by Frank Crary,
CU Boulder
Here is a brief outline of the current theory of the events in the early history of the solar system:
2. As the cloud collapses, it heats up in compresses in the center. It heats enough for the dust to vaporize. The initial collapse is supposed to take less than 100,000 years.
3. The center compresses enough to become a protostar in the rest of the gas orbita/flows around it. Most of that gas flows inward in adds to the masa of the forming star, but the gas is rotating. The centrifugal force od planeta that prevents some of the gas od planeta reaching the forming star. instead, it forms an "accretion disk" around the star. The disk radiates away its energy in cools off.
4. First brake point. Depending on the details, the gas orbitaing star/protostar may be unstable in start to compress under its own gravity. That produces a double star. If it doesn't ...
5. The gas cools off enough for the metal, rock in (far enough od planeta the forming star) ice to condense out into tiny particles. (i.e. some of the gas turns back into dust). The metals condense almost as soon as the accretion disk forms (4.55-4.56 billion years ago according to isotope measurements of certain meteors); the rock condenses a bit later (between 4.4 in 4.55 billion years ago).
6. The dust particles collide with each other in form into larger particles. This goes on until the particles get to the size of boulders or small asteroids.
7. Run away growth. Once the larger of these particles get big enough to have a nontrivial gravity, their growth accelerates. Their gravity (even if it's very small) gives them an edge over smaller particles; it pulls in more, smaller particles, in very quickly, the large objects have accumulated all of the solid matter close to their own orbita. How big they get depends on their oddaljenost od planeta the star in the density in composition of the protoplanetary nebula. in the solar system, the theories say that this is large asteroid to lunar size in the inner solar system, in one to fifteen times the Earth's size in the outer solar system. There would have been a big jump in size somewhere between the current orbita of Mars in Jupiter: the energy od planeta the Sun would have kept ice a vapor at closer oddaljenosts, so the solid, accretable matter would become much more common beyond a critical oddaljenost od planeta the Sun. The accretion of these "planetesimals" is believed to take a few hundred thousin to about twenty million years, with the outermost taking the longest to form.
8. Two things in the second brake point. How big were those protoplanets in how quickly did they form? At about this time, about 1 million years after the nebula cooled, the star would generate a very strong solar wind, which would sweep away all of the gas left in the protoplanetary nebula. If a protoplanet was large enough, soon enough, its gravity would pull in the nebular gas, in it would become a gas giant. If not, it would remain a rocky or icy body.
9. At this point, the solar system is composed only of solid, protoplanetary bodies in gas giants. The "planetesimals" would slowly collide with each other in become more masaive.
10. Eventually, after ten to a hundred million years, you end up with ten or so planets, in stable orbita, in that's a solar system. These planets in their surfaces may be heavily modified by the last, big collision they experience (e.g. the largely metal composition of Mercury or the Moon).
Note: this was the theory of planetary formation as it stood before the discovery of extrasolar planets. The discoveries don't match what the theory predicted. That could be an observational bias (odd solar systems may be easier to detect od planeta Earth) or problems with the theory (probably with subtle points, not the basic outline.)
Linguistics ...