# Planetary rotation

## Main Question or Discussion Point

How is it possible for one planet to rotate opposite the others and one to rotate 90 degrees axially from the others, and these continue to rotate without stopping?

Related Astronomy and Astrophysics News on Phys.org
I'm no expert, but the rotation of a planet is not affected by other planets; they are too far away to "notice." Moons orbit close enough to their parent to have their rotation affected, but the planets are too far apart. The real question is how odd rotations got started in the first place, not how is it they can continue. I think the prevailing theory is that massive collisions can do the trick. What doesn't get knocked completely loose is quickly reformed by gravity into a sphere (the planet) but the spin of the ball is redirected by some of the force of the impact (what didn't go into making the mess of fragments and heat.) There are not enough wild objects out there to do this sort of thing in our lifetime (close enough for us to see, that is), or at least we hope not.
As for how a planet keeps spinning, that's easy. Just spin a top and watch it. It spins for a long time because it loses very little energy to the air and off the tiny point on the floor. Planets spin in space, which is a vacuum, so no air there to lose spin energy to, and there is no point on a floor either. So they just keep on going.

Last edited:
the rotation of a planet is not affected by other planets
The rotation is affected by the gravity of other planets. Take Jupiter when it passes near the earth's rotation it affects the tides just like the Moon with its immense gravity even over long distances.

I do not see why a planet traveling the opposite direction as long as its Elliptical Keplerian characteristics support a healthy orbit but the gravity of other planets would be more intense because the planet passes by the other planets more quickly.

Although the early solar system probably would not support a planet going in a different direction because of all the other large asteroids would collide more ready knocking the planet off its course into larger planet.

mgb_phys
Homework Helper
The rotation is affected by the gravity of other otat. r
But not very much or they would all be tidally locked together.
It's because there is no real coupling that weird rotations can continue.

The planets all go around the sun in the same direction because of the rotation of the original proto disk that they and the sun formed from. They all tend to rotate the same way because of the differential rotation of this disk - but thats a smaller effect.

The odd rotation axis of uranus is thought to be because it got hit by something big.

qwe
but the gravity of other planets would be more intense because the planet passes by the other planets more quickly.
you mean less intense. the quicker you zip by a mass, the less acceleration you feel due to that mass overall