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From: jtk@mordor.UUCP (Jordan Kare)
Newsgroups: net.space
Subject: Re:  Tenth planet
Message-ID: <4940@mordor.UUCP>
Date: Wed, 8-Jan-86 00:29:56 EST
Article-I.D.: mordor.4940
Posted: Wed Jan  8 00:29:56 1986
Date-Received: Thu, 9-Jan-86 06:22:29 EST
References: <> <923@nmtvax.UUCP> <6258@utzoo.UUCP>
Reply-To: jtk@mordor.UUCP (Jordan Kare)
Organization: S-1 Project, LLNL
Lines: 46
Summary: The Reports of my Death Star are Greatly Exaggerated


Sorry I didn't catch this before my preceeding posting

>>      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

This is not correct.  Extensive simulations (Notably by Piet Hut
of the Princeton Institute for Advanced Studies) have shown that
the mean lifetime of Nemesis's orbit is roughly a billion years.
The orbit is disturbed by passing stars, dust clouds, etc. but
can easily remain stable enough to explain the few data we have,
which only cover the last 250 million years (a mere moment... :-))
If Nemesis was formed with the solar system, then it probably started
in a closer orbit and has been perturbed out to its present
distance; in another couple of billion years it might be gone
(so we need to find it quick :-)).

The evidence for periodic extinctions and periodic cratering, which
the Nemesis theory was created to explain, is subject to dispute.
(The evidence for catastrophic impacts associated with extinctions
is very strong; only the periodicity is speculative).
But IF periodic extinctions do occur, the Nemesis theory DOES 
explain them, and is still the ONLY theory which does so successfully.

Despite what you may read in the New York Times editorial pages, 
Nemesis lives on....

				Jordin Kare
				Formerly of UC Berkeley/LBL Astrophysics
				Home of Nemesis and much, much more....