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The Nucleus: Panel Discussion

Published online by Cambridge University Press:  12 April 2016

C. R. O’Dell

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My approach to the nature and origin of the nucleus is strongly influenced by the quantitative data on amounts of dust and gas being. released near perihelion. Calibrated spectra and photoelectric photometry (Gebel 1970, O’Dell 1971, Stokes 1972) have shown that the morphological division of Oort and Schmidt into dust-rich and dust-poor seems to be correct. More accurately, I can say that we have observed a wide variation in the ratio of scattered light continuum to molecular emission. This may or may not reflect a large variation of the dust to gas ratio in the nucleus. In fact, the apparently dustiest comets may have smallest dust to gas ratio at the nucleus! This is because the process of accelerating the particles out from the nucleus by means of viscous gas flow depends sensitively on the amount of gas leaving. (Finson and Probstein 1968). The comet with weak scattered light is probably one that is unable to lift the particles from the nucleus, leaving a residual surface of particles. Since small particles can be lifted more easily, the remaining surface would selectively become one of large particles, forming an insulating layer of low albedo with internal degas if ication occuring at an even slow rate. This in turn would diminish the particle loss rate, with a rapid convergence to a particle cover and nucleus. This model would explain the variation from continuum strong to continuum poor in the Oort-Schmidt new and old comets, in addition to the intrinsically low luminosity and photometric radius of old comet nuclei.

Type
Part II
Information
International Astronomical Union Colloquium , Volume 25 , Issue Part2: The Study of Comets , 1976 , pp. 588 - 596
Copyright
Copyright © NASA 1976

References

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