Sputnik Planum
A vast, icy plain on Pluto's surface, informally named after Earth's first artificial satellite, Sputnik. Characterized by its smooth, craterless terrain, it is believed to be composed primarily of nitrogen ice and exhibits signs of recent geological activity.
Source: nasa.gov
APODs including "Sputnik Planum"
Pluto's Sputnik Planum
22/11/2016
Is there an ocean below Sputnik Planum on Pluto? The unusually smooth 1000-km wide golden expanse, visible in the featured image from New Horizons, appears segmented into convection cells. But how was this region created? One hypothesis now holds the answer to be a great impact that stirred up an underground ocean of salt water roughly 100-kilometers thick. The featured image of Sputnik Planum, part of the larger heart-shaped Tombaugh Regio, was taken last July and shows true details in exaggerated colors. Although the robotic New Horizons spacecraft is off on a new adventure, continued computer-modeling of this surprising surface feature on Pluto is likely to lead to more refined speculations about what lies beneath.