On Pluto, 'X' Marks the Spot (Photo)

There's a big "X" on Pluto, and it marks buried treasure of a scientific kind. The X-shaped feature, on the huge Pluto nitrogen-ice plain known as Sputnik Planum, is visible in photos recently beamed home by NASA's New Horizons probe, which performed history's first-ever flyby of the dwarf planet on July 14, 2015. Sputnik Planum's surface is composed of many polygonal ice blocks that are between 10 miles (16 kilometers) and 25 miles (40 km) wide.