Moon of Neptune
Proteus
Proteus is a moon. It orbits Neptune. It is about 420 km across – smaller than our Moon. Proteus is Neptune's second-largest moon – yet it was not discovered until 1989, by Voyager 2, because it is dark and orbits close to bright Neptune.
Fact file
- Type
- Moon of Neptune
- Diameter
- 420 km
- Distance from Neptune
- 117,647 km
- Orbital period
- 1.1 days
- Temperature
- -222 °C on average
Proteus orbits Neptune.
Interesting facts about Proteus
- Proteus is Neptune's second-largest moon – yet it was not discovered until 1989, by Voyager 2, because it is dark and orbits close to bright Neptune.
- It is one of the largest bodies in the Solar System that are not round.
- Its largest crater, Pharos, is over 200 km across – more than half the size of the moon.
Frequently asked questions about Proteus
How big is Proteus?
Proteus has a diameter of 420 km. That is about 12% of the diameter of our Moon.
How far is Proteus from Neptune?
Proteus orbits Neptune at an average distance of 117,647 km.
How long does Proteus take to orbit Neptune?
Proteus orbits Neptune once every 26.9 hours.
How cold or warm is it on Proteus?
On Proteus the average temperature is −222 °C.
Formation
Proteus probably formed anew from debris after Triton had been captured and had thrown Neptune's original moons into disarray.
Atmosphere
No atmosphere.
Exploration
Photographed only by Voyager 2, in August 1989.
Compared with Earth
Around 420 km across – more than the whole of Switzerland from Geneva to Lake Constance.
Other moons of Neptune
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