Changing Planet

Pluto’s Newly Discovered Moons Get Official Names

The artist’s concept above shows the Pluto system from the surface of one of its tiny moons.Credit: NASA, ESA and G. Bacon (STScI)

Back in February we told you about an online naming contest for Pluto’s two newly discovered, smallest moons (P4 and P5). Now, nearly half million votes later, the moons have their official names.

Formally approved by the International Astronomical Union (IAU), the governing body that officially names celestial objects,  P4,  which is 15 miles (20 kilometers) across, has been named Kerberos, after the three-headed dog of ancient Greek legend. P5, at 20 miles (30 kilometers) in diameter, will now be known as Styx, after the mythological river that leads to the realm of the dead.

The new cosmic recruits join the family Pluto’s three other moons–Charon, Nix and Hydra–all named for characters associated with the Underworld of Greek and Roman mythology.

Dwarf planet Pluto has five moons, two of which have now received their official names. Courtesy of NASA, ESA, and M. Showalter (SETI Institute)
Dwarf planet Pluto has five moons, two of which have now received their official names. Courtesy of NASA, ESA, and M. Showalter (SETI Institute)

Both Kerberos and Styx were fist spotted by the Hubble Space Telescope in 2011 and 2012, as part of a survey of the Pluto system in preparation for a NASA probe flying by the dwarf planet in 2015. The spacecraft, called New Horizon, is still 600 million miles (1 billion kilometers) from the icy planet. But when it arrives in the neighborhood New Horizon is expected to get up-close portraits of Pluto’s recently discovered moons.

Vulcan Controversy?

This cosmic contest, which was started as a public educational initiative by the scientists who found these tiny moons, turned out to be quite popular worldwide. By the time the poll closed there were over 450,000 votes with front runners that included, other than the eventual winners, Persephone,Orpheus and the top vote getter – Vulcan.

However to the dismay of legions of Star Trek fans–and to the moons’ discoverer–the name ‘Vulcan’ did not make the grade with professional astronomers . It had been proposed by actor William Shatner, a.k.a Captain James T. Kirk.

“The IAU gave serious consideration to this name, which happens to be shared by the Roman god of volcanoes,”read an official statement from the SETI Institute, which had sponsored the naming contest. “However, because that name has already been used in astronomy, and because the Roman god is not closely associated with Pluto, this proposal was rejected.”

Within minutes of the announcement Shatner tweeted his disappointment.

What would Mr. Spock have to say about this decision?

Follow Andrew Fazekas, the Night Sky Guy, on Twitter and Facebook.



Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.
  • Dannyboy

    Ok so can Pluto be a planet again now???

  • Ted

    Can a non-planet have moons?

  • Mr Spock

    Their conclusion is irrefutably logical.

  • Steve Thomas


  • Chris Smith

    Pluto and Vulcan not closely related? Nonsense. Pluto is he God of the Underworld and Vulcan’s forge was under the earth. They were neighbors. Shatner was right. And he tried to lend his “Street Cred” to popularize Astronomy. Tssk!

  • Theresa

    It’s only logical.

  • Daniel

    Nice try, Captain Hell Toupee.

    I’m a little sad that Persephone/Proserpina didn’t get enough votes, but I suppose that a moon of that name would need a 6 month periodicity… maybe a comet that passes by both Pluto and Ceres?

  • S. Kyle Davis

    Spock would say that it is only logical.

    “[T]hat name has already been used in astronomy, and because the Roman god is not closely associated with Pluto.”

    Both valid points, and ones Spock would understand.

  • Brian

    “Its” versus “it’s” in the picture caption, please. I expect better penmanship from National Geographic.

  • Richard L. Kent Esq.

    I was pulling for Mickey and Donald.

  • M. Bacon

    Artist: G. Bacon , My Dad, & Brother are artist and also, G.K. Bacon. Interesting also, have a cousin from North Dakota B. Bacon an artist mainly Bill Board Sign Art. Art must run in the Bacon’s DNA.

  • awaked

    Pluto is a dwarf-planet, still a kind of planet-ian object. so: moons are cool 😀

  • Frank G. Gerigk

    I am very thankful that my proposal “Kerberos” for P4 was chosen. Before the voting, when I saw the proposal of Mr. Shatner, I was aware that there would be no chance for me to give a more popular name for P5. But his second proposal, “Remus & Romulus” for P4 & P5, could not persuade the voters. Until yesterday, I was sure, that Shatner’s “Vulcan” would be successful.

  • Sherida Gunness

    The names are logical? Is this a serious consideration? How can a non-planet have moons? NASA needs to revise its definition of a planet it seems. Either that or call Pluto and others an asteroid belt :p

  • Evan

    If a planet is named, and learned about by the world, then gets taken off the “official” planet list, then is considered a dwarf planet, but yet they find moons belonging to the dwarf planet’s gravity field, and are named, shouldn’t we be considering re-enlisting Pluto as a planet? It has it’s own gravity and moons in orbit. To me, that is a planet. So, regardless of the names of the moons, Pluto should be a planet again. otherwise we are naming asteroids that mean nothing essentially.

  • Ryan

    Technically speaking (though there is no technical definition of a moon or natural satellite) a moon is a natural satellite orbiting another celestial body. Therefore Pluto does not have to be a planet to possess moons.

    Also by this definition, though the situation hasn’t come to pass, a moon itself can have a moon. This, however, would likely have a highly unstable orbit.

  • Stan Reeves

    is this the same body that demoted Pluto in the first place? how can you not honor the top vote getter? They should take everyone of these “scientists” line them up and shoot every last one of them… they are nothing but trash and rubbish

  • Alexander

    I’m still disappointed that Hekate wasn’t even an option, but I’m glad they overturned the Vulcan vote… it wouldn’t have made much sense.

  • Thorsten Heil

    Hecate – The Goddess of The Underworld

  • Ira

    Brian- “its”, without an apostrophe, indicates possession. While “it’s” is a contraction for ‘it is’ or ‘it has’. I suggest you brush up on your Grade 4 English before criticizing others.

  • Danny Ellis (Ash Walker)

    After reading a this post on FB (where I ‘follow’), I was a tad surprised to read comment after comment about Pluto’s ‘sub planet’ status.

    The argument that Pluto must be a planet if it has a moon is invalid, since “a moon is a body that circles a larger planet or body”.

    To be a planet, a body must meet certain criteria, which Pluto does not.
    “1) is in orbit around the Sun
    2) has sufficient mass to assume hydrostatic equilibrium (a nearly round shape),
    3) has “cleared the neighbourhood” around its orbit.”

    Personally, I find the naming of the new ‘dwarf planet’ subclass a suitable cure to the pains of Pluto’s demotion.

    “Plutoids are celestial bodies in orbit around the Sun at a distance greater than that of Neptune, that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit.”

    Now if you’re still not happy, we have the the verb “to pluto (preterite and past participle: plutoed), which was coined in the aftermath of the 2006 IAU decision.”

    Finally, you could always report this post as spam or ‘unfriend’ me, for accepting change, & for possibly promoting it. I know it’s terribly sad, but Pluto is no longer a planet. If anyone needs a hug, there are apps for that. 😛

  • Hefesto

    Hey, haters, buy a τηλεσκόπιο and look for your own planets and moons… and then name them!
    And no, I have nothing to do with Hades!!!

    Hades -> Pluto
    Hefesto -> Vulcano
    Greek -> Roman

  • Ian Mackay

    Surely Cerberus is the more common form for the 3 headed underworld dog. The other form Kerberos is already used as a common computer security protocol, so it’d be nice if there was a distinction: Cerberus for the moon, and Kerberos for the protocol.

  • Jeremy Keller

    Prior to the discovery of Charon it was assumed that PLuto had no moons. Now it seems that Pluto has at least five. That piece of artwork is obviously an artist’s concept. But how would Pluto REALLY appear to an observer standing on the surface of that moon? I would really like to know this.

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  • Aleksandra

    Ara fish! Ara fish! 🙂

  • Abdullah Omar Nasseef

    I will vote the name thiviploton

  • Sam Sharp

    One hundred years ago when Abdul’Baha the son of Baha’u’llah visited Canada and America in one of his talks he clearly stated that Pluto had five moons.” Science should sustain Religion and Religion Should explain science were his other words.”

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