It has been a few months since NASA’s New Horizons space probe made headlines, but images from its historic July 14 flyby of the dwarf planet Pluto continue to arrive, much to the wonder and amazement of the scientists who launched the probe in 2006. According to a report from CS Monitor, the surprises are far from over. Scientists working with the New Horizons mission were stunned to find a strange “X” shape in the icy planes of Sputnik Planum.

The feature, dug into the nitrogen ice planes, has sparked the imaginations of scientists and space fans alike. The surface of Sputnik Planum is comprised of millions of polygonal ice chunks measuring up to 25 miles across. Scientists think the strange geometry on the surface of Pluto was most likely formed by the dwarf planet’s internal geology, which surprised many by its activity. Researchers believe that solid nitrogen trapped below Pluto’s surface is warmed by a mysterious source of internal heat, causing it to rise and sink.

According to William McKinnon, a researcher at Washington University in St. Louis and the deputy leader of New Horizons’ Geology, Geophysics, and Imaging team, this area of Pluto resembles a lava lamp that is roughly the same size and volume as the entire Hudson Bay.

The “X” discovered on Sputnik Planum is likely the convergence point of fur separate convection cells. Heat coming at one central from four different points would create cracks in the icy plain that resembles the shape of an “X.” Scientists believe that the dark patch on the upper left hand of the “X” could be a murky patch of water ice floating on top of the denser nitrogen ice.

The “X” photo is just the latest in a breathtaking series of New Horizons photos that have made their way back to Earth since the probe passed Pluto this summer. It was snapped with the probe’s Long Range Reconnaissance Imager (LORRI) camera, at a distance of roughly 10,000 miles over the dwarf planet’s surface.

Sputnik Planum’s icy fields stretch across an area roughly 50 miles wide and over 400 miles long. The resolution in the photo is roughly 250 feet per pixel, revealing features on the planet’s surface that are roughly the size of a city block.

To date, NASA researchers estimate the New Horizons has only sent back a quarter of the photos it took as it flew by Pluto this July. Scientists are enthralled by what they have seen so far, and nobody can accurately guess what secrets the New Horizons space probe is still waiting to reveal.

A NASA press release describing the newest photos from New Horizons can be found here.