Search Publications
Evidence for two classes of comets from their polarimetric properties at large phase angles.
Levasseur-Regourd, A. C.; Hadamcik, E.; Renard, J. B.
The dependence of the linear polarization of solar light scattered by cometary dust upon the phase angle has been studied, through appropriate fits, from a data base of 22 comets and 750 points (mainly in the green and red spectral domains). Although the whole coma polarization is found to slightly increase with the wavelength, all the data obtain…
Three-dimensional multiscale MHD model of cometary plasma environments
Gombosi, Tamas I.; De Zeeuw, Darren L.; Häberli, Roman M. +1 more
First results of a three-dimensional multiscale MHD model of the interaction of an expanding cometary atmosphere with the magnetized solar wind are presented. The model starts with a supersonic and super-Alfvènic solar wind far upstream of the comet (25 Gm upstream of the nucleus) with arbitrary interplanetary magnetic field orientation. The solar…
Heating of the thermal electrons in the coma of comet P/Halley
Geiss, Johannes; Altwegg, Kathrin; Balsiger, Hans +1 more
In the inner coma of a comet the total ion (or electron) density results from an equilibrium between ion production and ion destruction. The ions are mainly produced by photoionization of cometary gas, whereas the main destruction process is dissociative recombination of molecular ions with electrons. The reaction rate for the recombination depend…
Cometary ion pressure anisotropies at comets Halley and Grigg-Skjellerup
Coates, A. J.; Neubauer, F. M.; Johnstone, A. D.
Cometary water group ions are the dominant population controlling the interaction of comets with the solar wind. The distribution function of this population has important effects on the overall structure and boundaries in the comet-solar wind interaction and on the plasma wave activity produced. In this paper we present new results on the behavio…
On the Importance of Dust in Cometary Nuclei
Keller, H. U.; Kührt, E. K.
The icy conglomerate model introduced by Whipple more than 40 years ago has been widely accepted in cometary science because it is able to describe numerous cometary phenomena. In this model comets are described as a conglomerate of ices and dust where the ices represent the major component. However, some recent observations seem to favour dust ri…
Interpretation of HMC Images by a Combined Thermal and Gasdynamic Model
Kührt, E.; Keller, H. U.; Knollenberg, J.
Images of comet Halley's nucleus taken by the HMC camera during the GIOT-TO encounter in 1986 show that a major part of the total dust production is localized in a few active areas which are the sources of gas-dust jets. The global dust distribution in the inner coma is dominated by two main jets roughly directed to the sun. A combination of a 1D …
Upstream and downstream propagating waves generated by pickup ions near comet Halley
Glassmeier, K. -H.; Neubauer, F. M.; Krauklis, I. +3 more
It is well known that most of the Alfvén waves generated in the solar wind by cometary ion pickup are propagating upstream in the solar wind reference frame. However, the magnitude of the small proportion propagating downstream is extremely important because it controls the amount of ion acceleration driven by the second order Fermi process. The v…
Magnetic field structure in the comet Grigg-Skjellerup pileup region
Coates, A. J.; Neubauer, F. M.; Israelevich, P. L. +1 more
The position of the Giotto spacecraft relative to comet Grigg-Skjellerup is found from the draping geometry based on the vector magnetic field data. It is shown that Giotto passed the cometary nucleus on the nightside. The behavior of the magnetic field vectors exhibits two different types in the pileup region. In the outer pileup region, the magn…
Comparison of the wave energy transport at comets p/Halley and p/Giacobini-Zinner
Tsurutani, B. T.; Glassmeier, K. -H.; Neubauer, F. M. +2 more
Using magnetic field, plasma density and flow observations from spacecraft flybys of two comets, Elsässer variables are determined in order to study wave propagation directions. The inbound path of the Giotto spacecraft flyby of comet p/Halley is investigated outside the bow shock (between 10:36 and 19:11 UT on March 13, 1986, corresponding to dis…