On the hydromagnetic model of comets

Mendis, D. A.

doi:10.1007/bf00896490

Cited by 16 publications

(3 citation statements)

References 19 publications

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“…Collisional dissociation and ionization processes could also play a very important role, as was demonstrated by the earlier work of Mendis [1976a, 1977]. Mendis [1975, 1976b] (see also Mendis [1978] and Ip [1979b]) had shown that the interaction of the solar wind with the cometary ionosphere could cause the sporadic precipitation of large 1.5 X 1012 6.0 X 10 TM CH4 5.6 X 10 TM 3.0 X 10 TM NH3 5.6 X 10 TM 6.0 X 10 TM Table 3). Compositions 1 and 3 are based on the simplest molecules that contain C, O, N, and H (the solar nebula type models used by Huebner and Giguere [1980]), except that in composition 3 the abundance of NH3 is depleted, while N: is increased.…”

Section: C02 + H V• 0 + Co + + Ementioning

confidence: 99%

“…However, it must be pointed out that the 'reconnection' process may be taking place in the neutral sheet of the cometary magnetotail. In fact, Morrison and Mendis [ 1978] have argued that the smallscale structures observed close to the plasma tail axis of comets may be a consequence of the well-known 'tearing mode' instability (which is associated with magnetic 'merging' or 'reconnection') in the cross-tail current sheet in the cometary plasma tail. So far we have discussed only the morphology and dynamics of the plasma tail.…”

Section: Mendis and Morrison [1979] Have Criticized These Modelsmentioning

confidence: 99%

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The cometary atmosphere and its interaction with the solar wind

Mendis¹,

Houpis²

1982

Reviews of Geophysics

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The present state of both our knowledge and our understanding of cometary atmospheres and their interactions with the solar wind is critically reviewed. Following the introduction (section 1) the spectrophotometry of the cometary atmosphere and the tail is reviewed in section 2. The existing, rather fragmentary, knowledge about atmospheric abundances and the production rates of various molecular species is given in section 3. The deductions that can be made from these values about the chemical composition of the nucleus and their uncertainties are discussed. Existing models of the cometary atmosphere including the ionosphere are critically evaluated in section 4. The continuing dichotomy between models that concentrate on the chemistry while oversimplifying the dynamics and those that concentrate on the dynamics and thermodynamics while minimizing the chemistry is discussed. The need to combine these two approaches in the future is emphasized. The ionization processes in the cometary atmosphere are discussed in section 5. It is emphasized that besides photoionization and charge exchange ionization with the solar wind protons, other (collisional) ionization processes may play a role in the rapid ionization of cometary neutrals in certain situations. The overall nature of the solar wind‐comet interaction is discussed in section 6 with special emphasis on the strong coupling between the solar wind and cometary plasmas, which is responsible for the observed accelerations in the cometary tails. The complex and time‐varying fine structures observed in the plasma tails of comets are discussed next in section 7. The uses of these to infer the strength and morphology of the magnetic field and the associated currents in the plasma tail on one hand, and the varying conditions in the solar wind on the other, are emphasized. The detailed models of the comet‐solar wind interaction, from the earlier fluid dynamic models to the latest MHD models are critically evaluated in section 8, and their limitations are underscored. It is also pointed out that the nature of the solar wind interaction with the cometary atmosphere is highly variable and that in certain circumstances the nature of both the outer and the inner shocks could change. Also, the need for a detailed study of the solar wind interaction with the fledgling cometary atmosphere at larger heliocentric distances is stressed. The review is concluded with section 9, where the emphasis is on the outstanding problems of cometary atmospheres and their interactions with the solar wind.

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Section: C02 + H V• 0 + Co + + Ementioning

confidence: 99%

Section: Mendis and Morrison [1979] Have Criticized These Modelsmentioning

confidence: 99%

The cometary atmosphere and its interaction with the solar wind

Mendis¹,

Houpis²

1982

Reviews of Geophysics

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“…2) Inverted V events and the in-situ measurements of strong electric fields in the magnetosphere (105)(106) [28]. 6) In the interstellar medium and in interstellar clouds there is an abundance of filamentary structures, e.g., the Veil nebula, the Lagoon nebula, the Orion nebula (Fig.…”

Section: B Birkeland Currents In Cosmic Plasmamentioning

confidence: 99%

Evolution of the Plasma Universe: I. Double Radio Galaxies, Quasars, and Extragalactic Jets

Peratt

1986

IEEE Trans. Plasma Sci.

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Abstract-Cosmic plasma physics and our concept of the universe is in a state of rapid revision. This change started with in-situ measurements of plasmas in Earth's ionosphere, cometary atmospheres, and planetary magnetospheres; the translation of knowledge from laboratory experiments to astrophysical phenomena; discoveries of helical and filamentary plasma structures in the Galaxy and double radio sources; and the particle simulation of plasmas not accessible to in-situ measurement. Because of these, Birkeland (field-aligned) currents, double layers, and magnetic-field-aligned electric fields are now known to be far more important to the evolution of space plasma, including the acceleration of charged particles to high energies, than previously thought. This paper and its sequel investigate the observational evidence for a plasma universe threaded by Birkeland currents or filaments. This model of the universe was inspired by the advent of threedimensional fully electromagnetic particle simulations and their application to the study of laboratory z pinches. This study resulted in totally unexpected phenomena in the data post-processed from the simulation particle, field, and history dumps. In particular, when the simulation parameters were scaled to galactic dimensions, the interaction between pinched filaments led to synchrotron radiation whose emission properties were found to share the following characteristics with double radio galaxies and quasars: power magnitude, isophotal morphology, spectra, brightness along source, polarization, and jets. The evolution of these pinched synchrotron emitting plasmas to elliptical, peculiar, and spiral galaxies by continuing the simulation run is addressed in a sequel paper.

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Survey

Alfvén¹

1981

Cosmic Plasma

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On the hydromagnetic model of comets

Cited by 16 publications

References 19 publications

The cometary atmosphere and its interaction with the solar wind

The cometary atmosphere and its interaction with the solar wind

Evolution of the Plasma Universe: I. Double Radio Galaxies, Quasars, and Extragalactic Jets

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