Pluto Has a Blue Sky, Like Ours

New Horizons' flyby of Pluto this summer taught us a lot about the dwarf planet, including that it's 1,597 miles across and has a mountain range the size of the Rockies. But new surprises are emerging as data continues to be beamed back from 3.1 billion miles away. A recently received color image of Pluto's atmosphere, for example, shows the dwarf planet with a blue glow, meaning it has a blue sky similar to Earth's, reports Space.com. "Who would have expected a blue sky in the Kuiper Belt?" says a NASA scientist on the project. "It's gorgeous." The color of Earth's sky is the result of small nitrogen particles scattering blue light, explains NASA. In the case of Pluto, larger "soot-like particles" called tholins also scatter light in blue wavelengths.

But while Pluto may have a blue sky, another photo shows the dwarf planet has bright-red water ice scattered across its surface—or at least, frozen water in areas that appear to be bright red. "I'm surprised that this water ice is so red," says a researcher. "We don't yet understand the relationship between water ice and the reddish tholin colorants on Pluto's surface," she adds. Water ice probably covers most of the planet but is "masked by other, more volatile ices," another researcher says. "Understanding why water appears exactly where it does, and not in other places, is a challenge that we are digging into." New Horizons began sending all of its stored data to NASA last month and is expected to finish its transmission by the end of next year. (More Pluto stories.)