Thread: Planets spin

Not sure if this has been discussed before-planets spin at different rates, right? What determines the spin rate? For planets like Saturn, do the rings spin at the same rate as the planet?

However, I'm not talking about the points on the surface of a random distance from the core; we all know that effects the speed. I'm talking about from the same distance.

I have limited knowledge on astronomy but I'll provide you with what I can.

Well, the rings are just collective asteroids and dust orbiting around planets. I guess the pull of the planet could determine the spin rate. I doubt they'd spin at the same rate as the planet just from a logical observation. Earth doesn't spin at the same rate of the Sun, which it orbits around. Based on that, I'd assume the farther away the ring is from the planet, the slower it'd move, the closer it is, the faster. Also, I'm not sure if satellites can have rings.

Not only do planets spin (rotate) at different rates, but 2 (Venus-Uranus) rotate opposite the rest or the Sun. Pluto as well, if you count as a planet.
Mercury rotates once every 58 Earth days. Its said these rates were determined during the solar systems formation, as large objects collided with the forming planets, where trajectory and size could alter.

Interesting; are there any planets (Not sure if we can tell yet) in other solar system that have rings that rotate opposite of the planet? What about satellites?

No and no....We know of other solar system planets by irregular actions of there sun, or from spot darkness on there star.

So you didn't mis-understand; Rings around the gas planets rotate as the planet. Only some planets (2) rotate, other than the other 6 or sun...

We have no idea of moons in other systems...Logic and our system formation would suggest a good possibility.

Originally Posted by jackson33

Mercury rotates once every 58 Earth days. Its said these rates were determined during the solar systems formation, as large objects collided with the forming planets, where trajectory and size could alter.

Actually the rotation of Mercury is a bad example as this is determined by the gravity of the sun. Just like the Moon is so close to the Earth as to have the gravity influence it's rotation Mercury is so close to the sun that the rotation has almost the same periodicity as the orbit. I don't know the correct English expression but in German it's "gebundene Rotation". Anyone care to translate?

gebundene = binded = fixed = interlinked?

Mercury was a factual rotation to explain different rotations, not an example of *retrograde* or the planets that rotate opposite the sun.
There are several theory on why/how the differences happened, I mentioned the one which I agree with most...early formation chaos.

Is *tidal influence* what your thinking?

@Kalster

I think it's something like "bound rotation", but I'm not shure

@Jackson

It has to do with tidal forces but I gues this was not the term I was looking for.

Yeh sorry, no such word as "binded" What an oaf..

Why is that we cannot look at other planets, yet we can see so far into the universe? I know that planets (at least usually) do not give off light, and intense light is what makes everything else visible, but when you think about it, aren't some of hubble's pictures so far zoomed in, that its as if you are billions of light years away? With that much zoom and the right positioning (so that you see the planet when it is being lit by its star) it should be possible.

Originally Posted by Cold Fusion

Why is that we cannot look at other planets, yet we can see so far into the universe? I know that planets (at least usually) do not give off light, and intense light is what makes everything else visible, but when you think about it, aren't some of hubble's pictures so far zoomed in, that its as if you are billions of light years away? With that much zoom and the right positioning (so that you see the planet when it is being lit by its star) it should be possible.

The Hubble just can't "zoom in" that close. Even at a the distance of the nearest star, the Hubble can only resolve at 19,000,000 km. At that resolution any planets are lost in the glare of the star. The only candidate for a actual image of a extra-solar planet is an object that revolves around a brown dwarf.

Re: the rings

Saturn rotates once every however many hours (like 11 or something crazyfast).

The rings around it don't. They are little chunks of rock ice and whatnot in orbit. you can consider the idea that Saturn has billions of little tiny moons in a low equatorial orbit. Each one of these objects would have a specific orbital velocity depending on how high it was. Higher objects being slower than lower ones. Thus the outer edge of Saturns rings actually rotates around the planet slower than the inner edge. Much in the same way as a sattelite in orbit around the earth in a 200km circular orbit is going faster than one orbiting at 3000km high.


As far as rotations is concerned, try this thought experiment.

Have a large ball on a string so it can rotate freely but remove the friction of coming in contact with the ground.

Now get your hand and brush it lightly, not to impart momentum to the ball so it swings, but rather 'rub' the side so it spins around.

Now in your brain turn the ball into a planet and your hand into a big asteroid.

Add a few billion years and millions of collisions at random angles (but not that random, remember that most of the debris in the solar system is orbiting the sun in the same direction due to the fact it's all from the same nebulaic origin.) and you get 1: different inclinations of pole and 2: different rates of spinning.

Most asteroid strikes will probably be off objects with eliptical orbits, thus as they pass a circular orbit's altitude, they will be moving at a different rate to objects in more circular orbits. On the "Downward" (toward COG) side of the eliptical orbit, the object will be slower, and on the "Upward" (toward the furthest point of the orbit) side of the orbit, elliptical orbit objects will be faster than circular orbit objects at the same height.

If the objects meet with a glancing blow (think "nearly missed" but not quite) the impartation of momentum into the rotational velocity will be the greatest. If it does a headon dive straight in, most of the energy will turn into a crater or slow/speed up the larger objects velocity, changing it's trajectory slightly from that point (perhaps making it's orbit more or less eliptical depending what the angles are... of course destroying the small object in the process.

MA; Actually Jupiter rotates even quicker than Saturn. Per Earth Day Jupiter rotates in .41 day, Saturn in .44 day and even Neptune rotates in .72 day, as does the other gaseous planet Uranus, but retrograde.

Since were into hypotheticals, do you think it possible during formation of our star, other stars were forming. Seems to be the rule and many two and three stars systems can be seen today in orbit with each other.