Photoelectron fluxes in cometary atmospheres

Ashihara, O.

doi:10.1016/0019-1035(78)90089-1

Cited by 16 publications

(9 citation statements)

References 24 publications

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“…In contrast, the midpopulation had higher densities near the comet's flanks, but there was also a local maximum near closest approach. They concluded that the cold and midpopulation were likely of cometary origin [Ashihara, 1978;Cravens, 1987;Gan and Cravens, 1990;Marconi and Mendis, 1986;Häberli et al, 1996], and the hot population was likely the solar wind halo electrons [McComas et al, 1992]. Thomsen et al [1986] found that cometary electrons could be described with a flattop distribution, and that this behavior was similar to electrons observed elsewhere in the heliosphere that had passed through a weak shock [Feldman et al, 1983;Feldman, 1985;Scudder, 1995].…”

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Characterizing cometary electrons with kappa distributions

et al. 2016

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The Rosetta spacecraft has escorted comet 67P/Churyumov‐Gerasimenko since 6 August 2014 and has offered an unprecedented opportunity to study plasma physics in the coma. We have used this opportunity to make the first characterization of cometary electrons with kappa distributions. Two three‐dimensional kappa functions were fit to the observations, which we interpret as two populations of dense and warm (density = 10 cm−3, temperature = 2 × 105 K, invariant kappa index = 10−>1000), and rarefied and hot (density = 0.005 cm−3, temperature = 5 × 105 K, invariant kappa index = 1–10) electrons. We fit the observations on 30 October 2014 when Rosetta was 20 km from 67P, and 3 AU from the Sun. We repeated the analysis on 15 August 2015 when Rosetta was 300 km from the comet and 1.3 AU from the Sun. Comparing the measurements on both days gives the first comparison of the cometary electron environment between a nearly inactive comet far from the Sun and an active comet near perihelion. We find that the warm population density increased by a factor of 3, while the temperature cooled by a factor of 2, and the invariant kappa index was unaffected. We find that the hot population density increased by a factor of 10, while the temperature and invariant kappa index were unchanged. We conclude that the hot population is likely the solar wind halo electrons in the coma. The warm population is likely of cometary origin, but its mechanism for production is not known.

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Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Characterizing cometary electrons with kappa distributions

et al. 2016

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“…A Monte Carlo type model would be well suited to carry out such calculations, because nonradial transport is also possible. Ashihara [1978] did carry out such calculations for a pure H20 comet with a production rate Qn equal to 1030 s -x. The photoelectron fluxes calculated by Ashihara [1978] varied approximately as l/r, as one would expect for purely radial transport.…”

Section: Model Inputs and Parametersmentioning

confidence: 99%

“…Ashihara [1978] did carry out such calculations for a pure H20 comet with a production rate Qn equal to 1030 s -x. The photoelectron fluxes calculated by Ashihara [1978] varied approximately as l/r, as one would expect for purely radial transport. In the present calculations a two-stream model was used, which only allows for radial transport, with an additional constraint of a constant cross-sectional area for the flux; this is equivalent to assuming the presence of a constant, uniform, and radial magnetic field.…”

Section: Model Inputs and Parametersmentioning

confidence: 99%

A new model of cometary ionospheres

Kőrösmezey¹,

Cravens²,

Gombosi³

et al. 1987

J. Geophys. Res.

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The coupled continuity, momentum, and energy equations were solved for ionospheric conditions appropriate for comet Halley at 1 AU. The numerical scheme used is such that any shock transition appears naturally in the solution and no a priori assumptions are necessary. Solutions were obtained for a number of different assumptions concerning electron heating rates, but all showed that the electron temperatures increase rapidly and significantly at a distance from the nucleus where collisional electron‐neutral cooling becomes unimportant. This temperature increase is accompanied by a sharp increase in both the plasma pressure and its associated polarization electric field, causing the supersonic plasma flow to go subsonic. It is not clear at this time whether or not this sonic transition is accompanied by a shock.

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“…Though it is time consuming, but due to its probabilistic nature, it is an excellent technique for studying the energy degradation of particles, provided sufficient sample size is taken. Hence, Monte Carlo methods have been widely used in problems dealing with energetic particle degradation in gases and in applications to the planetary atmospheres [e.g., Cicerone and Bowhill , 1971; Ashihara , 1978; Green et al , 1977, 1985; Singhal et al , 1980; Singhal and Green , 1981; Singhal and Bhardwaj , 1991; Bhardwaj and Singhal , 1993; Michael and Bhardwaj , 2000; Bhardwaj and Michael , 1999a, 1999b; Shematovich et al , 2008].…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo model of electron energy degradation in a CO₂ atmosphere

Bhardwaj

Jain

2009

J. Geophys. Res.

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[ 1 ] AM onte Carlo model has been developed to study the degradation of 1000 eV electrons in an atmosphere of CO 2 ,w hich is one of the most abundant species in Mars' and Ve nus'sa tmospheres. The e-CO 2 cross sections are presented in an assembled set along with their analytical representations. Monte Carlo simulations are carried out at several energies to calculate the ''yield spectra,''w hich embodied all the information related to the electron degradation process and can be used to calculate ''yield'' (or population) for any inelastic process. The numerical yield spectra have been fitted analytically,r esulting in an analytical yield spectra. We have calculated the mean energy per ion pair and efficiencies for various inelastic processes, including the double and dissociative double ionization of CO 2 and negative ion formation. The energy distribution of the secondary electrons produced per incident electron is also presented at few incident energies. The mean energy per ion pair for CO 2 is 37.5 (35.8) eV at 200 (1000) eV, compared to the experimental value 32.7 eV at high energies. Ionization is the dominant loss process at energies above 50 eV with ac ontribution of 50%. Among the excitation processes, 13.6 eV and 12.4 eV states are the dominant loss processes consuming 28% energy above 200 eV.Around and below ionization threshold, 13.6 eV, 12.4 eV,a nd 11

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Photoelectron fluxes in cometary atmospheres

Cited by 16 publications

References 24 publications

Characterizing cometary electrons with kappa distributions

Characterizing cometary electrons with kappa distributions

A new model of cometary ionospheres

Monte Carlo model of electron energy degradation in a CO₂ atmosphere

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Photoelectron fluxes in cometary atmospheres

Cited by 16 publications

References 24 publications

Characterizing cometary electrons with kappa distributions

Characterizing cometary electrons with kappa distributions

A new model of cometary ionospheres

Monte Carlo model of electron energy degradation in a CO2 atmosphere

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Monte Carlo model of electron energy degradation in a CO₂ atmosphere