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The structure of a cometary Type I tail: Ground‐based and ice observations of P/Giacobini‐Zinner
Author(s) -
Slavin J. A.,
Goldberg B. A.,
Smith E. J.,
McComas D. J.,
Bame S. J.,
Strauss M. A.,
Spinrad H.
Publication year - 1986
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl013i011p01085
Subject(s) - physics , plasma sheet , comet , plasma , astrophysics , comet tail , ion , astronomy , magnetosphere , solar wind , quantum mechanics
The in situ magnetic field and plasma measurements from the International Cometary Explorer (ICE) Mission obtained on September 11, 1985 are compared with CCD images of P/Giacobini‐Zinner (G‐Z) acquired with the 3.6 m Canada‐France‐Hawaii Telescope (CFHT) on Mauna Kea, Hawaii and a slit spectrogram from Lick Observatory during the same period. The CFHT image at ∼3.5 hr after the ICE encounter showed a short central ion tail with a diameter of ∼3 × 10³ km and a length of ∼2 × 10 4 km as observed in the H 2 O + bandpass centered at 7025 Å. There was no distinct evidence of fine structure or ray activity. The Lick spectrogram of the H 2 O + emissions taken ∼0.5 hr post‐encounter with the slit perpendicular to the sun‐comet line showed an ion tail with a diameter of 1.2 × 10 4 km. The ICE observations revealed a well defined 9.6 × 10³ km diameter magnetotail composed of two magnetic lobes in pressure equilibrium with a high beta central plasma sheet. These differing measures of tail width are found to be mutually consistent if the ion emissions observed at Earth originate in a slab‐shaped plasma sheet whose orientation is controlled by the direction of the interplanetary magnetic field. The results of this study also suggest that some thinning and thickening of cometary type I tails, usually attributed to plasma instabilities, may be due to changes in the angle at which the plasma sheet is viewed as IMF direction varies.