Monday, July 25, 2011

Hubble Discovers the Fourth Moon of Dwarf Planet Pluto

Discovered by the Hubble Space Telescope through images taken of Pluto on June 28, 2011 (verified July 20); Hubble has discovered that Pluto has a fourth companion. Though this may not seem very impressive or such a big deal, finding moons around labeled dwarf planets is something rare, especially for those who only knew about Charon. Currently labeled S/2011 134340 1 P4 (or P4 for short), Hubble discovered this icy moon in a search for rings around the planet. This is peculiar, becasue so far, only gas giants are known to have rings, and Pluto is definitely not a gas giant!

According to recent statistics, P4 has an estimated diameter of 13 to 34 kilometers (8 to 21 miles) making it the smallest known moon  and orbits Pluto at a rapid rate: about every 32.1 Earth-Days, between the orbits of Nix and Hydra, the other moons. Its full orbit reaches 59,000 kilometers, which is about 37,000 miles in length; and is remarkably in a 1:5 resonance with Charon, despite the 0.6 % leftover time involved. This means every time P4 orbits, Charon does five times. Nix and Hydra are also in orbital resonance with Charon, 1:4 and 1:6, respectively.

Image of Pluto's full family; credit Hubble. The black strip down the center was placed to block out the unnecessary light that Pluto emitted. The glare prohibits the moons being seen. The 'cross' shape is an imaging error.

A few NASA scientists comment about the new moon: "I find it remarkable that Hubble's cameras enabled us to see such a tiny object so clearly from a distance of more than 3 billion miles (5 billion kilometers)," said Mark Showalter of the SETI Institute in Mountain View, Calif., who led this observing program with Hubble.

"Could this planet get any more interesting?" says New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder Colorado. "We already know that when New Horizons provides the first close-up look at Pluto in July 2015, we'll see planetary wonders we never could have expected. Yet this discovery gives us another hint of what awaits us in the Pluto system, and we're already thinking about how we want to study this new moon with New Horizons. What a bonus for planetary science and for New Horizons!"

Hubble helped to discover three of the four moons of dwarf planet Pluto. Nix and Hydra were discovered in 2005, and now P4 in 2011. Hubble could have discovered P4 in 2005, but there was a simple complication. When the images of Nix and Hydra were released in 2005, NASA scientists noticed a small 'smudge' in the picture (which we now know was P4), but disregarded it, for which I can assume for 'logical' reasons. Apparently, it was ignored on account of the fact that the speck was drowned out by a diffraction spike, or an error in imaging.

This is the new model for the Plutonian system. P4 is the third closest object in the image.

Something interesting to concern yourself with - what will this new moon be named? Of course we have to name it (who would wish to keep it at S/2011 134340 1 P4?!); in the most probable sense, it will be another name from mythology, like most moons and other astronomical bodies are; observe: Io, Callisto, and Europa (a few of Jupiter's satellites) come from Ovid's Metamorphoses (Roman Mythology), you have asteroid 2 Pallas (has a myriad of names for a myriad of people), and 1 Ceres (Roman goddess of the field), to name a few.

In naming of the Plutonian system, P4 will be named soon a name that follows after the 'tradition' of naming the Plutonian moons. It will have as name that reflects Hades and the Underworld in Greek Mythology. Pluto was named after the god of the Underworld; Charon, the ferryman that would take one's soul to the Underworld; Nix, (spelled Nyx in mythology), was the goddess of the night; and Hydra, an mythical creature with seven heads, one (the center) immortal. I am thinking that P4 will be named one of the following, but have no idea what it will be. When P4 is named, I'll post it. I am thinking possibly: Medusa, Persephone, or Styx. Medusa is a horrible monster that would turn onlookers into stone, living on an island in the river Styx; Persephone was the goddess of the Underworld, who was captured by Pluto to be his bride (it really is a myth in itself); and Styx, is a river in which leads to the underworld, where ferryman Charon rides.

"Pluto continues to amaze us," says Hal Weaver, a New Horizons project scientist. "Who would have thought a dwarf planet could support such a complex satellite system? The hunt will now be on for similarly complex systems around other Kuiper Belt objects."More news can be found here.

More awaits for us from the Plutonian system! It's peculiar to find a dwarf planet that has this many moons, but anything is possible. New Horizons will arrive in 2015, but until then; P5 may be around the corner...


  1. Here's what Sky & Telescope writes about the naming. Or it's not Sky&Telescope but the New Horizons scientists:

    And what about a fitting name for the new find? "Mark and I like the name Cerberus, the three-headed dog that guards Pluto's realm," Hamilton admits. "But the name is unofficial for now!"


  2. Fascinating! Why do you think NASA is looking for rings? It is amazing that this little guy (Pluto) has so much activity.
    I really do enjoy your site.