CAPE CANAVERAL - The New Horizons mission to Pluto is aptly named, its lead scientist says, because Earth has never sent a spacecraft there.

"I think this is probably the most historic mission NASA has flown in 25 years," said principal investigator Alan Stern of the Southwest Research Institute.

The mission, targeted to launch Jan. 11 from Cape Canaveral and fly by Pluto in 2015 at the earliest, offers the first opportunity to get a good look at the ninth planet.

Even in the best Hubble Space Telescope images, Pluto appears as a fuzzy circle with featureless areas of light and dark.

"We want to bring Pluto into the family as well," project scientist Hal Weaver said.

The planet is unique in many ways, making the mission worth the small risk of carrying nuclear fuel, scientists say. The plutonium-powered battery keeps the craft's instruments warm.

Some facts about Pluto that intrigue scientists:

• Pluto is considered a "twin planet" with its large moon, Charon. They might exchange atmospheric material. Two smaller moons recently were discovered and will be worked into New Horizons' observations.
   
• It's usually the farthest planet but sometimes slips within Neptune's orbit as it circles the sun. A Pluto year is 248 Earth years.
   
• Pluto chills as it moves farther from the sun, and its atmosphere "snows out," onto the ground. Scientists want to go now while it still has an atmosphere or risk waiting hundreds of years.
   
• The planet is king of the Kuiper Belt, the ring of icy objects at the edge of our solar system. "It's an ancient debris belt left over from planetary formation," Stern said.

A National Academy of Sciences panel advised NASA that studying Pluto and Kuiper Belt objects was its highest priority. New Horizons is expected to fly beyond Pluto and study one or two of these objects.

"This is going to revolutionize our knowledge of the solar system," Stern said.