The X-ray Spectrometer on the MESSENGER Spacecraft

Schlemm, C. E.; Starr, R.; Ho, G. C.; Bechtold, Katie; Hamilton, Sarah A.; Boldt, J.; Boynton, W. V.; Bradley, Walter; Fraeman, Martin E.; Gold, R. E.; Goldsten, J.; Hayes, J. R.; Jaskulek, S.; Rossano, E.; Rumpf, Robert A.; Schaefer, Edward D.; Strohbehn, K.; Shelton, Richard; Thompson, Raymond E.; Trombka, J. I.; Williams, Bruce D.

doi:10.1007/978-0-387-77214-1_11

Cited by 19 publications

(17 citation statements)

References 10 publications

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“…In short, the count rate is derived from the ACS's response integrated over its omnidirectional field of view, large geometric factor, particle species (energetic electrons, GCRs, and planetary neutrons), and particle energy. While the Energetic Particle Spectrometer (3 s resolution) (Andrews et al, ), X‐Ray Spectrometer (XRS, 40 s resolution) (Schlemm et al, ), and Neutron Spectrometer (NS, 20 s resolution) (Goldsten et al, ) instruments also observe energetic electrons, we focus on GRS observations because of the sensor's superior time resolution and its high sensitivity from its nearly omnidirectional response and large geometric factor. For simplicity, we use “GRS” to refer to the high‐time‐resolution ACS measurements except where noted otherwise.…”

Section: Data Sources and Event Identificationmentioning

confidence: 99%

Energetic Electron Acceleration and Injection During Dipolarization Events in Mercury's Magnetotail

et al. 2017

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Energetic particle bursts associated with dipolarization events within Mercury's magnetosphere were first observed by Mariner 10. The events appear analogous to particle injections accompanying dipolarization events at Earth. The Energetic Particle Spectrometer (3 s resolution) aboard MESSENGER determined the particle bursts are composed entirely of electrons with energies ≳ 300 keV. Here we use the Gamma‐Ray Spectrometer high‐time‐resolution (10 ms) energetic electron measurements to examine the relationship between energetic electron injections and magnetic field dipolarization in Mercury's magnetotail. Between March 2013 and April 2015, we identify 2,976 electron burst events within Mercury's magnetotail, 538 of which are closely associated with dipolarization events. These dipolarizations are detected on the basis of their rapid (~2 s) increase in the northward component of the tail magnetic field (ΔBz ~30 nT), which typically persists for ~10 s. Similar to those at Earth, we find that these dipolarizations appear to be low‐entropy, depleted flux tubes convecting planetward following the collapse of the inner magnetotail. We find that electrons experience brief, yet intense, betatron and Fermi acceleration during these dipolarizations, reaching energies ~130 keV and contributing to nightside precipitation. Thermal protons experience only modest betatron acceleration. While only ~25% of energetic electron events in Mercury's magnetotail are directly associated with dipolarization, the remaining events are consistent with the Near‐Mercury Neutral Line model of magnetotail injection and eastward drift about Mercury, finding that electrons may participate in Shabansky‐like closed drifts about the planet. Magnetotail dipolarization may be the dominant source of energetic electron acceleration in Mercury's magnetosphere.

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Section: Data Sources and Event Identificationmentioning

confidence: 99%

Energetic Electron Acceleration and Injection During Dipolarization Events in Mercury's Magnetotail

et al. 2017

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“…At the time of the solar flare in question, MESSENGER was at about 0.48 AU and 153°E relative to the Earth‐Sun line. Instruments aboard MESSENGER observed the flare through its signatures in 1–8 keV X‐rays [ Schlemm et al , 2007], electrons (and perhaps some ions) at energies between 65 keV and 1 MeV [ Andrews et al , 2007], characteristic variations in the IMF [ Anderson et al , 2007], and neutrons having apparent energies deposited in the NS between 0 and 7.5 MeV [ Goldsten et al , 2007]. No measurements of gamma rays are available during the 31 December 2007 event because the MESSENGER GRS was not turned on at the time.…”

Section: Observations By Messengermentioning

confidence: 99%

Evidence for extended acceleration of solar flare ions from 1–8 MeV solar neutrons detected with the MESSENGER Neutron Spectrometer

et al. 2010

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[1] Neutrons produced on the Sun during the M2 flare on 31 December 2007 were observed at 0.48 AU by the MESSENGER Neutron Spectrometer. These observations are the first detection of solar neutrons inside 1 AU. This flare contained multiple acceleration episodes as seen in type III radio bursts. After these bursts ended, both the energetic particle and neutron fluxes decayed smoothly to background with an e-folding decay time of 2.84 h, spanning a 9 h time period. This time is considerably longer than the mean lifetime of a neutron, which indicates that either the observed neutrons were generated in the spacecraft by solar energetic particle protons, or they originated on the Sun. If most of the neutrons came from the Sun, as our simulations of neutron production on the spacecraft show, they must have been continuously produced. A likely explanation of their long duration is that energetic ions were accelerated over an extended time period onto closed magnetic arcades above the corona and then slowly pitch angle-scattered by coronal turbulence into their chromospheric loss cones. Because of their relatively low energy loss in the Neutron Spectrometer (0.5-7.5 MeV), most of these neutrons beta decay to energetic protons and electrons close to the Sun, thereby forming an extended seed population available for further acceleration by subsequent shocks driven by coronal mass ejections in interplanetary space.

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“…During MESSENGER's four years in orbit, measurements made by its suite of geochemistry instruments—the X‐Ray Spectrometer (XRS) and Gamma Ray and Neutron Spectrometer (GRNS)—revealed the composition of a previously poorly constrained surface [ Nittler et al ., ; Peplowski et al ., , , , , ; Evans et al ., ; L. G. Evans et al , ; Starr et al ., ; Weider et al ., , ; Lawrence et al ., , ]. The highest resolution chemical maps are derived from the XRS, which detected the abundances of Mg, Al, Si, S, Ca, Ti, Cr, Mn, and Fe in the top few tens of microns of Mercury's surface [ Schlemm et al ., ]. The XRS revealed a surface that is intermediate in Mg/Si between terrestrial and lunar komatiites and basalts and the terrestrial oceanic crust but has lower Al/Si and Ca/Si than those basalts [ Nittler et al ., ; Weider et al ., , , ].…”

Section: Introductionmentioning

confidence: 99%

Evaluating an impact origin for Mercury's high‐magnesium region

et al. 2017

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During its four years in orbit around Mercury, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft's X‐ray Spectrometer revealed a large geochemical terrane in the northern hemisphere that hosts the highest Mg/Si, S/Si, Ca/Si, and Fe/Si and lowest Al/Si ratios on the planet. Correlations with low topography, thin crust, and a sharp northern topographic boundary led to the proposal that this high‐Mg region is the remnant of an ancient, highly degraded impact basin. Here we use a numerical modeling approach to explore the feasibility of this hypothesis and evaluate the results against multiple mission‐wide data sets and resulting maps from MESSENGER. We find that an ~3000 km diameter impact basin easily exhumes Mg‐rich mantle material but that the amount of subsequent modification required to hide basin structure is incompatible with the strength of the geochemical anomaly, which is also present in maps of Gamma Ray and Neutron Spectrometer data. Consequently, the high‐Mg region is more likely to be the product of high‐temperature volcanism sourced from a chemically heterogeneous mantle than the remains of a large impact event.

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The X-ray Spectrometer on the MESSENGER Spacecraft

Cited by 19 publications

References 10 publications

Energetic Electron Acceleration and Injection During Dipolarization Events in Mercury's Magnetotail

Energetic Electron Acceleration and Injection During Dipolarization Events in Mercury's Magnetotail

Evidence for extended acceleration of solar flare ions from 1–8 MeV solar neutrons detected with the MESSENGER Neutron Spectrometer

Evaluating an impact origin for Mercury's high‐magnesium region

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