Scientists Discover an Itty-Bitty Moon Orbiting Pluto

By Rebecca J. Rosen

Astronomers looking at data from NASA's Hubble Space Telescope have pinpointed a moon just six to 15 miles in diameter circling the dwarf planet.

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NASA

It's been six years since Pluto lost its designation as a planet, but it keeps getting new moons. Okay, the moons have likely been orbiting Pluto since a collision with a large Kuiper belt object billions of years ago, but they're new to us. Last year, astronomers found a small moon, called P4, in data from the Hubble Space Telescope, and today they have announced another -- you guessed it, P5.

P5 is the fifth known moon of the dwarf planet and it is, fittingly, quite tiny itself -- just six to 15 miles across. The diameter of its orbit around Pluto is estimated to be about 58,000 miles. The orbits of the moons all follow the same plane, forming "a series of neatly nested orbits, a bit like Russian dolls," according to Mark Showalter of the SETI Institute in Mountain View, California, who leads the team that found the moon.

Pluto itself wasn't even discovered until 1930. Its largest moon, Charon, was noticed in 1978. Two more moons, Nix and Hydra, were found shortly before Pluto's demotion from full-blown planet in 2006. Today scientists are carefully combing over Pluto's system in search of other small objects that could be hazardous to the spacecraft New Horizons when it passes through the area in 2015. The spacecraft is moving so fast (30,000 miles an hour) that even tiny objects could destroy it.

Even though Pluto isn't so far away by cosmic standards, but at an average distance of 3.6 billion miles, it's not exactly close either. At such a distance, it's pretty incredible that we have tools to see a rock that is smaller than many U.S. cities.

This article available online at:

http://www.theatlantic.com/technology/archive/2012/07/scientists-discover-an-itty-bitty-moon-orbiting-pluto/259708/