Scientists using the Hubble Space Telescope have discovered what they say are two more tiny moons orbiting the planet Pluto, the first evidence yet that any object in the solar system beyond Neptune has more than one satellite.
Pluto has one large moon - Charon, discovered in 1978 - in orbit about 12,000 miles from the planet, but until yesterday's announcement, neither Pluto nor any other object in the Kuiper Belt, a region of icy, rocky objects orbiting in the far reaches of the solar system, was known to have multiple companions.
The two moons were spotted in May by astronomers using Hubble to size up potential targets for investigation by NASA's New Horizons mission, scheduled to be launched early in 2006 on a multiyear expedition to Pluto and the Kuiper Belt.
On May 15, the New Horizons team took a series of eight-minute exposures showing two faint objects near Pluto, 3 billion miles from Earth.
"Three days later, the two objects were still there, and they were moving counterclockwise around Pluto," said team co-leader Harold A. Weaver of Johns Hopkins University's Applied Physics Laboratory. "It made for a convincing case."
Weaver said the team must confirm the discovery with a separate set of observations scheduled for mid-February. Meanwhile, a search of Pluto images made earlier by other scientists turned up a set of 2002 photographs that showed the two moons.
Despite new research possibilities, the discovery is unlikely to dispel the mysteries surrounding the Kuiper Belt and the objects that dwell there, including Pluto. Many astronomers do not regard Pluto, with a diameter of only 1,400 miles, as a full-fledged planet, The Washington Post reports.