Motion of Planets

Jonathan Silverlight wrote in
:

Actually it involves a loss of energy. As a planet (moon, whatever)
rotates, it's distorted by tidal forces. The direction of the
distortions relative to the "fixed" surface of the planet is constantly
changing, causing things to rub together. Energy is dissipated as
heat.


True, but once the planet is locked with one face to the sun, what
causes the rotation to go the other way? That's why I like the idea of
a "flipped" planet which hasn't yet reached tidal lock.

Yes. I didn't mean to address the retro-grade issue, just the locking
issue.

--
Steve Gray

"Jonathan Silverlight" wrote in message
...
In message , Steven Gray
writes
Jonathan Silverlight wrote in
:

We are probably just now viewing Venus in a (relatively)
brief phase of retrograde rotation before it eventually locks in
to its period of revolution around the Sun.

I'm sure this one's been thrashed out here and elsewhere before
(probably with the same participants !) but doesn't that involve some
sort of acceleration, which is hard to explain. Where does the energy
come from?

Actually it involves a loss of energy. As a planet (moon, whatever)
rotates, it's distorted by tidal forces. The direction of the
distortions
relative to the "fixed" surface of the planet is constantly changing,
causing things to rub together. Energy is dissipated as heat.


True, but once the planet is locked with one face to the sun, what
causes the rotation to go the other way? That's why I like the idea of a
"flipped" planet which hasn't yet reached tidal lock.

Unfortunately true. Since I suggested this in the first place, I'm a little
embarrased. But once a planet reaches the point where it stops short of a
full revolution, it won't complete a full revolution in the opposite
direction - it'll just rock back and forth from then on. Same principle as a
pendulum.