Hill sphere


Also found in: Wikipedia.

Hill sphere

The spherical region around a planet (or satellite) within which that body dominates the motion of particles. Once the core of a planet exceeds a mass of about 1023 kg, it gravitationally attracts gas from the Hill sphere and is able to form an atmosphere in this way. Jupiter's Hill sphere, for example, had a volume about 1000 times greater than that of the Earth.