Photoionization and photodissociation rates in solar and blackbody radiation fields

Huebner, W. F.; Mukherjee, J.

doi:10.1016/j.pss.2014.11.022

Cited by 192 publications

(187 citation statements)

References 59 publications

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“…In the absence of sources and losses, the F, Cl, and O element abundances must vary inversely with the square of the distance (except close to the nucleus) so that their ratios are constant. It is known that there is no significant loss of the hydrogen halides through photo-dissociation as the HF and HCl photo-dissociation length scales far exceed the cometocentric distances considered here; photo-destruction of the main oxygen-bearing species is a similarly slow process so that relatively little oxygen is lost (Huebner & Mukherjee 2015). Being close to the nucleus, losses through charge exchange, electron impact ionization, and ion-neutral reactions are thought to be of limited importance (Vinodkumar et al 2010;Nilsson et al 2015;Fuselier et al 2015).…”

Section: Discussionmentioning

confidence: 93%

Evidence for distributed gas sources of hydrogen halides in the coma of comet 67P/Churyumov–Gerasimenko

Keyser

Dhooghe

Altwegg

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Rosetta has detected the presence of the hydrogen halides HF, HCl, and HBr in the coma of comet 67P/Churyumov-Gerasimenko. These species are known to freeze out on icy grains in molecular clouds. Analysis of the abundances of HF and HCl as a function of cometocentric distance suggests that these hydrogen halides are released both from the nucleus surface and off dust particles in the inner coma. We present three lines of evidence. First, the abundances of HF and HCl relative to the overall neutral gas in the coma appear to increase with distance, indicating that a net source must be present; since there is no hint at any possible parent species with sufficient abundances that could explain the observed levels of HF or HCl, dust particles are the likely origin. Second, the amplitude of the daily modulation of the halide-to-water density due to the rotation and geometry of 67P's nucleus and the corresponding surface illumination is observed to progressively diminish with distance and comet dust activity; this can be understood from the range of dust particle speeds well below the neutral gas expansion speed, which tends to smooth the coma density profiles. Third, strong halogen abundance changes detected locally in the coma cannot be easily explained from composition changes at the surface, while they can be understood from differences in local gas production from the dust particles.

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Section: Discussionmentioning

confidence: 93%

Evidence for distributed gas sources of hydrogen halides in the coma of comet 67P/Churyumov–Gerasimenko

Keyser

Dhooghe

Altwegg

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…But according to NIST, its fragmentation does not produce SO ions. According to Huebner & Mukherjee (2015), the photodissociation rate for SO 2 to SO is at 1 au 1.59 × 10 −4 s −1 . As a consequence, the contribution to SO is negligible as the gas propagation time is merely seconds from the surface of the comet to Rosetta (see Table A1).…”

Section: Somentioning

confidence: 99%

“…Closer to the Sun, photodissociation and ionization potentially become more important for the coma composition since the rates increase. Photodissociation and ionization rates for most sulphur-bearing species in this study have been computed from the values by Huebner & Mukherjee (2015) at 1 au for active and quiet Sun. Here we used the values for quiet Sun.…”

Section: Impact Of Photodissociation and Ionization On Abundance Ratiosmentioning

confidence: 99%

Sulphur-bearing species in the coma of comet 67P/Churyumov–Gerasimenko

Calmonte

Altwegg

Balsiger

et al. 2016

Mon. Not. R. Astron. Soc.

204

300

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“…depending on solar conditions and should fall off as the square of the heliocentric distance [Huebner and Mukherjee, 2015]. Therefore, only a small fraction of the cometary molecules gets ionized in the vicinity of the comet.…”

Section: Introductionmentioning

confidence: 99%

Spatial distribution of low‐energy plasma around comet 67P/CG from Rosetta measurements

Edberg

Eriksson

Odelstad

et al. 2015

Geophysical Research Letters

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We use measurements from the Rosetta plasma consortium Langmuir probe and mutual impedance probe to study the spatial distribution of low‐energy plasma in the near‐nucleus coma of comet 67P/Churyumov‐Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e., the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be ∼1–2·10−6, at a cometocentric distance of 10 km and at 3.1 AU from the Sun. A clear 6.2 h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisionless plasma within 260 km from the nucleus falls off with radial distance as ∼1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low‐energy plasma around the comet.

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Photoionization and photodissociation rates in solar and blackbody radiation fields

Cited by 192 publications

References 59 publications

Evidence for distributed gas sources of hydrogen halides in the coma of comet 67P/Churyumov–Gerasimenko

Evidence for distributed gas sources of hydrogen halides in the coma of comet 67P/Churyumov–Gerasimenko

Sulphur-bearing species in the coma of comet 67P/Churyumov–Gerasimenko

Spatial distribution of low‐energy plasma around comet 67P/CG from Rosetta measurements

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