Oxygen Ion Energization Observed At High Altitudes

We present a case study of significant heating (up to 8 keV) perpendicular to the geomagnetic field of outflowing oxygen ions at high altitude (12 RE) above the polar cap. The shape of the distribution functions indicates that most of the heating occurs locally (within 0.2–0.4 RE in altitude). This is a clear example of local ion energization at much higher altitude than usually reported. In contrast to many events at lower altitudes, it is not likely that the locally observed wave fields can cause the observed ion energization. Also, it is not likely that the ions have drifted from some nearby energization region to the point of observation. This suggests that additional fundamentally different ion energization mechanisms are present at high altitudes. One possibility is that the magnetic moment of the ions is not conserved, resulting in slower outflow velocities and longer time for ion energization

The Hydrogen Exospheric Density Profile Measured with ASPERA-3/NPD

We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F10.7=100). We derive estimates for the hydrogen exobase density, n H = 1010 m−3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activit

Faire l’Union. La refondation des parties de droite après les élections de 2002

Un nouveau parti de droite, pour le moment dénommé UMP, a été mis en place entre des deux tours de l'élection présidentielle. Cet article se donne pour objectif d'analyser les enjeux de cette transformation. La genèse de l'UMP permet de saisir dans quelle mesure un parti poli-tique peut être conçu comme la connexion d'un ensemble de systèmes de coopération organisés autour de postes à conquérir. En effet, l'impératif d'unification de la droite française est lié au décalage persistant existant entre les systèmes de coopération législatif et présidentiel. Mais les questions soulevées par cette fusion partisane (l'UMP inclut le RPR, DL et une majeure partie de l'UDF) montrent que cette vision ne peut suffire et que les partis ne sont pas seulement des systèmes de coopération mais aussi des systèmes de production. Dès lors, leurs logiques d'organisation internes pèsent sur ce travail de transformation du social en politique, de la plu-ralité en homogénéité. Dans le cas de l'UMP, il s'agit d'abord de mettre en commun des modes de fonctionnement, en particulier de définir la place et la légitimité accordées respectivement aux adhérents et aux élus, mais aussi d'organiser l'expression de la pluralité idéologique par la mise en place de courants

First investigation of the diamagnetic cavity boundary layer with a 1D3V PIC simulation

Context. Amongst the different features and boundaries encountered around comets, one remains of particular interest to the plasma community: The diamagnetic cavity. Crossed for the first time at 1P/Halley during the Giotto flyby in 1986 and later met more than 700 times by the ESA Rosetta spacecraft around Comet 67P/Churyumov-Gerasimenko, this region, almost free of any magnetic field, surrounds nuclei of active comets. However, previous observations and modelling of this part of the coma have not yet provided a definitive answer as to the origin of such a cavity and on its border, the diamagnetic cavity boundary layer. Aims. We investigate which forces and equilibrium might be at play and balance the magnetic pressure at this boundary down to the spatial and temporal scales of the electrons in the 1D collisionless case. In addition, we scrutinise assumptions made in magneto-hydrodynamic and hybrid simulations of this environment and check for their validity. Methods. We simulated this region at the electron scale by means of 1D3V particle-in-cell simulations and SMILEI code. Results. Across this layer, depending on the magnetic field strength, the electric field is governed by different equilibria, with a thin double-layer forming ahead. In addition, we show that the electron distribution function departs from Maxwellian and/or gyrotropic distributions and that electrons do not behave adiabatically. We demonstrate the need to investigate this region at the electron scale in depth with fully kinetic simulations

Evolution of the ion environment of comet 67P during the Rosetta mission as seen by RPC-ICA

Rosetta has followed comet 67P from low activity at more than 3.6 au heliocentric distance to high activity at perihelion (1.24 au) and then out again. We provide a general overview of the evolution of the dynamic ion environment using data from the RPC-ICA ion spectrometer. We discuss where Rosetta was located within the evolving comet magnetosphere. For the initial observations, the solar wind permeated all of the coma. In 2015 mid-April, the solar wind started to disappear from the observation region, to re-appear again in 2015 December. Low-energy cometary ions were seen at first when Rosetta was about 100 km from the nucleus at 3.6 au, and soon after consistently throughout the mission except during the excursions to farther distances from the comet. The observed flux of low-energy ions was relatively constant due to Rosetta's orbit changing with comet activity. Accelerated cometary ions, moving mainly in the antisunward direction gradually became more common as comet activity increased. These accelerated cometary ions kept being observed also after the solar wind disappeared from the location of Rosetta, with somewhat higher fluxes further away from the nucleus. Around perihelion, when Rosetta was relatively deep within the comet magnetosphere, the fluxes of accelerated cometary ions decreased, as did their maximum energy. The disappearance of more energetic cometary ions at close distance during high activity is suggested to be due to a flow pattern where these ions flow around the obstacle of the denser coma or due to charge exchange losses

In Situ Observations of a Magnetosheath High-Speed Jet Triggering Magnetopause Reconnection

Magnetosheath high‐speed jets—localized dynamic pressure enhancements typically of ∼1 Earth radius in size—impact the dayside magnetopause several times per hour. Here we present the first in situ measurements suggesting that such an impact triggered magnetopause reconnection. We use observations from the five Time History of Events and Macroscale Interactions during Substorms spacecraft in a string‐of‐pearls configuration on 7 August 2007. The spacecraft recorded magnetopause in‐and‐out motion during an impact of a magnetosheath jet (VN∼−300 km/s along the magnetopause normal direction). There was no evidence for reconnection for the preimpact crossing, yet three probes observed reconnection after the impact. We infer that the jet impact compressed the originally thick (60–70 di), high magnetic shear (140–160° magnetopause until it was thin enough for reconnection to occur. Magnetosheath high‐speed jets could therefore act as a driver for bursty dayside reconnection

Birth of a comet magnetosphere: A spring of water ions

The Rosetta mission shall accompany comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 astronomical units through perihelion passage at 1.25 astronomical units, spanning low and maximum activity levels. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation, until the size and plasma pressure of the ionized atmosphere define its boundaries: A magnetosphere is born. Using the Rosetta Plasma Consortium ion composition analyzer, we trace the evolution from the first detection of water ions to when the atmosphere begins repelling the solar wind (~3.3 astronomical units), and we report the spatial structure of this early interaction. The near-comet water population comprises accelerated ions (<800 electron volts), produced upstream of Rosetta, and lower energy locally produced ions; we estimate the fluxes of both ion species and energetic neutral atoms