A year ago, I wrote that Pluto had four moons. Make that five. The cosmologists at the SETI (Search for Extraterrestrial Intelligence) Institute and NASA/ESA have found a fifth moon lurking in their Hubble images. They hadn’t even gotten around to naming the fourth moon yet, which is still designated ‘P4’. Consequently, the newest one is ‘P5’.
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
The four newer moons (Hydra, Nix, P4 and P5) were all also discovered in images from the Hubble Space Telescope. Charon, discovered in 1978, is the only one of Pluto’s moons that a person couldn’t easily circumnavigate on foot (especially considering that you’d be all but weightless). P5 is estimated to have an irregular shape that ranges from about 10 to 20 kilometers in diameter.
Although it’s not clear why tiny Pluto has a cluster of miniature moons, the leading hypothesis is that the grouping is the result of a collision that occurred soon after the formation of the solar system. It’s certainly possible that even more moons will be discovered in the future.
Not bad for an object that’s not even a planet.
You can hear a discussion about P5 on The Skeptics' Guide To The Universe - Podcast 366, starting at 27:30.