NASA announced the discovery of a fourth moon around Pluto last week! Astronomers were using the Hubble Space Telescope to look for rings around the dwarf planet when they discovered the new moon. It's currently designated P4 until they come up with a better name for it. The Hubble image above shows Pluto and its four moons. The big black bar down the center is used to block most of the light Pluto reflects so faint objects around it, like the moons, can be seen. P4 is only 8-21 miles wide, whereas Charon is 648 miles wide and Nix and Hydra are more like 20-70 miles wide. Pluto is a member of the Kuiper belt, along with 70,000+ other objects, so it's not surprising that Pluto has another moon that went undetected for years. It's difficult to see such small objects in space, even with Hubble! NASA's new horizon mission is currently on its way to Pluto to study the planet and its moons. It will be another ~5 years before New Horizons makes it there, but once it has arrived it will no doubt send back unprecedented information about Pluto and other outer solar system objects
Image Credit: NASA, ESA, and M. Showalter (SETI institute)
