Gas and dust jets in the inner coma of comet Halley

Cosmovici, C. B.; Schwarz, G.; Ip, W.-H.; Mack, Peter

doi:10.1038/332705a0

Cited by 48 publications

(17 citation statements)

References 15 publications

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“…The gas production was seen to be asymmetric, arising from isolated active regions occupying only a small percentage of the total surface. This was confirmed by ground-based observations of gas "jets" of several species (A'Hearn et al, 1986;Cosmovici et al, 1988;Clairemidi et al, 1990) and the Halley Multicolour Camera images showing dust "jets" in the near-nucleus region that act as tracers of the gas dynamics. The bulk of the neutral gas readily isotropizes into a nearly spherical distribution that becomes distorted, at distances greater than a few hundred thousand kilometers from the nucleus, by radiation pressure.…”

Section: Introductionsupporting

confidence: 52%

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Structure of the Coma: Chemistry and Solar Wind Interaction

Huebner

Boice

Schmidt

et al. 1991

International Astronomical Union Colloquium

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ABSTRACT. Much has been learned about the physics and chemistry of comets from the successful spacecraft encounters and intensive remote observing programs of Comets Halley and GiacobiniZinner. Instead of being the panacea for our comet curiosity, these tantalizing "snapshots" have raised new questions, and many fundamental problems remain unsolved. To reap fuller benefits, extensive modeling is necessary to characterize the physical structure and chemical properties of the coma and to infer the composition and structure of the nucleus.We review coma science from the bow shock to the nucleus-coma interface and the formation of the plasma tail. Surrounding the nucleus is a collision-dominated inner region with approximate spherical symmetry. Parent molecules leaving the surface are quickly transformed into a plethora of highly reactive radicals and ions by the attenuated solar ultraviolet (UV) flux and a variety of gas-phase reactions. Departures from spherical symmetry caused by nucleus activity, distributed sources, UV flux, and radiation pressure are discussed. At larger distances from the nucleus, species progressively separate into a multifluid ensemble. As a result, the thermal evolution of the neutral species, the production and energetics of the ions and electrons, and the dynamics of nonthermal atomic and molecular hydrogen must be considered. Dust is a distributed source for some coma species and may provide additional clues to the organic inventory of the nucleus.The solar wind is coupled to the cometary plasma and neutral gases via collisions and the interplanetary magnetic field (IMF). This interaction dramatically affect the plasma flow, resulting in the formation of the plasma tail and discontinuities, such as the bow shock and the contact surface. The Lorentz forces have been modeled in three dimensions with a steady IMF and in the limit of a rapidly changing IMF with averaged effects and detailed chemistry. Counter-and crossstreaming of the ions with respect to the neutrals further affects the plasma flow.Model results have been compared with observations with varying degrees of success. These results are reviewed to describe the cometary environment and to highlight outstanding problems for planning future cometary missions and research.

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Section: Introductionsupporting

confidence: 52%

“…Jet-like dust features had been detected in many comets, but jet-like structures in the coma gas were first identified in P/Halley (Millis and Schleicher, 1986;A'Hearn et al, 1986;Cosmovici et al 1988). The origin of these structures is not fully understood.…”

Section: 2 Asymmetriesmentioning

confidence: 99%

Structure of the Coma: Chemistry and Solar Wind Interaction

Huebner

Boice

Schmidt

et al. 1991

International Astronomical Union Colloquium

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“…The presence of gas structures are not always accompanied by the same features in the dust, and this phenomenon is sometimes noncorrelated and independent (i.e. Comet Halley, A 'Hearn et al 1986;Larson et al 1987;Cosmovici et al 1988;Schulz 1991; or C/1995 O1 (Hale-Bopp), Schulz et al 2000;or C/1996 Q1 (Tabur), Lara et al 2001).…”

Section: Discussionmentioning

confidence: 99%

Gas and dust in Comet C/2000 WM1 during its closest approach to Earth: Optical imaging and long-slit spectroscopy

Lara

Tozzi

Boehnhardt

et al. 2004

A&A

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Abstract. We have investigated the dust and gas coma of the comet C/2000 WM1 (LINEAR) during Dec. 2−4, 2001, its closest approach to Earth. The gaseous coma is slightly asymmetric in CN and C 2 , indicating the presence of some structures which are detected either by applying enhancement techniques or studying the azimuthal distribution of material. This asymmetry is due to the existence of a double jet in a direction almost perpendicular to the Sun-comet direction. These structures are not clearly detected in C 3 . The morphological analysis of the dust coma shows a faint, short and narrow sunward structure, besides the dust tail in a position angle of ∼60• . CN is produced at a rate of 2.43 × 10 26 s −1 with lifetimes that can be considered as representative of HCN being the parent species. In the case of C 2 , the use of usual lifetimes (τ p , τ d ) requires a modified two-steps photolytic model to account for the pronounced flatness of the column density profile in the inner coma. Usual steady-state model gives rise to a Q C 2 = 3.11 × 10 26 s −1 . Other gas species as C 3 and NH 2 have been also detected from the spectrum, although with a lower S/N. The computed production rates are 3.6 × 10 24 s −1 and 2.15 × 10 26 s −1 , respectively. Determination of the CN and C 2 production rates by means of the Haser modeling (Haser 1957) with customary scalelengths indicates that C/2000 WM1 is a C 2 -enriched comet at 1.178 AU heliocentric distance. The dust production rate, parameterised by A(θ) f ρ, is ∼300−400 cm when measured in two continuum regions, centered at 4845 and 6840 Å, whilst this value is slightly lower in Bessel R and Gunn i (∼230 cm). Thus, the gas-to-dust mass ratio is in the order of 6.3, a relatively gassy comet. The surface brightness profiles of the continuum, either azimuthally averaged profiles from the broadband images or in east−west direction from the long-slit spectrum, can be well fitted with m ≈ 1 in log B − log ρ representation. On the other hand, the study of the dust coma as imaged with the broadband and narrowband filters reveals that variations in the size and/or composition of the grains might be occurring while traveling outward. This fact is manifested as a sharp decrease of A f vs. ρ at 700 ≤ ρ ≤ 15 000 km. The fit of these A f profiles vs. ρ points to the existence of two different grain populations with their own scattering properties and scalelengths (i.e. lifetimes). These pronounced variations of A f vs. ρ are accompanied by clear dust color gradients in the 2D maps, unlike the dust color vs. ρ as derived from the spectrum. Since spectroscopic measurements are only obtained in east−west direction and with a very long exposure time, the effect of color variations inside the coma due to disintegrating grains is difficult to detect.

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“…On the other hand, well-defined gas structures have been observed in other comets, starting with the CN and C 2 jets in the coma of comet 1P/Halley (A' Hearn et al, 1986a,b). Since then, a wide range of structures have been observed in images of various gas species, including shells, fans, jets, and even helices (e.g., Schlosser et al, 1986;Cosmovici et al, 1988;Suzuki et al, 1990;Spinrad, 1991;Boehnhardt and Birkle, 1994;Mikuz, 1994;Eberhardy et al, 2000;Lederer and Campins, 2002;Veal et al, 2000;Schulz, 2002;Szabó et al, 2002;Lara et al, 2004;Farnham et al, 2007a;Lin et al, 2007). In some comets, the gas features are coincident with the dust, while in others there is no correlation.…”

Section: Collimation Of Cometary Emissionmentioning

confidence: 99%

“…This improves their measureability and makes them easier to interpret and model. Another benefit is that, not only are the gas features different from the dust features, but the features in one gas species are often different from those in another, revealing signatures of compositional inhomogeneites (Cosmovici et al, 1988;Boehnhardt and Birkle, 1994;Eberhardy et al, 2000;Lederer and Campins, 2002;Schulz, 2002;Lara et al, 2004;Feaga et al, 2007;Lin et al, 2007). If both dust and gas structures are observed in a comet, the results from the two components can be combined to compare the derived properties for consistency and to determine if the gas issues from the same sources as the dust.…”

Section: Morphology As a Diagnostic Toolmentioning

confidence: 99%

Coma morphology of Jupiter-family comets

Farnham

2009

Planetary and Space Science

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We present a general review of cometary coma morphology, with specific reference to how it used in studies of Jupiter family comets. We introduce the most common features that are seen in gas and dust observations, and summarize of how they are used to infer the properties of the nucleus and coma. We also expand the discussion to cover other topics relating to morphology, including the general shape of the coma (characterized by radial gradient profiles) and spatial maps of the color, albedo and polarization of the dust. We address the pros and cons of the different approaches used in the interpretation and analysis of the features. Finally, we review the results obtained for specific comets and compare the Jupiter family comets to those from other classes.

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Gas and dust jets in the inner coma of comet Halley

Cited by 48 publications

References 15 publications

Structure of the Coma: Chemistry and Solar Wind Interaction

Structure of the Coma: Chemistry and Solar Wind Interaction

Gas and dust in Comet C/2000 WM1 during its closest approach to Earth: Optical imaging and long-slit spectroscopy

Coma morphology of Jupiter-family comets

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