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When the solar system formed it began as a cloud of gas and dust. As the sun condensed out of the cloud the remaining gas and dust was drawn into orbit around i
by chongli 5y ago
When the solar system formed it began as a cloud of gas and dust. As the sun condensed out of the cloud the remaining gas and dust was drawn into orbit around it, forming a disk. Over time, larger rocks and pebbles in the disk accumulated the material around them during their orbit of the forming sun, like rolling snowballs getting larger and larger.
At some point during the formation of the sun, enough pressure builds up inside to allow ignition of its fusion fuel (mostly hydrogen). As the sun heats up it begins emitting radiation and the ejection of particles (solar wind). It’s this combination of stuff (light and particles) that pushes lighter gases out of the near orbital region (where the rocky planets formed). Those gases make their way out beyond the asteroid belt and get picked up by the forming gas giants. At the same time, the heavier dust and rocks don’t get pushed very far by the sun and instead get accumulated in the rocky inner planets.
This pattern is more or less consistent around all stars we see out there. Of course, it varies in strength based on the amount of radiation and particles emitted by the star and that is a complex topic all by itself. But I hope the basic picture I’ve given here is informative.
- sokoloff 5y agoThat was informative; thanks! What causes the initial stage to form a disc (rather than a progressively more dense cloud/sphere/blob)? Just the rotation? (In which case, where’s the rotation come from?)
- isatty 5y agoFrom my naive understanding the gas clouds have angular momentum which is conserved when the disk is formed.
- chongli 5y agoAt the beginning there is no rotation. The cloud may start with roughly uniform density along with some momentum. Over time, this density becomes higher in the middle and lower around the outside. Everything in the cloud begins accelerating toward the place of higher density which forms into the sun while at the same time continuing in the direction according to its initial momentum. This is what causes rotation that leads to the formation of a disk. Any time you have momentum in a direction other than the local centre of mass (star, planet, etc), your path of travel curves into a circle (actually an ellipse, but that’s another topic: see Kepler’s laws).
- kadonoishi 5y agoThis is a nice visual: https://youtu.be/tmNXKqeUtJM?t=100 https://youtu.be/tmNXKqeUtJM?t=100