Double planets

Alastair Reynolds · 13 Jul 1998, 13:00 · from whorl-v0008.mbox · original

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From: areynold at estsa2.estec.esa.nl (Alastair Reynolds)
Subject: Re: (whorl) Double planets
Date: Mon, 13 Jul 1998 15:00:38 +0200 (MET DST)
Message-ID: <whorl-v0008-0664 at digest.urth.net>
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Peter:

>=20
> Unfortunately, I don't think Blue and Green *have* a Lagrange point.
> Hal Clement has a short story called "A Little Knowledge", in which
> a fleeing criminal parks his spaceship what he fondly imagines is
> a Lagrangian point of a double star. But the two stars are too closely
> matched in mass for it to work: one mass has to be considerably bigger
> than the other. (If anyone has the story, and the ratio is 25.8 : 1,
> then I shall appear very clever; if it isn't, well, how can I be expected
> to remember a detail like that?) The story ends with the fugitive
> finally getting round to looking out of the window, to find himself
> plunging into one of the stars as it orbits towards him.
>=20

actually, any two orbiting point masses will always have five lagrangian=20
points around them; the one between them (exactly in the middle for equal=20
masses) is L1. L1 isn't stable - something placed at L1 only needs a=20
tiny nudge in either direction and off it goes.=20

The point HC might have been making is that L4 or L5 (the "usual" Lagrange=20
points, off to either side) might only be stable if the ratio is as above?

blimey - the first thing on the list I've responded to in ages!

al

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