A Heart of Ice
Pluto’s most famous feature is Tombaugh Regio, a bright, expansive region nicknamed ‘the heart’. Its western lobe, a sprawling basin called Sputnik Planitia, is larger than Texas and Oklahoma combined. This colossal glacier isn’t made of water ice like
those on Earth, but is instead filled with frozen nitrogen, mixed with smaller amounts of frozen methane and carbon monoxide. For years, scientists have been captivated by its surface, which is marked by city-sized polygonal cells that indicate a slow, churning convective movement, constantly renewing the ice. This process explains the near-total lack of impact craters, suggesting the surface is geologically young and active.
An Unexpected Discovery
Despite the slow churning of its surface, the dominant view of Pluto was of a profoundly frozen world. However, a recent analysis of the decade-old New Horizons data has challenged this perception. A team of researchers, led by the mission's principal investigator Alan Stern, noticed a network of dark, narrow streaks and broader shadowy patches along the northern boundaries of the glacier's convection cells. These features looked strangely familiar. They resembled patterns seen on glaciers in Greenland, where meltwater has emerged from beneath the ice or rained down, wetting the surface and making it appear darker.
Flowing Liquid in the Deep Freeze
Pluto's frigid atmosphere makes liquid nitrogen rain impossible. This led scientists to explore another, more radical idea: the liquid might be coming from below. Computer models suggest that deep beneath Sputnik Planitia's kilometers-thick ice sheet, the immense pressure could be just enough to melt the nitrogen ice at its base. This liquid nitrogen, being less dense than the solid ice above it, would be buoyant. It could then be forced upward through cracks and fissures in the glacier, a process compared to how magma finds its way through Earth's crust. It likely wouldn't be a steady trickle, but rather a periodic bursting forth after building up in underground reservoirs.
A World More Alive
This finding, published in The Planetary Science Journal, provides the first evidence for recently flowing liquid on Pluto's surface. The term 'recent' in geological time means it could have happened within the last million years, and the process could very well be ongoing today. These flows would briefly wet the surface before refreezing, leaving behind the dark stains observed by New Horizons. This recasts our understanding of the dwarf planet. Instead of a static, frozen ball of rock and ice, Pluto appears to be a geologically dynamic world with its own kind of subsurface 'plumbing'. This suggests the world is far more active than previously imagined, with processes capable of altering its landscape in the present day.
