Discovered by Stephen Synnott, on Voyager 2 photos, June 1989
Named after Proteus, the mythological son of Oceanus and Tethys
Orbital size 117,600 km (about 73,000 miles), about 92,800 km (57,700 miles) from Neptune's surface
Orbital eccentricity 0.04%
Orbital inclination 0 degrees
Orbital period 26 hr 56 min = 1.122315 days
Rotational period unknown
Diameter about 440 x 420 x 400 km (about 260 miles)
Mass unknown
Albedo (reflectivity) 6%