"Henry Spencer" wrote in message
...
In article ,
Mike Rhino wrote:
Except that such a situation is impossible. The only way it kind of
works
is if the moon somehow ended up in the sun-planet L2 position... which
is
unstable.

That was my first thought. Then it occurred to me that the moon might be
like our moon with 2 week days and 2 week nights. In that case, the moon
would not be unusual, but the planet would be. Mercury was thought to be
tidal locked to the sun at one time.

Actually, Mercury *is* tide-locked to the Sun -- it's just in an odd 3:2
lock rather than the usual 1:1 lock, due to its elliptical orbit.

Returning to the issue, though, there is nothing special about being
tide-locked to a tide-locked body that would give you the situation the
original poster wanted, where the *moon* has permanent darkness on one
side.
--
It seems to me that a tide-locked body in a dawn dusk polar
orbit could well have a permanantly dark side. It just doesn't
require that the primary be tide-locked.

MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |