This story was updated at 1:59 p.m.ET
The Hubble Space Telescope has returned the most detailed images of Pluto ever taken.
The new photos reveal the strange mini-world in near true-life color, close to what the dwarf planet would look like to an observer traveling toward it in a spacecraft, scientists said. The surface appears reddish, yellowish, grayish in places, with a mysterious bright spot that is particularly puzzling to scientists.
Some of the colors revealed in the new pictures of Pluto are thought to result from ultraviolet radiation from the sun interacting with methane in the tenuous atmosphere of the dwarf planet. The bright spot apparent near the equator has been found in other observations to be unusually rich in carbon monoxide frost.
"This is our best candidate, that it's carbon related," Marc Buie of the Southwest Research Institute, Boulder, Colo. said during a Thursday teleconference.
The new images should provide "a real treasure trove of information in understanding the nature of Pluto and how it evolved and changes with time," Buie said.
Pluto is a world on the fringe of the solar system with three small moons called Charon, Nix and Hydra. It was discovered in 1930 by astronomer Clyde Tombaugh, and was long considered a full-fledged planet. But in 2006, after much debate in the astronomical community, Pluto was downgraded to "dwarf planet" status, along with other cosmic bodies such as Ceres and Eris.
Scientist Mike Brown, professor of planetary astronomy at Caltech in Pasadena, Calif., who as discoverer of Eris was partly responsible for this demotion, says not to feel too bad for Pluto.
"Pluto is a fascinating world and it doesn't really care what we call it," Brown said. "I think this is an exciting thing to see and an exciting thing to try to understand how the entire solar system works."
Pluto is the destination for NASA's New Horizons probe, a spacecraft currently on a course to fly by Pluto and its moons in 2015.
"It's about halfway there already and when its gets there we're going to get all sorts of great pictures and great data," Buie said. "But these [Hubble] maps have been used already to help plan the encounter.
When compared to older data from 1994, the new photos ? taken by Hubble's Advanced Camera for Surveys ? reveal a surprising amount of change in the appearance of Pluto. Over that period, Pluto has gotten redder, while its northern polar region has gotten brighter and its southern hemisphere has gotten darker.
One reason for the variability, scientists say, is Pluto's highly eccentric ? or oblong ? orbit, which causes strong variations in temperature. Pluto takes 248 years to make a full orbit around the sun.
"Right now it's close to being springtime on Pluto," Brown said. "In the fall things will freeze out. It's just a ridiculously extreme place to be."
Since the dwarf planet is so small and so far away, it has been difficult to gather detailed data before. When New Horizons arrives, that probe should reveal even higher quality data. But until then, Hubble's vision is by far the best view we've ever gotten.
"This has taken four years and 20 computers operating continuously and simultaneously to accomplish," says Buie, who developed a special computer program to sharpen the Hubble data.
The findings are detailed in the March 2010 issue of the Astronomical Journal.
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