NASA on Thursday revealed another amazing Pluto factoid: the planet appears to have floating hills, or icebergs. The agency said the icebergs are floating in a vast sea of frozen nitrogen at Sputnik Planum, which rests within the planet’s “heart.”

“The hills are likely fragments of the rugged uplands that have broken away and are being carried by the nitrogen glaciers into Sputnik Planum,” NASA explained.

As the icebergs float across the frozen sea, they eventually cluster into groups that can reach miles across. In the image above, NASA says Challenger Coles is an especially large cluster of icebergs, measuring 37 by 22 miles. Because it’s such a large group, researchers believe this is an area where the icebergs have been “beached.”

We’ve already seen multiple close-up images of Pluto, along with some fascinating looks at the planet’s hazy atmosphere, and today’s picture further paints a picture of abundant geological activity. Here we thought Pluto was a barren wasteland quietly hiding in our solar system, but NASA’s finding that it’s much more than that.

NASA’s New Horizons spacecraft successfully performed a flyby of the planet last summer, and is still sending back data (and will continue to in the coming months).