Differences and similarities of nebular theory, encounter theory and proto planet theory?

Not that much but basically it can happen. The likely hood is rare but g should've been 9.8 m/s^2

All these theories, the nebular theory, the encounter theory and the planet theory explain phenomena in the Solar System.

According the nebular theory the planets originate in a dense disk formed from material in the gas and dust cloud that collapses to give us the Sun

The encounter theory is o ne of the earliest theories for the formation of the planets. According to this theory planets are formed from material ejected from the Sun or a companion star during an encounter with another object.

Proto planet theory is the current working model for the formation of the Solar System. According to this planet theory a dense interstellar cloud produces a cluster of stars.