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 cause the orbits of the other planets to precess, similar to but slower than the eTNOs, covering short arcs over the lifetime of the Solar System. These observations are consistent with the Planet Nine hypothesis but do not prove that Planet Nine exists as there are other potential explanations for the spin–orbit misalignment of the Solar System. Batygin was cautious in interpreting the results of the simulation developed for his and Brown's research article, saying, "Until Planet Nine is caught on camera it does not count as being real. All we have now is an echo." Brown put the odds