10 Proteus Moon Facts | Cool Facts about Proteus

Proteus is the second largest moon orbiting the planet Neptune. Although there’s still a lot we don’t know about it because of its dark surface, we do know some details about this oddly shaped object. It doesn’t take on a strictly spherical shape like some other moons that entered into Neptune’s equatorial plane. So, let’s look at some facts about the moon Proteus. 

Proteus Moon Facts

  1. Proteus has a radius of 210 km, making it the second biggest moon orbiting Neptune. It is still more than 5x smaller than the biggest moon of Neptune, Triton.
  2. Proteus was discovered in 1989 by the Voyager 2 mission. However, it was the third moon to be discovered.
  3. With massive Ganymede being the first moon to be discovered, the second Neptune moon was actually Nereid in 1956, so much earlier than Proteus.
  4. The reason for this is that Proteus is very dark and difficult to see; it’s described as one of the darkest objects in our solar system.
  5. Proteus orbits Neptune at a distance of more than 73,102 mi (117,647 km).
  6. Proteus is a moon with a lot of craters. The largest of the craters, named Pharos, has a diameter of more than 230km!
  7. Like many other smaller moons, astronomers don’t think Proteus was formed with the solar system. It’s more likely to be a collision between Triton and another object.
  8. Proteus takes around 27 hours to complete one full orbit around Neptune.
  9. It’s thought that Neptune’s smallest moon, Hippocamp, is actually a piece of Proteus, broken off in a collision with a comet.
  10. Proteus takes its name from the sea shepherd from Greek mythology.
This show just how small Proteus is in comparison to the other moons of Neptune and Jupiter! However, even though Proteus is extremely small, it does still have some surface gravity.

Common Questions about Proteus

Where does Proteus get it’s name?

Proteus, like many other moons and planets, takes it’s name from Greek mythology. It’s actually named after after Proteus the Sea Shepherd. He was one of Poseidon’s subjects, which makes sense as Poseidon is the Greek equivalent of Neptune! Proteus had the ability to shape shift and change it’s form, which might related to the strange shape of this moon, which is dented and quite rough.

What is Proteus made of?

We aren’t exactly sure what Proteus is made of. We think that this moon has a lot of water ice on it’s surface, but it is difficult to identify this from such a great distance. it’s also likely that it has a rocky interior, similar to that of an asteroid.

What is on Proteus surface?

Like I just mentioned, we think that Proteus is covered in a lot of ice. But as well as this, we know Proteus has many craters across it’s surface, including it’s largest crater, Pharos. Pharos has a depth of more than 15km and a diameter of more than 230km, which is a significant part of Proteus’s surface. There are also valleys across Proteus too. This is all likely caused by other objects and comets coming into collision with Proteus.

What shape is Proteus?

With larger moons, the gravity of them makes them spherical, and it pulls it out from each different angle. However for moons with a lower mass, this doesn’t typically happen, and this is a reason we get a moon like Proteus! Whilst Proteus is loosely shaped like an ellipse, it has a lot of dents and craters over it’s body, with some deviations of up to 20km making a noticeable difference in it’s shape.


All in all, Proteus is one of the more interesting moons and we will learn more and more about it over the coming years. Although it probably wasn’t formed with the solar system all those years ago, Proteus still makes up and important part of our universe.


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