WASHINGTON (AP) _ New telescopic images of Pluto show that the distant planet is a place of frozen gases, icy polar caps and clusters of bright and dark features that astronomers can't explain.

The Hubble Space Telescope photos, in which Pluto resembles a fuzzy soccer ball, have excited astronomers who say they show the planet is a place of surprises and mysterious processes.

``We can see from the images that Pluto is the most variegated, contrasty object in the outer solar system,'' said Alan Stern, an astronomer at the Southwest Research Institute in Boulder, Colo.

He said the images confirm the belief of experts that Pluto is one of the strangest of the nine planets orbiting the sun.

Bright patches of white on Pluto, a frozen world 29 times farther from the sun than is the Earth, are probably fields of frozen nitrogen, while the dark patches may be hydrocarbons from the chemical splitting and freezing of methane, Stern said.

``Pluto never fails to surprise,'' said Bruce Margon, an astronomy professor at the University of Washington.

``It is like an icy little dwarf on the outskirts of the solar system,'' said Anne L. Kinney of the Space Telescope Institute in Baltimore.

Discovered just 66 years ago, Pluto was the last of the solar system planets to be identified. It's moon, Charon, was found in 1978, and it was not until 1988 that scientists discovered Pluto had an atmosphere.

Pluto is so strange that some astronomers have argued that it isn't really a planet, but some other object, such as an asteroid.

``It is a planet,'' said Stern. ``It is round, it has a satellite (a moon), it has an atmosphere. There's only a minority view that it is not a planet.''

Pluto is turned on its side, in relation to its orbit. This is the result, astronomers believe, of a gigantic collision with a comet or an asteroid that caused the small planet to tilt.

The planet is about two-thirds the size of the Earth's moon and is so far from the sun that sunlight on its surface is about as intense as moonlight is on Earth. Temperatures on Pluto drop to about minus 380 degrees Fahrenheit when the planet is at its farthest from the sun. Pluto made its closest approach to the sun in 1989 and temperatures rose to a balmy minus-350.

Stern said the slight thaw caused some nitrogen ice to evaporate into the atmosphere. He said that over the next few years Pluto will again cool and the gases will ``snow'' back on the surface, perhaps covering some the dark spots seen in the Hubble photos.

Before the photos by the Earth-orbiting Hubble, Pluto had been seen as just a tiny spot of light faintly detected, 4 billion miles from Earth.

The new pictures, which astronomers said pushed the Hubble to the very limit of its ability, aren't good enough to determine if Pluto has mountains and valleys like those on Earth and Mars.

Pluto takes 248 years to circle the sun and during all but 20 of those years it is the farthest out of all the planets. It crossed inside the orbit of Neptune in 1979. In three years, it will again move out to resume its most-distant place.

A robot craft, called the Pluto Express, is scheduled to be launched toward Pluto in the next decade, but it will take 10 to 12 years for the craft to reach the planet.