Uncovering the magnetic environment of our solar system

Since its formation 4.6 billion years ago, our solar system has most likely crossed numerous magnetized interstellar clouds and bubbles of different sizes and contents on its path through the Milky Way. Having a reference model for how the heliosphere and interstellar winds interact is critical for understanding our current Galactic environment, and it requires untangling the roles of two major actors: the time-variable solar wind and the local interstellar magnetic field. Numerical simulations predict a distortion of the heliosphere caused by both solar wind anisotropy and interstellar magnetic field orientation. However, model comparison to deep space probes' measurements led to contradictory reports by Voyager 1 and Voyager 2 of both several crossings of the solar wind's termination shock and of the strength of the local interstellar field, with values ranging from 1.8 to 5.7 {\mu}G. Here, we show that Voyager 1 & 2 plasma, fields, and Lyman-{\alpha} sky background measurements, as well as space observations of high-energy particles of heliospheric origin, may all be explained by a rather weak interstellar field 2.2 +/- 0.1 {\mu}G pointing from Galactic coordinates (l,b) \sim (28, 52)+/- 3{\deg}. For the 2000 epoch Ulysses-based helium parameters assumed thus far, the interstellar bow shock must exist. By contrast, using the 2010 epoch IBEX-based He parameters and a stronger magnetic field leads to a plasma configuration that is not consistent with the Voyagers TS crossings. For the newly proposed interstellar He parameters, more simulations are required before one may determine whether the interstellar bow shock truly does disappear under those assumptions.Comment: 5 pages, 5 figures, in press in Astron. & Astrophy

Spectral, Spatial, and Time properties of the hydrogen nebula around exoplanet HD209458b

All far ultraviolet observations of HD209458 tend to support a scenario in which the inflated hydrogen atmosphere of its planetary companion strongly absorbs the stellar \lya flux during transit. However, it was not clear how the transit absorption depends on the selected wavelength range in the stellar line profile, nor how the atomic hydrogen cloud was distributed spatially around HD209458b. Here we report a sensitivity study of observed time and spectral variations of the stellar flux. In particular, the sensitivity of the absorption depth during transit to the assumed spectral range in the stellar line profile is shown to be very weak, leading to a transit depth in the range $(8.4-8.9)$ for all possible wavelength ranges, and thereby confirming our initially-reported absorption rate. Taking the ratio of the line profile during transit to the unperturbed line profile, we also show that the spectral signature of the absorption by the exoplanetary hydrogen nebula is symmetric and typical of a Lorentzian, optically thick medium. Our results question the adequacy of models that require a huge absorption and/or a strong asymmetry between the blue and red side of the absorption line during transit as no such features could be detected in the HST FUV absorption profile. Finally, we show that standard atmospheric models of HD209458b provide a good fit to the observed absorption profile during transit. Other hybrid models assuming a standard model with a thin layer of superthermal hydrogen on top remain possible.Comment: 10 pages, 7 figures, accepted for publication in Astrophysical Journa

Exoplanet HD209458b: inflated hydrogen atmosphere but no sign of evaporation

Many extrasolar planets orbit closely to their parent star. Their existence raises the fundamental problem of loss and gain in their mass. For exoplanet HD209458b, reports on an unusually extended hydrogen corona and a hot layer in the lower atmosphere seem to support the scenario of atmospheric inflation by the strong stellar irradiation. However, difficulties in reconciling evaporation models with observations call for a reassessment of the problem. Here, we use HST archive data to report a new absorption rate of ~8.9% +/- 2.1% by atomic hydrogen during the HD209458b transit, and show that no sign of evaporation could be detected for the exoplanet. We also report evidence of time variability in the HD209458 Lyman-a flux, a variability that was not accounted for in previous studies, which corrupted their diagnostics. Mass loss rates thus far proposed in the literature in the range 5x(10^{10}-10^{11} g s^{-1}) must induce a spectral signature in the Lyman-a line profile of HD209458 that cannot be found in the present analysis. Either an unknown compensation effect is hiding the expected spectral feature or else the mass loss rate of neutrals from HD209458 is modest.Comment: corrected for typos. Published 2007 December 10 in Apj

On the existence of energetic atoms in the upper atmosphere of exoplanet HD209458b

Stellar irradiation and particles forcing strongly affect the immediate environment of extrasolar giant planets orbiting near their parent stars. Here, we use far-ultraviolet emission spectra from HD209458 in the wavelength range (1180-1710)A to bring new insight to the composition and energetic processes in play in the gas nebula around the transiting planetary companion. In that frame, we consider up-to-date atmospheric models of the giant exoplanet where we implement non-thermal line broadening to simulate the impact on the transit absorption of superthermal atoms (HI, OI, and CII) populating the upper layers of the nebula. Our sensitivity study shows that for all existing models, a significant line broadening is required for OI and probably for CII lines in order to fit the observed transit absorptions. In that frame, we show that OI and CII are preferentially heated compared to the background gas with effective temperatures as large as T_{OI}/T_B~10 for OI and T_{CII}/T_B~5 for CII. By contrast, the situation is much less clear for HI because several models could fit the Lyman-a observations including either thermal HI in an atmosphere that has a dayside vertical column [HI]~1.05x10^{21} cm^{-2}, or a less extended thermal atmosphere but with hot HI atoms populating the upper layers of the nebula. If the energetic HI atoms are either of stellar origin or populations lost from the planet and energized in the outer layers of the nebula, our finding is that most models should converge toward one hot population that has an HI vertical column in the range [HI]_{hot}(2-4)x10^{13} cm^{-2} and an effective temperature in the range T_{HI}(1-1.3)x10^6 K, but with a bulk velocity that should be rather slow.Comment: 15 pages, 10 figures, corrected for typos, references remove

Saturn's atmospheric response to the large influx of ring material inferred from Cassini INMS measurements

During the Grand Finale stage of the Cassini mission, organic-rich ring material was discovered to be flowing into Saturn's equatorial upper atmosphere at a surprisingly large rate. Through a series of photochemical models, we have examined the consequences of this ring material on the chemistry of Saturn's neutral and ionized atmosphere. We find that if a substantial fraction of this material enters the atmosphere as vapor or becomes vaporized as the solid ring particles ablate upon atmospheric entry, then the ring-derived vapor would strongly affect the composition of Saturn's ionosphere and neutral stratosphere. Our surveys of Cassini infrared and ultraviolet remote-sensing data from the final few years of the mission, however, reveal none of these predicted chemical consequences. We therefore conclude that either (1) the inferred ring influx represents an anomalous, transient situation that was triggered by some recent dynamical event in the ring system that occurred a few months to a few tens of years before the 2017 end of the Cassini mission, or (2) a large fraction of the incoming material must have been entering the atmosphere as small dust particles less than ~100 nm in radius, rather than as vapor or as large particles that are likely to ablate. Future observations or upper limits for stratospheric neutral species such as HC$_3$N, HCN, and CO$_2$ at infrared wavelengths could shed light on the origin, timing, magnitude, and nature of a possible vapor-rich ring-inflow event.Comment: accepted in Icaru

Methodes numeriques pour la resolution de l'equation de transfert radiatif : application a l'etude de l'emission Lyman-alpha de Jupiter et d'Uranus en geometrie plan parallele : proposition de la methode spectrale pour la resolution de l'equation..

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Study of the interaction of the solar wind and the earth magnetosphere (theoretical model and application on the Halloween event data of october 2003)

Une nouvelle approche, utilisant un code électromagnétique en 3D (PIC), est présentée pour étudier la sensibilité de la magnétosphère de la terre à la variabilité du vent solaire. Avec un vent solaire empiétant sur une terre magnétisée, le temps a été laissé au système pour atteindre une structure magnétosphérique à l'état d'équilibre. Par la suite, afin de simuler une dépression dans la pression dynamique du vent solaire, une perturbation impulsive a été appliquée au système en changeant la vitesse du vent solaire, pour un champ magnétique interplanétaire(IMF) inexistant, orienté nord ou sud respectivement. La perturbation appliquée induit un effet de trou d'air qui pourrait être décrit comme un espace quasi-vide de largeur ~15Re, et qui est formé pour tous les cas de IMF. Dès que le trou d air atteint le bow shock de la magnétosphère régulière, une reconnexion entre le champ magnétique de la terre et le IMF sud a été notée sur le coté jour de la magnétopause(MP). Pendant la phase d'expansion du système, la frontière externe de la MP s est brisée côté jour lorsque l IMF=0, mais a conservé sa forme de balle pour un IMF orienté sud ou nord. Le temps de relaxation de la MP a été étudie par la suite pour les trois cas de IMF. Le code est finalement appliqué pour étudier l'événement d Halloween de l activité solaire en octobre 2003. Notre simulation a généré dans ce cas un espace raréfié, une sorte de trou d air, qui a été produit suite un gradient fort dans l IMF appliqué. Une telle structure est tout à fait semblable à l anomalie d écoulement chaud et peut en avoir la même originePARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF