A Heart That Isn't Frozen Still
Pluto’s most famous feature is a massive, heart-shaped basin of ice called Tombaugh Regio. The western lobe of this heart, known as Sputnik Planitia, is a colossal glacier of frozen nitrogen larger than Texas and Oklahoma combined. When the New Horizons
spacecraft flew by in 2015, it sent back images that stunned scientists. Instead of a static, heavily cratered surface, Sputnik Planitia was remarkably smooth, suggesting its surface was geologically young and constantly being renewed.
Signs of Flowing Liquid
Now, a recent analysis of those high-resolution images has uncovered the most compelling evidence yet of recent geological activity. Scientists have identified dark streaks and diffuse patterns along the northern edge of Sputnik Planitia. These features look strikingly similar to patterns on Earth's own glaciers, which are formed when water from beneath the ice seeps up and wets the surface. But on Pluto, where surface temperatures are unimaginably cold, water isn't the culprit. The prime suspect is liquid nitrogen.
An Underground Source
Pluto's thin atmosphere and frigid conditions make it physically impossible for liquid nitrogen rain to fall. This led researchers to a fascinating conclusion: the liquid must be coming from below. Computer models suggest that deep beneath the kilometers-thick glacier, the immense pressure can melt the nitrogen ice at its base. This liquid nitrogen, being slightly more buoyant, can then be forced upward through cracks and fissures in the ice, much like magma rising through Earth's crust. Once it reaches the surface, it can flow briefly before refreezing, staining the landscape with the dark patterns New Horizons observed.
A Geologically Active World
This discovery of what scientists call "basal melting" is a game-changer. It implies that Pluto is not a geologically dead world but a dynamic one, with active processes reshaping its surface from within. The lack of impact craters on Sputnik Planitia had already suggested that the surface was being constantly overturned, with some age estimates as young as a few hundred thousand years—a mere blink of an eye in geological time. The evidence of liquid flow adds another layer to this picture of an active world, powered by some form of internal heat or pressure. As Alan Stern, the principal investigator for the New Horizons mission, put it, "Pluto never stops surprising us."
Redefining the Outer Solar System
The findings on Pluto force a major rethink of what is possible in the cold, dark Kuiper Belt. These distant, icy bodies were once thought to be inert relics from the formation of the solar system. But the evidence for flowing glaciers, renewing surfaces, and potential subsurface liquids suggests they can be complex and active worlds. Understanding the engine driving Pluto's geology could provide crucial insights into other icy bodies in our solar system, such as Neptune's moon Triton or the moons of Jupiter and Saturn. The data gathered by New Horizons in a brief flyby over a decade ago continues to be a treasure trove, revealing that even the most remote corners of our cosmic neighbourhood are more alive than we ever imagined.
