Proteus

Neptune VIII - 1989N1

Proteus [PROH-tee-us], like all six of Neptune's newly discovered small satellites, is one of the darkest objects in the solar system -- "as dark as soot" is not too strong of a description. Like Saturn's satellite, Phoebe, it reflects only 6 percent of the sunlight that strikes it. Proteus is about 400 kilometers (250 miles) in diameter, larger than Nereid. It wasn't discovered from Earth because it is so close to Neptune that it is lost in the glare of reflected sunlight. Proteus circles Neptune at a distance of about 92,800 kilometers (57,700 miles) above the cloud tops, and completes one orbit in 26 hours, 54 minutes. Scientists say it is about as large as a satellite can be without being pulled into a spherical shape by its own gravity. Proteus is irregularly shaped and shows no sign of any geological modification. It circles the planet in the same direction as Neptune rotates, and remains close to Neptune's equatorial plane.

Proteus Statistics

Discovered by ............................... Stephen Synnott
Date of discovery ...................................... 1989

Mass (kg) ................................................. ?
Equatorial radius (km) .................................. 200
Equatorial radius (Earth = 1) .................... 3.1358e-02
Mean density (gm/cm^3) .................................... ?

Mean distance from Neptune (km) ..................... 117,600
Rotational period (days) .................................. ?
Orbital period (days) .............................. 1.122315
Mean orbital velocity (km/sec) ......................... 7.63

Orbital eccentricity ................................. 0.0004
Orbital inclination .................................... 0.04°

Visual geometric albedo ................................ 0.06
Magnitude (Vo) ......................................... 20.3

Views of Proteus

Proteus (GIF, 83K)
This image of Proteus was acquired by the Voyager 2 spacecraft on August 25, 1989. (Credit: Calvin J. Hamilton)

Shaded Relief Map of Proteus (GIF, 84K; caption)
This image is a shaded relief map of Proteus, a small inner satellite of Neptune. As with all maps, it is the cartographer's interpretation and not all features are necessarily certain given the limited data available. This interpretation stretches the data as far as is feasible. (Courtesy Phil Stooke)

Simple Cylindrical Map of Proteus (GIF, 126K; caption)
This image is a shaded relief map of Proteus, a small inner satellite of Neptune. As with all maps, it is the cartographer's interpretation and not all features are necessarily certain given the limited data available. This interpretation stretches the data as far as is feasible. This map is similar to the above map but was reprojected to the Simple Cylindrical projection. As with all cylindrical projections, this map is severely distorted near the poles (top and bottom edges). (Courtesy Phil Stooke)

Neptune Larissa Triton

Author: Calvin J. Hamilton.