A World That Never Stops Surprising
Ever since NASA’s New Horizons spacecraft flew past Pluto in 2015, it has been rewriting the book on this distant dwarf planet. Once dismissed as a static, cratered ice ball, Pluto has revealed itself to be a world of stunning complexity, with towering
ice mountains, vast nitrogen glaciers, and even a potential subsurface ocean. The latest discovery adds another layer of intrigue: evidence of recent liquid flows on its surface. A new study led by the Southwest Research Institute (SwRI) points to liquid nitrogen seeping up from below and wetting the surface of Pluto’s famous heart-shaped glacier, Sputnik Planitia.
The Telltale Dark Streaks
The evidence comes from a fresh analysis of high-resolution images of Sputnik Planitia, a colossal basin filled with frozen nitrogen that is larger than Texas and Oklahoma combined. Scientists noticed dark, linear streaks and diffuse patches along the boundaries of the glacier's city-sized convection cells. These features looked familiar. Researchers compared them to images of glaciers on Earth, like the Greenland ice sheet, where similar dark markings are created when meltwater wets the snow and ice. Since Pluto’s frigid atmosphere makes nitrogen rain impossible, the team concluded the liquid must be coming from below.
An Engine Under the Ice
How can liquid exist on a world where surface temperatures are unimaginably cold? It’s not a vast, sloshing ocean causing these flows, but a more localized process. Computer models suggest that the immense pressure from the kilometers-deep nitrogen glacier can be enough to melt the nitrogen ice at its very base, a process called basal melting. This newly formed liquid nitrogen, being more buoyant than the solid ice above it, could then be forced upward through cracks and conduits, much like magma in Earth's volcanoes. Once on the surface, the liquid nitrogen would flow briefly before refreezing, darkening the ice and creating the features New Horizons observed.
More Than Just Nitrogen?
While these recent findings point to liquid nitrogen, they exist alongside a larger, more tantalizing possibility: a deep, global ocean of liquid water. For years, scientists have puzzled over clues—like massive fractures in Pluto’s crust and its surprisingly spherical shape—that suggest a hidden ocean. This water ocean, if it exists, would be kept liquid not by surface processes, but by heat from radioactive elements decaying in Pluto’s rocky core and the insulating effect of the thick ice shell above it. Some theories suggest this ocean could be incredibly salty, which would act as an antifreeze. This water ocean is separate from the nitrogen flows but points to the same conclusion: Pluto's interior is warmer and more active than previously believed.
A New Kind of Geological Activity
The discovery of recent liquid nitrogen flows is significant because it shows Pluto is geologically active today, or at least in the very recent past. This activity is a new type of time-variable feature previously unseen on the dwarf planet. These processes join other evidence of geologic youth, such as the vast, crater-free expanse of Sputnik Planitia and the presence of giant cryovolcanoes—ice volcanoes that erupt a slushy mix of water, ammonia, or methane instead of rock. Some of these cryovolcanic terrains appear to be only a few million years old, a blink of an eye in cosmic terms, suggesting Pluto may still be capable of eruptions.
