Pluto-mod(AP) -- Newly released Hubble Space Telescope photos show Pluto is changing color and its ice sheets are shifting. That's got astronomers surprised.

The photos paint a Pluto that is significantly redder than it had been for the past several decades. To the layman, it has a yellow-orange hue, the color of molasses, but astronomers say it has about 20 percent more red than it used to have.

The pictures show nitrogen ice growing and shrinking, getting brighter in the north and darker in the south. Astronomers say Pluto is changing more than the surfaces of other bodies in the solar system. That's surprising because a season lasts 120 years in some regions of Pluto.

Once considered a planet, Pluto was demoted to a dwarf planet by astronomers in 2006.