Photochemistry of forbidden oxygen lines in the inner coma of 67P/Churyumov‐Gerasimenko

Cessateur, Gaël; Keyser, Johan De; Maggiolo, Romain; Gibbons, Andrew; Gronoff, Guillaume; Gunell, H.; Dhooghe, Frederik; Loreau, Jérôme; Vaeck, Nathalie; Altwegg, Kathrin; Bieler, André; Briois, C.; Calmonte, Ursina; Combi, M. R.; Fiethe, B.; Fuselier, S. A.; Gombosi, T. I.; Hässig, Myrtha; Roy, Léna Le; Neefs, Eddy; Rubin, Martin; Sémon, Thierry

doi:10.1002/2015ja022013

Cited by 11 publications

(20 citation statements)

References 36 publications

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“…The modelling work of Cessateur et al (2016a) has suggested that O 2 can play a significant role in determining the [OI] G/R ratio. By incorporating a small O 2 abundance, of 1% of the CO production rate, we find that the contribution of O 2 dissociative excitation is very small (more than two orders of magnitude to the total) in producing O( 1 S) whereas it is the third most important source of O( 1 D) for radial distances above 30 km (see Fig 4).…”

Section: Effect Of the Neutral Species Abundancesmentioning

confidence: 99%

“…These studies also constrained the photodissociation yield of water producing O( 1 S) at Lyman-α wavelength as about 1% of the total absorption cross section. After detection of molecular oxygen in comets 67P-Churyumov-Gerasimenko (Bieler et al 2015;Altwegg et al 2019) and 1P/Halley (Rubin et al 2015), the photochemical model developed by Cessateur et al (2016a) has shown that not considering the role of O 2 in the photochemistry of [OI] emissions leads to an underestimation of the CO 2 abundance in comets.…”

Section: Introductionmentioning

confidence: 99%

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Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

Raghuram

Hutsemékers

Opitom

et al. 2020

A&A

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Context. The N 2 and CO-rich and water-depleted comet C/2016 R2 (Pan-STARRS) (hereafter 'C/2016 R2') is a unique comet for detailed spectroscopic analysis. Aims. We aim to explore the associated photochemistry of parent species, which produces different metastable states and forbidden emissions, in this cometary coma of peculiar composition. Methods. We re-analyzed the high-resolution spectra of comet C/2016 R2, which were obtained in February 2018, using the UVES spectrograph of the European Southern Observatory (ESO) Very Large Telescope (VLT). Various forbidden atomic emission lines of [CI], [NI], and [OI] were observed in the optical spectrum of this comet when it was at 2.8 au from the Sun. The observed forbidden emission intensity ratios are studied in the framework of a couple-chemistry emission model. Results. The model calculations show that CO 2 is the major source of both atomic oxygen green and red-doublet emissions in the coma of C/2016 R2 (while for most comets it is generally H 2 O), whereas, CO and N 2 govern the atomic carbon and nitrogen emissions, respectively. Our modelled oxygen green to red-doublet and carbon to nitrogen emission ratios are higher by a factor of 3, when compared to the observations. These discrepancies can be due to uncertainties associated with photon cross sections or unknown production/loss sources. Our modelled oxygen green to red-doublet emission ratio is close to the observations, when we consider an O 2 abundance with a production rate of 30% relative to the CO production rate. We constrained the mean photodissociation yield of CO producing C( 1 S) as about 1%, a quantity which has not been measured in the laboratory. The collisional quenching is not a significant loss process for N( 2 D) though its radiative lifetime is significant (∼10 hrs). Hence, the observed [NI] doublet-emission ratio ([NI] 5198/5200) of 1.22, which is smaller than the terrestrial measurement by a factor 1.4, is mainly due to the characteristic radiative decay of N( 2 D).

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Section: Effect Of the Neutral Species Abundancesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

Raghuram

Hutsemékers

Opitom

et al. 2020

A&A

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“…Those lines are produced by prompt emission following the photodissociation of various parent molecules (H 2 O, CO 2 , CO, but also O 2 ) into a shortlived excited oxygen atoms (Festou and Feldman 1981;Cessateur et al 2016). The combination of measurements of two forbidden lines O 1 D and O 1 S shows that is possible to even estimate the CO 2 /H 2 O ratio (McKay et al 2012;Decock et al 2013;Cessateur et al 2016). The 6300.304 Å line, which is the brightest of the three forbidden oxygen lines has been successfully used to derive water production rates (e.g., Spinrad 1982;McKay et al 2012).…”

Section: Uv/visible Emission Featuresmentioning

confidence: 99%

The Main Belt Comets and ice in the Solar System

Snodgrass

Agarwal

Combi

et al. 2017

Astron Astrophys Rev

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We review the evidence for buried ice in the asteroid belt; specifically the questions around the so-called Main Belt Comets (MBCs). We summarise the evidence for water throughout the Solar System, and describe the various methods for detecting it, including remote sensing from ultraviolet to radio wavelengths. We review progress in the first decade of study of MBCs, including observations, modelling of ice survival, and discussion on their origins. We then look at which methods will likely be most effective for further progress, including the key challenge of direct detection of (escaping) water in these bodies.

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“…The photoionization of these neutrals by the solar extreme ultraviolet radiation (EUV) has been assumed to be the main source of ionization near comets (Mendis et al 1985), although both charge exchange with the solar wind protons and electron impact ionization have also been suggested (Wallis 1973;Kim & Huntress 1975;Kimura et al 2000;Tinck & Bogaerts 2016;López-Patiño et al 2017). The charge exchange between CO and H 2 O + at small distances and the reaction between CO and H 2 CO + at large distance from the cometary nucleus can contribute to CO + production (Haider & Bhardwaj 2005;Cessateur et al 2016). The high density of electrons and molecular ions in the cometary coma facilitates the reactive processes among them, such as the dissociative recombination (DR).…”

Section: Introductionmentioning

confidence: 99%

Reactive collision of electrons with CO⁺ in cometary coma

Moulane

Mezei

Laporta

et al. 2018

A&A

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Context. In order to improve our understanding of the kinetics of the cometary coma, theoretical studies of the major reactive collisions in these environments are needed. Deep in the collisional coma, inelastic collisions between thermal electrons and molecular ions result in recombination and vibrational excitation, the rates of these processes being particularly elevated due to the high charged particle densities in the inner region. Aims. This work addresses the dissociative recombination, vibrational excitation, and vibrational de-excitation of electrons with CO + molecular cations. The aim of this study is to understand the importance of these reactive collisions in producing carbon and oxygen atoms in cometary activity. Methods. The cross-section calculations were based on Multichannel Quantum Defect Theory. The molecular data sets, used here to take into account the nuclear dynamics, were based on ab initio R-matrix approach. Results. The cross sections for the dissociative recombination, vibrational excitation, and vibrational de-excitation processes, for the six lowest vibrational levels of CO + -relevant for the electronic temperatures observed in comets -are computed, as well as their corresponding Maxwell rate coefficients. Moreover, final state distributions for different dissociation pathways are presented. Conclusions. Among all reactive collisions taking place between low-energy electrons and CO + , the dissociative recombination is the most important process at electronic temperatures characterizing the comets. We have shown that this process can be a major source of O( 3 P), O( 1 D), O( 1 S), C( 3 P) and C( 1 D) produced in the cometary coma at small cometocentric distances.

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Photochemistry of forbidden oxygen lines in the inner coma of 67P/Churyumov‐Gerasimenko

Cited by 11 publications

References 36 publications

Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

The Main Belt Comets and ice in the Solar System

Reactive collision of electrons with CO⁺ in cometary coma

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Photochemistry of forbidden oxygen lines in the inner coma of 67P/Churyumov‐Gerasimenko

Cited by 11 publications

References 36 publications

Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

The Main Belt Comets and ice in the Solar System

Reactive collision of electrons with CO+ in cometary coma

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Reactive collision of electrons with CO⁺ in cometary coma