pulses. V. Instrument Standards. VI. Summary Of Pulse-Processing Units. VII. Application Specific Integrated Circuits (ASICS). VIII. Components Common To Many Applications. Chapter 17 Pulse Shaping, Counting, And Timing. I. Pulse Shaping. II. Pulse Counting Systems. III. Pulse Height Analysis Systems. IV. Digital Pulse Processing. V. Systems Involving Pulse Timing. VI. Pulse Shape Discrimination. Chapter 18 Multichannel Pulse Analysis. I. Single-Channel Methods. II. General Multichannel Characteristics. III. The Multichannel Analyzer. IV. Spectrum Stabilization And Relocation. V. Spectrum Analysis. Chapter 19 Miscellaneous Detector Types. I. Cherenkov Detectors. II. Gas-Filled Detectors In Self-Quenched Streamer Mode. III. High-Pressure Xenon Spectrometers. IV. Liquid Ionization And Proportional Counters. V. Cryogenic Detectors. VI. Photographic Emulsions. VII. Thermoluminescent Dosimeters And Image Plates. VIII. Track-Etch Detectors. IX. Superheated Drop Or "Bubble Detectors". X. Neutron Detection By Activation. XI. Detection Methods Based On Integrated Circuit Components. Chapter 20 Background And Detector Shielding. I. Sources Of Background. II. Background In Gamma-Ray Spectra. III. Background In Other Detectors. IV. Shielding Materials. V. Active Methods Of Background Reduction. Appendix A The NIM, CAMAC, And VME Instrumentation Standards. Appendix B Derivation Of The Expression For Sample Variance In Chapter 3. Appendix C Statistical Behavior Of Counting Data For Variable Mean Value. Appendix D The Shockley-Ramo Theorem For Induced Charge.
8,458 citations
TL;DR: In this paper, the role of oxidation reduction equilibria during the formation of terrestrial planets is discussed and it is concluded that the differing zero-pressure densities of the planets are caused dominantly by differing mean states of oxidation which were established during the primary accretion processes.
431 citations
"The X-Ray Spectrometer on the MESSE..." refers background in this paper
...In one hypothesis Mercury formed in the hottest regions near the Sun, where silicates were vaporized by solar radiation early in the Sun's evolution (Bullen 1952; Ringwood 1966), depleting FeO and volatiles while enriching refractory elements....
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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 Maryland, College Park7, University of Michigan8, 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
"The X-Ray Spectrometer on the MESSE..." refers background in this paper
...Mercury has been difficult to study because of its close proximity to the Sun, but its chemical composition is important for the clues it offers to the formation of the planets (Solomon et al. 2001)....
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TL;DR: MDIS will acquire four main data sets at Mercury during three flybys and the two-Mercury-solar-day nominal mission: a monochrome global image mosaic at near-zero emission angles and moderate incidence angles, a stereo-complement map at off-nadir geometry and near-identical lighting, multicolor images at low incidence angles and targeted high-resolution images of key surface features.
Abstract: The Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft will provide critical measurements tracing Mercury’s origin and evolution MDIS consists of a monochrome narrow-angle camera (NAC) and a multispectral wide-angle camera (WAC) The NAC is a 15° field-of-view (FOV) off-axis reflector, coaligned with the WAC, a four-element refractor with a 105° FOV and 12-color filter wheel The focal plane electronics of each camera are identical and use a 1,024×1,024 Atmel (Thomson) TH7888A charge-coupled device detector Only one camera operates at a time, allowing them to share a common set of control electronics The NAC and the WAC are mounted on a pivoting platform that provides a 90° field-of-regard, extending 40° sunward and 50° anti-sunward from the spacecraft +Z-axis—the boresight direction of most of MESSENGER’s instruments Onboard data compression provides capabilities for pixel binning, remapping of 12-bit data into 8 bits, and lossless or lossy compression MDIS will acquire four main data sets at Mercury during three flybys and the two-Mercury-solar-day nominal mission: a monochrome global image mosaic at near-zero emission angles and moderate incidence angles, a stereo-complement map at off-nadir geometry and near-identical lighting, multicolor images at low incidence angles, and targeted high-resolution images of key surface features These data will be used to construct a global image base map, a digital terrain model, global maps of color properties, and mosaics of high-resolution image strips Analysis of these data will provide information on Mercury’s impact history, tectonic processes, the composition and emplacement history of volcanic materials, and the thickness distribution and compositional variations of crustal materials This paper summarizes MDIS’s science objectives and technical design, including the common payload design of the MDIS data processing units, as well as detailed results from ground and early flight calibrations and plans for Mercury image products to be generated from MDIS data
259 citations
01 Dec 2007-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In the past year, the Linear Collider Flavour Identification (LCFI) Collaboration has taken significant steps towards having a sensor suitable for use in the silicon vertex detector of the International Linear Collider (ILC) as mentioned in this paper.
Abstract: In the past year, the Linear Collider Flavour Identification (LCFI) Collaboration has taken significant steps towards having a sensor suitable for use in the silicon vertex detector of the International Linear Collider (ILC). The goal of the collaboration is to develop the sensors, electronic systems and mechanical support structures necessary for the construction of a high performance vertex detector and to investigate the contribution such a vertex detector can make to the physics accessible at the ILC. Particular highlights include the delivery and testing of both a second-generation column parallel CCD (CP-CCD), design of the next-generation readout ASIC (CPR2a) and a dedicated ASIC for driving the CP-CCD. This paper briefly describes these and other highlights.
251 citations