[meteorite-list] Simulation of Solar System with 2 Equal Earth-Like Planets in same orbit

From: Francis Graham <francisgraham_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:51 2004
Message-ID: <20040317125800.58584.qmail_at_web40109.mail.yahoo.com>

  Bob Mateson's discussion about a good planet
definition ended with the interesting follow-up
question of what would happen if we had 2 large
planets sharing the same orbit.
  In 1994 the science fiction reviewer William B. Hall
of Pittsburgh discussed the science-fiction idea of an
Anti-Earth, which cropped up in several stories and at
least one movie, about an earth in the opposite side
of the Earth's orbit around the sun, orbiting with the
same period, perpetually hidden by the glare of the
sun. This literary device made for much interesting
science-fiction as you can imagine.
  Of course such a body if it existed would have been
detected in the 19th century because of orbital
perturbations on the other planets, which had been
measurable to sufficient accuracy then.
  Nonetheless Bill and I wondered about the stability
of an Anti-Earth in the solar system. It certainly
would seem it could not be hidden for long, but due to
perturbations would creep around and eventually
interact with Earth. So, we set up a GravSim program
(operating on a 286 machine!) and ran it with an
Anti-Earth over-night. Ejection of one of the Earths
from the solar system took place within 100,000 years.
 Even if the GravSim program had gross limitations (it
likely did) such a fast ejection would likely not be
ameliorated by a more precise algorithm.
  There was no publication of this expected result
except in a small local newsletter devoted to space
travel. ("The Anti-Earth" Rocket Mail, Vol 2 No. 5
Feb. 7, 1994). But it was fun, and so was the movie,
whose title ten years later I can't recall but which
starred Roy Thinnes.
  Anyway, for two planets of the same size
diametrically opposed at least, Bob , your definition
is safe: it seems this is dynamically unstable, and so
the concern is moot.

Francis Graham

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Received on Wed 17 Mar 2004 07:58:00 AM PST

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