Moon
One of the darkest objects in the solar system, so close to Neptune that it is difficult to observe from Earth.
| Type | Moon |
|---|---|
| Orbits | Neptune |
| Distance from parent body | 117,647 km |
| Diameter | 420 km |
| Mass | 3.87 × 10^19 kg |
| Surface gravity | 0.0597 m/s² |
| Temperature | -222°C |
| Orbital period | 1 days |
| Apparent magnitude | 19.7 |
| Redshift | 0 |
| Discovered | 1989 |
At 420 km across, Proteus is 12 percent of the diameter of Earth's Moon.
Its mass is less than a thousandth of the mass of Earth.
It orbits Neptune at 117,647 km, closer in than the Moon orbits Earth.
A single orbit takes 1.1 days.
An average temperature of 51 K works out at -222 degrees Celsius, colder than the 15 degrees Earth averages.
It has been on record since 1989.
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