Planet consists mostly of planets the size of Neptune and smaller, down to smaller than Mercury. There are types of planets that do not exist in the Solar System: super-Earths and mini-Neptunes, which could be rocky like Earth or a mixture of volatiles and gas like Neptune—a radius of 1.75 times that of Earth is a possible dividing line between the two types of planet. There are hot Jupiters that orbit very close to their star and may evaporate to become chthonian planets, which are the leftover cores. Another possible type of planet is carbon planets, which form in systems with
Planet Nine the disk had a distant inner edge, 100–200 AU, a planet encountering Neptune would have a 20% chance of being captured in an orbit similar to that proposed for Planet Nine. The observed clustering is more likely if the inner edge is at 200 AU. Unlike the gas nebula the planetesimal disk is likely to be long lived, potentially allowing a later capture. Planet Nine could have been captured from beyond the Solar System during a close encounter between the Sun and another star in its birth cluster. Three-body interactions during these encounters can perturb the path of planets on