Demoted from planet status, Pluto changes its look

WASHINGTON - Spurned Pluto is changing its looks, donning more rouge in its complexion and altering its iceball surface here and there.

Color astronomers surprised.

Newly released Hubble Space Telescope photos show the distant onetime planet, demoted to "dwarf planet" status in 2006, is changing color and its ice sheets are shifting.

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

The pictures show icy frozen nitrogen on Pluto's surface growing and shrinking, brightening in the north and darkening in the south.

"It's a little bit of a surprise to see these changes happening so big and so fast," said astronomer Marc Buie of the Southwest Research Institute in Boulder, Colo. "This is unprecedented."

From 1954 to 2000, Pluto didn't change in color when it was photographed from Earth. But after that, the red levels increased by 20 percent to 30 percent, and stabilized from about 2000 to 2002, Buie said. It's not as red as Mars, however, he said.

Buie said he can explain the redness, but not why it changed so dramatically and so recently. The planet has a lot of methane, which contains carbon and hydrogen atoms. The hydrogen gets stripped off by solar winds and other factors, leaving carbon-rich areas on the surface, which tend to be red and dark.

The Hubble photos were taken in 2002 and the analysis took a few years. Why Pluto changed so quickly was such a mystery that Buie held off for years on announcing what he had found, worried that he might be wrong. Pluto's moon Charon hadn't changed color in the same telescope images, so he decided the findings weren't an instrument mistake.

- AP