On Sat, Mar 05, 2016 at 08:43:52PM -0500, Richard Aiken wrote:
> Just a thought: does this make the satellite a relatively-recent
> (geologically speaking) capture by the planet? And/or mean that it's
> in an unstable orbit (destined to eventually either leave or crash
> into the planet)?

Its orbit is prograde, so tidal forces would generally be lengthening
the distance from the planet and its orbital period.  However, tidal
forces are finicky things -- the timescale can vary by factors of a
hundred depending on many things.

If the satellite is small, tidal interactions between the satellite's
orbit and the planet's rotation will be very weak and it may have been
there for billions of years.  A satellite the size of Earth's Moon
wouldn't stay long in such an orbit, though.

The main tidal interaction would be a locking of the satellite's
rotation to face the planet (near closest approach, if elliptical),
and much weaker ones that very slowly make the orbit less eccentric
and tending toward equatorial.

- Tim