Cast your vote to name Pluto’s two smallest moons


Pluto may only be a dwarf planet now, but it still has five moons, and two of them need names. And the folks at the SETI Institute who discovered those two nameless moons are asking for your help.

Mark Showalter, a planetary astronomer with SETI’s Carl Sagan Center for the Study of Life in the Universe, has issued a public appeal to vote on permanent names for the bodies currently known as P4 and P5. Here’s what you need to know before voting on the 12 candidates:

“By tradition, the names of Pluto’s moons come from Greek and Roman mythology, and are related to the ancient tales about Hades and the Underworld,” according to the election website Pluto Rocks. Pluto, of course, is ruler of the underworld and the brother of Zeus (ruler of the heavens) and Poseidon (ruler of the seas). As this website on mythology from Princeton explains, Pluto used to be known as Hades, but that name came to describe the underworld itself.


Pluto’s three named moons are Charon (who ferried the souls of the dead across the rivers Styx and Acheron), Nix (goddess of the night and mother of Charon) and Hydra (a nine-headed monster who was guardian of the underworld).

Most likely, these moons will be joined by two of the following:

  • Acheron
  • Alecto
  • Cerberus
  • Erebus
  • Eurydice
  • Hercules
  • Hypnos
  • Lethe
  • Obol
  • Orpheus
  • Persephone
  • Styx

To learn more about the mythological significance of these names and their relationship to Pluto, check out this page on the Pluto Rocks site.

If you can’t narrow it down to your favorite two, don’t worry -- you can vote for as many selections as you’d like. But to give everyone a fair chance, Showalter asks that you not vote more than once a day. So far, Styx and Cerberus are in the lead.

And if you don’t like any of those, you can offer a new suggestion on this write-in form. (Be prepared to justify your nomination.)

You can vote up until 9 a.m. Pacific time Feb. 25. After all the votes are counted, the results will be taken into consideration by the SETI scientists who will formally propose names for P4 and P5. The official names will be made public only after they are approved by the International Astronomical Union.

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