So – You’re Still Interested in Astronomy? Pluto4 min read

Hello again.

Last time we looked at the amazing satellites surrounding Neptune. This time around we’ll take a look at the moons of some of the smaller bodies in our Solar System. Today, I thought we’d concentrate on somewhere that was once classed as a planet, Pluto.

 1. So – which particular moons are we looking at?

Today we’ll take a look at all 5 of the moons belonging to the most infamous dwarf planet we have, Pluto. As you will see, although there’s not a lot to say, they are still interesting in their own way. In order of distance from the planet, they are: Charon, Styx, Nix, Kerberos and Hydra

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2. Charon

Charon is 1,208 km (758 miles) in diameter, just over half that of Pluto and larger than one of the other dwarf planets – Ceres.
Charon is sufficiently massive to have collapsed into a spheroid under her own gravity. Observations of her surface show a predominance of cryogeysers and cryovolcanoes, so as you can imagine, the surface is pretty topsy-turvy.

3. Are there any interesting facts about Charon we need to know?

Oh yes, Charon is so massive (1/8 the mass of Pluto) that the Pluto/Charon barycenter lies 960 km (597 miles) up from Pluto’s surface. This means if you could plot their mutual orbit, it would make it look like they’re waltzing around a common center. Both bodies are also tidally locked, so they always present the same surface toward each other.

4. Anything else?

Actually there is.
In 2006, the International Astronomical Union General Assembly considered Pluto and Charon be reclassified as a Double Planet. Sadly, that proposal didn’t go through, as it would have made our Solar System even more diverse than it already is.


5. Styx

Styx is a small natural satellite first seen on July 11 2012. She is the second moon of Pluto by distance and the fifth discovered. The unusually complex relationship of the smaller bodies of the Plutonian system may be the result of a previous collision between Pluto and a sizeable Kuiper Belt object at some time in the far distant past. So although classed as a natural satellite, Styx might have coalesced from the debris of a much older event.
Styx is tiny, at a mere 25 km (15 miles) diameter at most.
(That’s only half the size of the island I live on.) Cool!

6. Nix

At 46 km (28 miles) in diameter, Nyx is another natural satellite discovered in June 2005. Named after the Greek goddess of darkness and light, this little moon is a dark object and is shaped like a potato.


As you can see, she has a distinctive reddish tint like her mother planet, although these tones might be restricted those regions around her largest craters.

7. Kerberos

Kerberos is another natural satellite discovered on July 20 2011. At 30km (19 miles) in diameter, she is positioned between Nix and Hydra.
Kerberos was the fourth moon of Pluto to be discovered and orbits her parent body every 32 days.

8. Hydra

Hydra possesses a diameter of 61 km (37 miles) and was discovered in June 2005 along with Nix. Of note is the fact that Hydra orbits the barycenter of this system along the same plane as Charon and Nix.

9. Is there anything else we need to know about Pluto’s moons?

Of course.
Although it’s small, the Plutonian system has a number of interesting parallels.
Styx, Nix and Hydra are in a 3 body orbital resonance (They exert a regular – periodic – gravitational influence on each other)
What’s more, because of the interaction between Pluto and Charon, the local gravitational field is rather chaotic, and the ripples between Nix, Hydra, and possibly Kerberos cause all sorts of wild fluctuations.
(NOTE: Nix actually flips its entire pole. You could spend a day on Nix where the sun rises in the east and sets in the north. Super cool!)

10. And finally

The Plutonian system is highly compact and largely empty. A recent fly-by conducted by the New Horizons spacecraft suggested there could be further moons just waiting to be discovered. However, they are so distant and so faint; it would be hard to spot them. BUT, we are still awaiting some of the data to be analyzed, so who knows…by the time you read this, Pluto could be the proud owner of even more satellites.

Weird eh?

But that’s what makes our small Solar System so fascinating.


So there we go. That’s our brief look at the wonderful world of Pluto and her Moons.
Next time, we’ll move on to take a closer peek at the remaining Dwarf Planets to see if they hold any secrets, AND we’ll discover if any of them have their own moons.

You’ll be surprised.

I can’t wait to see you then…

Andrew Weston
Andrew Weston

Andrew P. Weston is Royal Marine and Police veteran from the UK who now lives on the beautiful Greek island of Kos with his wife, Annette, and their growing family of rescue cats. An astronomy and law graduate, he is the creator of the international number one bestseller, The IX, and also has the privilege of being a member of the Science Fiction and Fantasy Writers of America and the British Fantasy Society. When not writing, Andrew devotes some of his spare time to assisting NASA with one of their remote research projects, and writes educational articles for and Amazing Stories. He also enjoys Greek dancing and language lessons, being told what to do by his wife, and drinking Earl Grey Tea. If you would like to find out more, visit his blog or website at:

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