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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.space
Subject: Re:  Tenth planet
Message-ID: <6258@utzoo.UUCP>
Date: Fri, 3-Jan-86 11:37:30 EST
Article-I.D.: utzoo.6258
Posted: Fri Jan  3 11:37:30 1986
Date-Received: Fri, 3-Jan-86 11:37:30 EST
References: <>, <923@nmtvax.UUCP>
Organization: U of Toronto Zoology
Lines: 18

>      Perhaps the "tenth planet" is not actually a planet, but perhaps a weak
> stellar companion to Sol, already known as "Nemesis".

Alas, Nemesis has met its fate :-).

(Quick digression:  the theory alluded to here is the notion that periodic
extinctions are caused by near approaches of a companion star, which is in a
*very* long-period orbit [30MY or so], stirring up the Oort cloud and causing
a rain of comets into the inner Solar System.)

The problem with making the Sun a binary star is that Nemesis has to be a
godawful long way out to have such a long orbital period, and it appears
that such an orbit simply is not very stable over geological time scales.
It is not consistent with extinctions at clockwork-regular intervals, at
the very least.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry