The Velocity Distribution of Pickup He+ Measured at 3.0 AU By Messenger

During its interplanetary trajectory in 2007–2009, the MErcury Surface, Space ENvrionment, GEochemistry, and Ranging (MESSENGER) spacecraft passed through the gravitational focusing cone for interstellar helium multiple times at a heliocentric distance R ≈ 0.3 AU. Observations of He+ interstellar pickup ions made by the Fast Imaging Plasma Spectrometer sensor on MESSENGER during these transits provide a glimpse into the structure of newly formed inner heliospheric pickup-ion distributions. This close to the Sun, these ions are picked up in a nearly radial interplanetary magnetic field. Compared with the near-Earth environment, pickup ions observed near 0.3 AU will not have had sufficient time to be energized substantially. Such an environment results in a nearly pristine velocity distribution function that should depend only on pickup-ion injection velocities (related to the interstellar gas), pitch-angle scattering, and cooling processes. From measured energy-per-charge spectra obtained during multiple spacecraft observational geometries, we have deduced the phase-space density of He+ as a function of magnetic pitch angle. Our measurements are most consistent with a distribution that decreases nearly monotonically with increasing pitch angle, rather than the more commonly modeled isotropic or hemispherically symmetric forms. These results imply that pitch-angle scattering of He+ may not be instantaneous, as is often assumed, and instead may reflect the velocity distribution of initially injected particles. In a slow solar wind stream, we find a parallel-scattering mean free path of λ ∼ 0.1 AU and a He+ production rate of ∼0.05 m−3 s−1 within 0.3 AU

Post-processing modeling and removal of background noise in space-based time-of-flight sensors

This paper develops and implements a mathematical framework that enables noise modeling and removal for any sensor that relies on discretely measured events. Here, we apply this technique to data from the Fast Imaging Plasma Spectrometer (FIPS), a time-of-flight mass spectrometer on the MESSENGER spacecraft. An iterative Monte Carlo event-processing algorithm is used to probabilistically separate instrument measurements into real and noise-based events. Kernel density estimation is employed as a smoothing technique to enable noise removal for datasets comprised of only a few events. Given an accurate noise model, the overall misidentification of events is expected to be less than 25% even for datasets having low signal-to-noise (SNR) ratios, with substantially improved results expected for progressively larger accumulations of data. These techniques are shown to successfully recover heavy ion events from in-flight FIPS data both inside and outside Mercury's magnetosphere. Such data analysis methods not only drive a more in-depth understanding of sensor operation, but also provide a unique post-processing approach that can result in the improvement of in-flight SNR without any modifications to instrument settings. In addition, these method are readily applicable to existing archived datasets of past missions.The MESSENGER project is supported by the NASA Discovery Program under contracts NAS5-97271 to The Johns Hopkins University Applied Physics Laboratory and NASW-00002 to the Carnegie Institution of Washington. This work was also supported by the NASA Graduate Student Research Program grant NNX09AL50H (DJG).http://deepblue.lib.umich.edu/bitstream/2027.42/100358/1/gershman_noisepaper2.pd

MESSENGER observations of solar energetic electrons within Mercury’s magnetosphere

During solar energetic particle (SEP) events, the inner heliosphere is bathed in MeV electrons. Through magnetic reconnection, these relativistic electrons can enter the magnetosphere of Mercury, nearly instantaneously filling the regions of open field lines with precipitating particles. With energies sufficient to penetrate solid aluminum shielding more than 1 mm thick, these electrons were observable by a number of sensors on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Because of its thin shielding, frequent sampling, and continuous temporal coverage, the Fast Imaging Plasma Spectrometer provided by far the most sensitive measurements of MeV electrons of all MESSENGER sensors. Sharp changes in energetic electron flux coincided with topological boundaries in the magnetosphere, including the magnetopause, polar cap, and central plasma sheet. Precipitating electrons with fluxes equal to ~40% of their corresponding upstream levels were measured over the entire polar cap, demonstrating that electron space weathering of Mercury’s surface is not limited to the cusp region. We use these distinct precipitation signatures acquired over 33 orbits during 11 SEP events to map the full extent of Mercury’s northern polar cap. We confirm a highly asymmetric polar cap, for which the dayside and nightside boundary latitudes range over ~50–70°N and ~30–60°N, respectively. These latitudinal ranges are consistent with average models of Mercury’s magnetic field but exhibit a large variability indicative of active dayside and nightside magnetic reconnection processes. Finally, we observed enhanced electron fluxes within the central plasma sheet. Although these particles cannot form a stable ring current around the planet, their motion results in an apparent trapped electron population at low latitudes in the magnetotail.Key PointsSolar energetic electrons map Mercury’s magnetospheric topologySolar wind electrons likely produce polar rain at MercuryMeV electrons can be quasi‐trapped in Mercury’s magnetotailPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136321/1/jgra52111.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136321/2/jgra52111_am.pd

Distribution and Compositional Variations of Plasma Ions in Mercury's Space Environment: The First Three Mercury Years of MESSENGER Variations

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 degrees 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

Distribution and compositional variations of plasma ions in Mercury's space environment: The first three Mercury years of MESSENGER observations

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 He 2+ , 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. Key Points Na+-group ions are enhanced in northern cusp and pre‐midnight sector Planetary ion species show distinct dependences on altitude and local time May be first observation of non‐adiabatic effects in Mercury's magnetospherePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98388/1/jgra50016.pd

Mutant Neurogenin-3 in congenital malabsorptive diarrhea

Background: Neurogenin-3 (NEUROG3) is expressed in endocrine progenitor cells and is required for endocrine-cell development in the pancreas and intestine. The NEUROG3 gene (NEUROG3) is therefore a candidate for the cause of a newly discovered autosomal recessive disorder characterized by generalized malabsorption and a paucity of enteroendocrine cells. Methods: We screened genomic DNA from three unrelated patients with sparse enteroendocrine cells for mutations of NEUROG3. We then tested the ability of the observed mutations to alter NEUROG3 function, using in vitro and in vivo assays. Results: The patients had few intestinal enteroendocrine cells positive for chromogranin A, but they had normal numbers of Paneth\u27s, goblet, and absorptive cells. We identified two homozygous mutations in NEUROG3, both of which rendered the NEUROG3 protein unable to activate NEUROD1, a downstream target of NEUROG3, and compromised the ability of NEUROG3 to bind to an E-box element in the NEUROD1 promoter. The injection of wild-type but not mutant NEUROG3 messenger RNA into xenopus embryos induced NEUROD1 expression. Conclusions: A newly discovered disorder characterized by malabsorptive diarrhea and a lack of intestinal enteroendocrine cells is caused by loss-of-function mutations in NEUROG3. Copyright © 2006 Massachusetts Medical Society

Solar wind forcing at Mercury: WSA‐ENLIL model results

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97237/1/jgra50070.pd

Solar wind forcing at Mercury: WSA-ENLIL model results

Analysis and interpretation of observations from the MESSENGER spacecraft in orbit about Mercury require knowledge of solar wind “forcing” parameters. We have utilized the Wang-Sheeley-Arge (WSA)-ENLIL solar wind modeling tool in order to calculate the values of interplanetary magnetic field (IMF) strength (B), solar wind velocity (V) and density (n), ram pressure (~nV2), cross-magnetosphere electric field (V × B), Alfvén Mach number (MA), and other derived quantities of relevance for solar wind-magnetosphere interactions. We have compared upstream MESSENGER IMF and solar wind measurements to see how well the ENLIL model results compare. Such parameters as solar wind dynamic pressure are key for determining the Mercury magnetopause standoff distance, for example. We also use the relatively high-time-resolution B-field data from MESSENGER to estimate the strength of the product of the solar wind speed and southward IMF strength (Bs) at Mercury. This product VBs is the electric field that drives many magnetospheric dynamical processes and can be compared with the occurrence of energetic particle bursts within the Mercury magnetosphere. This quantity also serves as input to the global magnetohydrodynamic and kinetic magnetosphere models that are being used to explore magnetospheric and exospheric processes at Mercury. Moreover, this modeling can help assess near-real-time magnetospheric behavior for MESSENGER or other mission analysis and/or ground-based observational campaigns. We demonstrate that this solar wind forcing tool is a crucial step toward bringing heliospheric science expertise to bear on planetary exploration programs

Alcohol Binge Drinking:Negative and Positive Valence System Abnormalities

This work was supported by an award from Dundee University Medical School (ref. AT27) to ST and JDS. Spectroscopy was supported by an unrestricted ‘Work in Progress’ agreement with Siemens.Background: Three million deaths occur each year due to alcohol misuse. Translational studies are crucial to translate preclinical findings to patients. Preclinical studies have highlighted abnormalities in specific brain systems with these forming the basis of allostasis theory. However, few studies have tested predictions in humans using neuroimaging. Methods: Here we used a Research Domain Criteria (RDoC) approach to testallostasis theory predictions of blunted positive valence system (PVS) and abnormally increased negative valence system (NVS) responses in fifty-seven binge alcohol drinking subjects and healthy controls who completed an instrumental task during fMRI. Results: As hypothesised, binge alcohol drinkers showed abnormally increased activity in NVS-linked regions such as the hippocampus and dorsal cingulate, and abnormally blunted activity in PVS-linked regions such as the striatum, compared to controls. Higher measures of problematic alcohol use were associated with more abnormal brain activity, only for binge drinkers who had been most recently drinking. Conclusions: These results support allostasis theory predictions of abnormally increased NVS and blunted PVS responses in binge alcohol drinkers. Further similar translational neuroimaging studies are indicated, particularly focusing on the NVSPostprintPeer reviewe

The Plasma Environment at Mercury

Mercury is the least explored terrestrial planet, and the one subjected to the highest flux of solar radiation in the heliosphere. Its highly dynamic, miniature magnetosphere contains ions from the exosphere and solar wind, and at times may allow solar wind ions to directly impact the planet's surface. Together these features create a plasma environment that shares many features with, but is nonetheless very different from, that of Earth. The first in situ measurements of plasma ions in the Mercury space environment were made only recently, by the Fast Imaging Plasma Spectrometer (FIPS) during the MESSENGER spacecraft's three flybys of the planet in 2008-2009 as the probe was en route to insertion into orbit about Mercury earlier this year. Here. we present analysis of flyby and early orbital mission data with novel techniques that address the particular challenges inherent in these measurements. First. spacecraft structures and sensor orientation limit the FIPS field of view and allow only partial sampling of velocity distribution functions. We use a software model of FIPS sampling in velocity space to explore these effects and recover bulk parameters under certain assumptions. Second, the low densities found in the Mercury magnetosphere result in a relatively low signal-to-noise ratio for many ions. To address this issue, we apply a kernel density spread function to guide removal of background counts according to a background-signature probability map. We then assign individual counts to particular ion species with a time-of-flight forward model, taking into account energy losses in the carbon foil and other physical behavior of ions within the instrument. Using these methods, we have derived bulk plasma properties and heavy ion composition and evaluated them in the context of the Mercury magnetosphere