Laboratory simulation of plasma phenomena in comets

Danielsson, Lars; Kasai, G. H.

doi:10.1029/ja073i001p00259

Cited by 43 publications

(10 citation statements)

References 14 publications

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“…An apparently good agreement with the mean distance of several groups of satellites, such as the terrestrial and the giant planets, or the Galilean moons in the Jovian system, has been pointed out by Alfv6n. Apart from this basic cosmogonic question the process is sometimes discussed as being responsible for the observed rapid ionization in cometary comae (Danielsson and Kasai, 1968).…”

Section: Introductionmentioning

confidence: 99%

A Spacelab experiment on the critical ionization velocity

Möbius¹,

Boswell²,

Piel³

et al. 1979

Geophysical Research Letters

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Although the existence of a critical ionization velocity has been shown in laboratory experiments certain difficulties remain when one tries to scale the parameters to cosmic dimensions. These problems are discussed in the light of recent theoretical developments, and a possible experiment is described which makes use of the high orbital velocity of spacelab and the large uniform plasma through which it travels.

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Section: Introductionmentioning

confidence: 99%

A Spacelab experiment on the critical ionization velocity

Möbius¹,

Boswell²,

Piel³

et al. 1979

Geophysical Research Letters

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“…The appearance of submicron dust at large distances from the Sun is presumably associated with some other mechanism, such as that suggested by Dolginov (1967).…”

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confidence: 99%

“…Another example of laboratory simulation of cometary phenomena may be seen in the work of Danielsson and Kasai (1968). Their purpose was to study the ionization of molecules and the acceleration mechanisms in cometary atmospheres, as represented in the interaction of C0 2 ice and hydrogen plasma.…”

mentioning

confidence: 99%

“…Studying the behaviour of such systems under conditions of high vacuum and low temperature is of interest both to the physics of solids and to the physics of comets. For instance, Delsemme and Swings (1952) are of the opinion that parent-molecules must be present in cometary nuclei, not as pure ices but as hydrates of the general form BnU 2 0, where B is the appropriate parent-molecule and «H 2 0 is the number of water molecules with which it is combined.…”

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confidence: 99%

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Laboratory Simulation of Icy Cometary Nuclei

Kajmakov¹,

Sharkov²

1972

Symp. - Int. Astron. Union

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Abstract. The problems of laboratory simulation of cometary phenomena are discussed. Results are given of experimental investigations of the thermodynamic parameters of H 2 0 ice and of frozen mixtures of electrolytes during sublimation under conditions of high vacuum and low tem perature. At a distance of 1 AU from the Sun the equilibrium temperature of H 2 0 ice is shown to be about -75 °C. Conditions are determined for the formation and disintegration of dust matrices during the sublimation of ices containing small dust particles. Dust particles are shown to leave the surface of the ice in the form of conglomerates of primary particles. The outflow velocities of the particles are found to be as high as several metres per second. The results obtained are discussed in relation to cometary phenomena.The great strides made by man in gaining mastery over cosmic space have been res ponsible for the vigorous development of research in astrophysics in many directions. Because of their rapid variations, comets are of particular interest to astrophysicists. Since comets are sensitive to electrical and magnetic fields and to the solar wind they can be visualized as cosmic space probes. Observations of changes in their shapes and sizes, as well as in their spectra, permit us to study conditions prevailing in regions of space as yet inaccessible to man-made space probes (Beller, 1963).According to the most widely accepted hypothesis, cometary nuclei consist of mixtures of various ices and particles of high melting point. Solar radiation causes sublimation of the ices, accompanied by ejection of the particles. There are many additional factors that greatly complicate the picture.Most of the molecules, atoms and ions present in cometary atmospheres are formed as a result of ionization and dissociation of primary, or 'parent' molecules. Among these parent-molecules are H 2 0, C0 2 , NH 3 , CH 4 , (CN) 2 and several other organic and inorganic molecules of greater or less complexity (Donn, 1964). The best defined features in cometary spectra are bands corresponding to CN, C 2 , OH and other mole cules.Many cometary phenomena await clarification. There are still a great many un solved problems relating to the compactness and chemical composition of the nucleus, formation of the dust component in the coma, outbursts in brightness, etc. Individual hypotheses fail to explain all the observed facts.Experimental research on comets is nowadays being conducted in many directions, using up-to-date techniques and modern instrumentation. We make particular refer ence to the use of telescopes in conjunction with sophisticated spectrographs and image converters, permitting radical reductions in exposure times; this method has already yielded important results (Rylov, 1967). Another new technique is the use of satellites and spacecraft for photography and spectroscopy of comets in the ultraviolet and infrared. Such studies ensure freedom from the influence of the Earth's atmosphere, enabling new data to be obtained and earlier results to b...

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“…The critical value of the relative velocity is. given by Vc = x/2e q) /M, There are other potential situations where CIV has been proposed to explain the observations: (1) Since the magnetosphere of Jupiter is rotating at high speed while the moon Io is ejecting streams of neutral gas from its volcanoes, CIV may play an important role in the ionization of the neutral gas in the Io system [Cloutier et al, 1978;Debi, 1995]; (2) CIV may also occur in comet tails [Danielsson and Kasai, 1968;Formisano et al, 1982], which generally consist of neutral gas ejected from the comet nucleus [Hughes, 1994]. The tail interacts with the magnetized plasma of the solar wind.…”

Section: Introductionmentioning

confidence: 99%

A review of critical ionization velocity

Lai¹

2001

Reviews of Geophysics

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Abstract. This paper reviews the critical ionization velocity (CIV) phenomenon, with inclusion of recent research. CIV, suggested by Alfv6n in 1954 as part of a larger cosmological theory accounting for the formation of the solar system, is controversial in that laboratory and space experiments to confirm its validity have yielded conflicting results. Theoretical analysis has suggested that the driving mechanism for CIV is some form of beam-plasma instability, such as the lower hybrid instability, which leads to rapid energization of ambient electrons so that they gain enough energy to ionize the beam of neutral atoms by electron impact. The newly created beam ions energize the instability, thus fostering a cyclic process that may lead to an avalanche ionization. Because which the laboratory and the space experiments are carried out and highlight the differences, some of which may explain the different results. INTRODUCTIONThe concept of critical ionization velocity (CIV) [Alfv•n, 1954[Alfv•n, , 1960] is deceptively simple: When a neutral gas travels through a magnetized plasma with a relative velocity exceeding a critical value, rapid ionization of the neutral gas occurs (Figure 1). The critical value of the relative velocity is. given by Vc = x/2e q) /M,where e q) is the ionization energy of a neutral particle and M is its mass. Several reviews of this theory and experimental tests have appeared [Sherman, 1973;Danielsson, 1973;Newell, 1985;Torbert, 1988Torbert, , 1990, the most recent and the most thorough being that by Brenning [1992]. Our aim in this review is to present a more thorough review, giving the pertinent information about the work in the field without going into more detail than necessary. Figure 2 shows, the critical velocities of elements group into bands. As the neutral atoms ionized, they were trapped by the magnetic field, where they underwent collisions to form clusters and other complex ionic species, which were eventually neutralized. Thus, according to Alfv6n, it was this process of condensation and subsequent neutralization that led to the formation of the planets. Since the critical velocities Vc of the elements fall roughly into several bands, several planets were formed, each with a different chemical composition. As will be discussed in the nextRecently, the line widths of the HI (neutral hydrogen emission) lines in interstellar filaments have been oh-

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Laboratory simulation of plasma phenomena in comets

Cited by 43 publications

References 14 publications

A Spacelab experiment on the critical ionization velocity

A Spacelab experiment on the critical ionization velocity

Laboratory Simulation of Icy Cometary Nuclei

A review of critical ionization velocity

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