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1. Localized ejection of dust and chunks on comet 67P/Churyumov–Gerasimenko: testing how comets work.

Author

Attree, N, Schuckart, C, Bischoff, D, Gundlach, B, and Blum, J

Subjects
*CHURYUMOV-Gerasimenko comet, *HEAT radiation & absorption, *COMETS, *SOLAR radiation, *SURFACE area, *MATERIAL erosion
Abstract

We extend an existing thermophysical activity model of comet 67P/Churyumov–Gerasimenko to include pressure build-up inside the pebbles making up the nucleus. We test various quantities of H |$_{2}$| O and CO |$_{2}$|⁠ , in order to simulate the material inside and outside of proposed water enriched bodies (WEBs). We find that WEBs can reproduce the peak water flux observed by Rosetta , but that the addition of a time-resolved heat-flow reduces the water fluxes away from perihelion as compared to the previously assumed equilibrium model. Our modelled WEBs eject dust continuously but with a rate that is much higher than the observed erosion and mass-loss, thus requiring an active area smaller than the total comet surface area or very large quantities of dust fallback. When simulating the CO |$_{2}$| -rich non-WEB material, we only find the ejection of large chunks under specific conditions (e.g. low diffusivities between the pebbles or intense insolation at southern summer), while we also find CO |$_{2}$| outgassing rates that are much greater than observed. This is a general problem in models where CO |$_{2}$| drives erosion, alongside difficulties in simultaneously ejecting chunks from deep while eroding the surface layer. We therefore conclude that ejection of chunks by CO |$_{2}$| must be a localized phenomenon, occurring separately in space or time from surface erosion and water emission. Simulating the global production rates of gas, dust, and chunks from a comet thus remains challenging, while the activity mechanism is shown to be very sensitive to the material structure (i.e. porosity and diffusivity) at various scales. [ABSTRACT FROM AUTHOR]

Published
2024
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2. Cometary ion drift energy and temperature at comet 67P/Churyumov–Gerasimeko.

Author

Williamson, Hayley N, Johansson, Annie, Canu-Blot, Romain, Stenberg Wieser, Gabriella, Nilsson, Hans, Johansson, Fredrik L, and Moeslinger, Anja

Subjects
*ION energy, *SPACE plasmas, *POPULATION density, *IONS spectra, *SPACE vehicles, *CHURYUMOV-Gerasimenko comet, *COMETS
Abstract

The Ion Composition Analyzer (ICA) on the Rosetta spacecraft observed both the solar wind and the cometary ionosphere around comet 67P/Churyumov–Gerasimenko for nearly two years. However, observations of low energy cometary ions were affected by a highly negative spacecraft potential, and the ICA ion density estimates were often much lower than plasma densities found by other instruments. Since the low energy cometary ions are often the highest density population in the plasma environment, it is nonetheless desirable to understand their properties. To do so, we select ICA data with densities comparable to those of Rosetta 's Langmuir Probe (LAP)/Mutual Impedance Probe (MIP) throughout the mission. We then correct the cometary ion energy distribution of each energy-angle scan for spacecraft potential and fit a drifting Maxwell–Boltzmann distribution, which gives an estimate of the drift energy and temperature for 3521 scans. The resulting drift energy is generally between 11–18 eV and the temperature between 0.5–1 eV. The drift energy shows good agreement with published ion flow speeds from LAP/MIP during the same time period and is much higher than the cometary neutral speed. We see additional higher energy cometary ions in the spectra closest to perihelion that would be well described by a second Maxwellian-like distribution. The energy and temperature are negatively correlated with heliocentric distance, with a stronger dependence on heliocentric distance for temperature. It cannot be quantitatively determined whether this trend is primarily due to heliocentric distance or spacecraft distance to the comet, which increased with decreasing heliocentric distance. [ABSTRACT FROM AUTHOR]

Published
2024
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3. On positively charged dust in the coma of comet 67P.

Author

Vigren, E, Eriksson, A I, and Bergman, S

Subjects
*CHURYUMOV-Gerasimenko comet, *ELECTRON emission, *MOMENTS method (Statistics), *ELECTRON density, *LANGMUIR probes, *DUST, *PHOTOEMISSION
Abstract

Moment analysis of ion spectrograms measured by the Ion Composition Analyser (ICA) in the coma of comet 67P typically produces an ion number density estimate markedly lower than the number density of free electrons as measured by the Mutual Impedance Probe and the dual Langmuir Probe. While there are good reasons to distrust the ion density moment estimate in these circumstances, the issue cannot yet be considered fully understood and it is of interest to see whether any natural non-instrumental cause is possible. An obvious such cause would be whether a significant fraction of the positive charge density resides in positively charged dust grains that are not measured by the ICA. Here, we show that this scenario is highly unlikely, even near perihelion where photoemission is the strongest. In our semi-analytical grain charging model, we balance the current contributions to grains of photoelectron emission and electron attachment so as to find the expected charge state for a grain of a given radius. The charge state is affected by the ambient electron number density, the electron temperature, and the heliocentric distance. While at times the bulk of the dust population around comet 67P could be charged positive, dust charging, including photoelectron emission, should have a negligible influence on the overall ionization balance in the cometary coma simply because the dust particles are not ubiquitous enough. [ABSTRACT FROM AUTHOR]

Published
2022
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4. Cometary ion drift energy and temperature at comet 67P/Churyumov–Gerasimeko

Author

Williamson, Hayley N., Johansson, Annie, Canu Blot, Romain, Stenberg Wieser, Gabriella, Nilsson, Hans, Johansson, Fredrik L., Möslinger, Anja, Williamson, Hayley N., Johansson, Annie, Canu Blot, Romain, Stenberg Wieser, Gabriella, Nilsson, Hans, Johansson, Fredrik L., and Möslinger, Anja

Abstract

The Ion Composition Analyzer (ICA) on the Rosetta spacecraft observed both the solar wind and the cometary ionosphere around comet 67P/Churyumov–Gerasimenko for nearly two years. However, observations of low energy cometary ions were affected by a highly negative spacecraft potential, and the ICA ion density estimates were often much lower than plasma densities found by other instruments. Since the low energy cometary ions are often the highest density population in the plasma environment, it is nonetheless desirable to understand their properties. To do so, we select ICA data with densities comparable to those of Rosetta’s Langmuir Probe (LAP)/Mutual Impedance Probe (MIP) throughout the mission. We then correct the cometary ion energy distribution of each energy-angle scan for spacecraft potential and fit a drifting Maxwell–Boltzmann distribution, which gives an estimate of the drift energy and temperature for 3521 scans. The resulting drift energy is generally between 11–18 eV and the temperature between 0.5–1 eV. The drift energy shows good agreement with published ion flow speeds from LAP/MIP during the same time period and is much higher than the cometary neutral speed. We see additional higher energy cometary ions in the spectra closest to perihelion that would be well described by a second Maxwellian-like distribution. The energy and temperature are negatively correlated with heliocentric distance, with a stronger dependence on heliocentric distance for temperature. It cannot be quantitatively determined whether this trend is primarily due to heliocentric distance or spacecraft distance to the comet, which increased with decreasing heliocentric distance.

Published
2024
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5. Dynamics of irregularly shaped cometary particles subjected to outflowing gas and solar radiative forces and torques.

Author

Moreno, Fernando, Guirado, Daniel, Muñoz, Olga, Zakharov, Vladimir, Ivanovski, Stavro, Fulle, Marco, Rotundi, Alessandra, Frattin, Elisa, and Bertini, Ivano

Subjects
*RADIATIVE forcing, *CHURYUMOV-Gerasimenko comet, *AERODYNAMIC load, *TORQUE, *EQUATIONS of motion, *PARTICLE dynamics
Abstract

The dynamics of irregularly shaped particles subjected to the combined effect of gas drag and radiative forces and torques in a cometary environment is investigated. The equations of motion are integrated over distances from the nucleus surface up to distances where the gas drag is negligible. The aerodynamic forces and torques are computed assuming a spherically symmetric expanding gas. The calculations are limited to particle sizes in the geometric optics limit, which is the range of validity of our radiative torque calculations. The dynamical behaviour of irregular particles is quite different to those exhibited by non-spherical but symmetric particles such as spheroids. An application of the dynamical model to comet 67P/Churyumov–Gerasimenko, the target of the Rosetta mission, is made. We found that, for particle sizes larger than ∼10 μm, the radiative torques are negligible in comparison with the gas-driven torques up to a distance of ∼100 km from the nucleus surface. The rotation frequencies of the particles depend on their size, shape, and the heliocentric distance, while the terminal velocities, being also dependent on size and heliocentric distance, show only a very weak dependence on particle shape. The ratio of the sum of the particles projected areas in the sun-to-comet direction to that of the sum of the particles projected areas in any direction perpendicular to it is nearly unity, indicating that the interpretation of the observed u-shaped scattering phase function by Rosetta /OSIRIS on comet 67P coma cannot be linked to mechanical alignment of the particles. [ABSTRACT FROM AUTHOR]

Published
2022
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6. Remote sensing of cometary bow shocks: modelled asymmetric outgassing and pickup ion observations.

Author

Alho, Markku, Jarvinen, Riku, Simon Wedlund, Cyril, Nilsson, Hans, Kallio, Esa, and Pulkkinen, Tuija I

Subjects
*REMOTE sensing, *SOLAR wind, *INTERPLANETARY magnetic fields, *PLASMA sheaths, *OUTGASSING, *HYBRID computer simulation, *IONS
Abstract

Despite the long escort by the ESA Rosetta mission, direct observations of a fully developed bow shock around 67P/Churyumov–Gerasimenko have not been reported. Expanding on our previous work on indirect observations of a shock, we model the large-scale features in cometary pickup ions, and compare the results with the ESA Rosetta Plasma Consortium Ion Composition Analyser ion spectrometer measurements over the pre-perihelion portion of the escort phase. Using our hybrid plasma simulation, an empirical, asymmetric outgassing model for 67P, and varied interplanetary magnetic field (IMF) clock angles, we model the evolution of the large-scale plasma environment. We find that the subsolar bow shock standoff distance is enhanced by asymmetric outgassing with a factor of 2 to 3, reaching up to |$18\,000\, \rm {km}$| approaching perihelion. We find that distinct spectral features in simulated pickup ion distributions are present for simulations with shock-like structures, with the details of the spectral features depending on shock standoff distance, heliocentric distance, and IMF configuration. Asymmetric outgassing along with IMF clock angle is found to have a strong effect on the location of the spectral features, while the IMF clock angle causes no significant effect on the bow shock standoff distance. These dependences further complicate the interpretation of the ion observations made by Rosetta. Our data-model comparison shows that the large-scale cometary plasma environment can be probed by remote sensing the pickup ions, at least when the comet's activity is comparable to that of 67P, and the solar wind parameters are known. [ABSTRACT FROM AUTHOR]

Published
2021
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7. D/H in the refractory organics of comet 67P/Churyumov-Gerasimenko measured by Rosetta/COSIMA.

Author

Paquette, J A, Fray, N, Bardyn, A, Engrand, C, Alexander, C M O'D, Siljeström, S, Cottin, H, Merouane, S, Isnard, R, Stenzel, O J, Fischer, H, Rynö, J, Kissel, J, and Hilchenbach, M

Subjects
*CHURYUMOV-Gerasimenko comet, *SOLAR system, *DUST, *SPACE sciences, *SEAWATER, *CHEMICAL species
Abstract

The D/H ratio is a clue to the origin and evolution of hydrogen-bearing chemical species in Solar system materials. D/H has been observed in the coma of many comets, but most such measurements have been for gaseous water. We present the first in situ measurements of the D/H ratios in the organic refractory component of cometary dust particles collected at very low impact speeds in the coma of comet 67P/Churyumov-Gerasimenko (hereafter 67P) by the COSIMA instrument onboard Rosetta. The values measured by COSIMA are spatial averages over an approximately 35 × 50 µm2 area. The average D/H ratio for the 25 measured particles is (1.57 ± 0.54) × 10−3, about an order of magnitude higher than the Vienna Standard Mean Ocean Water (VSMOW), but more than an order of magnitude lower than the values measured in gas-phase organics in solar-like protostellar regions and hot cores. This relatively high averaged value suggests that refractory carbonaceous matter in comet 67P is less processed than the most primitive insoluble organic matter (IOM) in meteorites, which has a D/H ratio in the range of about 1 to 7 × 10−4. The cometary particles measured in situ also have a higher H/C ratio than the IOM. We deduce that the measured D/H in cometary refractory organics is an inheritance from the presolar molecular cloud from which the Solar system formed. The high D/H ratios observed in the cometary particles challenges models in which high D/H ratios result solely from processes that operated in the protosolar disc. [ABSTRACT FROM AUTHOR]

Published
2021
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8. Average cometary ion flow pattern in the vicinity of comet 67P from moment data.

Author

Nilsson, Hans, Williamson, Hayley, Bergman, Sofia, Stenberg Wieser, Gabriella, Wieser, Martin, Behar, Etienne, Eriksson, Anders I, Johansson, Fredrik L, Richter, Ingo, and Goetz, Charlotte

Subjects
*CHURYUMOV-Gerasimenko comet, *COMETS, *ION energy, *ELECTRIC windings, *ELECTRIC fields, *SOLAR wind, *COORDINATES
Abstract

Average flow patterns of ions around comet 67P detected by the RPC-ICA instrument onboard Rosetta are presented both as a time series and as a spatial distribution of the average flow in the plane perpendicular to the comet – Sun direction (Y–Z plane in the coordinate systems used). Cometary ions in the energy range up to 60 eV flow radially away from the nucleus in the Y–Z plane, irrespective of the direction of the magnetic field, throughout the mission. These ions may however be strongly affected by the spacecraft potential, the uncertainty due to this is briefly discussed. Inside the solar wind ion cavity and in the periods just before and after, the cometary pick up ions moving antisunward are deflected against the inferred solar wind electric field direction. This is opposite to what is observed for lower levels of mass-loading. These pick up ions are behaving in a similar way to the solar wind ions and are deflected due to mass-loading. A spatial asymmetry can be seen in the observations of deflected pick up ions, with motion against the electric field primarily within a radius of 200 km of the nucleus and also in the negative electric field hemisphere. Cometary ions observed by RPC-ICA typically move in the antisunward direction throughout the mission. These are average patterns, full-resolution data show very much variability. [ABSTRACT FROM AUTHOR]

Published
2020
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9. On positively charged dust in the coma of comet 67P

Author

Vigren, Erik, Eriksson, A. , I, Bergman, S., Vigren, Erik, Eriksson, A. , I, and Bergman, S.

Abstract

Moment analysis of ion spectrograms measured by the Ion Composition Analyser (ICA) in the coma of comet 67P typically produces an ion number density estimate markedly lower than the number density of free electrons as measured by the Mutual Impedance Probe and the dual Langmuir Probe. While there are good reasons to distrust the ion density moment estimate in these circumstances, the issue cannot yet be considered fully understood and it is of interest to see whether any natural non-instrumental cause is possible. An obvious such cause would be whether a significant fraction of the positive charge density resides in positively charged dust grains that are not measured by the ICA. Here, we show that this scenario is highly unlikely, even near perihelion where photoemission is the strongest. In our semi-analytical grain charging model, we balance the current contributions to grains of photoelectron emission and electron attachment so as to find the expected charge state for a grain of a given radius. The charge state is affected by the ambient electron number density, the electron temperature, and the heliocentric distance. While at times the bulk of the dust population around comet 67P could be charged positive, dust charging, including photoelectron emission, should have a negligible influence on the overall ionization balance in the cometary coma simply because the dust particles are not ubiquitous enough.

Published
2022
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10. Isotopic composition of CO2 in the coma of 67P/Churyumov-Gerasimenko measured with ROSINA/DFMS.

Author

Hässig, M., Altwegg, K., Balsiger, H., Berthelier, J. J., Bieler, A., Calmonte, U., Dhooghe, F., Fiethe, B., Fuselier, S. A., Gasc, S., Gombosi, T. I., Le Roy, L., Luspay-Kuti, A., Mandt, K., Rubin, M., Tzou, C.-Y., Wampfler, S. F., and Wurz, P.

Subjects
*COMET formation, *ISOTOPIC fractionation, *SOLAR system, *PROTOPLANETARY disks, *ISOTOPOLOGUES, SOLAR evolution
Abstract

Context. Measurements of isotopic abundances in cometary ices are key to understanding and reconstructing the history and origin of material in the solar system. Comets are considered the most pristine material in the solar system. Isotopic fractionation (enrichment of an isotope in a molecule compared to the initial abundance) is sensitive to environmental conditions at the time of comet formation. Therefore, measurements of cometary isotope ratios can provide information on the composition, density, temperature, and radiation during formation of the molecules, during the chemical evolution from the presolar cloud to the protosolar nebula, and the protoplanetary disk before accretion in solid bodies. Most isotopic abundances of 12C/13C and 16O/18O in comets to date are in agreement with terrestrial abundances. Prior to the Rosetta mission, measurements of 12C/13C in comets were only available for HCN, CN, and C2 and for 16O/18O in H2O. Measurements of 12C/13C in comets were only available from ground based observations and remote sensing, while 16O/18O in H2O had also been measured in-situ. To date, no measurements of the CO2 isotopologues in comets were available. Aims. This paper presents the first measurements of the CO2 isotopologues in the coma of 67P/Churyumov-Gerasimenko (67P). Methods. We analyzed measurements taken by the Double Focusing Mass Spectrometer (DFMS) of the ROSINA experiment on board the ESA spacecraft Rosetta in the coma of 67P. Results. The CO2 isotopologues results for 67P are: 12C/13C = 84 ± 4, 16O/18O = 494 ± 8, and 13C16O2/16C18O16O = 5.87 ± 0.07. The oxygen isotopic ratio is within error bars compatible with terrestrial abundances but not with solar wind measurements. Conclusions. The carbon isotopic ratio and the combined carbon and oxygen isotopic ratio are slightly (14%) enriched in 13C, within 1σ uncertainty, compared to solar wind abundances and solar abundances. The small fractionation of 12C/13C in CO2 is probably compatible with an origin of the material in comets from the native cloud. [ABSTRACT FROM AUTHOR]

Published
2017
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11. Dynamics of irregularly-shaped cometary particles subjected to outflowing gas and solar radiative forces and torques

Author

Fernando Moreno, Daniel Guirado, Olga Muñoz, Vladimir Zakharov, Stavro Ivanovski, Marco Fulle, Alessandra Rotundi, Elisa Frattin, Ivano Bertini, European Commission, Ministerio de Ciencia e Innovación (España), and Junta de Andalucía

Subjects
Earth and Planetary Astrophysics (astro-ph.EP), numerical [Methods], Methods: numerical, Space and Planetary Science, Comets: Individual: 67P, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Earth and Planetary Astrophysics, individual: 67P [Comets], Astrophysics - Earth and Planetary Astrophysics
Abstract

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited, The dynamics of irregularly shaped particles subjected to the combined effect of gas drag and radiative forces and torques in a cometary environment is investigated. The equations of motion are integrated over distances from the nucleus surface up to distances where the gas drag is negligible. The aerodynamic forces and torques are computed assuming a spherically symmetric expanding gas. The calculations are limited to particle sizes in the geometric optics limit, which is the range of validity of our radiative torque calculations. The dynamical behaviour of irregular particles is quite different to those exhibited by non-spherical but symmetric particles such as spheroids. An application of the dynamical model to comet 67P/Churyumov–Gerasimenko, the target of the Rosetta mission, is made. We found that, for particle sizes larger than ∼10 μm, the radiative torques are negligible in comparison with the gas-driven torques up to a distance of ∼100 km from the nucleus surface. The rotation frequencies of the particles depend on their size, shape, and the heliocentric distance, while the terminal velocities, being also dependent on size and heliocentric distance, show only a very weak dependence on particle shape. The ratio of the sum of the particles projected areas in the sun-to-comet direction to that of the sum of the particles projected areas in any direction perpendicular to it is nearly unity, indicating that the interpretation of the observed u-shaped scattering phase function by Rosetta/OSIRIS on comet 67P coma cannot be linked to mechanical alignment of the particles. © The Author(s) 2021. Published by Oxford University Press on behalf of Royal Astronomical Society., FM, DG, and OM acknowledge financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). FM and DG also acknowledge financial support from the Spanish Plan Nacional de Astronomía y Astrofísica LEONIDAS project RTI2018-095330-B-100, and project P18-RT-1854 from Junta de Andalucía.

Published
2021

12. Remote sensing of cometary bow shocks: Modelled asymmetric outgassing and pickup ion observations

Author

Cyril Simon Wedlund, Riku Jarvinen, Tuija Pulkkinen, Markku Alho, Hans Nilsson, Esa Kallio, Department of Electronics and Nanoengineering, Esa Kallio Group, Austrian Academy of Sciences, Swedish Institute of Space Physics, Aalto-yliopisto, Aalto University, Doctoral Programme in Particle Physics and Universe Sciences, Space Physics Research Group, Particle Physics and Astrophysics, and Department of Physics

Subjects
Shock wave, 010504 meteorology & atmospheric sciences, IMPACT, FLOW, Flow (psychology), 114 Physical sciences, 01 natural sciences, miscellaneous [techniques], methods: numerical, comets: individual: 67P, individual: 67P [comets], NEUTRAL COMPOUNDS, Ionization, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, DENSITY DISTRIBUTION, Physics, PLASMA, 67P/CHURYUMOV-GERASIMENKO, Astronomy and Astrophysics, numerical [methods], Plasma, shock waves, plasmas, Computational physics, Pickup Ion, Solar wind, Outgassing, techniques: miscellaneous, GAS, 13. Climate action, Space and Planetary Science, Remote sensing (archaeology), SOLAR-WIND, IONIZATION, ATMOSPHERES
Abstract

Despite the long escort by the ESA Rosetta mission, direct observations of a fully developed bow shock around 67P/Churyumov–Gerasimenko have not been reported. Expanding on our previous work on indirect observations of a shock, we model the large-scale features in cometary pickup ions, and compare the results with the ESA Rosetta Plasma Consortium Ion Composition Analyser ion spectrometer measurements over the pre-perihelion portion of the escort phase. Using our hybrid plasma simulation, an empirical, asymmetric outgassing model for 67P, and varied interplanetary magnetic field (IMF) clock angles, we model the evolution of the large-scale plasma environment. We find that the subsolar bow shock standoff distance is enhanced by asymmetric outgassing with a factor of 2 to 3, reaching up to $18\,000\, \rm {km}$ approaching perihelion. We find that distinct spectral features in simulated pickup ion distributions are present for simulations with shock-like structures, with the details of the spectral features depending on shock standoff distance, heliocentric distance, and IMF configuration. Asymmetric outgassing along with IMF clock angle is found to have a strong effect on the location of the spectral features, while the IMF clock angle causes no significant effect on the bow shock standoff distance. These dependences further complicate the interpretation of the ion observations made by Rosetta. Our data-model comparison shows that the large-scale cometary plasma environment can be probed by remote sensing the pickup ions, at least when the comet’s activity is comparable to that of 67P, and the solar wind parameters are known.

Published
2021

13. A charging model for the Rosetta spacecraft

Author

Johansson, Fredrik, Eriksson, Anders, Gilet, N., Henri, P., Wattieaux, G., Taylor, M. G. G. T., Imhof, C., Cipriani, F., Johansson, Fredrik, Eriksson, Anders, Gilet, N., Henri, P., Wattieaux, G., Taylor, M. G. G. T., Imhof, C., and Cipriani, F.

Abstract

Context. The electrostatic potential of a spacecraft, V-S, is important for the capabilities of in situ plasma measurements. Rosetta has been found to be negatively charged during most of the comet mission and even more so in denser plasmas.Aims. Our goal is to investigate how the negative V-S correlates with electron density and temperature and to understand the physics of the observed correlation.Methods. We applied full mission comparative statistics of V-S, electron temperature, and electron density to establish V-S dependence on cold and warm plasma density and electron temperature. We also used Spacecraft-Plasma Interaction System (SPIS) simulations and an analytical vacuum model to investigate if positively biased elements covering a fraction of the solar array surface can explain the observed correlations.Results. Here, the V-S was found to depend more on electron density, particularly with regard to the cold part of the electrons, and less on electron temperature than was expected for the high flux of thermal (cometary) ionospheric electrons. This behaviour was reproduced by an analytical model which is consistent with numerical simulations.Conclusions. Rosetta is negatively driven mainly by positively biased elements on the borders of the front side of the solar panels as these can efficiently collect cold plasma electrons. Biased elements distributed elsewhere on the front side of the panels are less efficient at collecting electrons apart from locally produced electrons (photoelectrons). To avoid significant charging, future spacecraft may minimise the area of exposed bias conductors or use a positive ground power system.

Published
2020
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14. Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko

Author

Gilet, N., Henri, P., Wattieaux, G., Traore, N., Eriksson, Anders, Vallieres, X., More, J., Randriamboarison, O., Odelstad, Elias, Johansson, Fredrik, Rubin, M., Gilet, N., Henri, P., Wattieaux, G., Traore, N., Eriksson, Anders, Vallieres, X., More, J., Randriamboarison, O., Odelstad, Elias, Johansson, Fredrik, and Rubin, M.

Abstract

Context. The Mutual Impedance Probe (MIP) of the Rosetta Plasma Consortium (RPC) onboard the Rosetta orbiter which was in operation for more than two years, between August 2014 and September 2016 to monitor the electron density in the cometary ionosphere of 67P/Churyumov-Gerasimenko. Based on the resonance principle of the plasma eigenmodes, recent models of the mutual impedance experiment have shown that in a two-electron temperature plasma, such an instrument is able to separate the two isotropic electron populations and retrieve their properties.Aims. The goal of this paper is to identify and characterize regions of the cometary ionized environment filled with a mix of cold and warm electron populations, which was observed by Rosetta during the cometary operation phase.Methods. To reach this goal, this study identifies and investigates the in situ mutual impedance spectra dataset of the RPC-MIP instrument that contains the characteristics of a mix of cold and warm electrons, with a special focus on instrumental signatures typical of large cold-to-total electron density ratio (from 60 to 90%), that is, regions strongly dominated by the cold electron component.Results. We show from the observational signatures that the mix of cold and warm cometary electrons strongly depends on the cometary latitude. Indeed, in the southern hemisphere of 67P, where the neutral outgassing activity was higher than in northern hemisphere during post-perihelion, the cold electrons were more abundant, confirming the role of electron-neutral collisions in the cooling of cometary electrons. We also show that the cold electrons are mainly observed outside the nominal electron-neutral collision-dominated region (exobase), where electrons are expected to have cooled down. This which indicates that the cold electrons have been transported outward. Finally, RPC-MIP detected cold electrons far from the perihelion, where the neutral outgassing activity is lower, in regions where no electron exob

Published
2020
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15. ROSINA ion zoo at Comet 67P

Author

Beth, Arnaud, Altwegg, K., Balsiger, H., Berthelier, J. -J., Combi, M. R., De Keyser, J., Fiethe, B., Fuselier, S. A., Galand, M., Gombosi, T. I., Rubin, M., Semon, T., Beth, Arnaud, Altwegg, K., Balsiger, H., Berthelier, J. -J., Combi, M. R., De Keyser, J., Fiethe, B., Fuselier, S. A., Galand, M., Gombosi, T. I., Rubin, M., and Semon, T.

Abstract

Context: The Rosetta spacecraft escorted Comet 67P/Churyumov-Gerasimenko for 2 yr along its journey through the Solar System between 3.8 and 1.24 au. Thanks to the high resolution mass spectrometer on board Rosetta, the detailed ion composition within a coma has been accurately assessed in situ for the very first time. Aims: Previous cometary missions, such as Giotto, did not have the instrumental capabilities to identify the exact nature of the plasma in a coma because the mass resolution of the spectrometers onboard was too low to separate ion species with similar masses. In contrast, the Double Focusing Mass Spectrometer (DFMS), part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis on board Rosetta (ROSINA), with its high mass resolution mode, outperformed all of them, revealing the diversity of cometary ions. Methods: We calibrated and analysed the set of spectra acquired by DFMS in ion mode from October 2014 to April 2016. In particular, we focused on the range from 13–39 u q−1. The high mass resolution of DFMS allows for accurate identifications of ions with quasi-similar masses, separating 13C+ from CH+, for instance. Results: We confirm the presence in situ of predicted cations at comets, such as CHm+ (m = 1−4), HnO+ (n = 1−3), O+, Na+, and several ionised and protonated molecules. Prior to Rosetta, only a fraction of them had been confirmed from Earth-based observations. In addition, we report for the first time the unambiguous presence of a molecular dication in the gas envelope of a Solar System body, namely CO2++.

Published
2020
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16. Beginning of activity in 67P/Churyumov-Gerasimenko and predictions for 2014-2015.

Author

Snodgrass, C., Tubiana, C., Bramich, D. M., Meech, K., Boehnhardt, H., and Barrera, L.

Subjects
*ASTRONOMY, *VARIABLE stars, *SOLAR activity, *ASTRONOMICAL observations, *ASTRONOMICAL measurements
Abstract

Context. Comet 67P/Churyumov-Gerasimenko was selected in 2003 as the new target of the Rosetta mission. It has since been the subject of a detailed campaign of observations to characterise its nucleus and activity. Aims. We present previously unpublished data taken around the start of activity of the comet in 2007/8, before its last perihelion passage. We constrain the time of the start of activity, and combine this with other data taken throughout the comet's orbit to make predictions for its likely behaviour during 2014/5 while Rosetta is operating. Methods. A considerable difficulty in observing 67P during the past years has been its position against crowded fields towards the Galactic centre for much of the time. The 2007/8 data presented here were particularly difficult, and the comet will once again be badly placed for Earth-based observations in 2014/5. We make use of the difference image analysis technique, which is commonly used in variable star and exoplanet research, to remove background sources and extract images of the comet. In addition, we reprocess a large quantity of archival images of 67P covering its full orbit, to produce a heliocentric lightcurve. By using consistent reduction, measurement and calibration techniques we generate a remarkably clean lightcurve, which can be used to measure a brightnessdistance relationship and to predict the future brightness of the comet. Results. We determine that the comet was active around November 2007, at a pre-perihelion distance from the Sun of 4.3 AU. The comet will reach this distance, and probably become active again, in March 2014. We find that the dust brightness can be well described by Af ρ α r-3:2 pre-perihelion and / r-3:4 post-perihelion, and that the comet has a higher dust-to-gas ratio than average, with log(Af ρ αQ(H2O)) = -24:94 ± 0:22 cm s molecule-1 at r < 2 AU. A model fit to the photometric data suggests that only a small fraction (1.4%) of the surface is active. [ABSTRACT FROM AUTHOR]

Published
2013
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17. Ionospheric total electron content of comet 67P/Churyumov-Gerasimenko

Author

Zoltán Németh, Martin Rubin, Pierre Henri, Marina Galand, Nicolas Gilet, Rajkumar Hajra, L. Bucciantini, Bruce T. Tsurutani, Xavier Vallières, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Indian Institute of Technology Indore (IITI), Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Imperial College London, University of Bern, California Institute of Technology (CALTECH), Hungarian Wigner Research Centre for Physics, ANR-15-CE31-0009,SPECTRA,Sonder le Plasma dans l'Environnement d'une ComètE avec RosettA(2015), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and Science and Technology Facilities Council (STFC)

Subjects
010504 meteorology & atmospheric sciences, TEC, media_common.quotation_subject, Comet, Astrophysics, Astronomy & Astrophysics, 01 natural sciences, Asymmetry, comets: individual: 67P, Sun: activity, 0201 Astronomical and Space Sciences, 0103 physical sciences, 010303 astronomy & astrophysics, Southern Hemisphere, 0105 earth and related environmental sciences, media_common, Churyumov-Gerasimenko, Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 520 Astronomy, comets: general, Northern Hemisphere, Astronomy and Astrophysics, Plasma, 620 Engineering, Sun: UV radiation, methods: data analysis, 13. Climate action, Space and Planetary Science, Orders of magnitude (length), Ionosphere
Abstract

We study the evolution of a cometary ionosphere, using approximately two years of plasma measurements by the Mutual Impedance Probe on board the Rosetta spacecraft monitoring comet 67P/Churyumov-Gerasimenko (67P) during August 2014–September 2016. The in situ plasma density measurements are utilized to estimate the altitude-integrated electron number density or cometary ionospheric total electron content (TEC) of 67P based on the assumption of radially expanding plasma. The TEC is shown to increase with decreasing heliocentric distance (rh) of the comet, reaching a peak value of ~(133 ± 84) × 109cm−2averaged around perihelion (rh< 1.5 au). At large heliocentric distances (rh> 2.5 au), the TEC decreases by ~2 orders of magnitude. For the same heliocentric distance, TEC values are found to be significantly larger during the post-perihelion periods compared to the pre-perihelion TEC values. This “ionospheric hysteresis effect” is more prominent in the southern hemisphere of the comet and at large heliocentric distances. A significant hemispheric asymmetry is observed during perihelion with approximately two times larger TEC values in the northern hemisphere compared to the southern hemisphere. The asymmetry is reversed and stronger during post-perihelion (rh> 1.5 au) periods with approximately three times larger TEC values in the southern hemisphere compared to the northern hemisphere. Hemispheric asymmetry was less prominent during the pre-perihelion intervals. The correlation of the cometary TEC with the incident solar ionizing fluxes is maximum around and slightly after perihelion (1.5 au 2.5 au) where the photo-ionization contribution to the TEC variability decreases. The results are discussed based on cometary ionospheric production and loss processes.

Published
2020
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18. Ionospheric plasma of comet 67P probed byRosettaat 3 au from the Sun

Author

Martin Rubin, Jean-Pierre Lebreton, Peter Wurz, A. J. Allen, Elias Odelstad, Karl-Heinz Glassmeier, T. W. Broiles, Anders Eriksson, Luc Sagnières, Erik Vigren, Kathleen Mandt, James L. Burch, Xavier Vallières, Chia-Yu Tzou, Chris Carr, K. L. Heritier, Steven J. Schwartz, F. L. Johansson, Arnaud Beth, Thierry Sémon, Emanuele Cupido, Hans Nilsson, Pierre Henri, Marina Galand, Kathrin Altwegg, Ingo Richter, Science and Technology Facilities Council (STFC), Imperial College Trust, Science and Technology Facilities Council [2006-2012], Department of Physics [Imperial College London], Imperial College London, Swedish Institute of Space Physics [Kiruna] (IRF), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Southwest Research Institute [San Antonio] (SwRI), Physikalisches Institut [Bern], Universität Bern [Bern], Swedish Institute of Space Physics [Uppsala] (IRF), Institut für Geophysik und Extraterrestrische Physik [Braunschweig] (IGEP), and Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig]

Subjects
010504 meteorology & atmospheric sciences, 530 Physics, Comet, Coma (optics), Astrophysics, Astronomy & Astrophysics, ROSINA, 7. Clean energy, 01 natural sciences, Fusion, plasma och rymdfysik, comets: individual: 67P, individual: 67P [comets], Ionization, 0201 Astronomical and Space Sciences, 0103 physical sciences, data analysis [methods], WATER, NUMBER DENSITIES, ION, DIAMAGNETIC CAVITY, NUCLEUS, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, UV radiation [Sun], ENVIRONMENT, Science & Technology, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 520 Astronomy, 67P/CHURYUMOV-GERASIMENKO, Astronomy, Astronomy and Astrophysics, Plasma, Comets: individual: 67P Plasmas Sun: UV radiation Methods: data analysis, 620 Engineering, plasmas, Sun: UV radiation, Fusion, Plasma and Space Physics, methods: data analysis, ELECTRON SENSOR, 13. Climate action, Space and Planetary Science, Physics::Space Physics, Physical Sciences, RPC, Astrophysics::Earth and Planetary Astrophysics, Ionosphere
Abstract

We propose to identify the main sources of ionization of the plasma in the coma of comet 67P/Churyumov-Gerasimenko at different locations in the coma and to quantify their relative importance, for the first time, for close cometocentric distances (< 20 km) and large heliocentric distances (> 3 au). The ionospheric model proposed is used as an organizing element of a multi-instrument data set from the Rosetta Plasma Consortium (RPC) plasma and particle sensors, from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis and from the Microwave Instrument on the Rosetta Orbiter, all on board the ESA/Rosetta spacecraft. The calculated ionospheric density driven by Rosetta observations is compared to the RPC-Langmuir Probe and RPC-Mutual Impedance Probe electron density. The main cometary plasma sources identified are photoionization of solar extreme ultraviolet (EUV) radiation and energetic electron-impact ionization. Over the northern, summer hemisphere, the solar EUV radiation is found to drive the electron density - with occasional periods when energetic electrons are also significant. Over the southern, winter hemisphere, photoionization alone cannot explain the observed electron density, which reaches sometimes higher values than over the summer hemisphere; electron-impact ionization has to be taken into account. The bulk of the electron population is warm with temperature of the order of 7-10 eV. For increased neutral densities, we show evidence of partial energy degradation of the hot electron energy tail and cooling of the full electron population. QC 20200602

Published
2016
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19. Distributed glycine in comet 67P/Churyumov-Gerasimenko

Author

P. Zapf, Stavro Ivanovski, Yves Bénilan, V. Della Corte, Katia Hadraoui, Kathrin Altwegg, Hervé Cottin, V.V. Zakharov, Alessandra Rotundi, Nicolas Fray, Jérémie Lasue, Sihane Merouane, N. Biver, Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA (UMR_7583)), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), INAF - Osservatorio Astronomico di Trieste (OAT), Istituto Nazionale di Astrofisica (INAF), University of Bern, Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Universita degli studi di Napoli 'Parthenope' [Napoli], Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Sonnensystemforschung (MPS), Max-Planck-Gesellschaft, Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Università degli Studi di Napoli 'Parthenope' = University of Naples (PARTHENOPE), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), and Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research (MPS)

Subjects
Astrochemistry, 010504 meteorology & atmospheric sciences, Comet, Dust particles, Astrophysics, Mass spectrometry, 01 natural sciences, Atmosphere, comets: individual: 67P, 0103 physical sciences, medicine, Astrophysics::Solar and Stellar Astrophysics, Nuclear Experiment, Comets: individual: 67P/Churyumov-Gerasimenko, 010303 astronomy & astrophysics, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Churyumov-Gerasimenko, Physics, [PHYS]Physics [physics], Quantitative Biology::Biomolecules, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astronomy and Astrophysics, medicine.anatomical_structure, 13. Climate action, Space and Planetary Science, Glycine, Sublimation (phase transition), Astrophysics::Earth and Planetary Astrophysics, Nucleus
Abstract

International audience; Most of the gaseous molecules that are detected in cometary atmospheres are produced through sublimation of nucleus ices. Distributed sources may also occur, that is, production within the coma, from the solid component of dust particles that are ejected from the nucleus. Glycine, the simplest amino acid, was observed episodically in the atmosphere of comet 67P/Churyumov-Gerasimenko (67P) by the ROSINA mass spectrometer on board the Rosetta probe. A series of measurements on 28 March 2015 revealed a distributed density profile at between 14 and 26 km away from the nucleus. We here present and discuss three study cases: (i) glycine emitted directly and only from the nucleus, (ii) glycine emitted from the sublimation of solid-state glycine on the dust particles that are ejected from the nucleus, and (iii) glycine molecules embedded in water ice that are emitted from the sublimation of this ice from the dust particles that are ejected from the nucleus. A numerical model was developed to calculate the abundance of glycine in the atmosphere of comet 67P as a function of the distance from the nucleus, and to derive its initial abundance in the lifted dust particles. We show that a good fit to the observations corresponds to a distributed source of glycine that is embedded in sublimating water ice from dust particles that are ejected from the nucleus (iii). The few hundred ppb of glycine embedded in water ice on dust particles (nominally 170 ppb by mass) agree well with the observed distribution.

Published
2019
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21. VIRTIS-H observations of the dust coma of comet 67P/Churyumov-Gerasimenko: spectral properties and color temperature variability with phase and elevation

Author

Stéphane Erard, Pierre Drossart, Mauro Ciarniello, Gabriele Arnold, M. T. Capria, David Kappel, Giovanna Rinaldi, Andrea Longobardo, F. Andrieu, Fabrizio Capaccioni, J. Crovisier, Fredric W. Taylor, Pedro Hasselmann, M. C. De Sanctis, Dominique Bockelée-Morvan, C. Leyrat, Gianrico Filacchione, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), DLR Institut für Planetenforschung, University of Oxford [Oxford], and PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Asteroiden und Kometen, 010504 meteorology & atmospheric sciences, Comet, Coma (optics), Astrophysics, Color temperature, 01 natural sciences, comets: individual: 67P, Phase (matter), 0103 physical sciences, infrared: planetary systems, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Churyumov-Gerasimenko, Physics, [PHYS]Physics [physics], comets: general, Spectral properties, Leitungsbereich PF, Elevation, comets: individual: 67P/Churyumov-Gerasimenko, Astronomy and Astrophysics, 13. Climate action, Space and Planetary Science, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - Earth and Planetary Astrophysics
Abstract

We analyze 2–5μm spectroscopic observations of the dust coma of comet 67P/Churyumov-Gerasimenko obtained with the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H) instrument on board Rosetta from 3 June to 29 October 2015 at heliocentric distancesrh= 1.24–1.55 AU. The 2–2.5μm color, bolometric albedo, and color temperature were measured using spectral fitting. Data obtained atα= 90° solar phase angle show an increase in bolometric albedo (0.05–0.14) with increasing altitude (0.5–8 km), accompanied by a possible marginal decrease in color and color temperature. Possible explanations include dark particles on ballistic trajectories in the inner coma and radial changes in particle composition. In the phase angle range 50°–120°, phase reddening is significant (0.031%/100 nm deg−1) for a mean color of 2%/100 nm atα= 90°, which might be related to the roughness of the dust particles. Moreover, a decrease in color temperature with decreasing phase angle is also observed at a rate of ~0.3 K deg−1, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. Comparing data acquired at fixed phase angle (α= 90°), a 20% increase in bolometric albedo is observed near perihelion. Heliocentric variations in dust color are not significant in the time period we analyzed. The measured color temperatures vary from 260 to 320 K, and follow arh−0.6variation in therh= 1.24–1.5 AU range, which is close to the expectedrh−0.5value.

Published
2019
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22. Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission

Author

Ingo Richter, Pierre Henri, Xavier Vallières, F. L. Johansson, Hugo Breuillard, Anders Eriksson, Charlotte Goetz, Elias Odelstad, Rajkumar Hajra, L. Bucciantini, Martin Volwerk, Tomas Karlsson, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Laboratoire de Physique des Plasmas (LPP), Université Paris-Sud - Paris 11 (UP11)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-École polytechnique (X)-Sorbonne Universités-Sorbonne Université (SU)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Space Research Institute of Austrian Academy of Sciences (IWF), Austrian Academy of Sciences (OeAW), Department of Space and Plasma Physics [Stockholm], KTH School of Electrical Engineering, Royal Institute of Technology [Stockholm] (KTH )-Royal Institute of Technology [Stockholm] (KTH ), Swedish Institute of Space Physics [Uppsala] (IRF), Technische Universität Braunschweig [Braunschweig], Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Université Paris-Saclay-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Sud - Paris 11 (UP11)-École polytechnique (X)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), and Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig]

Subjects
010504 meteorology & atmospheric sciences, Comet, observational [methods], Astrophysics, 01 natural sciences, general [comets], Fusion, plasma och rymdfysik, comets: individual: 67P, Astronomi, astrofysik och kosmologi, Physics::Plasma Physics, 0103 physical sciences, data analysis [methods], Astronomy, Astrophysics and Cosmology, waves, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Churyumov-Gerasimenko, Physics, Spacecraft, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], business.industry, comets: general, Astronomy, Astronomy and Astrophysics, Plasma, plasmas, Methods observational, methods: data analysis, Fusion, Plasma and Space Physics, On board, 13. Climate action, Space and Planetary Science, Physics::Space Physics, Astrophysics::Earth and Planetary Astrophysics, methods: observational, business, individual: 67P/Churyumov-Gerasimenko [comets]
Abstract

Using in situ measurements from different instruments on board the Rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67P/Churyumov-Gerasimenko. These waves are thought to be generated by a modified ion-Weibel instability that grows due to a beam of water ions created by water molecules that outgass from the comet. We take advantage of a cometary outburst event that occurred on 2016 February 19 to probe this generation mechanism. We analyze the 3D magnetic field waveforms to infer the properties of the magnetic oscillations of the cometary ion waves. They are observed in the typical frequency range (similar to 50 mHz) before the cometary outburst, but at similar to 20 mHz during the outburst. They are also observed to be elliptically right-hand polarized and to propagate rather closely (similar to 0-50 degrees) to the background magnetic field. We also construct a density dataset with a high enough time resolution that allows us to study the plasma contribution to the ion cometary waves. The correlation between plasma and magnetic field variations associated with the waves indicates that they are mostly in phase before and during the outburst, which means that they are compressional waves. We therefore show that the measurements from multiple instruments are consistent with the modified ion-Weibel instability as the source of the singing comet wave activity. We also argue that the observed frequency of the singing comet waves could be a way to indirectly probe the strength of neutral plasma coupling in the 67P environment.

Published
2019
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23. The root of a comet tail: Rosetta ion observations at comet 67P/Churyumov–Gerasimenko

Author

Melaine Saillenfest, Holger Nilsson, Charlotte Goetz, Gabriella Stenberg Wieser, Benoît Tabone, L. Berčič, Etienne Behar, Martin Wieser, Georgios Nicolaou, Pierre Henri, Swedish Institute of Space Physics [Kiruna] (IRF), Swedish Institute of Space Physics [Uppsala] (IRF), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Mullard Space Science Laboratory (MSSL), University College of London [London] (UCL), Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA (UMR_8112)), Sorbonne Université (SU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut de Mécanique Céleste et de Calcul des Ephémérides (IMCCE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Lille-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut für Geophysik und Extraterrestrische Physik [Braunschweig] (IGEP), Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], ANR-15-CE31-0009,SPECTRA,Sonder le Plasma dans l'Environnement d'une ComètE avec RosettA(2015), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Cergy Pontoise (UCP), and Université Paris-Seine-Université Paris-Seine-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)

Subjects
010504 meteorology & atmospheric sciences, Comet, FOS: Physical sciences, Context (language use), Astrophysics, 01 natural sciences, Ion, Atmosphere, comets: individual: 67P, Electric field, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, space vehicles: instruments, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, Earth and Planetary Astrophysics (astro-ph.EP), [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Comet tail, comets: general, Astronomy and Astrophysics, plasmas, Magnetic field, Solar wind, 13. Climate action, Space and Planetary Science, Physics::Space Physics, Astrophysics::Earth and Planetary Astrophysics, methods: observational, Astrophysics - Earth and Planetary Astrophysics
Abstract

The first 1000 km of the ion tail of comet 67P/Churyumov-Gerasimenko were explored by the European Rosetta spacecraft, 2.7 au away from the Sun. We characterised the dynamics of both the solar wind and the cometary ions on the night-side of the comet's atmosphere. We analysed in situ ion and magnetic field measurements and compared the data to a semi-analytical model. The cometary ions are observed flowing close to radially away from the nucleus during the entire excursion. The solar wind is deflected by its interaction with the new-born cometary ions. Two concentric regions appear, an inner region dominated by the expanding cometary ions and an outer region dominated by the solar wind particles. The single night-side excursion operated by Rosetta revealed that the near radial flow of the cometary ions can be explained by the combined action of three different electric field components, resulting from the ion motion, the electron pressure gradients, and the magnetic field draping. The observed solar wind deflection is governed mostly by the motional electric field., Comment: 11 pages, 7 figures

Published
2018
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24. Erratum: Evolution of the ion environment of comet 67P during the Rosetta mission as seen by RPC-ICA

Author

Hans Nilsson, Gabriella Stenberg Wieser, Etienne Behar, Herbert Gunell, Martin Wieser, Marina Galand, Cyril Simon Wedlund, Markku Alho, Charlotte Goetz, Masatoshi Yamauchi, Pierre Henri, Elias Odelstad, Erik Vigren, and Science and Technology Facilities Council (STFC)

Subjects
0201 Astronomical And Space Sciences, Science & Technology, comets: individual: 67P, Space and Planetary Science, Physical Sciences, Astronomy and Astrophysics, Astronomy & Astrophysics, plasmas, methods: data analysis
Published
2017

25. Constraints on cometary surface evolution derived from a statistical analysis of 67P's topography

Author

E. Kuehrt, Luca Penasa, Giampiero Naletto, Marco Fulle, A. Gicquel, Cesare Barbieri, Francesco Marzari, J. L. Bertaux, Stefano Mottola, Ivano Bertini, F. Preusker, Carsten Güttler, Jakob Deller, Gabriele Cremonese, Zhong-Yi Lin, F. Scholten, Géza Kovács, Hans Rickman, Steve Boudreault, Monica Lazzarin, Jörg Knollenberg, L. M. Lara, V. Da Deppo, M. A. Barucci, Michael Küppers, Holger Sierks, Stubbe F. Hviid, Detlef Koschny, J. J. Lopez Moreno, M. De Cecco, P. Gutiérrez-Marquez, Nicolas Thomas, Björn Davidsson, Cecilia Tubiana, Xian Shi, Imre Toth, N. Oklay, Philippe Lamy, Stefano Debei, Maurizio Pajola, X. Hu, Wing-Huen Ip, J. B. Vincent, J.-R. Kramm, Laurent Jorda, Sonia Fornasier, D. de Niem, Marc Hofmann, P. J. Gutierrez, Clement Feller, R. Rodrigo, M. F. A'Hearn, Olivier Groussin, Horst Uwe Keller, DLR Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), Institut für Geophysik und Extraterrestrische Physik [Braunschweig] (IGEP), Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], Jet Propulsion Laboratory (JPL), California Institute of Technology (CALTECH)-NASA, INAF - Osservatorio Astronomico di Trieste (OAT), Istituto Nazionale di Astrofisica (INAF), NASA Ames Research Center (ARC), Centro di Ateneo di Studi e Attività Spaziali 'Giuseppe Colombo' (CISAS), Universita degli Studi di Padova, Max-Planck-Institut für Sonnensystemforschung (MPS), Max-Planck-Gesellschaft, Department of Physics and Astronomy [Uppsala], Uppsala University, Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Department of Astronomy [College Park], University of Maryland [College Park], University of Maryland System-University of Maryland System, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Dipartimento di Fisica e Astronomia 'Galileo Galilei', Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Centro de Astrobiologia [Madrid] (CAB), Instituto Nacional de Técnica Aeroespacial (INTA)-Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), International Space Science Institute [Bern] (ISSI), European Space Research and Technology Centre (ESTEC), European Space Agency (ESA), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), INAF - Osservatorio Astronomico di Padova (OAPD), CNR Institute for Photonics and Nanotechnologies (IFN), Consiglio Nazionale delle Ricerche [Roma] (CNR), Department of Industrial Engineering [Padova], University of Trento [Trento], Instituto de Astrofísica de Andalucía (IAA), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), Space Science Institute [Macau] (SSI), Macau University of Science and Technology (MUST), Department of Information Engineering [Padova] (DEI), Operations Department (ESAC), European Space Astronomy Centre (ESAC), European Space Agency (ESA)-European Space Agency (ESA), Dipartimento di Geoscienze [Padova], Center for Space and Habitability (CSH), University of Bern, Physikalisches Institut [Bern], Universität Bern [Bern], Konkoly Observatory, Research Centre for Astronomy and Earth Sciences [Budapest], Hungarian Academy of Sciences (MTA)-Hungarian Academy of Sciences (MTA), NASA-California Institute of Technology (CALTECH), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC)-Instituto Nacional de Técnica Aeroespacial (INTA), Università degli Studi di Padova = University of Padua (Unipd), Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research (MPS), Agence Spatiale Européenne = European Space Agency (ESA), National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR), Agence Spatiale Européenne = European Space Agency (ESA)-Agence Spatiale Européenne = European Space Agency (ESA), and Universität Bern [Bern] (UNIBE)

Subjects
Surface (mathematics), 010504 meteorology & atmospheric sciences, Distribution (number theory), Comet, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], FOS: Physical sciences, 01 natural sciences, comet, surface evolution, topography, statistical analysis, Rosetta, 0103 physical sciences, Statistical analysis, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Earth and Planetary Astrophysics (astro-ph.EP), Physics, [PHYS]Physics [physics], 67P, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], 520 Astronomy, Comets: individual: 67P, Astronomy and Astrophysics, Geophysics, Comets: general, 620 Engineering, 13. Climate action, Space and Planetary Science, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - Earth and Planetary Astrophysics
Abstract

We present a statistical analysis of the distribution of large-scale topographic features on comet 67P/Churyumov-Gerasimenko.We observe that the cumulative cliff height distribution across the surface follows a power law with a slope equal to -1.69 ± 0.02. When this distribution is studied independently for each region, we find a good correlation between the slope of the power law and the orbital erosion rate of the surface. For instance, the Northern hemisphere topography is dominated by structures on the 100 m scale, while the Southern hemisphere topography, illuminated at perihelion, is dominated by 10 m scale terrain features. Our study suggests that the current size of a cliff is controlled not only by material cohesion but also by the dominant erosional process in each region. This observation can be generalized to other comets, where we argue that primitive nuclei are characterized by the presence of large cliffs with a cumulative height-power index equal to or above -1.5, while older, eroded cometary surfaces have a power index equal to or below -2.3. In effect, our model shows that a measure of the topography provides a quantitative assessment of a comet's erosional history, that is, its evolutionary age. © 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Published
2017
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26. Vertical structure of the near-surface expanding ionosphere of comet 67P probed by Rosetta

Author

Emanuele Cupido, Anders Eriksson, Arnaud Beth, K. L. Heritier, Kathrin Altwegg, Pierre Henri, Chris Carr, Martin Rubin, Erik Vigren, Holger Nilsson, Elias Odelstad, T. W. Broiles, Xavier Vallières, Marina Galand, F. L. Johansson, Etienne Behar, James L. Burch, Imperial College Trust, Science and Technology Facilities Council (STFC), Science and Technology Facilities Council [2006-2012], European Space Agency / Estec, Imperial College London, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Swedish Institute of Space Physics [Uppsala] (IRF), Swedish Institute of Space Physics [Kiruna] (IRF), Physikalisches Institut [Bern], Universität Bern [Bern], Department of Physics [Imperial College London], Space Science Division [San Antonio], Southwest Research Institute [San Antonio] (SwRI), Space and Atmospheric Physics Group [London], Blackett Laboratory, and Imperial College London-Imperial College London

Subjects
Electron density, 010504 meteorology & atmospheric sciences, 530 Physics, Electron, Astronomy & Astrophysics, 7. Clean energy, 01 natural sciences, law.invention, Orbiter, comets: individual: 67P, law, Ionization, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 520 Astronomy, Astronomy, Astronomy and Astrophysics, Plasma, plasmas, Sun: UV radiation, 620 Engineering, methods: data analysis, Computational physics, Outgassing, 0201 Astronomical And Space Sciences, 13. Climate action, Space and Planetary Science, Extreme ultraviolet, Physics::Space Physics, Astrophysics::Earth and Planetary Astrophysics, Ionosphere
Abstract

International audience; The plasma environment has been measured for the first time near the surface of a comet. This unique data set has been acquired at 67P/Churyumov–Gerasimenko during ESA/Rosetta spacecraft's final descent on 2016 September 30. The heliocentric distance was 3.8 au and the comet was weakly outgassing. Electron density was continuously measured with Rosetta Plasma Consortium (RPC)–Mutual Impedance Probe (MIP) and RPC–LAngmuir Probe (LAP) during the descent from a cometocentric distance of 20 km down to the surface. Data set from both instruments have been cross-calibrated for redundancy and accuracy. To analyse this data set, we have developed a model driven by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis–COmetary Pressure Sensor total neutral density. The two ionization sources considered are solar extreme ultraviolet radiation and energetic electrons. The latter are estimated from the RPC–Ion and Electron Sensor (IES) and corrected for the spacecraft potential probed by RPC–LAP. We have compared the results of the model to the electron densities measured by RPC–MIP and RPC–LAP at the location of the spacecraft. We find good agreement between observed and modelled electron densities. The energetic electrons have access to the surface of the nucleus and contribute as the main ionization source. As predicted, the measurements exhibit a peak in the ionospheric density close to the surface. The location and magnitude of the peak are estimated analytically. The measured ionospheric densities cannot be explained with a constant outflow velocity model. The use of a neutral model with an expanding outflow is critical to explain the plasma observations.

Published
2017
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27. Diamagnetic region(s): structure of the unmagnetized plasma around Comet 67P/CG

Author

Marina Galand, James L. Burch, Karl-Heinz Glassmeier, Martin Rubin, Pierre Henri, Charlotte Goetz, Bruce T. Tsurutani, Ingo Richter, Chris Carr, Anders Eriksson, Zoltán Németh, Arnaud Beth, Erik Vigren, Holger Nilsson, Gaëtan Wattieaux, Xavier Vallières, Rajkumar Hajra, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], Imperial College London, Physikalisches Institut [Bern], Universität Bern [Bern], Swedish Institute of Space Physics [Kiruna] (IRF), Wigner Research Centre for Physics [Budapest], Hungarian Academy of Sciences (MTA), Swedish Institute of Space Physics [Uppsala] (IRF), Department of Physics [Imperial College London], Southwest Research Institute [San Antonio] (SwRI), Space and Atmospheric Physics Group [London], Blackett Laboratory, Imperial College London-Imperial College London, Jet Propulsion Laboratory (JPL), California Institute of Technology (CALTECH)-NASA, NASA-California Institute of Technology (CALTECH), Imperial College Trust, Science and Technology Facilities Council (STFC), and European Space Agency / Estec

Subjects
010504 meteorology & atmospheric sciences, 530 Physics, Comet, Context (language use), Astrophysics, Astronomy & Astrophysics, 01 natural sciences, Comet nucleus, Ionization, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 520 Astronomy, Comets: individual: 67P, Astronomy and Astrophysics, Plasma, plasmas, 620 Engineering, methods: data analysis, 0201 Astronomical And Space Sciences, Solar wind, Outgassing, 13. Climate action, Space and Planetary Science, Ionosphere
Abstract

International audience; 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.

Published
2017
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28. The dust environment of comet 67P/Churyumov-Gerasimenko: results from Monte Carlo dust tail modelling applied to a large ground-based observation data set

Author

Luisa Lara, Olga Muñoz, Fernando Moreno, Masafumi Yagi, Pedro J. Gutiérrez, Vincenzo Della Corte, Zhong Y. Lin, Colin Snodgrass, Alessandra Rotundi, ITA, and ESP

Subjects
Physics, 010504 meteorology & atmospheric sciences, Methods: numerical, Infrared, Monte Carlo method, Comet, Comets: individual: 67P, Astronomy, Astronomy and Astrophysics, Radius, 01 natural sciences, Power law, Methods: numerical, Comets: general, Comets: individual: 67P, Comets: general, Space and Planetary Science, Comet nucleus, 0103 physical sciences, Orbit (dynamics), Particle, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract

We present an extensive data set of ground-based observations and models of the dust environment of comet 67P/Churyumov–Gerasimenko covering a large portion of the orbital arc from about 4.5 au pre-perihelion through 3.0 au post-perihelion, acquired during the current orbit. In addition, we have also applied the model to a dust trail image acquired during this orbit, as well as to dust trail observations obtained during previous orbits, in both the visible and the infrared. The results of the Monte Carlo modelling of the dust tail and trail data are generally consistent with the in situ results reported so far by the Rosetta instruments Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) and Grain Impact Analyser and Dust\ud Accumulator (GIADA). We found the comet nucleus already active at 4.5 au pre-perihelion, with a dust production rate increasing up to ∼3000 kg s−1 some 20 d after perihelion passage. The dust size distribution at sizes smaller than r = 1 mm is linked to the nucleus seasons, being described by a power law of index −3.0 during the comet nucleus southern hemisphere winter but becoming considerably steeper, with values between −3.6 and −4.3, during the nucleus southern hemisphere summer, which includes perihelion passage (from about 1.7 au inbound to 2.4 au outbound). This agrees with the increase of the steepness of the dust size distribution found from GIADA measurements at perihelion showing a power index of −3.7. The size distribution at sizes larger than 1 mm for the current orbit is set to a power law of index −3.6, which is near the average value of in situ measurements by OSIRIS on large particles. However, in order to fit the trail data acquired during past orbits previous to the 2009 perihelion passage, a steeper power-law index of −4.1 has been set at those dates, in agreement with previous trail modelling. The particle sizes are set at a minimum of r = 10 μm, and a maximum size, which increases with decreasing heliocentric distance, in the 1–40 cm radius domain. The particle terminal velocities are found to be consistent with the in situ measurements as derived from the instrument GIADA on board Rosetta.

Published
2017

29. Structure and evolution of the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko

Author

Hans Nilsson, Christoph Koenders, Charlotte Goetz, Bruce T. Tsurutani, Chris Carr, Holger Sierks, Pierre Henri, Dennis Frühauff, Kirk C. Hansen, Ingo Richter, Anders Eriksson, Martin Volwerk, Martin Rubin, Karl-Heinz Glassmeier, Carsten Güttler, James L. Burch, Institut für Geophysik und Extraterrestrische Physik [Braunschweig] (IGEP), Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], Department of Atmospheric, Oceanic, and Space Sciences [Ann Arbor] (AOSS), University of Michigan [Ann Arbor], University of Michigan System-University of Michigan System, Southwest Research Institute [San Antonio] (SwRI), Space and Atmospheric Physics Group [London], Blackett Laboratory, Imperial College London-Imperial College London, Swedish Institute of Space Physics [Uppsala] (IRF), Max-Planck-Institut für Sonnensystemforschung (MPS), Max-Planck-Gesellschaft, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Jet Propulsion Laboratory (JPL), California Institute of Technology (CALTECH)-NASA, and Science and Technology Facilities Council (STFC)

Subjects
010504 meteorology & atmospheric sciences, 530 Physics, ROSETTA PLASMA CONSORTIUM, Comet, Astrophysics, Astronomy & Astrophysics, ROSINA, magnetic fields, 01 natural sciences, REGION, Fusion, plasma och rymdfysik, comets: individual: 67P, individual: 67P [comets], 0103 physical sciences, data analysis [methods], ION, PROBE, 010303 astronomy & astrophysics, Short duration, HALLEY, MAGNETOMETER, 0105 earth and related environmental sciences, Physics, Science & Technology, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 520 Astronomy, Astronomy, Astronomy and Astrophysics, Plasma, 620 Engineering, plasmas, Fusion, Plasma and Space Physics, methods: data analysis, [PHYS.PHYS.PHYS-SPACE-PH]Physics [physics]/Physics [physics]/Space Physics [physics.space-ph], Magnetic field, 0201 Astronomical And Space Sciences, 13. Climate action, Space and Planetary Science, SOLAR-WIND, Physical Sciences, MAGNETIC CAVITY, Diamagnetism, Astrophysics::Earth and Planetary Astrophysics, PERIHELION
Abstract

International audience; The long duration of the Rosetta mission allows us to study the evolution of the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko in detail. From 2015 April to 2016 February 665 intervals could be identified where Rosetta was located in a zero-magnetic-field region. We study the temporal and spatial distribution of this cavity and its boundary and conclude that the cavity properties depend on the long-term trend of the outgassing rate, but do not respond to transient events at the spacecraft location, such as outbursts or high neutral densities. Using an empirical model of the outgassing rate, we find a functional relationship between the outgassing rate and the distance of the cavity to the nucleus. There is also no indication that this unexpectedly large distance is related to unusual solar wind conditions. Because the deduced shape of the cavity boundary is roughly elliptical on small scales and the distances of the boundary from the nucleus are much larger than expected we conclude that the events observed by Rosetta are due to a moving instability of the cavity boundary itself.

Published
2017
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30. Measurements of the electrostatic potential of Rosetta at comet 67P

Author

Odelstad, Elias, Stenberg-Wieser, Gabriella, Wieser, Martin, Eriksson, Anders I., Nilsson, Hans, Johansson, Fredrik L., Odelstad, Elias, Stenberg-Wieser, Gabriella, Wieser, Martin, Eriksson, Anders I., Nilsson, Hans, and Johansson, Fredrik L.

Abstract

We present and compare measurements of the spacecraft potential (Vs/c) of the Rosetta spacecraft throughout its stay in the inner coma of comet 67P/Churyumov-Gerasimenko, by the Rosetta Plasma Consortium-LAngmuir Probe (RPC-LAP) and Ion Composition Analyzer (RPC-ICA) instruments. Vs/c has mainly been negative, driven by the high temperature (~5-10 eV) of the coma photoelectrons. The magnitude of the negative Vs/c traces heliocentric, cometocentric, seasonal and diurnal variations in cometary outgassing, consistent with production at or inside the cometocentric distance of the spacecraft being the dominant source of the observed plasma. LAP only picks up a portion of the full Vs/c since the two probes, mounted on booms of 2.2 and 1.6 m length, respectively, are generally inside the potential field of the spacecraft. Comparing with the minimum energy of positive ions collected by ICA, we find numerous cases with strong correlation between the two instruments, from which the fraction of Vs/c picked up by LAP is found to vary between about 0.7 and 1. We also find an ICA energy offset of 13.7 eV (95 per cent CI: [12.5, 15.0]). Many cases of poor correlation between the instruments are also observed, predominantly when local ion production is weak and accelerated ions dominate the flux, or during quiet periods with low dynamic range in Vs/c and consequently low signal-to-noise ratios.

Published
2017
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31. Diamagnetic region(s) : structure of the unmagnetized plasma around Comet 67P/CG

Author

Henri, P., Vallieres, X., Hajra, R., Goetz, C., Richter, I., Glassmeier, K. -H, Galand, M., Rubin, M., Eriksson, Anders I., Nemeth, Z., Vigren, Erik, Beth, A., Burch, J. L., Carr, C., Nilsson, H., Tsurutani, B., Wattieaux, G., Henri, P., Vallieres, X., Hajra, R., Goetz, C., Richter, I., Glassmeier, K. -H, Galand, M., Rubin, M., Eriksson, Anders I., Nemeth, Z., Vigren, Erik, Beth, A., Burch, J. L., Carr, C., Nilsson, H., Tsurutani, B., and Wattieaux, G.

Abstract

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 similar to 100 to similar 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.

Published
2017
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32. Constraints on cometary surface evolution derived from a statistical analysis of 67P's topography

Author

Vincent, J. -B, Hviid, S. F., Mottola, S., Kuehrt, E., Preusker, F., Scholten, F., Keller, H. U., Oklay, N., de Niem, D., Davidsson, B., Fulle, M., Pajola, M., Hofmann, M., Hu, X., Rickman, Hans, Lin, Z. -Y, Feller, C., Gicquel, A., Boudreault, S., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marzari, F., Naletto, G., Penasa, L., Shi, X., Thomas, N., Toth, I., Tubiana, C., Vincent, J. -B, Hviid, S. F., Mottola, S., Kuehrt, E., Preusker, F., Scholten, F., Keller, H. U., Oklay, N., de Niem, D., Davidsson, B., Fulle, M., Pajola, M., Hofmann, M., Hu, X., Rickman, Hans, Lin, Z. -Y, Feller, C., Gicquel, A., Boudreault, S., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marzari, F., Naletto, G., Penasa, L., Shi, X., Thomas, N., Toth, I., and Tubiana, C.

Abstract

We present a statistical analysis of the distribution of large-scale topographic features on comet 67P/Churyumov-Gerasimenko. We observe that the cumulative cliff height distribution across the surface follows a power law with a slope equal to -1.69 +/- 0.02. When this distribution is studied independently for each region, we find a good correlation between the slope of the power law and the orbital erosion rate of the surface. For instance, the Northern hemisphere topography is dominated by structures on the 100 m scale, while the Southern hemisphere topography, illuminated at perihelion, is dominated by 10 m scale terrain features. Our study suggests that the current size of a cliff is controlled not only by material cohesion but also by the dominant erosional process in each region. This observation can be generalized to other comets, where we argue that primitive nuclei are characterized by the presence of large cliffs with a cumulative height-power index equal to or above -1.5, while older, eroded cometary surfaces have a power index equal to or below -2.3. In effect, our model shows that a measure of the topography provides a quantitative assessment of a comet's erosional history, that is, its evolutionary age.

Published
2017
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33. Ion composition at comet 67P near perihelion : Rosetta observations and model-based interpretation

Author

Heritier, K. L., Altwegg, K., Balsiger, H., Berthelier, J. -J, Beth, A., Bieler, A., Biver, N., Calmonte, U., Combi, M. R., De Keyser, J., Eriksson, Anders I., Fiethe, B., Fougere, N., Fuselier, S. A., Galand, M., Gasc, S., Gombosi, T. I., Hansen, K. C., Hassig, M., Kopp, E., Odelstad, Elias, Rubin, M., Tzou, C. -Y, Vigren, Erik, Vuitton, V., Heritier, K. L., Altwegg, K., Balsiger, H., Berthelier, J. -J, Beth, A., Bieler, A., Biver, N., Calmonte, U., Combi, M. R., De Keyser, J., Eriksson, Anders I., Fiethe, B., Fougere, N., Fuselier, S. A., Galand, M., Gasc, S., Gombosi, T. I., Hansen, K. C., Hassig, M., Kopp, E., Odelstad, Elias, Rubin, M., Tzou, C. -Y, Vigren, Erik, and Vuitton, V.

Abstract

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, only NH4+ has 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.

Published
2017
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34. Vertical structure of the near-surface expanding ionosphere of comet 67P probed by Rosetta

Author

Heritier, K. L., Henri, P., Vallieres, X., Galand, M., Odelstad, Elias, Eriksson, Anders I., Johansson, F. L., Altwegg, K., Behar, E., Beth, A., Broiles, T. W., Burch, J. L., Carr, C. M., Cupido, E., Nilsson, H., Rubin, M., Vigren, Erik, Heritier, K. L., Henri, P., Vallieres, X., Galand, M., Odelstad, Elias, Eriksson, Anders I., Johansson, F. L., Altwegg, K., Behar, E., Beth, A., Broiles, T. W., Burch, J. L., Carr, C. M., Cupido, E., Nilsson, H., Rubin, M., and Vigren, Erik

Abstract

The plasma environment has been measured for the first time near the surface of a comet. This unique data set has been acquired at 67P/Churyumov-Gerasimenko during ESA/Rosetta spacecraft's final descent on 2016 September 30. The heliocentric distance was 3.8 au and the comet was weakly outgassing. Electron density was continuously measured with Rosetta Plasma Consortium (RPC)-Mutual Impedance Probe (MIP) and RPC-LAngmuir Probe (LAP) during the descent from a cometocentric distance of 20 km down to the surface. Data set from both instruments have been cross-calibrated for redundancy and accuracy. To analyse this data set, we have developed a model driven by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis-COmetary Pressure Sensor total neutral density. The two ionization sources considered are solar extreme ultraviolet radiation and energetic electrons. The latter are estimated from the RPC-Ion and Electron Sensor (IES) and corrected for the spacecraft potential probed by RPC-LAP. We have compared the results of the model to the electron densities measured by RPC-MIP and RPC-LAP at the location of the spacecraft. We find good agreement between observed and modelled electron densities. The energetic electrons have access to the surface of the nucleus and contribute as the main ionization source. As predicted, the measurements exhibit a peak in the ionospheric density close to the surface. The location and magnitude of the peak are estimated analytically. The measured ionospheric densities cannot be explained with a constant outflow velocity model. The use of a neutral model with an expanding outflow is critical to explain the plasma observations.

Published
2017
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35. Evolution of the ion environment of comet 67P during the Rosetta mission as seen by RPC-ICA

Author

Nilsson, Hans, Wieser, Gabriella Stenberg, Behar, Etienne, Gunell, Herbert, Wieser, Martin, Galand, Marina, Wedlund, Cyril Simon, Alho, Markku, Goetz, Charlotte, Yamauchi, Masatoshi, Henri, Pierre, Odelstad, Elias, Vigren, Erik, Nilsson, Hans, Wieser, Gabriella Stenberg, Behar, Etienne, Gunell, Herbert, Wieser, Martin, Galand, Marina, Wedlund, Cyril Simon, Alho, Markku, Goetz, Charlotte, Yamauchi, Masatoshi, Henri, Pierre, Odelstad, Elias, and Vigren, Erik

Abstract

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.

Published
2017
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36. Investigating short-time-scale variations in cometary ions around comet 67P

Author

Wieser, Gabriella Stenberg, Odelstad, Elias, Wieser, Martin, Nilsson, Hans, Goetz, Charlotte, Karlsson, Tomas, André, Mats, Kalla, Leif, Eriksson, Anders, Nicolaou, Georgios, Wedlund, Cyril Simon, Richter, Ingo, Gunell, Herbert, Wieser, Gabriella Stenberg, Odelstad, Elias, Wieser, Martin, Nilsson, Hans, Goetz, Charlotte, Karlsson, Tomas, André, Mats, Kalla, Leif, Eriksson, Anders, Nicolaou, Georgios, Wedlund, Cyril Simon, Richter, Ingo, and Gunell, Herbert

Abstract

The highly varying plasma environment around comet 67P/Churyumov-Gerasimenko inspired an upgrade of the ion mass spectrometer (Rosetta Plasma Consortium Ion Composition Analyzer) with new operation modes, to enable high time resolution measurements of cometary ions. Two modes were implemented, one having a 4 s time resolution in the energy range 0.3-82 eV/q and the other featuring a 1 s time resolution in the energy range 13-50 eV/q. Comparing measurements made with the two modes, it was concluded that 4 s time resolution is enough to capture most of the fast changes of the cometary ion environment. The 1462 h of observations done with the 4 s mode were divided into hour-long sequences. It is possible to sort 84 per cent of these sequences into one of five categories, depending on their appearance in an energy-time spectrogram. The ion environment is generally highly dynamic, and variations in ion fluxes and energies are seen on time-scales of 10 s to several minutes.

Published
2017
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37. Instrumental and environmental effects on RPC-ICA measurements of the cometary ion dynamics at comet 67P/CG

Author

Berčič, Laura and Berčič, Laura

Abstract

Observations provided from RPC-ICA in combination with the data from RPC-MAG and ROSINA-COPS show that many aspects of the time variability of the detected ions is correlated with the magnetic field or -- to a smaller extent -- with neutral atmosphere density. We also show that not all changes in the cometary ion data reflect the nature of the plasma dynamics, but are a consequence of the instrumental limitations. The main outcome of the article in Appendix 1 is that the cometary ions can be divided into two populations with distinct characteristics. One population we termed the convecting population, is accelerated to higher energies through the interaction with the solar wind. The other population we termed the expanding population is moving radially away from the nucleus in the terminator plane. Both populations exhibit a significant anti-sunward component.In addition we present in this thesis a case with observations day-side of the terminator plane. There we show how the expanding population has a sunward component, consistent with initial radial expansion of the ions from the nucleus which gradually turn into an anti-sunward flow which is then observed in the terminator plane.

Published
2017

38. First in situ detection of the cometary ammonium ion NH4+ (protonated ammonia NH3) in the coma of 67P/C-G near perihelion

Author

M. Hässig, Michael R. Combi, Thierry Sémon, Ursina Calmonte, Martin Rubin, B. Fiethe, Tamas I. Gombosi, K. Mandt, E. Vigren, J. De Keyser, Kathrin Altwegg, Léna Le Roy, Kirk C. Hansen, Arnaud Beth, S. Peroy, Chia-Yu Tzou, K. L. Heritier, Marina Galand, S. A. Fuselier, Sébastien Gasc, Frederik Dhooghe, Hans Balsiger, Jean-Jacques Berthelier, E. Kopp, Department of Physics [Imperial College London], Imperial College London, Physikalisches Institut [Bern], Universität Bern [Bern] (UNIBE), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), HELIOS - LATMOS, Department of Atmospheric, Oceanic, and Space Sciences [Ann Arbor] (AOSS), University of Michigan [Ann Arbor], University of Michigan System-University of Michigan System, Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique (BIRA-IASB), Institute of Computer and Network Engineering [Braunschweig] (IDA), Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], Southwest Research Institute [San Antonio] (SwRI), UTSA Department of Physics and Astronomy [San Antonio], The University of Texas at San Antonio (UTSA), Swedish Institute of Space Physics [Uppsala] (IRF), Department of Physics [London], Universität Bern [Bern], IMPEC - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales ( LATMOS ), Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), HEPPI - LATMOS, Department of Atmospheric, Oceanic, and Space Sciences [Ann Arbor] ( AOSS ), Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique ( BIRA-IASB ), Institute of Computer and Network Engineering [Braunschweig] ( IDA ), Technische Universität Braunschweig [Braunschweig], Southwest Research Institute [San Antonio] ( SwRI ), The University of Texas at San Antonio ( UTSA ), Swedish Institute of Space Physics [Uppsala] ( IRF ), Imperial College Trust, Science and Technology Facilities Council (STFC), and Science and Technology Facilities Council [2006-2012]

Subjects
[ SDU.OCEAN ] Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, Analytical chemistry, Coma (optics), Astrophysics, 01 natural sciences, chemistry.chemical_compound, VOLATILE COMPOSITION, CHEMISTRY, PRODUCTION-RATES, 010303 astronomy & astrophysics, Physics, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, astrochemistry, ROSINA/DFMS, Sun, Fusion, Plasma and Space Physics, 103P/HARTLEY 2, Physical Sciences, P/HALLEY, Astrochemistry, Data analysis, Context (language use), Astronomy & Astrophysics, Mass spectrometry, UV radiation, Ion, Ammonia, Fusion, plasma och rymdfysik, comets: individual: 67P, individual: 67P [comets], 0103 physical sciences, Comets, data analysis [methods], Ammonium, HALLEY, 0105 earth and related environmental sciences, UV radiation [Sun], Science & Technology, Spectrometer, 67P/CHURYUMOV-GERASIMENKO, Astronomy and Astrophysics, 2010 APPARITION, Sun: UV radiation, plasmas, methods: data analysis, 0201 Astronomical And Space Sciences, chemistry, MASS-SPECTROMETER, Space and Planetary Science, Plasmas
Abstract

International audience; In this paper, we report the first in-situ detection of the ammonium ion NH4+ at 67P/Churyumov-Gerasimenko (67P/C-G) in a cometary coma, using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) / Double Focusing Mass Spectrometer (DFMS). Unlike neutral and ion spectrometers onboard previous cometary missions, the ROSINA/DFMS spectrometer, when operated in ion mode, offers the capability to distinguish NH4+ from H2O+ in a cometary coma. We present here the ion data analysis of mass-to-charge ratios 18 and 19 at high spectral resolution and compare the results with an ionospheric model to put the these results into context. The model confirms that the ammonium ion NH4+ is one of the most abundant ion species, as predicted, in the coma near perihelion.

Published
2016
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39. Ionospheric plasma of comet 67P probed by Rosetta at 3 au from the Sun

Author

Galand, M., Heritier, K. L., Odelstad, Elias, Henri, P., Broiles, T. W., Allen, A. J., Altwegg, K., Beth, A., Burch, J. L., Carr, C. M., Cupido, E., Eriksson, Anders, Glassmeier, K. -H, Johansson, Fredrik L., Lebreton, J. -P, Mandt, K. E., Nilsson, H., Richter, I., Rubin, M., Sagnieres, L. B. M., Schwartz, S. J., Semon, T., Tzou, C. -Y, Vallieres, X., Vigren, Erik, Wurz, P., Galand, M., Heritier, K. L., Odelstad, Elias, Henri, P., Broiles, T. W., Allen, A. J., Altwegg, K., Beth, A., Burch, J. L., Carr, C. M., Cupido, E., Eriksson, Anders, Glassmeier, K. -H, Johansson, Fredrik L., Lebreton, J. -P, Mandt, K. E., Nilsson, H., Richter, I., Rubin, M., Sagnieres, L. B. M., Schwartz, S. J., Semon, T., Tzou, C. -Y, Vallieres, X., Vigren, Erik, and Wurz, P.

Abstract

We propose to identify the main sources of ionization of the plasma in the coma of comet 67P/Churyumov-Gerasimenko at different locations in the coma and to quantify their relative importance, for the first time, for close cometocentric distances (< 20 km) and large heliocentric distances (> 3 au). The ionospheric model proposed is used as an organizing element of a multi-instrument data set from the Rosetta Plasma Consortium (RPC) plasma and particle sensors, from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis and from the Microwave Instrument on the Rosetta Orbiter, all on board the ESA/Rosetta spacecraft. The calculated ionospheric density driven by Rosetta observations is compared to the RPC-Langmuir Probe and RPC-Mutual Impedance Probe electron density. The main cometary plasma sources identified are photoionization of solar extreme ultraviolet (EUV) radiation and energetic electron-impact ionization. Over the northern, summer hemisphere, the solar EUV radiation is found to drive the electron density - with occasional periods when energetic electrons are also significant. Over the southern, winter hemisphere, photoionization alone cannot explain the observed electron density, which reaches sometimes higher values than over the summer hemisphere; electron-impact ionization has to be taken into account. The bulk of the electron population is warm with temperature of the order of 7-10 eV. For increased neutral densities, we show evidence of partial energy degradation of the hot electron energy tail and cooling of the full electron population., QC 20200602

Published
2016
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40. Structure and evolution of the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko

Author

Goetz, C., Koenders, C., Hansen, K. C., Burch, J., Carr, C., Eriksson, Anders, Fruehauff, D., Guettler, C., Henri, P., Nilsson, H., Richter, I., Rubin, M., Sierks, H., Tsurutani, B., Volwerk, M., Glassmeier, K. H., Goetz, C., Koenders, C., Hansen, K. C., Burch, J., Carr, C., Eriksson, Anders, Fruehauff, D., Guettler, C., Henri, P., Nilsson, H., Richter, I., Rubin, M., Sierks, H., Tsurutani, B., Volwerk, M., and Glassmeier, K. H.

Abstract

The long duration of the Rosetta mission allows us to study the evolution of the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko in detail. From 2015 April to 2016 February 665 intervals could be identified where Rosetta was located in a zero-magnetic-field region. We study the temporal and spatial distribution of this cavity and its boundary and conclude that the cavity properties depend on the long-term trend of the outgassing rate, but do not respond to transient events at the spacecraft location, such as outbursts or high neutral densities. Using an empirical model of the outgassing rate, we find a functional relationship between the outgassing rate and the distance of the cavity to the nucleus. There is also no indication that this unexpectedly large distance is related to unusual solar wind conditions. Because the deduced shape of the cavity boundary is roughly elliptical on small scales and the distances of the boundary from the nucleus are much larger than expected we conclude that the events observed by Rosetta are due to a moving instability of the cavity boundary itself.

Published
2016
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41. First in situ detection of the cometary ammonium ion NH4+ (protonated ammonia NH3) in the coma of 67P/C-G near perihelion

Author

Beth, A., Altwegg, K., Balsiger, H., Berthelier, J. -J, Calmonte, U., Combi, M. R., De Keyser, J., Dhooghe, F., Fiethe, B., Fuselier, S. A., Galand, M., Gasc, S., Gombosi, T. I., Hansen, K. C., Hassig, M., Heritier, K. L., Kopp, E., Le Roy, L., Mandt, K. E., Peroy, S., Rubin, M., Semon, T., Tzou, C. -Y, Vigren, Erik, Beth, A., Altwegg, K., Balsiger, H., Berthelier, J. -J, Calmonte, U., Combi, M. R., De Keyser, J., Dhooghe, F., Fiethe, B., Fuselier, S. A., Galand, M., Gasc, S., Gombosi, T. I., Hansen, K. C., Hassig, M., Heritier, K. L., Kopp, E., Le Roy, L., Mandt, K. E., Peroy, S., Rubin, M., Semon, T., Tzou, C. -Y, and Vigren, Erik

Abstract

In this paper, we report the first in situ detection of the ammonium ion NH4+ at 67P/Churyumov-Gerasimenko (67P/C-G) in a cometary coma, using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Double Focusing Mass Spectrometer (DFMS). Unlike neutral and ion spectrometers onboard previous cometary missions, the ROSINA/DFMS spectrometer, when operated in ion mode, offers the capability to distinguish NH4+ from H2O+ in a cometary coma. We present here the ion data analysis of mass-to-charge ratios 18 and 19 at high spectral resolution and compare the results with an ionospheric model to put these results into context. The model confirms that the ammonium ion NH4+ is one of the most abundant ion species, as predicted, in the coma near perihelion.

Published
2016
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42. Evolution of the ion environment of comet 67P during the Rosetta mission as seen by RPC-ICA

Author

Etienne Behar, Elias Odelstad, Pierre Henri, Hans Nilsson, Marina Galand, Martin Wieser, Charlotte Goetz, Herbert Gunell, Cyril Simon Wedlund, Erik Vigren, Markku Alho, Masatoshi Yamauchi, Gabriella Stenberg Wieser, Swedish Institute of Space Physics, Luleå University of Technology, Royal Belgian Institute for Space Aeronomy, Imperial College London, University of Oslo, Department of Electronics and Nanoengineering, Technical University of Braunschweig, Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, Aalto-yliopisto, Aalto University, Swedish Institute of Space Physics [Kiruna] (IRF), Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique (BIRA-IASB), University of Oslo (UiO), School of Electrical Engineering [Aalto Univ], Institut für Geophysik und Extraterrestrische Physik [Braunschweig] (IGEP), Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Imperial College Trust, Science and Technology Facilities Council (STFC), and European Space Agency / Estec

Subjects
plasmas -methods, data analysis -comets, 010504 meteorology & atmospheric sciences, Comet, Astronomy & Astrophysics, 01 natural sciences, Ion, Astrobiology, comets: individual: 67P, individual: 67P [comets], 0103 physical sciences, data analysis [methods], High activity, individual, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, 67P, ta115, Low activity, Astronomy and Astrophysics, plasmas, methods: data analysis, 0201 Astronomical And Space Sciences, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics]
Abstract

International audience; 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 reappear 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.

Published
2017
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