Entropy Generation Across Earth's Bow Shock

Earth's bow shock is a transition layer that causes an irreversible change in the state of plasma that is stationary in time. Theories predict entropy increases across the bow shock but entropy has never been directly measured. Cluster and Double Star plasma experiments measure 3D plasma distributions upstream and downstream of the bow shock that allow calculation of Boltzmann's entropy function H and his famous H-theorem, dH/dt ~ O. We present the first direct measurements of entropy density changes across Earth's bow shock. We will show that this entropy generation may be part of the processes that produce the non-thermal plasma distributions is consistent with a kinetic entropy flux model derived from the collisionless Boltzmann equation, giving strong support that solar wind's total entropy across the bow shock remains unchanged. As far as we know, our results are not explained by any existing shock models and should be of interests to theorists

Etude du champ magnétique et de l'environnement ionisé de la planète Mars à l'aide de la sonde Mars global surveyor

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Interactions of the heliospheric current and plasma sheets with the bow shock: Cluster and Polar observations in the magnetosheath

On 12 March 2001, the Polar and Cluster spacecraft were at subsolar and cusp latitudes in the dayside magnetosheath, respectively, where they monitored the passage by Earth of a large-scale planar structure containing the high-density heliospheric plasma sheet (HPS) and the embedded current sheet. Over significant intervals, as the magnetic hole of the HPS passed Cluster and Polar, magnetic field strengths ∣B∣ were much smaller than expected for the shocked interplanetary magnetic field. For short periods, ∣B∣ even fell below values measured by ACE in the upstream solar wind. Within the magnetic hole the ratio of plasma thermal and magnetic pressures (plasma β) was consistently \u3e100 and exceeded 1000. A temporary increase in lag times for identifiable features in B components to propagate from the location of ACE to those of Cluster and Polar was associated with the expansion (and subsequent compression) of the magnetic field and observed low ∣B∣. Triangulation of the propagation velocity of these features across the four Cluster spacecraft configuration showed consistency with the measured component of ion velocity normal to the large-scale planar structure. B experienced large-amplitude wave activity, including fast magnetosonic waves. Within the low ∣B∣ region, guiding center behavior was disrupted and ions were subject to hydrodynamic rather than magnetohydrodynamic forcing. Under the reported conditions, a significant portion of the interplanetary coupling to the magnetosphere should proceed through interaction with the low-latitude boundary layer. Data acquired during a nearly simultaneous high-latitude pass of a Defense Meteorological Satellites Program satellite are consistent with this conjecture

Inventory of Volatiles in the Coma of Comet 67P/Churyumov-Gerasimenko from Rosetta ROSINA – An Overview of First Results

International audienceThe European Space Agency’s Rosetta spacecraft is now close in a bound orbit around comet 67P/Churyumov-Gerasimenko (67P/C-G). On board is the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument suite. ROSINA consists of two mass spectrometers, the Double Focusing Mass Spectrometer (DFMS) and the Reflectron-type Time-Of-Flight (RTOF), as well as the COmet Pressure Sensor (COPS). ROSINA is designed to detect and monitor the neutral gas and thermal plasma environment in the comet’s coma by in situ investigation. The two mass spectrometers have high dynamic ranges and complement each other with high mass resolution (DFMS) and high time resolution and large mass range (RTOF). Especially the unprecedented sensitivity and mass resolution of DFMS together with the large mass range of RTOF will allow determining precisely light species (e.g. isotopologues) as well as detecting heavy organics. The pressure sensor COPS is capable to derive total gas densities, velocities, and temperatures. To date only limited data for the composition of cometary comae at heliocentric distances of more than 2.5 AU are available. The set is dominated by CO and daughter species of water from bright comets originating in the Oort cloud. While some molecules can be detected from far by remote sensing (e.g. CO) other molecules are much more difficult to observe from ground (e.g. CO2). The Rosetta mission presents a unique opportunity to directly probe the parent species in the thin cometary atmosphere of a Kuiper-belt object at more than 2.5 AU from the Sun and relate it to ground-based observations. Distances that far from the Sun are of particular interest as the comet’s activity transitions from being super volatiles dominated to being water dominated. We will report on the first measurements of the volatile inventory obtained from ROSINA observations as Rosetta is following comet 67P/C-G in close vicinity