If you had asked me in June 2013 how many moons Neptune had, I would have told you the answer was 13.  If you asked me in August 2013 how many moons Neptune had, my answer would be 14!  2013 marks the year when a new moon has been found orbiting this giant gas planet.

First, a few facts about Neptune:

Neptune was discovered in 1846 and is the farthest planet from the Sun (after Pluto was demoted to being a “dwarf Planet”).  To find Neptune in the night sky you would need a telescope or a good set of binoculars as it is extremely dim.  In fact Galileo observed Neptune between 1612 and 1613 but mistook it for a dim star.  It takes 164 years to orbit around the Sun and it is named after the Roman god of the sea.  Its astronomical symbol is ♆, a version of the god Neptune’s trident.


Image of Neptune taken by Voyager 2 Credit: NASA

Image of Neptune taken by Voyager 2
Credit: NASA


So how was this Moon discovered?

It was discovered by Mark Showalter who is a Senior Research Scientist at the SETI Institute.  Mark now has six moon discoveries to his credit and has discovered three planetary rings.  On July 1, 2013 he first observed something that he thought could have been a moon whilst studying the planets rings.  “There was a little dot sitting there, it looked like it could be a moon”, he said.  Because the object was so dim he needed confirmation that this was indeed a new moon.  On July 15, 2013, a team of astronomers led by Mark combined and aligned about 15 sets of Hubble images taken between 2004 and 2009.  Roughly 150 images helped them to confirm that this was a satellite.  Mark said, “You can’t see it in the individual images, but when you combine images, it turns up and it turns up consistently”.  It is interesting to note that the Voyager spacecraft failed to spot this satellite when it passed close by Neptune in 1989 to survey its moons and rings.


: Mark Showalter who discover Neptune’s new moon Credit: Wikipedia

Mark Showalter who discovered Neptune’s new moon
(image credit: Wikipedia)


So Neptune has its fourteenth moon!  The as yet unnamed moon, currently known as S/2004 N 1, is thought to measure no more than 20km in diameter (12 miles) and orbits around the planet every 23 hours.  Compare this to Neptune’s largest moon called Triton which is 2705km in diameter.  Triton is a strange moon as it orbits Neptune backwards travelling in the opposite direction to the planet’s rotation.  S/2004 N 1 is wedged between two much bigger moons, Proteus and Larissa, and Mark believes that this is interesting as we can determine how it came to be positioned here and survive the chaos from when the moons were formed early in the Solar System, “maybe this new moon can help us understand more about that early history”.



So now the naming process will begin, S/2004 N 1 doesn’t exactly roll of the tongue!  But there are some rules you need to be aware of when naming a newly discovered object.  The International Astronomical Union (IAU) is the arbiter of naming all things celestial.  You may have heard of this organisation before when they hit the headlines back in 2006 when they decided to reclassify Pluto from being a Planet to now being called a Dwarf Planet.  It was on the final day of the IAU General Assembly conference that year when a resolution was passed establishing a formal definition for the word “planet,” and Pluto did not meet the requirements.  So the IAU will have the final say over what name Neptune’s new moon will have.


The IAU rules on naming S/2004 N1 are:

  • 16 characters or less in length, preferably a single word
  • pronounceable in as many languages as possible
  • names of a purely or principally commercial nature are not allowed
  • not too similar to an existing name of an astronomical object
  • non-offensive in any language or culture
  • names of pet animals are discouraged
  • names of individuals, places or events principally known for political or military activities are unsuitable

The discoverer of the moon gets to suggest a name, but the final say on moon naming will go to the International Astronomical Union (IAU).  Usually a natural satellite’s name is somehow related to that of the planet it orbits. Jupiter, for instance, has moons that are named after the god’s lovers.  This summer the newly discovered moons of Pluto, formerly known as P4 and P5 discovered in 2011 and 2012, have been named Kerberos and Styx after two figures of the underworld in Greek mythology.  The IAU put its foot down when it came to naming one of them Vulcan.  Trekkies out there will know that this name is associated with Star-Trek but it already refers to a planet once proposed to exist between Mercury and the Sun thus did not fit in with IAU rules.  Another point to note is that it deviated from the underworld theme Pluto’s other moons are named after.



So, the name for Neptune’s new moon should fit in with the theme used for Neptune’s other moons: Triton, Nereid, Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Halimede, Psamathe, Sao, Laomedeia and Neso.  These are names associated with minor water deities in Greek and Roman mythology.  Showalter has some ideas for the new name.  Polyphemus is his favourite which comes from The Odyssey where Odysseus and his crew are on an island with a giant cyclops named Polyphemus.  A close second is the name Lamia who is a goddess and was the daughter of Poseidon.  Lamia got into trouble with Zeus, the king of the gods, and was turned into a horrible creature that would eat children.

Organisation who name celestial objects Credit: IAU

The people who get to name worlds
(Image credit: IAU)


It will be interesting to see what happens over the next few months in relation to the naming of this moon and if the public will be encouraged to get involved.  Perhaps anyone reading this article would have a great name for this new moon of Neptune and who knows, it could be taken into consideration.  You can email your suggestion to iaupublic@iap.fr and don’t forget to mention that you read this article from Armagh Planetarium!

(Article by Sinead McNicholl, Education Support Officer)



shash kush · March 14, 2018 at 03:57

how many rings are there on neptune . . . .
are they actual or a myth

Mimi Gerstell · February 2, 2016 at 15:08

“Styx” is not a “figure” of the underworld, it is one of the riviers surrounding the underworld in Greek mythology.

    admin · February 2, 2016 at 21:08

    Dear Mimi, thank you for your comment. While you are correct that the Styx was one of the rivers around the Underworld, it was also the name of the goddess of the river, and the moon of Pluto is named after her.

spankylover101 · September 23, 2015 at 18:33

Why does neptune have so many moons?

    admin · September 24, 2015 at 09:18

    Dear SL, giant planets like Neptune have lots of moons because they are big and exert a major gravitational pull. This means in the distant past they were able to attract more material around them to form moons and since then have been able to capture passing asteroids to add to their collection of moons.

    I hope this has helped.

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