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

Héritier, K. L.; Altwegg, Kathrin; Balsiger, H.; Berthelier, Jean‐Jacques; Beth, Arnaud; Bieler, André; Biver, Nicolás; Calmonte, Ursina; Combi, M. R.; Keyser, Johan De; Eriksson, Anders; Fiethe, B.; Fougere, N.; Fuselier, S. A.; Galand, M.; Gombosi, T. I.; Hansen, K. C.; Hässig, Myrtha; Kopp, E.; Odelstad, Elias; Rubin, Martin; Tzou, Chia-Yu; Vigren, Erik; Vuitton, V.

doi:10.1093/mnras/stx1912

Cited by 38 publications

(57 citation statements)

References 83 publications

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“…In contrast, abundant N 2 H + is not expected in gas generated from the destruction of volatile-rich solid bodies because the proton affinity of N 2 is lower than that of H 2 O, the major volatile component of comets. This is supported by analysis of the ion chemistry of comet 67P, which reveals that the dominant ion species generated are produced from neutral species with proton affinities higher than that of H 2 O (Heritier et al 2017).…”

Section: Introductionmentioning

confidence: 80%

Probing the Gas Content of Late-stage Protoplanetary Disks with N₂H⁺

Anderson

Blake

Bergin

et al. 2019

ApJ

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The lifetime of gas in circumstellar disks is a fundamental quantity that informs our understanding of planet formation. Studying disk gas evolution requires measurements of disk masses around stars of various ages. Because H 2 gas is unobservable under most disk conditions, total disk masses are based on indirect tracers such as sub-mm dust and CO emission. The uncertainty in the relation between these tracers and the disk mass increases as the disk evolves. In a few well-studied disks, CO exhibits depletions of up to 100× below the assumed interstellar value. Thus, additional tracers are required to accurately determine the total gas mass. The relative lack of nitrogen found in solid solar system bodies may indicate that it persists in volatile form, making nitrogen-bearing species more robust tracers of gas in more evolved disks. Here we present Atacama Large Millimeter/submillimeter Array detections of N 2 H + in two mature, ∼5-11 Myr old disks in the Upper Scorpius OB Association. Such detections imply the presence of H 2-rich gas and sources of ionization, both required for N 2 H + formation. The Upper Sco disks also show elevated N 2 H + /CO flux ratios when compared to previously observed disks with 10× higher CO fluxes. Based on line ratio predictions from a grid of thermochemical disk models, a significantly reduced CO/H 2 abundance of <10 −6 for a gas-to-dust ratio of 100 is required to produce the observed N 2 H + fluxes. These systems appear to maintain H 2 gas reservoirs and indicate that carbon-and nitrogen-bearing species follow distinct physical or chemical pathways as disks evolve.

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Section: Introductionmentioning

confidence: 80%

Probing the Gas Content of Late-stage Protoplanetary Disks with N₂H⁺

Anderson

Blake

Bergin

et al. 2019

ApJ

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“…We have assessed the effect of the solar absorption on the ionospheric densities as a function of the cometocentric distance using the ionospheric model presented in Heritier et al (2017b). However, unlike this previous study in which adiabatic expansion was included, the runs here presented assume a constant neutral outflow velocity, as the impact of adiabatic expansion onto the total ionospheric density is not critical, except for the final plunge onto the comet.…”

Section: Photo-absorption and Beer-lambert Lawmentioning

confidence: 99%

“…This paper mostly assesses the total ion number density without giving further details on the ion chemical composition. The reader is invited to consult Heritier et al (2017b), Beth et al (2016), and Fuselier et al ( , 2016, for more information on the ion composition of comet 67P.…”

Section: Introductionmentioning

confidence: 99%

Plasma source and loss at comet 67P during the Rosetta mission

Héritier

Galand

Henri

et al. 2018

A&A

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114

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Context. The Rosetta spacecraft provided us with a unique opportunity to study comet 67P/Churyumov–Gerasimenko (67P) from a close perspective and over a 2-yr time period. Comet 67P is a weakly active comet. It was therefore unexpected to find an active and dynamic ionosphere where the cometary ions were largely dominant over the solar wind ions, even at large heliocentric distances. Aims. Our goal is to understand the different drivers of the cometary ionosphere and assess their variability over time and over the different conditions encountered by the comet during the Rosetta mission. Methods. We used a multi-instrument data-based ionospheric model to compute the total ion number density at the position of Rosetta. In-situ measurements from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the Rosetta Plasma Consortium (RPC)–Ion and Electron Sensor (IES), together with the RPC–LAngmuir Probe instrument (LAP) were used to compute the local ion total number density. The results are compared to the electron densities measured by RPC–Mutual Impedance Probe (MIP) and RPC–LAP. Results. We were able to disentangle the physical processes responsible for the formation of the cometary ions throughout the 2-yr escort phase and we evaluated their respective magnitudes. The main processes are photo-ionization and electron-impact ionization. The latter is a significant source of ionization at large heliocentric distance (>2 au) and was predominant during the last 4 months of the mission. The ionosphere was occasionally subject to singular solar events, temporarily increasing the ambient energetic electron population. Solar photons were the main ionizer near perihelion at 1.3 au from the Sun, during summer 2015.

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“…Marshall et al () used a range of 400 m/s to 1 km/s, with a preferred value of 700 m/s, to obtain local effective production rates of H 2 O from

{normalH}_{2}^{16} normalO false/ {normalH}_{2}^{18}

O line area ratios obtained by Microwave Instrument on the Rosetta Orbiter for the entire period from August 2014 to April 2016, though no more specific values are given from within this period. Heritier et al () used a one‐dimensional model for the neutral gas based on an adiabatic fluid expansion around the nucleus driven by inner boundary conditions on gas outflow velocity from Huebner and Markiewicz () and temperature from the thermophysical model of Davidsson and Gutiérrez () to find terminal velocities of about 800 m/s. For the purpose of comparison to observed ion velocities in this study, we note simply that the neutral outgassing velocity is on the order of 1 km/s, and that exact values are likely to be lower than this estimate rather than higher.…”

Section: Introductionmentioning

confidence: 99%

Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P

et al. 2018

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A major point of interest in cometary plasma physics has been the diamagnetic cavity, an unmagnetized region in the innermost part of the coma. Here we combine Langmuir and Mutual Impedance Probe measurements to investigate ion velocities and electron temperatures in the diamagnetic cavity of comet 67P, probed by the Rosetta spacecraft. We find ion velocities generally in the range 2–4 km/s, significantly above the expected neutral velocity ≲1 km/s, showing that the ions are (partially) decoupled from the neutrals, indicating that ion‐neutral drag was not responsible for balancing the outside magnetic pressure. Observations of clear wake effects on one of the Langmuir probes showed that the ion flow was close to radial and supersonic, at least with respect to the perpendicular temperature, inside the cavity and possibly in the surrounding region as well. We observed spacecraft potentials ≲−5 V throughout the cavity, showing that a population of warm (∼5 eV) electrons was present throughout the parts of the cavity reached by Rosetta. Also, a population of cold ( ≲0.11emeV) electrons was consistently observed throughout the cavity, but less consistently in the surrounding region, suggesting that while Rosetta never entered a region of collisionally coupled electrons, such a region was possibly not far away during the cavity crossings.

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

Cited by 38 publications

References 83 publications

Probing the Gas Content of Late-stage Protoplanetary Disks with N₂H⁺

Probing the Gas Content of Late-stage Protoplanetary Disks with N₂H⁺

Plasma source and loss at comet 67P during the Rosetta mission

Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P

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

Cited by 38 publications

References 83 publications

Probing the Gas Content of Late-stage Protoplanetary Disks with N2H+

Probing the Gas Content of Late-stage Protoplanetary Disks with N2H+

Plasma source and loss at comet 67P during the Rosetta mission

Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P

Contact Info

Product

Resources

About

Probing the Gas Content of Late-stage Protoplanetary Disks with N₂H⁺

Probing the Gas Content of Late-stage Protoplanetary Disks with N₂H⁺