Date: Wed, 18 Jun 2003 00:05:40 -0400
From: Steve Smith <sgs@aginc.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?

"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.
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.

For an explanation of the Lagrange points (with a nice graphic) see:
<http://map.gsfc.nasa.gov/m_mm/ob_techorbit1.html>

--
Steve Smith                                           sgs@aginc.net
Agincourt Computing                            http://www.aginc.net
"Truth is stranger than fiction because fiction has to make sense."