Hypothesised ninth planet, illustration. Planet Nine is a hypothesized massive planet, first proposed in 2014, that is speculated to orbit far out in the solar system. It has not been detected formally. Instead, astronomers have inferred its presence from perceived perturbations of the orbits of some Trans-Neptunian Objects (TNOs). The planet is estimated to be 2 to 4 times the radius, and about ten times the mass of the Earth. It is most likely a gas or ice giant, such as Neptune or Jupiter. The orbit of Planet Nine would be highly elliptical, with its distance from the Sun varying from 200 to 700 astronomical units (7 to 23 times the distance of Neptune). A couple of moons are also shown here, in this view of the sunlight side of the planet.