Polarization, circular, comet

The first successful detection of circular polarization in comet IP/Halley by Metz and Haether [5], Dollfiis and Suchail [6], Morozhenko et al. [7]. There is strong evidence that aligned non-spherical dust particles are present in eometary atmospheres. 

Measurements of circular polarization are rare and conditions for producing circular polarization in comets are poorly understood. According to theoretical... 

In this paper, we provide both a brief historical review of the polarimetric researches of comets and analysis of the observed angular and spectral characteristics of linear and circular polarization of the scattered solar light by dust particles in order to reveal principal regularities in the polarimetric properties of cometary dust. 

The first comet, for which circular polarization has been found, was comet Halley. Left handed (negative) circular polarization was detected on March 16-20, 1986 [6], but on April 8-28 it had variable sign [5,7], The observed circular polarization was highly variable over the coma and showed temporal variations, from 0.04% up to 2.3%. The degree of circular polarization was found to be strongly dependent on the aperture size. It should be noted that these observations had a very low accuracy. 

Figure 7. Variations of the degree of circular polarization with the cometocentric distance for comet C/1995 01 (Hale-Bopp).

The spatial distribution of circular polarization along the cut through the coma and nucleus in the solar and antisolar directions was investigated for comet S4 (LINEAR) [86]. Its maximum value reached up to 1%. At most times, the degree of circular polarization at the cometary nucleus was close to zero. The left handed as well as right handed polarization was observed over the coma although left-circularly polarized light was systematically observed in the sunward part of the... 

The trend of the averaged degree of circular polarization on the tailward side (Fig. 10) differs considerably from that of the sunward side. It is remarkable that the variations of circular polarization coincide in time with the outbursts, which were caused by fragmentation of the nucleus. During observations from June 28 to July 22, 2000, the comet was in a very active state. The nucleus underwent multiple fragmentations culminating in complete disintegration around July 20. 

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