Astronomers using the Hubble Space Telescope discovered a fourth moon orbiting the icy dwarf planet Pluto in 2011. The tiny, new satellite - temporarily designated S/2011 (134340) 1 (and sometimes called P4) - was uncovered in a Hubble survey searching for rings around the dwarf planet.
The new moon is the smallest discovered around Pluto. It has an estimated diameter of 8 to 21 miles (13 to 34 km). By comparison, Charon, Pluto's largest moon, is 648 miles (1,043 km) across, and the other moons, Nix and Hydra, are in the range of 20 to 70 miles in diameter (32 to 113 km).
The finding is a result of ongoing work to support NASA's New Horizons mission, scheduled to fly through the Pluto system in 2015. The mission is designed to provide new insights about worlds at the edge of our solar system. Hubble's mapping of Pluto's surface and discovery of its satellites have been invaluable to planning for New Horizons' close encounter.
The new moon is located between the orbits of Nix and Hydra, which Hubble discovered in 2005. Charon was discovered in 1978 at the U.S. Naval Observatory and first resolved using Hubble in 1990 as a separate body from Pluto.
The dwarf planet's entire moon system is believed to have formed by a collision between Pluto and similar-sized body early in the history of the solar system. The smashup flung material that coalesced into the family of satellites observed around Pluto. There may be even more moons to discover.
Lunar rocks returned to Earth from the Apollo missions led to the theory that our moon was the result of a similar collision between Earth and a Mars-sized body 4.4 billion years ago. Scientists believe material blasted off Pluto's moons by micrometeoroid impacts may form rings around the dwarf planet, but the Hubble photographs have not detected any so far.
S/2011 (134340) 1 was first seen in a photo taken with Hubble's Wide Field Camera 3 on June 28, 2011. It was confirmed in subsequent Hubble pictures taken on July 3 and July 18. The moon was not seen in earlier Hubble images because the exposure times were shorter. There is a chance it appeared as a very faint smudge in 2006 images, but was overlooked because it was obscured.
S/2011 (134340) 1 was discovered on June 28, 2011 by a large team led by Mark Showalter using the Hubble Space Telescope.
How S/2011 (134340) 1 Got its Name:
S/2011 (134340) 1 was so designated because it is a satellite (S) that was discovered in 2011, and was the 1st satellite of dwarf planet Pluto [designated with its minor planet number (134340)] to be found that year.