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Alessandro Maturilli - One of the best experts on this subject based on the ideXlab platform.
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komatiites as Mercury Surface analogues spectral measurements at pel
Earth and Planetary Science Letters, 2014Co-Authors: Alessandro Maturilli, Jörn Helbert, James St John, J W Head, William M Vaughan, Mario Damore, Matthias Gottschalk, Sabrina FerrariAbstract:Article history: The elemental composition of Mercury's Surface, which has been recently measured by the NASA Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, suggests a mineralogy dominated by magnesium-rich orthopyroxene and feldspar. The most magnesium-rich and aluminium-poor regions of Mercury's Surface (which are presumably orthopyroxene-rich) have compositions, and possibly mineralogies, analogous to terrestrial boninites and basaltic komatiites. Unfortunately, little is known about the spectral properties of komatiites, especially at the high Surface temperatures of Mercury. We therefore have collected three terrestrial komatiites with different compositions plus a synthetic komatiitic sample, and measured their reflectances in the visible and thermal infrared spectral ranges. Samples divided into four grain size ranges (when enough material was available) were measured fresh and after thermal processing in vacuum (10 Pa) at 500 ◦ C, comparable to Mercury peak Surface temperatures. Our measurements show that spectral changes between fresh and thermally processed samples occur in both spectral channels, but are stronger in the visible range, with reddening affecting all the samples, while darkening is more selective. It is important to note that darkening and reddening after thermally processing the samples are independent of the komatiites ferrous iron content. In fact the synthetic sample which is nearly iron-free is most strongly affected. From our study it turns out that thermally processing the samples in vacuum at Mercury Surface temperature produces the removal of samples' colour centres. The results of our study show also that the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on MESSENGER orbiting Mercury currently cannot distinguish between different compositions of komatiites, while the future Mercury Radiometer and Thermal infrared Imaging Spectrometer (MERTIS) on the upcoming ESA BepiColombo mission will resolve their differences in the 7−14 μm spectral range.
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raman measurements of a fine grained labradorite sample heated to typical Mercury dayside temperatures
epsc, 2009Co-Authors: Ute Bottger, Alessandro Maturilli, Jörn Helbert, Heinz-wilhelm HubersAbstract:Labradorite is considered as a Mercury Surface analogue and is investigated for a better understanding of the processes on the Surface of Mercury. For this purpose mid-infrared and Raman measurements of labradorite were performed in the Institute of Planetary Research at DLR in Berlin. The measurements indicate significant changes of the spectral features in the midinfrared region at high temperatures and some of these changes were still observable after cooling the sample to room temperature. This led Helbert et al. [1] to the assumption that labradorite during the heating process undergoes an irreversible structural change. Here we present the Raman spectra of labradorite. The results are complementary to the mid-infrared measurements. As for the mid-infrared spectra the Raman spectra show differences for the heated and unheated samples.
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the emissivity of a fine grained labradorite sample at typical Mercury dayside temperatures
Earth and Planetary Science Letters, 2009Co-Authors: Jörn Helbert, Alessandro MaturilliAbstract:Abstract Analyzing the Surface composition of Mercury's regolith from remote-sensing measurements is a challenging task. In support of the National Aeronautics and Space Agency's Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission and especially in preparation for the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument on the BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency, we are developing a Planetary Emissivity Laboratory at Deutsches Zentrum fur Luft-und Rahmfahrt (DLR) in Berlin. Here we present the first measurements of labradorite as a Mercury Surface analog obtained with a test setup at a temperature of 420 °C, appropriate for the dayside of Mercury. Because of limitations on the current test apparatus, we present here data only for mid-infrared wavelengths. The spectra show strong indications of significant changes in spectral features in the mid-infrared with changing temperature. This result introduces an additional complication to the analysis of spectra obtained from the Surface of Mercury, as the Surface temperature and the thermal history of an observed area must be taken into account in the interpretation of the spectra. This inference implies that the latitude, and possibly also the time of day, must be considered when analyzing a spectrum. In particular, the Surface at the equator might exhibit different spectral characteristics than the Surface at high latitudes even for the same composition. These observations, while still preliminary, underscore strongly the need for temperature-dependent measurements of emissivity of candidate planetary Surface materials.
Jörn Helbert - One of the best experts on this subject based on the ideXlab platform.
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komatiites as Mercury Surface analogues spectral measurements at pel
Earth and Planetary Science Letters, 2014Co-Authors: Alessandro Maturilli, Jörn Helbert, James St John, J W Head, William M Vaughan, Mario Damore, Matthias Gottschalk, Sabrina FerrariAbstract:Article history: The elemental composition of Mercury's Surface, which has been recently measured by the NASA Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, suggests a mineralogy dominated by magnesium-rich orthopyroxene and feldspar. The most magnesium-rich and aluminium-poor regions of Mercury's Surface (which are presumably orthopyroxene-rich) have compositions, and possibly mineralogies, analogous to terrestrial boninites and basaltic komatiites. Unfortunately, little is known about the spectral properties of komatiites, especially at the high Surface temperatures of Mercury. We therefore have collected three terrestrial komatiites with different compositions plus a synthetic komatiitic sample, and measured their reflectances in the visible and thermal infrared spectral ranges. Samples divided into four grain size ranges (when enough material was available) were measured fresh and after thermal processing in vacuum (10 Pa) at 500 ◦ C, comparable to Mercury peak Surface temperatures. Our measurements show that spectral changes between fresh and thermally processed samples occur in both spectral channels, but are stronger in the visible range, with reddening affecting all the samples, while darkening is more selective. It is important to note that darkening and reddening after thermally processing the samples are independent of the komatiites ferrous iron content. In fact the synthetic sample which is nearly iron-free is most strongly affected. From our study it turns out that thermally processing the samples in vacuum at Mercury Surface temperature produces the removal of samples' colour centres. The results of our study show also that the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on MESSENGER orbiting Mercury currently cannot distinguish between different compositions of komatiites, while the future Mercury Radiometer and Thermal infrared Imaging Spectrometer (MERTIS) on the upcoming ESA BepiColombo mission will resolve their differences in the 7−14 μm spectral range.
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raman measurements of a fine grained labradorite sample heated to typical Mercury dayside temperatures
epsc, 2009Co-Authors: Ute Bottger, Alessandro Maturilli, Jörn Helbert, Heinz-wilhelm HubersAbstract:Labradorite is considered as a Mercury Surface analogue and is investigated for a better understanding of the processes on the Surface of Mercury. For this purpose mid-infrared and Raman measurements of labradorite were performed in the Institute of Planetary Research at DLR in Berlin. The measurements indicate significant changes of the spectral features in the midinfrared region at high temperatures and some of these changes were still observable after cooling the sample to room temperature. This led Helbert et al. [1] to the assumption that labradorite during the heating process undergoes an irreversible structural change. Here we present the Raman spectra of labradorite. The results are complementary to the mid-infrared measurements. As for the mid-infrared spectra the Raman spectra show differences for the heated and unheated samples.
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the emissivity of a fine grained labradorite sample at typical Mercury dayside temperatures
Earth and Planetary Science Letters, 2009Co-Authors: Jörn Helbert, Alessandro MaturilliAbstract:Abstract Analyzing the Surface composition of Mercury's regolith from remote-sensing measurements is a challenging task. In support of the National Aeronautics and Space Agency's Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission and especially in preparation for the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument on the BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency, we are developing a Planetary Emissivity Laboratory at Deutsches Zentrum fur Luft-und Rahmfahrt (DLR) in Berlin. Here we present the first measurements of labradorite as a Mercury Surface analog obtained with a test setup at a temperature of 420 °C, appropriate for the dayside of Mercury. Because of limitations on the current test apparatus, we present here data only for mid-infrared wavelengths. The spectra show strong indications of significant changes in spectral features in the mid-infrared with changing temperature. This result introduces an additional complication to the analysis of spectra obtained from the Surface of Mercury, as the Surface temperature and the thermal history of an observed area must be taken into account in the interpretation of the spectra. This inference implies that the latitude, and possibly also the time of day, must be considered when analyzing a spectrum. In particular, the Surface at the equator might exhibit different spectral characteristics than the Surface at high latitudes even for the same composition. These observations, while still preliminary, underscore strongly the need for temperature-dependent measurements of emissivity of candidate planetary Surface materials.
Sean C Solomon - One of the best experts on this subject based on the ideXlab platform.
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comprehensive survey of energetic electron events in Mercury s magnetosphere with data from the messenger gamma ray and neutron spectrometer
Journal of Geophysical Research, 2015Co-Authors: D J Lawrence, B J Anderson, D N Baker, R L Mcnutt, Sean C Solomon, Patrick N Peplowski, H Korth, W C Feldman, R StarrAbstract:Data from the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Gamma-Ray and Neutron Spectrometer have been used to detect and characterize energetic electron (EE) events in Mercury's magnetosphere. This instrument detects EE events indirectly via bremsstrahlung photons that are emitted when instrument and spacecraft materials stop electrons having energies of tens to hundreds of keV. From Neutron Spectrometer data taken between 18 March 2011 and 31 December 2013 we have identified 2711 EE events. EE event amplitudes versus energy are distributed as a power law and have a dynamic range of a factor of 400. The duration of the EE events ranges from tens of seconds to nearly 20 min. EE events may be classified as bursty (large variation with time over an event) or smooth (small variation). Almost all EE events are detected inside Mercury's magnetosphere on closed field lines. The precise occurrence times of EE events are stochastic, but the events are located in well-defined regions with clear boundaries that persist in time and form what we call “quasi-permanent structures.” Bursty events occur closer to dawn and at higher latitudes than smooth events, which are seen near noon-to-dusk local times at lower latitudes. A subset of EE events shows strong periodicities that range from hundreds of seconds to tens of milliseconds. The few-minute periodicities are consistent with the Dungey cycle timescale for the magnetosphere and the occurrence of substorm events in Mercury's magnetotail region. Shorter periods may be related to phenomena such as north-south bounce processes for the energetic electrons.
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magnetic flux pileup and plasma depletion in Mercury s subsolar magnetosheath
Journal of Geophysical Research, 2013Co-Authors: B J Anderson, Thomas H. Zurbuchen, D N Baker, Sean C Solomon, J A Slavin, Jim M Raines, Daniel J Gershman, H KorthAbstract:[1] Measurements from the Fast Imaging Plasma Spectrometer (FIPS) and Magnetometer (MAG) on the Mercury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft during 40 orbits about Mercury are used to characterize the plasma depletion layer just exterior to the planet's dayside magnetopause. A plasma depletion layer forms at Mercury as a result of piled-up magnetic flux that is draped around the magnetosphere. The low average upstream Alfvenic Mach number (MA ~3–5) in the solar wind at Mercury often results in large-scale plasma depletion in the magnetosheath between the subsolar magnetopause and the bow shock. Flux pileup is observed to occur downstream under both quasi-perpendicular and quasi-parallel shock geometries for all orientations of the interplanetary magnetic field (IMF). Furthermore, little to no plasma depletion is seen during some periods with stable northward IMF. The consistently low value of plasma β, the ratio of plasma pressure to magnetic pressure, at the magnetopause associated with the low average upstream MA is believed to be the cause for the high average reconnection rate at Mercury, reported to be nearly 3 times that observed at Earth. Finally, a characteristic depletion length outward from the subsolar magnetopause of ~300 km is found for Mercury. This value scales among planetary bodies as the average standoff distance of the magnetopause.
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the messenger mission to Mercury spacecraft and mission design
Planetary and Space Science, 2001Co-Authors: A G Santo, R E Gold, R L Mcnutt, Sean C Solomon, Carl J Ercol, Robert W Farquhar, Theodore J Hartka, Jason E Jenkins, James V Mcadams, Larry E MosherAbstract:Abstract A Mercury orbiter mission is challenging from thermal and mass perspectives. The Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission overcomes these challenges while avoiding esoteric technologies by using an innovative approach with commonly available materials, minimal moving parts, and maximum heritage. This approach yields a spacecraft with good margins in all categories and low technical risk. The key concepts are a ceramic-cloth sunshade, an integrated lightweight structure and high- performance propulsion system, and a solar array incorporating optical solar reflectors (OSRs). The sunshade maintains the spacecraft at room temperature. The integrated structure and propulsion system provides ample mass margin. The solar array with OSRs, which has already undergone significant testing, provides thermal margin even if the panels are inadvertently pointed directly at the Sun at 0.3 AU. 0.3 AU .
B J Anderson - One of the best experts on this subject based on the ideXlab platform.
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comprehensive survey of energetic electron events in Mercury s magnetosphere with data from the messenger gamma ray and neutron spectrometer
Journal of Geophysical Research, 2015Co-Authors: D J Lawrence, B J Anderson, D N Baker, R L Mcnutt, Sean C Solomon, Patrick N Peplowski, H Korth, W C Feldman, R StarrAbstract:Data from the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Gamma-Ray and Neutron Spectrometer have been used to detect and characterize energetic electron (EE) events in Mercury's magnetosphere. This instrument detects EE events indirectly via bremsstrahlung photons that are emitted when instrument and spacecraft materials stop electrons having energies of tens to hundreds of keV. From Neutron Spectrometer data taken between 18 March 2011 and 31 December 2013 we have identified 2711 EE events. EE event amplitudes versus energy are distributed as a power law and have a dynamic range of a factor of 400. The duration of the EE events ranges from tens of seconds to nearly 20 min. EE events may be classified as bursty (large variation with time over an event) or smooth (small variation). Almost all EE events are detected inside Mercury's magnetosphere on closed field lines. The precise occurrence times of EE events are stochastic, but the events are located in well-defined regions with clear boundaries that persist in time and form what we call “quasi-permanent structures.” Bursty events occur closer to dawn and at higher latitudes than smooth events, which are seen near noon-to-dusk local times at lower latitudes. A subset of EE events shows strong periodicities that range from hundreds of seconds to tens of milliseconds. The few-minute periodicities are consistent with the Dungey cycle timescale for the magnetosphere and the occurrence of substorm events in Mercury's magnetotail region. Shorter periods may be related to phenomena such as north-south bounce processes for the energetic electrons.
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magnetic flux pileup and plasma depletion in Mercury s subsolar magnetosheath
Journal of Geophysical Research, 2013Co-Authors: B J Anderson, Thomas H. Zurbuchen, D N Baker, Sean C Solomon, J A Slavin, Jim M Raines, Daniel J Gershman, H KorthAbstract:[1] Measurements from the Fast Imaging Plasma Spectrometer (FIPS) and Magnetometer (MAG) on the Mercury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft during 40 orbits about Mercury are used to characterize the plasma depletion layer just exterior to the planet's dayside magnetopause. A plasma depletion layer forms at Mercury as a result of piled-up magnetic flux that is draped around the magnetosphere. The low average upstream Alfvenic Mach number (MA ~3–5) in the solar wind at Mercury often results in large-scale plasma depletion in the magnetosheath between the subsolar magnetopause and the bow shock. Flux pileup is observed to occur downstream under both quasi-perpendicular and quasi-parallel shock geometries for all orientations of the interplanetary magnetic field (IMF). Furthermore, little to no plasma depletion is seen during some periods with stable northward IMF. The consistently low value of plasma β, the ratio of plasma pressure to magnetic pressure, at the magnetopause associated with the low average upstream MA is believed to be the cause for the high average reconnection rate at Mercury, reported to be nearly 3 times that observed at Earth. Finally, a characteristic depletion length outward from the subsolar magnetopause of ~300 km is found for Mercury. This value scales among planetary bodies as the average standoff distance of the magnetopause.
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distribution and compositional variations of plasma ions in Mercury s space environment the first three Mercury years of messenger observations
Journal of Geophysical Research, 2013Co-Authors: Jim M Raines, B J Anderson, Thomas H. Zurbuchen, J A Slavin, M Sarantos, Daniel J Gershman, H Korth, Jason A Gilbert, G GloecklerAbstract:[1] We have analyzed measurements of planetary ions near Mercury made by the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Fast Imaging Plasma Spectrometer (FIPS) over the first three Mercury years of orbital observations (25 March 2011 through 31 December 2011). We determined the composition and spatial distributions of the most abundant species in the regions sampled by the MESSENGER spacecraft during that period. In particular, we here focus on altitude dependence and relative abundances of species in a variety of spatial domains. We used observed density as a proxy for ambient plasma density, because of limitations to the FIPS field of view. We find that the average observed density is 3.9 × 10–2 cm–3 for He2+, 3.4 × 10–4 cm–3 for He+, 8.0 × 10–4 cm–3 for O+-group ions, and 5.1 × 10–3 cm–3 for Na+-group ions. Na+-group ions are particularly enhanced over other planetary ions (He+ and O+ group) in the northern magnetospheric cusp (by a factor of ~2.0) and in the premidnight sector on the nightside (by a factor of ~1.6). Within 30° of the equator, the average densities of all planetary ions are depressed at the subsolar point relative to the dawn and dusk terminators. The effect is largest for Na+-group ions, which are 49% lower in density at the subsolar point than at the terminators. This depression could be an effect of the FIPS energy threshold. The three planetary ion species considered show distinct dependences on altitude and local time. The Na+ group has the smallest e-folding height at all dayside local times, whereas He+ has the largest. At the subsolar point, the e-folding height for Na+-group ions is 590 km, and that for the O+ group and He+ is 1100 km. On the nightside and within 750 km of the geographic equator, Na+-group ions are enhanced in the premidnight sector. This enhancement is consistent with nonadiabatic motion and may be observational evidence that nonadiabatic effects are important in Mercury's magnetosphere.
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messenger observations of magnetopause structure and dynamics at Mercury
Journal of Geophysical Research, 2013Co-Authors: Gina A. Dibraccio, B J Anderson, Scott A. Boardsen, Haje Korth, Justin M. Raines, James A. Slavin, Thomas H. Zurbuchen, D N Baker, Ralph L. McnuttAbstract:[1] On 18 March 2011, Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) became the first spacecraft to orbit Mercury, providing a new opportunity to study the outer boundary of the planet’s magnetosphere—the magnetopause. Here we characterize Mercury’s magnetopause using measurements collected by MESSENGER’s Magnetometer and Fast Imaging Plasma Spectrometer. Analysis of measurements from two of MESSENGER’s “hot seasons,” when the orbital periapsis is on Mercury’s dayside and the magnetopause crossing takes place in the subsolar region, resulted in 43 events with well-determined boundary normals. The typical duration of a magnetopause traversal was ~5 s. The average normal magnetic field component was ~20 nT, and the dimensionless reconnection rate, i.e., the ratio of the normal magnetic field component to the total field magnitude just inside the magnetopause, was 0.15 � 0.02. This rate is a factor of ~3 larger than values found during the most extensive surveys at Earth. The ratio of the reconnection rate at Mercury to that of the Earth is comparable to the ratio of the solar wind Alfven speeds at their respective orbits. We also find that the magnetopause reconnection rate at Mercury is independent of magnetic field shear angle, but it varies inversely with plasma b, the ratio of total thermal pressure to magnetic pressure, in the magnetosheath. These results suggest that reconnectionatMercuryisnotonlymoreintensethanatEarthbutalsothatitoccursfornearly allorientationsofthe interplanetarymagnetic field duetothe low-bnatureof thesolar windin the inner heliosphere.
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evidence for water ice near Mercury s north pole from messenger neutron spectrometer measurements
Science, 2013Co-Authors: D J Lawrence, B J Anderson, R L Mcnutt, William C Feldman, J Goldsten, S Maurice, Patrick N Peplowski, David Bazell, Larry R Nittler, T H PrettymanAbstract:Measurements by the Neutron Spectrometer on the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show decreases in the flux of epithermal and fast neutrons from Mercury’s north polar region that are consistent with the presence of water ice in permanently shadowed regions. The neutron data indicate that Mercury’s radar-bright polar deposits contain, on average, a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer 10 to 30 cm thick that is less rich in hydrogen. Combined neutron and radar data are best matched if the buried layer consists of nearly pure water ice. The upper layer contains less than 25 weight % water-equivalent hydrogen. The total mass of water at Mercury’s poles is inferred to be 2 × 1016 to 1018 grams and is consistent with delivery by comets or volatile-rich asteroids.
R L Mcnutt - One of the best experts on this subject based on the ideXlab platform.
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statistical study of Mercury s energetic electron events as observed by the gamma ray and neutron spectrometer instrument onboard messenger
Journal of Geophysical Research, 2018Co-Authors: R Nikoukar, Haje Korth, D N Baker, D J Lawrence, Patrick N Peplowski, R M Dewey, R L McnuttAbstract:We present results from a statistical analysis of Mercury's energetic electron (EE) events as observed by the gamma-ray and neutron spectrometer instrument onboard the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. The main objective of this study is to investigate possible anisotropic behavior of EE events using multiple data sets from MESSENGER instruments. We study the data from the neutron spectrometer (NS) and the gamma-ray spectrometer anticoincidence shield (ACS) because they use the same type of borated plastic scintillator and, hence, they have very similar response functions, and their large Surface areas make them more sensitive to low-intensity EE events than MESSENGER's particle instrumentation. The combined analysis of NS and ACS data reveals two different classes of energetic electrons: "Standard" events and "ACS-enhanced" events. Standard events, which comprise over 90% of all events, have signal sizes that are the same in both the ACS and NS. They are likely gyrating particles about Mercury's magnetic field following a 90° pitch angle distribution and are located in well-defined latitude and altitude regions within Mercury's magnetosphere. ACS-enhanced events, which comprise less than 10% of all events, have signal sizes in the ACS that are 10 to 100 times larger than those observed by the NS. They follow a beam-like distribution and are observed both inside and outside Mercury's magnetosphere with a wider range of latitudes and altitudes than Standard events. The difference between the Standard and ACS-enhanced event characteristics suggests distinct underyling acceleration mechanisms.
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comprehensive survey of energetic electron events in Mercury s magnetosphere with data from the messenger gamma ray and neutron spectrometer
Journal of Geophysical Research, 2015Co-Authors: D J Lawrence, B J Anderson, D N Baker, R L Mcnutt, Sean C Solomon, Patrick N Peplowski, H Korth, W C Feldman, R StarrAbstract:Data from the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Gamma-Ray and Neutron Spectrometer have been used to detect and characterize energetic electron (EE) events in Mercury's magnetosphere. This instrument detects EE events indirectly via bremsstrahlung photons that are emitted when instrument and spacecraft materials stop electrons having energies of tens to hundreds of keV. From Neutron Spectrometer data taken between 18 March 2011 and 31 December 2013 we have identified 2711 EE events. EE event amplitudes versus energy are distributed as a power law and have a dynamic range of a factor of 400. The duration of the EE events ranges from tens of seconds to nearly 20 min. EE events may be classified as bursty (large variation with time over an event) or smooth (small variation). Almost all EE events are detected inside Mercury's magnetosphere on closed field lines. The precise occurrence times of EE events are stochastic, but the events are located in well-defined regions with clear boundaries that persist in time and form what we call “quasi-permanent structures.” Bursty events occur closer to dawn and at higher latitudes than smooth events, which are seen near noon-to-dusk local times at lower latitudes. A subset of EE events shows strong periodicities that range from hundreds of seconds to tens of milliseconds. The few-minute periodicities are consistent with the Dungey cycle timescale for the magnetosphere and the occurrence of substorm events in Mercury's magnetotail region. Shorter periods may be related to phenomena such as north-south bounce processes for the energetic electrons.
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evidence for water ice near Mercury s north pole from messenger neutron spectrometer measurements
Science, 2013Co-Authors: D J Lawrence, B J Anderson, R L Mcnutt, William C Feldman, J Goldsten, S Maurice, Patrick N Peplowski, David Bazell, Larry R Nittler, T H PrettymanAbstract:Measurements by the Neutron Spectrometer on the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show decreases in the flux of epithermal and fast neutrons from Mercury’s north polar region that are consistent with the presence of water ice in permanently shadowed regions. The neutron data indicate that Mercury’s radar-bright polar deposits contain, on average, a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer 10 to 30 cm thick that is less rich in hydrogen. Combined neutron and radar data are best matched if the buried layer consists of nearly pure water ice. The upper layer contains less than 25 weight % water-equivalent hydrogen. The total mass of water at Mercury’s poles is inferred to be 2 × 1016 to 1018 grams and is consistent with delivery by comets or volatile-rich asteroids.
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the messenger mission to Mercury spacecraft and mission design
Planetary and Space Science, 2001Co-Authors: A G Santo, R E Gold, R L Mcnutt, Sean C Solomon, Carl J Ercol, Robert W Farquhar, Theodore J Hartka, Jason E Jenkins, James V Mcadams, Larry E MosherAbstract:Abstract A Mercury orbiter mission is challenging from thermal and mass perspectives. The Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission overcomes these challenges while avoiding esoteric technologies by using an innovative approach with commonly available materials, minimal moving parts, and maximum heritage. This approach yields a spacecraft with good margins in all categories and low technical risk. The key concepts are a ceramic-cloth sunshade, an integrated lightweight structure and high- performance propulsion system, and a solar array incorporating optical solar reflectors (OSRs). The sunshade maintains the spacecraft at room temperature. The integrated structure and propulsion system provides ample mass margin. The solar array with OSRs, which has already undergone significant testing, provides thermal margin even if the panels are inadvertently pointed directly at the Sun at 0.3 AU. 0.3 AU .