The Heart of a Distant World
Since NASA’s New Horizons spacecraft flew by Pluto in 2015, scientists have been captivated by a vast, bright feature dominating its surface: a heart-shaped region named Tombaugh Regio. The western lobe of this heart, known as Sputnik Planitia, is an enormous
basin filled with frozen nitrogen, methane, and carbon monoxide. Larger than Texas and Oklahoma combined, this colossal glacier is not a static sheet of ice. Its surface is broken into city-sized polygonal cells, which indicates a slow, churning process of convection, where warmer ice rises and cooler ice sinks, constantly renewing the surface. This continuous renewal explains why the region is almost entirely free of impact craters, suggesting it is geologically young and active.
A Surprising Sign of Liquid
The latest groundbreaking theory comes from a new analysis of the New Horizons data, led by researchers at the Southwest Research Institute. Scientists noticed thin, dark lines and broader dark patches tracing the boundaries of Sputnik Planitia's convection cells. These features bear a striking resemblance to wetted areas on Earth's own glaciers, like those on the Greenland ice sheet, where liquid water has flowed. However, Pluto’s frigid atmosphere makes liquid nitrogen rain an impossibility. This led the research team to an intriguing conclusion: the liquid must be coming from beneath the surface.
Pluto's Internal Plumbing
So, how could liquid exist on a world where surface temperatures hover around minus 230 degrees Celsius? The answer may lie deep within. Computer models suggest that even the faint heat emanating from Pluto’s rocky core could be enough to melt the nitrogen ice at the very bottom of the kilometers-thick glacier. According to these simulations, this liquid nitrogen, being less dense than the solid ice above it, would then be forced upwards. It would travel through small conduits or cracks in the ice, driven by buoyancy and pressure, in a process that some have compared to lava moving through tubes on Earth. Upon reaching the surface, the liquid nitrogen would briefly flow before refreezing, darkening the ice and creating the distinct patterns observed by New Horizons.
A New Chapter for a Dwarf Planet
This discovery marks the first evidence for recently flowing liquid on Pluto. It fundamentally changes our perception of the dwarf planet from a static, frozen outpost to a geologically dynamic world with ongoing processes shaping its landscape. The lead author of the study, Alan Stern, who is also the principal investigator for the New Horizons mission, noted that “Pluto never stops surprising us.” The idea that Pluto has active, time-variable features powered by subsurface liquids opens up a new realm of possibilities for understanding cold, distant worlds. It suggests that similar processes might be at play on other icy bodies in the Kuiper Belt, such as Neptune's moon Triton or the dwarf planets Eris and Makemake.
