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Hydrodynamic Models of the Cometary Atmosphere

Published online by Cambridge University Press:  30 March 2016

D. A. Mendis
D. A. Mendis*
Affiliation:
Department of Electrical Engineering and Computer Sciences, University of California, San Diego, La Jolla, CA 92093

Extract

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As a cometary nucleus, regarded as an admixture of ices and dust (Whipple, 1950), approaches the sun, the ices sublimate and the resulting gases freely expand dragging along some of the dust.

For a typical medium bright comet (e.g., P/Halley) at 1 AU, the cometary atmosphere is collision dominated within a radius Rc, within which the collision mean free path is equal to the radial distance itself. Within this radius, the cometary atmosphere may be considered as a continuum, and described by hydrodynamic equations. Admittedly, this definition of the regime of hydrodynamic flow is rather crude, and what one has is a gradual transition from pure hydrodynamic flow when r << Rc to slip and transitional flow when r ≈ Rc, to free molecular flow when r > Rc. Depending on whether one considers neutral-neutral collisions or neutral-ion collisions Rc ~ 5 × 103 – 104 km for a medium bright comet at a heliocentric distance of 1 AU.

Type
Joint Commission Meetings
Information
Highlights of Astronomy , Volume 6: Highlights of Astronomy. As presented at the XVIIIth General Assembly of the IAU, 1982 , 1983 , pp. 707 - 712
Copyright
Copyright © Reidel 1983

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