104 results found
Beth A, Galand MIF, 2018, Effects of the convective field on weakly outgassing comets., Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S824-S841, ISSN: 0035-8711
By applying a kinetic approach, we have developed two models in order to assess the influence of one main driver of plasma acceleration, the convective electric field, on the cometary ion distribution at 67P/Churyumov-Gerasimenko (67P/C-G). This electric field is carried by the solar wind and corresponds to the acceleration undergone by cometary ions ultimately picked up. We have quantified its contribution on ion number density and mean velocity profiles, supported by an intercomparison with the recent literature. We found that the ion number density should reflect a departure from the observed ∼1/r law. We discuss reasons for this discrepancy.
Heritier KL, Altwegg K, Berthelier J-J, et al., 2018, On the origin of molecular oxygen in cometary comae., Nat Commun, Vol: 9
Moore L, Galand M, Kliore AJ, et al., 2018, Saturn's Ionosphere, Saturn in the 21st Century, Editors: Baines, Publisher: Cambridge University Press
This chapter summarizes our current understanding of the ionosphere ofSaturn. We give an overview of Saturn ionospheric science from the Voyager erato the present, with a focus on the wealth of new data and discoveries enabledby Cassini, including a massive increase in the number of electron densityaltitude profiles. We discuss recent ground-based detection of the effect of"ring rain" on Saturn's ionosphere, and present possible model interpretationsof the observations. Finally, we outline current model-data discrepancies andindicate how future observations can help in advancing our understanding of thevarious controlling physical and chemical processes.
Chadney JM, Koskinen TT, Galand M, et al., 2017, Effect of stellar flares on the upper atmospheres of HD 189733b and HD 209458b, ASTRONOMY & ASTROPHYSICS, Vol: 608, ISSN: 1432-0746
Eriksson AI, Engelhardt IAD, Andre M, et al., 2017, Cold and warm electrons at comet 67P/Churyumov-Gerasimenko, ASTRONOMY & ASTROPHYSICS, Vol: 605, ISSN: 1432-0746
Hajra R, Henri P, Vallieres X, et al., 2017, Impact of a cometary outburst on its ionosphere Rosetta Plasma Consortium observations of the outburst exhibited by comet 67P/Churyumov-Gerasimenko on 19 February 2016, ASTRONOMY & ASTROPHYSICS, Vol: 607, ISSN: 1432-0746
Henri P, Vallières X, Hajra R, et al., 2017, Diamagnetic region(s): structure of the unmagnetized plasma around Comet 67P/CG, Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S372-S379, ISSN: 0035-8711
The ESA’s comet chaser Rosetta has monitored the evolution of the ionized atmosphere of comet 67P/Churyumov–Gerasimenko (67P/CG) and its interaction with the solar wind, during more than 2 yr. Around perihelion, while the cometary outgassing rate was highest, Rosetta crossed hundreds of unmagnetized regions, but did not seem to have crossed a large-scale diamagnetic cavity as anticipated. Using in situ Rosetta observations, we characterize the structure of the unmagnetized plasma found around comet 67P/CG. Plasma density measurements from RPC-MIP are analysed in the unmagnetized regions identified with RPC-MAG. The plasma observations are discussed in the context of the cometary escaping neutral atmosphere, observed by ROSINA/COPS. The plasma density in the different diamagnetic regions crossed by Rosetta ranges from ∼100 to ∼1500 cm−3. They exhibit a remarkably systematic behaviour that essentially depends on the comet activity and the cometary ionosphere expansion. An effective total ionization frequency is obtained from in situ observations during the high outgassing activity phase of comet 67P/CG. Although several diamagnetic regions have been crossed over a large range of distances to the comet nucleus (from 50 to 400 km) and to the Sun (1.25–2.4 au), in situ observations give strong evidence for a single diamagnetic region, located close to the electron exobase. Moreover, the observations are consistent with an unstable contact surface that can locally extend up to about 10 times the electron exobase.
Heritier KL, Altwegg K, Balsiger H, et al., 2017, Ion composition at comet 67P near perihelion: Rosetta observations and model-based interpretation, Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S427-S442, ISSN: 0035-8711
We present the ion composition in the coma of comet 67P with newly detected ion species over the 28–37 u mass range, probed by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Double Focusing Mass Spectrometer (DFMS). In summer 2015, the nucleus reached its highest outgassing rate and ion-neutral reactions started to take place at low cometocentric distances. Minor neutrals can efficiently capture protons from the ion population, making the protonated version of these neutrals a major ion species. So far, onlyNH+4has been reported at comet 67P. However, there are additional neutral species with proton affinities higher than that of water (besides NH3) that have been detected in the coma of comet 67P: CH3OH, HCN, H2CO and H2S. Their protonated versions have all been detected. Statistics showing the number of detections with respect to the number of scans are presented. The effect of the negative spacecraft potential probed by the Rosetta Plasma Consortium/LAngmuir Probe on ion detection is assessed. An ionospheric model has been developed to assess the different ion density profiles and compare them to the ROSINA/DFMS measurements. It is also used to interpret the ROSINA/DFMS observations when different ion species have similar masses, and their respective densities are not high enough to disentangle them using the ROSINA/DFMS high-resolution mode. The different ion species that have been reported in the coma of 67P are summarized and compared with the ions detected at comet 1P/Halley during the Giotto mission.
Heritier KL, Henri P, Vallières X, et al., 2017, Vertical structure of the near-surface expanding ionosphere of comet 67P probed by Rosetta, Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S118-S129, ISSN: 0035-8711
During the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's deep-dip #2 campaign of 17–22 April 2015, spacecraft instruments observed all of the physical parameters needed to assess the photo-chemical-equilibrium (PCE) explanation for ionospheric variability at a fixed altitude (135 km) near the peak of the Martian ionosphere. MAVEN measurements of electron density, electron temperature, neutral CO2 density, and solar irradiance were collected during 28 orbits. When inserted into the PCE equation, the measurements of varying PCE drivers correlated with the observed electron density variations to within instrumental uncertainty levels. The dominant source of this positive correlation was the variability of CO2 densities associated with the longitudinal wave-2 component of nonmigrating tides in the Martian thermosphere.
Nilsson H, Wieser GS, Behar E, et al., 2017, Evolution of the ion environment of comet 67P during the Rosetta mission as seen by RPC-ICA, Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S252-S261, ISSN: 0035-8711
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.
Vigren E, Altwegg K, Edberg NJT, et al., 2017, MODEL-OBSERVATION COMPARISONS OF ELECTRON NUMBER DENSITIES IN THE COMA OF 67P/CHURYUMOV-GERASIMENKO DURING 2015 JANUARY (vol 152, 59, 2016), ASTRONOMICAL JOURNAL, Vol: 153, ISSN: 0004-6256
Vigren E, André M, Edberg NJT, et al., 2017, Effective ion speeds at ∼200–250 km from comet 67P/Churyumov–Gerasimenko near perihelion, Monthly Notices of the Royal Astronomical Society, Vol: 469, Pages: S142-S148, ISSN: 0035-8711
In 2015 August, comet 67P/Churyumov–Gerasimenko, the target comet of the ESA Rosetta mission, reached its perihelion at ∼1.24 au. Here, we estimate for a three-day period near perihelion, effective ion speeds at distances ∼200–250 km from the nucleus. We utilize two different methods combining measurements from the Rosetta Plasma Consortium (RPC)/Mutual Impedance Probe with measurements either from the RPC/Langmuir Probe or from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Comet Pressure Sensor (COPS) (the latter method can only be applied to estimate the effective ion drift speed). The obtained ion speeds, typically in the range 2–8 km s−1, are markedly higher than the expected neutral outflow velocity of ∼1 km s−1. This indicates that the ions were de-coupled from the neutrals before reaching the spacecraft location and that they had undergone acceleration along electric fields, not necessarily limited to acceleration along ambipolar electric fields in the radial direction. For the limited time period studied, we see indications that at increasing distances from the nucleus, the fraction of the ions’ kinetic energy associated with radial drift motion is decreasing.
Beth A, Altwegg K, Balsiger H, et al., 2016, First in situ detection of the cometary ammonium ion NH4+ (protonated ammonia NH3) in the coma of 67P/C-G near perihelion, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 462, Pages: S562-S572, ISSN: 0035-8711
Chadney JM, Galand M, Koskinen TT, et al., 2016, EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars, ASTRONOMY & ASTROPHYSICS, Vol: 587, ISSN: 1432-0746
Fuselier SA, Altwegg K, Balsiger H, et al., 2016, Ion chemistry in the coma of comet 67P near perihelion, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 462, Pages: S67-S77, ISSN: 0035-8711
Galand M, Heritier KL, Odelstad E, et al., 2016, Ionospheric plasma of comet 67P probed by Rosetta at 3 au from the Sun, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 462, Pages: S331-S351, ISSN: 0035-8711
Grun E, Agarwal J, Altobelli N, et al., 2016, The 2016 Feb 19 outburst of comet 67P/CG: an ESA Rosetta multi-instrument study, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 462, Pages: S220-S234, ISSN: 0035-8711
Mandt KE, Eriksson A, Edberg NJT, et al., 2016, RPC observation of the development and evolution of plasma interaction boundaries at 67P/Churyumov-Gerasimenko, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 462, Pages: S9-S22, ISSN: 0035-8711
Moore L, Stallard T, Galand MIF, 2016, Upper atmospheres of the giant planets, Heliophysics: Active Stars, their Astrospheres, and Impacts on Planetary Environments, Editors: Schrijver, Bagenal, Sojka, Publisher: Cambridge University Press, Pages: 175-200, ISBN: 9781107090477
Raghuram S, Bhardwaj A, Galand M, 2016, PREDICTION OF FORBIDDEN ULTRAVIOLET AND VISIBLE EMISSIONS IN COMET 67P/CHURYUMOV-GERASIMENKO, ASTROPHYSICAL JOURNAL, Vol: 818, ISSN: 0004-637X
Vigren E, Altwegg K, Edberg NJT, et al., 2016, MODEL-OBSERVATION COMPARISONS OF ELECTRON NUMBER DENSITIES IN THE COMA OF 67P/CHURYUMOV-GERASIMENKO DURING 2015 JANUARY, ASTRONOMICAL JOURNAL, Vol: 152, ISSN: 0004-6256
Vigren E, Galand M, Wellbrock A, et al., 2016, SUPRATHERMAL ELECTRONS IN TITAN'S SUNLIT IONOSPHERE: MODEL-OBSERVATION COMPARISONS, ASTROPHYSICAL JOURNAL, Vol: 826, ISSN: 0004-637X
Badman SV, Branduardi-Raymont G, Galand M, et al., 2015, Auroral Processes at the Giant Planets: Energy Deposition, Emission Mechanisms, Morphology and Spectra, SPACE SCIENCE REVIEWS, Vol: 187, Pages: 99-179, ISSN: 0038-6308
Chadney JM, Galand M, Unruh YC, et al., 2015, XUV-driven mass loss from extrasolar giant planets orbiting active stars, ICARUS, Vol: 250, Pages: 357-367, ISSN: 0019-1035
Cui J, Galand M, Yelle RV, et al., 2015, Day-to-night transport in the Martian ionosphere: Implications from total electron content measurements, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 2333-2346, ISSN: 2169-9380
Cui J, Galand M, Zhang SJ, et al., 2015, The electron thermal structure in the dayside Martian ionosphere implied by the MGS radio occultation data, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 120, Pages: 278-286, ISSN: 2169-9097
Fuselier SA, Altwegg K, Balsiger H, et al., 2015, ROSINA/DFMS and IES observations of 67P: Ion-neutral chemistry in the coma of a weakly outgassing comet, ASTRONOMY & ASTROPHYSICS, Vol: 583, ISSN: 1432-0746
Haessig M, Altwegg K, Balsiger H, et al., 2015, Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko, SCIENCE, Vol: 347, ISSN: 0036-8075
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