The crossword solution for the term 'Neptune Neighbor' is 'URANUS', which is a gas giant planet located in the Solar System. It is the seventh planet from the Sun and the third-largest in the Solar System, after Jupiter and Saturn. URANUS is the only planet whose name is derived from a figure from Greek mythology, namely the god of the sky, URANUS. It is also the coldest planet in the Solar System, with an average temperature of -224°C.