Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984pggp.rept...51w&link_type=abstract
In NASA. Washington Repts. of Planetary Geol. Program p 51-53 (SEE N84-23431 13-91)
Astronomy and Astrophysics
Astronomy
Astronomical Models, Celestial Mechanics, Comet Nuclei, Dust, Ejecta, Ice, Orbits, Stellar Atmospheres, Stellar Rotation, Deposition, Mass Distribution, Stellar Luminosity, Stellar Magnitude, Surface Reactions, Trajectories
Scientific paper
On the basis of the icy conglomerate model of cometary nuclei, various observations demonstrate the spotted nature of many or most nuclei, i.e., regions of unusual activity, either high or low. Rotation periods, spin axes and even precession of the axes are determined. The observational evidence for variations in activity over the surfaces of cometary nuclei are listed and discussed. On June 11 the comet IRAS-ARAKI-ALCOCK approached the Earth to a distance of 0.031 AU, the nearest since C/Lexell, 1770 I, providing a unique opportunity for near-nucleus observations. Preliminary analysis of these images establishes the spin axis of the nucleus, with an oblioquity to the orbit plane of approximately 50 deg, and a lag angle of sublimation approximately 35 deg from the solar meridian on the nucleus. Asymmetries of the inner coma suggests a crazy-quilt distribution of ices with differing volatility over the surface of the nucleus. The observations of Comet P/Homes 1892 III, exhibiting two 8-10 magnitude bursts, are carefully analyzed. The grazing encounter produced, besides the first great burst, an active area on the nucleus, which was rotating retrograde with a period of 16.3hr and inclination nearly 180 deg. After the first burst the total magnitude fell less than two magnitudes from November 7 to November 30 (barely naked eye) while the nuclear region remained diffuse or complex, rarely if ever showing a stellar appearance. The fading was much more rapid after the second burst. The grazing encounter distributed a volume of large chunks in the neighborhood of the nucleus, maintaining activity for weeks.
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