Who Got Moons?

Two small moons have been discovered orbiting Pluto, bringing the planet's retinue of known satellites to three and leaving scientists to wonder how it could be.

The newfound moons orbit about 27,000 miles (44,000 kilometers) from Pluto, more than twice as far as Charon, Pluto's other satellite. They are 5,000 times dimmer than Charon.

While scientists had predicted there might be more moons, the newfound setup is surprising nonetheless, in part because Pluto is smaller than our own Moon.

"It's almost like a mini solar system," said Hal Weaver of the Johns Hopkins Applied Physics Laboratory. "How can something about 70% the size of Earth's Moon have all these satellites? How can that happen? We're going to have to explain that."

The two new moons are between 30 and 100 miles (45 to 160 kilometers) in diameter, Weaver said. There is not enough data to pin their size down exactly, however. Pluto is 1,430 miles wide and Charon's diameter is about 730 miles.

The moons were found using the Hubble Space Telescope. The presumed moons are 23rd magnitude, far to dim to be seen with a typical backyard telescope but "relatively easy to see with Hubble," Weaver said.

From an article appearing in Space.com