Proteus

Neptune VIII

   Proteus ("PROH tee us") is the sixth of Neptune's known satellites and the second largest:

        orbit:    117,600 km from Neptune
        diameter: 418 km (436 x 416 x 402)
        mass:     ?

   Proteus was a sea god who could change his shape at will.

   Discovered in 1989 by Voyager 2. Though it is larger than Nereid, it was not discovered earlier because it is very dark and so close to Neptune that it is difficult to see in the glare of the much brighter planet.

   Proteus is irregular (non-spherical) in shape. Proteus is probably about as big as an irregular body can be before its gravity pulls it into a more spherical shape.

   The heavily cratered surface shows no signs of geologic activity.

Open Issues

• We know next to nothing about Proteus.