A Heart That Still Beats
When NASA’s New Horizons spacecraft flew past Pluto in 2015, it revealed a stunning, heart-shaped feature on its surface. This massive glacier of frozen nitrogen, larger than Texas and Oklahoma combined, is known as Sputnik Planitia. Initial images already
showed that this region was surprisingly young and active, with a surface divided into city-sized cells that slowly churn like a cosmic lava lamp. Now, a fresh analysis of that same data provides the first evidence that liquid nitrogen may have recently seeped from beneath the ice, staining the surface and hinting at a dynamic interior. “Pluto never stops surprising us,” said Alan Stern, the principal investigator for the New Horizons mission.
The Telltale Stains
The new study, published in the Planetary Science Journal, focuses on a series of dark, narrow streaks and wider patches observed at the northern edge of Sputnik Planitia. These markings trace the boundaries of the large, polygonal convection cells on the glacier's surface. For years, their origin was a mystery. Researchers have now compared these features to satellite imagery of glaciers in Greenland. On Earth, similar dark patterns form when meltwater from beneath the ice sheet emerges and wets the surface snow and ice before refreezing. Because Pluto’s thin atmosphere and extreme cold make nitrogen rain impossible, the clues point to a liquid source from below.
A Subsurface Plumbing System
So, how could liquid exist on a world where surface temperatures hover around -230 degrees Celsius? The answer may lie deep within the ice. Computer models suggest that the immense pressure at the base of Sputnik Planitia’s nitrogen glacier, which is several kilometres deep, could be enough to melt the nitrogen ice. This liquid nitrogen, being less dense than the solid ice above it, would then become buoyant. Scientists propose that this liquid collects in reservoirs before being forced upward through fractures and conduits in the ice, similar to how magma moves through volcanic systems on Earth. It wouldn’t be a steady trickle, but likely short, intense pulses that release large volumes of liquid over hours or days before it spreads and refreezes on the frigid surface.
Why This Finding Matters
The suggestion of recent liquid flow fundamentally changes our picture of Pluto. It implies that the dwarf planet is not a static, frozen ball of ice and rock, but a geologically dynamic world that remains active billions of years after its formation. The presence of such a process requires more internal heat than previously thought, a puzzle for a small, isolated world without a giant planet nearby to gravitationally churn its interior. This activity also means the surface we see is constantly being reshaped. Scientists estimate the surface of Sputnik Planitia is less than a million years old, a geological blink of an eye. The discovery paints a portrait of a far more complex world, with active “plumbing” that connects a deep interior to the visible surface.
