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(CNN) — Pluto’s icy wonderland keeps mystifying scientists.

On Thursday, NASA released a photo of what they are calling Pluto’s “floating hills.” The images were captured by New Horizons spacecraft during its historic 2015 fly by.

The hill clusters lie in a vast ice plain inside the dwarf planet’s “heart” region. It’s believed that the frozen formations stretch for miles. Experts at NASA theorize that the mysterious floating hills are fragments of water ice that resemble giant glaciers, similar to the icebergs we see on Earth.

Since water ice is lighter than nitrogen ice, the hills are floating above a sea of nitrogen. These huge chucks of water ice move much like the icebergs that float in Earth’s Arctic Ocean, NASA scientists said in a statement.

It’s likely that the floating hills are fragmented water ice that have broken away from the rugged uplands and are gliding towards the Sputnik Planum.

This photo comes after NASA announced in January that the dwarf planet is covered with way more water ice than the American space agency initially expected. The water ice discovery came after NASA stitched together two infrared images taken by New Horizons.

Since it’s initial flyby, the images captured by New Horizons continue to reveal new characteristics about the dwarf planet.

The floating hills are joining Pluto’s already fascinating geographic activity from its towering ice mountains to its potential ice volcanoes.