Date: Wed, 18 Jun 2003 00:15:41 -0400 (EDT)
From: "Keith F. Lynch" <kfl@KeithLynch.net>
To: WSFA members <WSFAlist@KeithLynch.net>
Subject: [WSFA] Re: Constructing Realsitic Solar Systems
Reply-To: WSFA members <WSFAlist@keithlynch.net>

Ted White wrote:

> What about the "Twin Earths" concept -- two planets in the same
> orbit, but on opposite sides of the sun at all times?

Steve Smith wrote:

> "Counter Earth?"  Unfortunately, no.  While the "counter earth"
> position (technically, the Lagrange L3 position) is in gravitational
> balance, it is not stable -- any small perturbation will throw it
> out of alignment.  Perturbations come from the gravitational fields
> of other planets.

Right.  And even if there weren't any other planets in that solar
system, it would still drift off.  It would just take a little longer.
It's like trying to balance a pencil on its point.  Not only will it
soon fall to one side or the other, but there's no plausible natural
way it could have gotten into that state in the first place.

> Only the L4 and L5 points are stable -- if an object there is
> perturbed, it will go into an orbit around the Lagrange point
> instead of heading for parts unknown.

Right.  You could have two earth-like planets in the same orbit, 60
degrees apart, forming an equilateral triangle with their sun.
That should be stable for the long run.

But, once again, there's no plausible way a solar system could have
gotten into that state in the first place.  Unless you postulate feats
of massive engineering.
--
Keith F. Lynch - kfl@keithlynch.net - http://keithlynch.net/
I always welcome replies to my e-mail, postings, and web pages, but
unsolicited bulk e-mail (spam) is not acceptable.  Please do not send me
HTML, "rich text," or attachments, as all such email is discarded unread.