115 results found
Beth A, Galand M, Heritier K, Comparative study of photo-produced ionosphere in the close environment of comets, Astronomy & Astrophysics, ISSN: 0004-6361
Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using know
Hajra R, Henri P, Myllys M, et al., 2018, Cometary plasma response to interplanetary corotating interaction regions during 2016 June-September: a quantitative study by the Rosetta Plasma Consortium, Monthly Notices of the Royal Astronomical Society, Vol: 480, Pages: 4544-4556, ISSN: 0035-8711
Four interplanetary corotating interaction regions (CIRs) were identified during 2016 June–September by the Rosetta Plasma Consortium (RPC) monitoring in situ the plasma environment of the comet 67P/Churyumov–Gerasimenko (67P) at heliocentric distances of ∼3–3.8 au. The CIRs, formed in the interface region between low- and high-speed solar wind streams with speeds of ∼320–400 km s−1 and ∼580–640 km s−1, respectively, are characterized by relative increases in solar wind proton density by factors of ∼13–29, in proton temperature by ∼7–29, and in magnetic field by ∼1–4 with respect to the pre-CIR values. The CIR boundaries are well defined with interplanetary discontinuities. Out of 10 discontinuities, four are determined to be forward waves and five are reverse waves, propagating at ∼5–92 per cent of the magnetosonic speed at angles of ∼20°–87° relative to ambient magnetic field. Only one is identified to be a quasi-parallel forward shock with magnetosonic Mach number of ∼1.48 and shock normal angle of ∼41°. The cometary ionosphere response was monitored by Rosetta from cometocentric distances of ∼4–30 km. A quiet time plasma density map was developed by considering dependences on cometary latitude, longitude, and cometocentric distance of Rosetta observations before and after each of the CIR intervals. The CIRs lead to plasma density enhancements of ∼500–1000 per cent with respect to the quiet time reference level. Ionospheric modelling shows that increased ionization rate due to enhanced ionizing (>12–200 eV) electron impact is the prime cause of the large cometary plasma density enhancements during the CIRs. Plausible origin mechanisms of the cometary ionizing electron enhancements are discussed.
Heritier KL, Galand M, Henri P, et al., 2018, Plasma source and loss at comet 67P during the Rosetta mission, ASTRONOMY & ASTROPHYSICS, Vol: 618, ISSN: 1432-0746
Heritier KL, Altwegg K, Berthelier J-J, et al., 2018, On the origin of molecular oxygen in cometary comae, NATURE COMMUNICATIONS, Vol: 9, ISSN: 2041-1723
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
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
Hajra R, Henri P, Vallières 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 and Astrophysics, Vol: 607, ISSN: 0004-6361
© ESO, 2017. We present a detailed study of the cometary ionospheric response to a cometary brightness outburst using in situ measurements for the first time. The comet 67P/Churyumov-Gerasimenko (67P) at a heliocentric distance of 2.4 AU from the Sun, exhibited an outburst at ∼1000 UT on 19 February 2016, characterized by an increase in the coma surface brightness of two orders of magnitude. The Rosetta spacecraft monitored the plasma environment of 67P from a distance of 30 km, orbiting with a relative speed of ∼0.2 m s-1. The onset of the outburst was preceded by pre-outburst decreases in neutral gas density at Rosetta, in local plasma density, and in negative spacecraft potential at ∼0950 UT. In response to the outburst, the neutral density increased by a factor of ∼1.8 and the local plasma density increased by a factor of ∼3, driving the spacecraft potential more negative. The energetic electrons (tens of eV) exhibited decreases in the flux of factors of ∼2 to 9, depending on the energy of the electrons. The local magnetic field exhibited a slight increase in amplitude (~5 nT) and an abrupt rotation (∼36.4°) in response to the outburst. A weakening of 10-100 mHz magnetic field fluctuations was also noted during the outburst, suggesting alteration of the origin of the wave activity by the outburst. The plasma and magnetic field effects lasted for about 4 h, from ∼1000 UT to 1400 UT. The plasma densities are compared with an ionospheric model. This shows that while photoionization is the main source of electrons, electron-impact ionization and a reduction in the ion outflow velocity need to be accounted for in order to explain the plasma density enhancement near the outburst peak.
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.
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
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, Vallieres 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
Beth A, Galand M, 2017, Effects of the convective field on weakly outgassing comets, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 469, Pages: S824-S841, ISSN: 0035-8711
Nilsson H, Wieser GS, Behar E, et al., 2017, Erratum: 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: S804-S804, ISSN: 0035-8711
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.
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.
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.
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
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
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
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
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
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
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
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
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
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
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