Re: CONCULTURE: dual planets
|Date:||Thursday, November 18, 2004, 20:31|
----- Original Message -----
From: Sally Caves <>
Sent: Wednesday, November 17, 2004 4:52 PM
Subject: Re: CONCULTURE: dual planets
> ----- Original Message -----
> From: "Andreas Johansson" <andjo@...>
> Sooo, if my two roughly Earth-sized planets were tidally locked to one
> another, thus causing enormous tidal effects, would their mutual orbitshave
> to be elliptical to cause these tides? Because you say that if theirorbits
> are close to circular, the mutual tides would be unnoticeable. I want the
> tidal effects. (Am I misunderstanding you, as I think I am?) I also want
> them to present the same face to the other, but I could dispense with that
> feature. If they present the same face, each is slowing down the other's
> rotation, right?
over the course of geologic time, yes. by the same token, the Moon has
been spinning away from Earth for a long while now -- since at least the
death of the Dinosaurs.
> So their days and nights would be longer?
as I understand it, day and night (at least in single-planet settings) are
reliant upon the sunlight from the ignited primary. light reflected from
the Moon is negligable).
in this double system, I can imagine that, being bigger, there might be a
larger surface for light to reflect off the atmosphere/ice of one world, to
the eyes of anyone on the other world...on the other hand, the two worlds
can't be *too* close to one another.
so, even when part of one world is facing the sun (say, New York), it'll
still be having night-time, since the second world might be between the
first world and the sun. if they are
tidally-locked/geologically-syncronized or some such, some parts of the
world would be almost polar in their day-night cycles, experiencing "day"
only when the two worlds are *both* side-by-side & exposed to light from the
did that make any sense?
> Ooh. How could
> life survive in that condition? Would any one planet seem to rise and set
> for the other?
*everything* would rise and set...though, if they're locked to one another,
I'd guess that the folks on teh side facing the other world wouldn't have
much (if any) astronomy: no way to see stars, not with the light of that
other world, or the shadow of that same world, in the way.
> In brief, how would an elliptical orbit affect tides,
> rotation, etc.?
if they're not locked, the tides would follow the orbitting planet......if
they are locked, the sea level would be permanently higher facing the other
planet, though neap (solar) tides would still give at least a little wave
> One planet would be slightly smaller than the other: I'm
> imagining a planet earth's size, and another planet bigger than Mars, but
> not as big as earth. Both support life. The bigger planet has larger seas
makes sense: more gravity (that's my assumption: size = mass, though it
may not be true).