Dark Pluto Bares Its Heart

By Geoff Brumfiel

Published July 24, 2015 at 3:18 PM CDT

Scientists with NASA's mission to Pluto revealed stunning new images of the dwarf planet on Friday. Researchers say the pictures suggest an icy world complete with glaciers and "snow" that falls through a wispy atmosphere.

The New Horizons spacecraft zipped past Pluto on July 14. It was traveling too fast to stop, but it snapped a trove of photos as it flew by. Because deep-space communication happens at sub-dial-up speeds, it will take months for all of the photos and data to come back.

But the 5 percent or so of data the spacecraft has returned has scientists gripped with excitement. "If you're seeing a cardiologist, you may want to leave the room," Alan Stern, the principal investigator of the New Horizons mission, said before unveiling the latest photos.

The images show Pluto is far from a dead lump of rock and ice. It appears that it experiences seasons during its 248-year orbit around the sun, according to Cathy Olkin, a scientist on the mission from the Southwest Research Institute in Boulder, Colo. In hotter times, the sun causes ice on the surface to evaporate and then settle in other regions.

Detailed images of the surface also show glaciers. A vast patch of the surface known as "Sputnik Planum" appears to be covered in what could be ice made of solid nitrogen. Even though it's a frosty -391 Fahrenheit, nitrogen ice is soft enough to flow, says Bill McKinnon, a geologist at Washington University in St. Louis, Mo. There is clear evidence that the nitrogen is flowing into craters and around mountains, which are believed to be made of solid water-ice.

The source of the nitrogen ice is unknown. It could have been deposited when an icy body smashed into Pluto, or it could be upwelling from deep within the planet. "We're enjoying a great deal of animated discussion," McKinnon says.

Perhaps the most confounding image is one taken as New Horizons flew away from Pluto. It shows the planet back-lit by the sun, with its atmosphere clearly visible. Researchers say the atmosphere is much thinner than expected. One theory is that it may be "collapsing" as Pluto moves away from the sun and toward many years of cold, dark winter at the edge of the solar system.