NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/sci/astro/12034

Internet Message Format | 1992-11-15 | 1.7 KB

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From: [e-mail] (C.E. Thompson)
Newsgroups: sci.astro
Subject: Re: Swift_tuttle's orbit
Message-ID: <[e-mail]>
Date: 16 Nov 92 00:35:04 GMT
References: <[e-mail]>
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In article <[e-mail]>, [e-mail] writes:
|>
|>                                       In 2126 the Earth will intersect
|> the shower maximum on August 14.3, when it will have  r = 1.01338 au.
|> For the comet to be at its descending node ( r = 1.01001 au ) at the
|> same time requires that it have a perihelion passage time of July 26.43.

This raises a point that has been been worrying me in all these probability
estimates. With these figures, even if Swift-Tuttle arrives at the node at
exactly the right time, it *still* misses the earth by 80 earth radii,
because the distances from the sun are not identical. Obviously the value
of r at the node for Swift-Tuttle is uncertain (how uncertain?) but there
must be a substantial factor in the odds due to this which seems to be being
ignored by all those treating the problem as a linear one.

(Note that because of the high relative velocity at which Swift-Tuttle will
be passing by, the capture cross-section does not significantly exceed the
geometrical cross-section of the earth.)

Chris Thompson
JANET:    [e-mail]
Internet: [e-mail]