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Monday, July 22, 2013

Congratulations, Pluto, your moons have names

Pluto may not be a planet anymore, but it has more moons than the Earth does. Pluto’s 4th and 5th moons were discovered in 2011 and 2012. At that time, only three of Pluto’s moons had been named. Recently, the International Astronomical Union (IAU) chose two proper names for the previously dubbed P4 and P5. Those moons will henceforth be known as Kerberos and Styx, respectively.

This discovery image, taken by the NASA/ESA Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The darker stripe in the centre of the image is because the picture is constructed from a long exposure designed to capture the comparatively faint satellites of Nix, Hydra, Kerberos and Styx, and a shorter exposure to capture Pluto and Charon, which are much brighter. Kerberos has an estimated diameter of 13 to 34 kilometres, and Styx is thought to be irregular in shape and 10 to 25 kilometres across. 
Credit: NASA, ESA and M. Showalter (SETI Institute)

The IAU gave the public a chance to weigh in on the name choices. All the selections had to fit with Pluto’s ‘theme’, which is Greek/Roman mythology related to the underworld. Pluto’s three other moons are Charon, Nix and Hydra, so Kerberos and Styx will fit in nicely with them.

In case you’re interested, Styx was a goddess who ruled the underworld river by the same name, and Kerberus is an alternative spelling for ‘Cerberus’, the three-headed dog that guards the underworld. Nix (or Nyx) is the goddess of the night. Charon is the ferryman who transports souls across the river Styx. Finally, Hydra was a many-headed beast that was eventually killed by Hercules.

All four of the newer moons (Hydra, Nix, Kerberos and Styx) were discovered in images from the Hubble Space Telescope. They’re also all tiny. Charon, discovered in 1978, is the only one of Pluto’s moons that a person couldn’t easily circumnavigate on foot.

Here's an older pre-name change family picture:

Hubble image of Pluto and its moons

This image, taken by NASA's Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The green circle marks the newly discovered moon, designated P5, as photographed by Hubble's Wide Field Camera 3 on July 7.
Credit: NASA; ESA; M. Showalter, SETI Institute