What set the planets into motion?

Question

Going way back to when planets and the sun were forming from small particles being attracted to each other, what set these bodies into motion? I realize that the inertia the planets hold prevent them from being pulled together, but where did this inertia originate? What first made the planets spin and revolve?

Answer 1

The motion of the planets is a result of the intitial accretion of matter as our solar system was formed from interstellar dust. The suns in our nearby cluster formed from a largish nebula about 4 to 5 billion years ago. This nebula was itself made up of material that had originally been in multiple stars that burnt out and supernova'd, dispersing their material throughout local space. As an amusing side note, all elements heavier than hydrogen are naturally formed only by the fusion process in stars - so even if we exclude the hydrogen component of water at least 45% of the matter which composes your body was at one time part of a star.

When the elements of the early stars began to coalesce, the linear motion given to them by the supernova of their originating stars was modified by gravitic attraction of nearby particles to circular motion. As a metaphor, consider the motion of water going down a drain. The early solar system was a diffuse disc of small particles that were locally attracted. These lumped up to form the various planets. When the individual particles glommed together, the inertia they originally had was not destroyed, it was combined with that of the other elements that composed the planet.

So in a manner that is similar to Coriolis force, any particle that orbited farther from the sun had a bit more energy than a particle orbiting nearer the sun. When gravity brought them together, the linear energy was converted into rotational energy. The sum of all the energies of component particles is what makes the planets spin.

Answer 2

The solar system formed from a collapsing cloud of gas and dust. A large cloud.

Since most "young" stars are born in clusters, the cloud may have been large enough to form many stars.

As the cloud collapses, the rotational inertia that is already present will cause the cloud to take the form of a disk and rotate around its centre of gravity.

Even if there is no net rotation over the entire cloud, there may be regions of local rotation in a large enough cloud and many of these may become separate systems.

When the star and planets form, the disk already has rotational energy. The planets are simply continuing on the rotation that existed in the original cloud.

What started the rotation? Any random movement of particles within the cloud, or any presence of non-symmetric masses in the vicinity. In fact, it is statistically very improbable that a large cloud would collapse without at least some regions ending up with some rotation. It is not impossible, just rare.

Answer 3

When gravity pulled the small particles together, any small motion that they had already turned into a rotation around the center or mass (the sun), and the rotation accelerated as the stuff got closer to the sun.
It's like if you twirl a ball on a string and start making the string shorter. The ball speeds up. It doesn't take much initial motion to get it started.

Answer 4

My understanding is that the energy created through the chemical reactions of the initial explosion of the Big Bang is the initial energy source. From there that momentum as well as the energy of transferrence from one body to another set things in motion. Then when looking at the specific orbits that the planets and other bodies maintain we must consider magnetisms role as well as Newton's Law of motion - A body in motion tends to stay in motion.

I think that's a pretty good summary of the process. I may have left out a few concepts, but I hope what I have written will help.
Good Luck!

Answer 5

the sun sets the planets in position because the planets are trapped in the suns gravitational pull what sets the planets in motion is inertia.. i think.. or its gravity too...but because when the planets came to the solar system as asteriods or whatever they were moving very fast and they couldnt just stop so it kind of slingshoted its way around the sun because it was close enough to get sucked into the pull and they just kept going around the sun

Answer 6

Hi. The conservation of angular momentum.