From: "Ted White" <twhite8@cox.net>
To: "WSFA members" <WSFAlist@keithlynch.net>
Subject: [WSFA] Re: Constructing Realsitic Solar Systems
Date: Tue, 17 Jun 2003 23:25:17 -0400
Reply-To: WSFA members <WSFAlist@keithlynch.net>

----- Original Message -----
From: "Keith F. Lynch" <kfl@KeithLynch.net>
To: "WSFA members" <WSFAlist@KeithLynch.net>
Sent: Tuesday, June 17, 2003 10:38 PM
Subject: [WSFA] Re: Constructing Realsitic Solar Systems

> > Ladies and gentlemen:  I request some help in constructing a
> > realistic solar system for a fantasy novel universe.
>
> Fantasy?  Or Science Fiction?  For fantasy, make up your own rules.
> Anything goes.
>
[...]
>
> Planets' orbits can't be closely spaced, since they'd strongly perturb
> each other's orbits.  And probably end up colliding within a few
> centuries.  However, there's no known reason one earthlike planet
> can't be the moon of another one.  Of course they'd have to be about
> the same size.  Unfortunately, you probably can't have a *triple*
> planet.  While three earthlike planets *could* orbit a the common
> center of an equilateral triangle, this arrangement isn't stable in
> the long term.  Nor is it clear how it could get started that way.
>
> The late Robert Forward depicted such a double planet with the planets
> almost touching, making it possible to fly between worlds in an
> airplane.  He did point out that this wasn't stable in the long run,
> and the planets would collide and merge in a few million years, which
> would certainly kill all life on both worlds.
>
> If you were to replace our moon with a second earth in the same
> place, it would raise enormous tides.  People could only live in the
> mountains.  Except that the planets probably would have become tidally
> locked to each other eons ago, causing days to be very long, with very
> cold nights and very hot days.  The "moon" would remain stationary in
> the sky, like a synchronous satellite.
>
> A better plan might be be to replace the moon with a second earth four
> times further away, so that it would be the same size in their sky as
> our moon is for us.  It would still raise higher tides than the moon,
> but only by a factor of two or so.  Then neither world would be
> tidally locked, and people on one world could see all the continents,
> in turn, on the other world, and could tell, even in prehistory, that
> it was rotating, and make maps of it.
>
> I wonder if they could communicate before the invention of radio.
> Giant heliographs, perhaps?  Too bad it's not plausible that people on
> both planets would be at anything remotely close to the same level of
> development.  Just by chance, one would be millions of years ahead
> of the other.  Their Neil Armstrong might find the equivalent of
> dinosaurs on the other world, but probably not cavemen, much less
> any kind of civilization.

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

Separately, and in the "fantasy" category, I wrote a story, "And Another
World Above," which appeared in FANTASTIC in the mid-'70s, about a *flat*
Earth, which is paralleled by a flat world overhead.  It is sufficiently
distant -- and with a thick atmosphere inbetween -- that geographic details
are indistinct...but sometimes lights are seen to twinkle at night.  I
always meant to write more stories in that series, and at some point a
character would use a hot air balloon to try to fly to the other world.

--Ted White