A new study of the geological makeup of Pluto indicates that the tiny planet on the outer fringes of the solar system is not an asteroid or a moon that escaped from neighboring Neptune, but developed like other planets, space scientists said.

"Pluto is not an asteroid," said astronomer William McKinnon. "It has a lot of ice, which the asteroids do not have. It also has a satellite, which asteroids do not have, and because it never was part of the asteroid belt it couldn't have formed there."Pluto has been the source of controversy of one sort or another ever since it was discovered," said McKinnon, a specialist in the study of Pluto and its extremely eccentric orbit.

McKinnon, of the McDonnell Center for Space Sciences at Washington University in St. Louis, reported new results of studies involving Pluto's geological composition and that of its moon Charon in Wednesday's issue of the British journal Nature.

He said he found an unusually high ratio of rock to other materials on the planet, which suggests a very high density. The study also revealed an icy crust most likely composed of methane and water, making Pluto "a new kind of world."