Why does the solar nebula theory predict that planetary systems are common?

Answer 1

The very way it describes the formation of solar systems kind of demands that at least one planet form, and statistically several. If stellar dust particles agglomerate into larger chunks and planetessimals in a spinning disk of debris, the stuff at the outer edges will tend to be much more attracted to other particles close by rather than the center of stellar gravity, since gravity does follow the inverse square rule; by the time the center of the disk collects enough mass to begin undergoing fusion, the other planetessimals will have likewise formed and would be more inclined to orbit the newly formed sun rather than spiral into it. It is much less likely that all the material in a solar nebula would be drawn completely into the center and form a planetless sun.

Answer 2

The solar nebula theory predict that planetary systems are common because planet formation is a natural part of star formation.

Answer 3

Everything in the universe spins a little, there is no such thing as zero spin. So when a nebula (which is already spinning)contracts, it spins faster and faster and faster and this excessive spinning tends to cancel the gravitational force in the plane perpendicular to the spin axis. This causes the contracting, spinning nebula to assume a disk shape, which then spawns planets. Our sun contains 99% of the mass but only 2% of the spin(angular momentum) of our solar system. Planets HAVE to form in order to conserve the total angular momentum of the system, which is required by law(the law of conservation of angular momentum)