Proteus is Neptune's sixth closest known moon. Proteus's orbit is about 73,000 miles from Neptune and has a diameter of 260 miles. The name Proteus comes from a sea god who could change his shape at will. Proteus was discovered by Voyager 2 in 1989. Proteus is irregular in shape and is probably about as big of an object that can be irregular before its gravity pulls it into a sphere.