オールトの雲
Objects may also have been captured earlier and from other sources. As the sun left its birth cluster objects could have been captured in the Oort cloud from other stars. If the gas disk extended beyond the orbits of the giant planets when they cleared their neighborhoods comet-sized object are slowed by gas drag preventing them from reaching the Oort cloud. However, if Uranus and Neptune formed late, some of the objects cleared from their neighborhood after the gas disk dissipates may be captured in the Oort cloud. If the Sun remained in its birth cluster at this time, or during the planetary migration if that occurred early, the Oort cloud formed would be more compact.