Magnetic topology is important for understanding the Martian plasma environment, including particle precipitation, energy transport, cold ion escape, and wave‐particle interaction. In this study, we ...combine two independent but complementary methods in order to determine magnetic topology based on superthermal electron energy and pitch angle distributions. This approach removes ambiguities that result from using either energy or pitch angle alone, providing a more accurate and comprehensive determination of magnetic topology than previous studies. By applying this combined technique, we are able to identify seven magnetic topologies, including four types of closed field lines, two types of open field lines, and draped. All seven topologies are present in the Mars environment and are mapped in longitude, latitude, solar zenith angle, and altitude with the combined technique near the terminator. We find that closed field lines with double‐sided loss cones are frequently present over stronger crustal field regions at higher altitudes. We also show that the cross‐terminator closed field lines are more spatially confined over strong crustal regions, likely connecting nearby magnetic crustal patches. In contrast, cross‐terminator closed loops over weak crustal regions have more distantly separated foot points, most likely connecting distant crustal patches.
Key Points
A technique combining e‐ pitch angle and energy distribution is developed to most accurately infer up to seven magnetic topologies at Mars
Closed magnetic loops with trapped electrons occur frequently over stronger crustal field regions at higher altitudes
Cross‐terminator closed loops are more spatially confined over strong crustal regions and distantly separated over weak crustal regions
Initial results from the MAVEN mission to Mars Jakosky, Bruce M.; Grebowsky, Joseph M.; Luhmann, Janet G. ...
Geophysical research letters,
16 November 2015, Letnik:
42, Številka:
21
Journal Article
Recenzirano
Odprti dostop
The Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars orbiter has been gathering information on the Mars upper atmosphere, ionosphere, and solar and solar wind interactions since its orbit ...insertion in September 2014. MAVEN's science goals are to understand processes driving the escape of atmospheric gases to space at the present epoch, and their variations with solar and local heliospheric conditions together with geographical and seasonal influences. This introduction and the accompanying articles provide a selection of key results obtained up to the time of writing, including measurements of the overall geometry and variability of the Martian magnetosphere, upper atmosphere, and ionosphere and their responses to interplanetary coronal mass ejections and solar energetic particle influxes. The ultimate goal is to use these results to determine the integrated loss to space through time and its role in overall Mars atmosphere evolution.
Key Points
MAVEN science results at Mars affect our understanding of the history of Mars volatiles
Results integrate all aspects of the Mars upper atmosphere system
To investigate the prognostic relevance of temporal muscle thickness (TMT) as a surrogate parameter of skeletal muscle status in patients with newly diagnosed glioblastoma.
We assessed TMT in cranial ...MRI of 755 patients enrolled in the CENTRIC EORTC 26071-22072 study (
= 508) and CORE study (
= 247). We used predefined sex-specific TMT cut-off values to categorize "patients at risk of sarcopenia" and "patients with normal muscle status" at baseline. Furthermore, we categorized patients according to the extent of TMT loss over time. Associations with progression-free survival (PFS) and overall survival (OS) were evaluated using the Cox model adjusted for other exploratory variables.
Patients at risk of sarcopenia (CENTRIC;
= 158/508, 31.1%; CORE;
= 87/247, 35.2%) at baseline had significantly higher risk of progression and death than patients with normal muscle status in both study cohorts CENTRIC: PFS = HR 0.16; 95% confidence interval (CI), 0.12-0.21;
< 0.001; OS = HR 0.341; 95% CI, 0.27-0.44;
< 0.001; CORE: PFS = HR 0.29; 95% CI, 0.21-0.39;
< 0.001; OS = HR, 0.365; 95% CI, 0.27-0.49;
< 0.001. Similar results were obtained in multivariate Cox models adjusted for other important prognostic parameters. The extent of TMT loss over time showed a significant inverse correlation with median OS times in patients at risk for sarcopenia (CENTRIC:
< 0.001; CORE:
= 0.005), but not in patients with normal baseline muscle mass (CENTRIC:
= 0.538; CORE:
= 0.28).
TMT identifies ambulatory patients with newly diagnosed glioblastoma at risk for progressive sarcopenia and adverse outcomes. Early intervention may prevent skeletal muscle loss and improve patient outcome.
Electron precipitation is usually the dominant source of energy input to the nightside Martian atmosphere, with consequences for ionospheric densities, chemistry, electrodynamics, communications, and ...navigation. We examine downward‐traveling superthermal electron flux on the Martian nightside from May 1999 to November 2006 at 400 km altitude and 2 A.M. local time. Electron precipitation is geographically organized by crustal magnetic field strength and elevation angle, with higher fluxes occurring in regions of weak and/or primarily vertical crustal fields, while stronger and more horizontal fields retard electron access to the atmosphere. We investigate how these crustal field‐organized precipitation patterns vary with proxies for solar wind (SW) pressure and interplanetary magnetic field (IMF) direction. Generally, higher precipitating fluxes accompany higher SW pressures. Specifically, we identify four characteristic spectral behaviors: (1) “stable” regions where fluxes increase mildly with SW pressure, (2) “high‐flux” regions where accelerated (peaked) spectra are more common and where fluxes below ~500 eV are largely independent of SW pressure, (3) permanent plasma voids, and (4) intermittent plasma voids where fluxes depend strongly on SW pressure. The locations, sizes, shapes, and absence/existence of these plasma voids vary significantly with solar wind pressure proxy and moderately with IMF proxy direction; average precipitating fluxes are 40% lower in strong crustal field regions and 15% lower globally for approximately southwest proxy directions compared with approximately northeast directions. This variation of the strength and geographic pattern of the shielding effect of Mars' crustal fields exemplifies the complex interaction between those fields and the solar wind.
Key Points
Mars' crustal fields control electron precipitation patterns on the nightside
These patterns are affected by the solar wind pressure and IMF direction
Electron fluxes in “intermittent plasma voids” vary by 3–4 orders of magnitude
The localized crustal magnetic fields of Mars play an important role in the planet’s ionosphere‐solar wind interaction. Various physical processes in the induced magnetosphere, such as particle ...precipitation, field‐aligned currents, and ion outflow, are usually associated with the crustal magnetic cusp regions, where field lines are mostly vertical and open to space. Due to the small spatial scale (a few hundred km) of the Martian crustal magnetic cusps, localized models with high spatial resolutions and ion kinetics are needed to understand the physical processes. We adapt the simulation platform HYB developed at the Finnish Meteorological Institute to a moderately strong magnetic cusp above the Martian exobase with a 2‐D simulation domain assuming periodic boundary conditions on the third dimension. Two plasma sources are included in the simulation: hot protons from the induced magnetosphere and cold heavy ions (O+) from the ionosphere. Our model results can qualitatively reproduce the vertical electric potential drop, particle transport, and field aligned current in the cusp region. The vertical electric potential is built up mostly by the Hall electric field as a result of the separation between ion and electron fluxes of the downward plasma flow. By varying the model inputs, we found that the vertical potential drop depends on ionospheric ion density and magnetic field strength. These results tell us that energy is transferred from magnetospheric plasma to ionospheric plasma through the vertical electric potential buildup in magnetic cusps and how this process may affect electron precipitation, ion escape, and ionosphere conditions at Mars.
Key Points
A hybrid model qualitatively reproduced the vertical potential drop and field aligned currents in Martian crustal magnetic cusp regions
The vertical electric potential drop is mostly from the Hall electric field as a result of energy input from the downward plasma flow
The vertical electric potential drop decreases with ionospheric ion density and increases with magnetic field strength
Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field ...(IMF) BY. We find that the magnetotail lobes exhibit a ~45deg twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross-tail current sheet is rotated away from the expected location for a Venus-like induced magnetotail based on nominal IMF draping. Data-model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth.
Direct interaction between the solar wind (SW) and the Martian upper atmosphere forms a characteristic region, called the induced magnetosphere between the magnetosheath and the ionosphere. Since the ...SW deceleration due to increasing mass loading by heavy ions plays an important role in the induced magnetosphere formation, the ion composition is also expected to change around the induced magnetosphere boundary (IMB). Here we report on relations of the IMB, the ion composition boundary (ICB), and the pressure balance boundary based on a statistical analysis of about 8 months of simultaneous ion, electron, and magnetic field observations by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We chose the period when MAVEN observed the SW directly near its apoapsis to investigate their dependence on SW parameters. Results show that IMBs almost coincide with ICBs on the dayside and locations of all three boundaries are affected by the SW dynamic pressure. A remarkable feature is that all boundaries tend to locate at higher altitudes in the southern hemisphere than in the northern hemisphere on the nightside. This clear geographical asymmetry is permanently seen regardless of locations of the strong crustal B fields in the southern hemisphere, while the boundary locations become higher when the crustal B fields locate on the dayside. On the nightside, IMBs usually locate at higher altitude than ICBs. However, ICBs are likely to be located above IMBs in the nightside, southern, and downward ESW hemisphere when the strong crustal B fields locate on the dayside.
Key Points
Locations of boundaries (the IMB, the ICB, and the β∗) at Mars show a north‐south asymmetry mainly on the nightside
IMBs coincide with ICBs on the dayside, and all boundaries depend on the SW dynamic pressure and the southern crustal B fields
IMBs and ICBs tend to be located at high altitudes in the nightside, southern, and downward ESW hemisphere
The interaction between Mars and the solar wind results in different plasma regimes separated by several boundaries, among which the separation between the sheath flow and the ionosphere is ...complicated. Previous studies have provided different and sometimes opposite findings regarding this region. In this study, we utilize observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission to revisit boundaries within this region and perhaps reconcile some differences. More specifically, we start with the photoelectron boundary (PEB), a topological boundary that separates magnetic field lines having access to the dayside ionosphere (open or closed) from those connected to the solar wind on both ends (draped). We find that large gradients in the planetary ion densiti occur across the PEB and that the dominant ion switches from heavy planetary ions to protons near the PEB, indicating that the PEB falls within the ion composition boundary (ICB). Furthermore, our results show that the PEB is not a pressure balance boundary; rather the magnetic pressure dominates both sides of the PEB. Meanwhile, we find that the PEB is located where the shocked solar wind flow stops penetrating deeper into the ionosphere. These findings suggest the PEB marks the top of the Mars dayside ionosphere and also the interface where the sheath plasma flow deflects around the obstacle going downstream.
Key Points
Large gradients in planetary ion density occur across the photoelectron boundary (PEB) and the PEB falls within the ion composition boundary
The PEB can be considered as the top of the Mars dayside ionosphere
The PEB is not a pressure balance boundary but is located where the shocked sheath flow is diverted around the ionosphere
We outline an ambitious project to characterize the genetic and epigenetic regulation of multiple facets of transcription in distinct brain regions across the human lifespan in samples of major ...neuropsychiatric disorders and controls. Initially focused on schizophrenia and mood disorders, the goal of this consortium is to elucidate the underlying molecular mechanisms of genetic associations with the goal of identifying novel therapeutic targets. The consortium currently consists of seven pharmaceutical companies and a not-for-profit medical research institution working as a precompetitive team to generate and analyze publicly available archival brain genomic data related to neuropsychiatric illness.
The BrainSeq precompetitive consortium of seven pharmaceutical companies harnesses genomics, transcriptomics, and epigenomics from multiple brain regions across the human lifespan for spatio-temporal analyses of molecular mechanisms associated with psychiatric risk loci, empowering finding therapeutic solutions for psychiatric disorders.
We analyzed Mars Atmosphere and Volatile Evolution (MAVEN) and Venus Express (VEX) data of magnetic flux ropes observed in both Mars and Venus nightside induced magnetosphere, in order to understand ...their statistical characteristics and possible formation processes. We statistically identified 382 (286) events at Mars (Venus) via the minimum variance analysis and investigated the flux rope properties including their geometrical configurations of axial core field direction and spatial distributions. Interestingly, there is no significant difference with respect to the variety of the flux rope axial orientation between Mars and Venus, indicating that about at least one fourth of events do not necessitate magnetotail reconnection for their formations. However, the spatial distribution shows that flux ropes at Venus tend to be observed near the central plasma sheet, whereas those at Mars are more spread out. Moreover, the events tend to be observed more frequently in the −E hemisphere, where the solar wind electric field (ESW) is pointing toward the planet, rather than in +E hemisphere, where the ESW direction is away from the planet. The geographical distribution shows that flux ropes at Mars tend to be observed more frequently in the southern hemisphere where the strong crustal magnetic fields are primarily distributed. Therefore, such a tendency indicates that the Martian crustal magnetic fields could play significant roles on generating flux ropes in the nightside magnetosphere of Mars.
Key Points
We statistically investigated how to create flux ropes in the nightside magnetosphere of Mars and Venus
We found the similar variety of the flux ropes axial orientation between Mars and Venus
Flux ropes in Mars magnetotail concentrate above the strong crustal magnetic field region
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