Production, ionization and redistribution of O2 in Saturn's ring atmosphere

Johnson, R. E.; Luhmann, J. G.; Tokar, R. L.; Bouhram, M.; Berthelier, J. J.; Sittler, E. C.; Cooper, J. F.; Hill, T. W.; Smith, H. T.; Michael, M.; Liu, M.; Crary, F. J.; Young, D. T.

doi:10.1016/j.icarus.2005.08.021

Cited by 104 publications

(148 citation statements)

References 45 publications

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“…The different media show an O 2 abundance generally lower than that predicted by models, even if significant progress in modelling has been made (Hincelin et al 2011;Melnick & Kaufman 2015). Abundances of O 2 are also very low in planetary atmospheres (Hall et al 1995;Johnson et al 2006), although physical conditions and processes at play are very different from those in comet nuclei.…”

Section: Introductionmentioning

confidence: 95%

Production of O₂ through dismutation of H₂O₂ during water ice desorption: a key to understanding comet O₂ abundances

Dulieu

Minissale

Bockelée‐Morvan

2016

A&A

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Context. Detection of molecular oxygen and prediction of its abundance have long been a challenge for astronomers. The low abundances observed in few interstellar sources are well above the predictions of current astrochemical models. During the Rosetta mission, an unexpectedly high abundance of O 2 was discovered in the comet 67P/Churyumov-Gerasimenko's coma. A strong correlation between O 2 and H 2 O productions is observed, whereas no such correlation is observed between O 2 and either of CO or N 2 . Aims. We suggest that the O 2 molecule may be formed during the evaporation of water ice. We propose a possible reaction:, a molecule which should be co-produced during the water ice mantle growth on dust grains. We aim to test this hypothesis under realistic experimental conditions. Methods. We performed two sets of experiments. They consist of producing a mixture of D 2 O and D 2 O 2 via the reaction of O 2 and D on a surface held at 10 K. The first set is made on a silicate substrate, and explores the limit of thin films, in order to prevent any complication due to trapping during the desorption. The second set is performed on a pre-deposited H 2 O ice substrate and mimics the desorption of mixed ice. Results. In thin films, O 2 is produced by the dismutation of H 2 O 2 , even at temperatures as low as 155 K. Mixed with water, H 2 O 2 desorbs after the water ice sublimation and even more desorption of O 2 is observed. Conclusions. H 2 O 2 , synthesised during the growth of interstellar ices (or by later processing), desorbs at the latest stage of the water sublimation and undergoes the dismutation reaction. Therefore an O 2 release in the gas phase should occur at the end of the evaporation of ice mantles. Temperature gradients along the geometry of clouds, or interior of comets, should blend the different stages of the sublimation. Averaged along the whole process, a mean value of the O 2 /H 2 O ratio of a few percent in the gas phase seems plausible.

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Section: Introductionmentioning

confidence: 95%

Production of O₂ through dismutation of H₂O₂ during water ice desorption: a key to understanding comet O₂ abundances

Dulieu

Minissale

Bockelée‐Morvan

2016

A&A

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“…Therefore, for the largest methane loss rates proposed, carbon-containing ions should dominate oxygen ions near Titan's orbit. This is the case since the latter must be scattered to the outer magnetosphere from the Enceladus and OH tori (Johnson et al 2006a) or from the ring atmosphere (Johnson et al 2006b). However, the plasma upstream from Titan has been shown to contain a substantial fraction of O C (Hartle et al 2006b).…”

Section: Discussionmentioning

confidence: 99%

Sputtering and heating of Titan's upper atmosphere

Johnson

2008

Phil. Trans. R. Soc. A.

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Titan is an important endpoint for understanding atmospheric evolution. Prior to Cassini's arrival at Saturn, modelling based on Voyager data indicated that the hydrogen escape rate was large (1-3!10 28 amu s K1), but the escape rates for carbon and nitrogen species were relatively small (5!10 26 amu s K1) and dominated by atmospheric sputtering. Recent analysis of the structure of Titan's thermosphere and corona attained from the Ion and Neutral Mass Spectrometer and the Huygens Atmospheric Structure Instrument on Cassini have led to substantially larger estimates of the loss rate for heavy species (0.3-5!10 28 amu s K1). At the largest rate suggested, a mass that is a significant fraction of the present atmosphere would have been lost to space in 4 Gyr; hence, understanding the nature of the processes driving escape is critical. The recent estimates of neutral escape are reviewed here, with particular emphasis on plasma-induced sputtering and heating. Whereas the loss of hydrogen is clearly indicated by the altitude dependence of the H 2 density, three different one-dimensional models were used to estimate the heavy-molecule loss rate using the Cassini data for atmospheric density versus altitude. The solar heating rate and the nitrogen density profile versus altitude were used in a fluid dynamic model to extract an average net upward flux below the exobase; the diffusion of methane through nitrogen was described below the exobase using a model that allowed for outward flow; and the coronal structure above the exobase was simulated by presuming that the observed atmospheric structure was due to solar-and plasma-induced hot particle production. In the latter, it was hypothesized that hot recoils from photochemistry or plasma-ion-induced heating were required. In the other two models, the upward flow extracted is driven by heat conduction from below, which is assumed to continue to act above the nominal exobase, producing a process referred to as 'slow hydrodynamic' escape. These models and the resulting loss rates are reviewed and compared. It is pointed out that preliminary estimates of the composition of the magnetospheric plasma at Titan's orbit appear to be inconsistent with the largest loss rates suggested for the heavy species, and the mean upward flow extracted in the one-dimensional models could be consistent with atmospheric loss by other mechanisms or with transport to other regions of Titan's atmosphere.

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“…Indeed O 2 has been detected to form a tenuous atmosphere around the moons (Johnson et al 2008). However, at present, there is no experimental evidence of the formation of appreciable quantity of ozone after ion bombardment of pure water ice.…”

Section: Ices In Solar System Objectsmentioning

confidence: 99%

“…Boduch et al 2011). O 3 has also been observed in the atmosphere of Dione and Rhea, possibly as a consequence of its release from radiolysed surfaces (Johnson et al 2008). N 2 has been firmly identified on Pluto Douté et al 1999) and Triton ).…”

Section: Introductionmentioning

confidence: 96%

Chemistry induced by energetic ions in water ice mixed with molecular nitrogen and oxygen

Boduch

Domaracka

Fulvio

et al. 2012

A&A

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Context. Several molecular species have been observed as frozen gases in cold environments such as grains in the interstellar/circumstellar medium or icy objects in the outer solar system. Because N 2 and O 2 are homonuclear, symmetric molecules are not easily observed. It is therefore relevant to find indirect methods to prove their presence from astronomical observations. Aims. Here we investigate one of the possible indirect methods, namely the formation of specific molecules by cosmic ion bombardment of ices in astrophysical environments that contain O 2 and N 2 . The observation of these molecules in astronomical environments could act as a trojan horse to detect the presence of frozen molecular oxygen and/or nitrogen. Methods. We have conducted ion bombardment experiments of frozen O 2 , H 2 O and their mixtures with N 2 at the laboratories of CIMAP-GANIL at Caen (France) and LASp at Catania (Italy). Different ions ( 13 C 2+ , Ar 2+ and H + ) and energies (30-200 keV) have been used. Results. We have found that 13 CO 2 is formed when carbon ions are implanted in ices containing H 2 O and/or O 2 . Ozone and nitrogen oxides (NO, N 2 O, NO 2 ) are formed in the studied ices containing O 2 and N 2 with different relative abundances. Conclusions. We suggest that ozone and nitrogen oxides are present and have to be searched for in some specific environments such as dense clouds in the interstellar medium and the surfaces of Pluto, Charon and Triton. Their observation could demonstrate the presence of molecular oxygen and/or nitrogen. A possible interest for the observations of atmospheres in exo-planetary objects is also discussed.

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Production, ionization and redistribution of O2 in Saturn's ring atmosphere

Cited by 104 publications

References 45 publications

Production of O₂ through dismutation of H₂O₂ during water ice desorption: a key to understanding comet O₂ abundances

Production of O₂ through dismutation of H₂O₂ during water ice desorption: a key to understanding comet O₂ abundances

Sputtering and heating of Titan's upper atmosphere

Chemistry induced by energetic ions in water ice mixed with molecular nitrogen and oxygen

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Production, ionization and redistribution of O2 in Saturn's ring atmosphere

Cited by 104 publications

References 45 publications

Production of O2 through dismutation of H2O2 during water ice desorption: a key to understanding comet O2 abundances

Production of O2 through dismutation of H2O2 during water ice desorption: a key to understanding comet O2 abundances

Sputtering and heating of Titan's upper atmosphere

Chemistry induced by energetic ions in water ice mixed with molecular nitrogen and oxygen

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Product

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Production of O₂ through dismutation of H₂O₂ during water ice desorption: a key to understanding comet O₂ abundances

Production of O₂ through dismutation of H₂O₂ during water ice desorption: a key to understanding comet O₂ abundances