Time scales for formation and spreading of velocity shells of pickup ions in the solar wind

Gaffey, J. D.; Winske, D.; Wu, C. S.

doi:10.1029/ja093ia06p05470

Cited by 69 publications

(25 citation statements)

References 68 publications

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“…Using these observations and an estimate of the convection speed of the initial ring distribution toward the comet, these authors estimate an upper limit to the pitch angle scattering 10 4 s, which is equivalent to 60τ g , where τ g is the gyroperiod of an oxygen ion. This is broadly consistent with theoretical estimates of the scattering time, τ , which varies between a few τ g and almost 100τ g (Gary et al 1986;Price & Wu 1987;Gaffey et al 1988). Incidentally, by the time the cometary bow shock was approached at 1.2 × 10 6 km (i.e., just outside), the complete shell was also broadened, showing some energy diffusion as well.…”

Section: Wave-particle Interactions: Role In the Shock Positionsupporting

confidence: 73%

The Global Morphology of the Solar Wind Interaction With Comet Churyumov-Gerasimenko

Mendis

Horányi

2014

ApJ

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The forthcoming Rosetta-Philae mission to comet 67P/Churyumov-Gerasimenko provides a novel opportunity to observe the variable nature of the solar wind interaction with a comet over an extended range of heliocentric distance. We use a simple analytical one-dimensional MHD model to estimate the sizes of the two most prominent features in the global structure of the solar wind interaction with a comet. When the heliocentric distance of the comet reaches d 1.51 AU, we expect a sharp shock to be observed, whose size would increase monotonically as the comet approaches the Sun, reaching a value 15,000 km at perihelion (d 1.29 AU). Upstream of the shock, we expect the velocity-space distribution of the picked up cometary ions to be essentially gyrotropic. A well-defined ionopause is predicted when d 1.61 AU, though its size is expected to be only 25 km at perihelion, and it is expected to be susceptible to the "flute" instability due to its small size. Consequently, we expect the magnetic field to penetrate all the way to the surface of the nucleus. We conclude with a brief discussion of the response of the comet's plasma environment to fast temporal variations in the solar wind.

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Section: Wave-particle Interactions: Role In the Shock Positionsupporting

confidence: 73%

The Global Morphology of the Solar Wind Interaction With Comet Churyumov-Gerasimenko

Mendis

Horányi

2014

ApJ

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“…These simulations used the same Winske and Leroy (1985) code with one important difference: instead of a constant beam component density, the tenuous ion component is injected at a constant rate throughout the simulation in order to model the ionization of cometary neutrals. These self-consistent simulations, as well as those of Gaffey et al (1988) and the test particle computations of Wu et aL (1986) and Price and Wu (1987), demonstrate that pitch-angle scattering by enhanced low-frequency electromagnetic waves leads to the formation of relatively complete velocity shell distributions similar to those observed in the distant environment of Comet Halley. Wu et aL (1986) and Gaffey et al (1988) also have emphasized that the time for pitch-angle scattering to a relatively thin, relatively complete shell in velocity space is considerably faster than the energy scattering time for broadening of the shell toward a thermal distribution.…”

Section: Computer Simulationsmentioning

confidence: 51%

Electromagnetic ion/ion instabilities and their consequences in space plasmas: A review

1991

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Abstract. This paper reviews recent research on the theory and computer simulations of electromagnetic ion/ion instabilities and their consequences in space plasmas. 'Ion/ion' instabilities are growing modes in a collisionless plasma driven unstable by the relative streaming velocity v o of two distinct ion components such that Vo is parallel or antiparallel to the uniform background magnetic field Bo. The space physics regimes which display enhanced fluctuations due to these instabilities and which are reviewed in this paper include the solar wind, the terrestrial foreshock, the plasma sheet boundary layer, and distant cometary environments.

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“…They are decelerated and brought to solar wind velocity (≈ 100 km/s directed away from the sun at 2.2R sun ) by outward propagating fluctuations in the solar magnetic field (e.g. Gaffey et al 1988). While a quantitative treatment of this process is beyond the scope of the present paper, we expect acceleration to occur fast because of the high power of ion-cyclotron waves close to the sun.…”

Section: Size Of the Cloud Of Sublimating Materialsmentioning

confidence: 94%

Sungrazing Comets: Properties of Nuclei and in Situ Detectability of Cometary Ions at 1 AU

Iseli

Küppers

Benz

et al. 2002

Icarus

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A one dimensional sublimation model for cometary nuclei is used to derive size limits for the nuclei of sungrazing comets, and to estimate oxygen ion fluxes at 1 AU from their evaporation. Given that none of the ≈ 300 sungrazers detected by the SOlar and Heliospheric Observatory (SOHO) was observed after disappearing behind the sun, and that small nuclei with a radius of ≈ 3.5 m could be observed, it is assumed that all SOHO sungrazers were completely destroyed. For the case that sublimation alone is sufficient for destruction, the model yields an upper size limit as a function of nuclear density ̺, albedo A and perihelion distance q. If the density of the nuclei is that typical of porous ice (600 kg m −3 ), the maximum size is 63 m. These results confirm similar model calculations by Weissman (1983). An analytical expression is derived that approximates the model results well. We discuss possible modifications of our results by different disruption mechanisms. While disruption by thermal stress does not change the upper size limits significantly, they may be somewhat increased by tidal disruption (up to 100 m for a density of 600 kg m −3 ) dependent on the isotropy of the sublimation process and the tensile strength of the comet. Implications for the Kreutz family of sungrazers are discussed.Oxygen ions from the sublimation of sungrazing comets form a tail. Fluxes from this tail are sufficiently high to be measured at 1 AU by particle detectors on spacecraft, but the duration of a tail crossing is only about half an hour. Therefore the probability of a spacecraft actually encountering a tail of an evaporating sungrazer is only of the order of two percent per year.

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Time scales for formation and spreading of velocity shells of pickup ions in the solar wind

Cited by 69 publications

References 68 publications

The Global Morphology of the Solar Wind Interaction With Comet Churyumov-Gerasimenko

The Global Morphology of the Solar Wind Interaction With Comet Churyumov-Gerasimenko

Electromagnetic ion/ion instabilities and their consequences in space plasmas: A review

Sungrazing Comets: Properties of Nuclei and in Situ Detectability of Cometary Ions at 1 AU

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