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August 7, 2011
A New Moon is Discovered Around Pluto
Pluto may no longer be considered a full planet, but NASA scientists using the Hubble telescope recently discovered a new moon orbiting around it. This new moon is temporarily being called P4 and it is Pluto's smallest moon with an estimated diameter between 8 and 21 miles.
Pluto shown with previously known three moons
Scientists already knew of three other moons that orbit Pluto. They are called Chiron, Nix, and Hydra. Chiron is the largest of Pluto's moons by far with a diameter of 648 miles, while Nix and Hydra are only slightly larger than the newly discovered P4. Chiron was discovered in 1978, while Nix and Hydra were recently discovered in 2005.
How did they find it?
P4 was found while scientists were using the Hubble telescope to try and find rings around Pluto. Although a moon that is several miles wide may seem pretty big, it is very tiny when looking at it from over 3 billion miles away. That is how far Pluto is from the Earth. It is thought that the moon P4 wasn't discovered earlier because previous pictures taken with the Hubble telescope had shorter exposure times. Because they were looking for rings, the exposure times were longer and the moon can be clearly seen.
Pluto is considered a dwarf planet. It had been considered a planet up until 2006 when the International Astronomical Union (IAU) came up with an official definition of a planet and Pluto wasn't large enough. It is the second largest dwarf planet and the tenth largest object orbiting the Sun. The largest dwarf planet is Eris.
New Horizons Mission
This discovery comes at a good time for NASA. The New Horizons space mission will be doing a fly by of Pluto in 2015. With this new information, NASA scientists can also plan the mission to observe P4.
What will the new name be?
P4 is just a temporary name. The scientific designation is S/2011 P 1. But that's sort of hard to say! What happens next is that the team of scientists that discovered the moon will propose a name to the IAU. If the IAU agrees, then that will be the new name. The leader of the team, Mark Showalter, says they will likely propose a name from Greek mythology.