In the year since NASA’s New Horizons spacecraft flew by Pluto, the dwarf planet has maintained its icy heart.

But closer analysis of the trove of data collected by the space probe reveals intriguing clues to other possible features – including whether Pluto has a sloshing underground ocean of liquid water. And the data has confirmed some ideas like how Pluto and its moons formed.

Scientists have been sifting through the information that has been sent back intermittently since the flyby on July 14, 2015.

“It almost simultaneously seems like forever, and it seems like no time at all,” said S. Alan Stern, the mission’s principal investigator, of the months that have elapsed since the flyby. “We’ve been super busy the whole time.”



Within days of the flyby, data from New Horizons unveiled Pluto’s diverse terrain and surroundings. It was not a bland snowball, but a world covered with strikingly complex icescapes, from plains to soaring mountains. The scientists described signs of active tectonics, a thin but hazy atmosphere, and other perplexing features.

“It’s much more complex than people, ourselves as experts included, expected,” Dr. Stern said. “It rivals Mars.”

For the most part, the first impressions have have held up. Dr. Stern cited 40 scientific papers, hundreds of hours of teleconferences among the scientists, and 200 scientific talks. “We’ve added a lot of detail,” he said.

The story of Pluto is still largely a story of ice.

On Earth, the only ice is frozen water. On Pluto, nitrogen, methane and carbon monoxide also freeze solid.

The most striking feature that NASA’s New Horizons spacecraft saw when it flew past Pluto last July was a heart-shaped region now named Tombaugh Regio after Clyde Tombaugh, the discoverer of Pluto.

The left half is covered by mostly nitrogen snow; the right side is more methane ice.