Comet showers and the steady-state infall of comets from the Oort cloud
The appearance of an inner edge to the Oort comet cloud at a semimajor axis of a = (1--2) x 10/sup 4/ AU is an observational artifact. Stellar perturbations are frequent enough and strong enough to assure that a constant fraction of the comets with semimajor axes greater than this are in orbits which bring them within the planetary region. Only infrequent, close stellar encounters are able to repopulate the planet-crossing orbits of comets with smaller semimajor axes. Owing to their relatively short orbital periods which return them frequently to the planetary system, the comets in these more tightly bound orbits will be deflected by Jupiter into drastically different orbits or be destroyed by solar heating before another close stellar passage repopulates their numbers. Comets with semimajor axes less than 2 x 10/sup 4/ AU appear in the inner solar system only in intense bursts or showers which last for a few orbital periods after the close passage of a star to the Sun. This is followed by a much longer span of time during which only comets with a>2 x 10/sup 4/ AU enter the planetary system. The theoretically determined location of the boundary between the semimajor axes of those comets which enter the planetary system only in bursts or showers and those which arrive in a steady stream is very abrupt and falls at the observed inner edge of the Oort cloud. We propose that the comets formed in the outer parts of the collapsing protosun, which had a radius of less than 5 x 10/sup 3/ AU. If this produced a first-generation comet cloud with a radius of 10/sup 3/ AU or greater, the coupled dynamical perturbations of passing stars and Jupiter will, of necessity, lead to the formation of a comet cloud similar that of the observed Oort comet cloud.
- Research Organization:
- Jet Propulsion Laboratory, Pasadena, California 91103
- OSTI ID:
- 5873135
- Journal Information:
- Astron. J.; (United States), Journal Name: Astron. J.; (United States) Vol. 86:11; ISSN ANJOA
- Country of Publication:
- United States
- Language:
- English
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