While reviewing photos from the New Horizons spacecraft, astronomers at NASA noticed an "X" on Pluto's surface, so naturally they went looking for treasure.

According to Space.com, they found ice blocks ranging from 10 miles to 25 miles wide in an area of the dwarf planet's surface they named Sputnik Planum. The area's altitude is a few miles below the surface around it and acts "like a lava lamp."

"This part of Pluto is acting like a lava lamp, if you can imagine a lava lamp as wide as, and even deeper than, the Hudson Bay," William McKinnon, deputy lead of the New Horizons Geology, Geophysics and Imaging team at Washington University in St. Louis, said in a press release.

New Horizons delivered the photos of Sputnik Planum on Christmas Eve, though NASA did not release them until Thursday, Jan. 7. The probe has only delivered about a quarter of the data it collected from its historic flyby of the distant dwarf planet, Space.com noted. However, New Horizons has already delivered its high-resolution images and should be able to unload the rest of its data by the end of this year.

"Computer models by the New Horizons team show that these blobs of overturning solid nitrogen can slowly evolve and merge over millions of years," NASA stated in its release. "The ridged margins, which mark where cooled nitrogen ice sinks back down, can be pinched off and abandoned. The 'X' feature is likely one of these-a former quadruple junction where four convection cells meet. Numerous, active triple junctions can be seen elsewhere in the LORRI mosaic."