A Bleeding Heart of Nitrogen
Scientists re-examining images from the 2015 New Horizons flyby have found compelling evidence of a new type of geological activity. Dark streaks observed along the northern edge of Sputnik Planitia, the vast, heart-shaped glacier, look remarkably like
areas on Earth's own ice sheets where liquid has flowed. The new research, led by Southwest Research Institute's Dr. Alan Stern, suggests these are stains left behind by liquid nitrogen that has welled up from beneath the surface and flowed before refreezing. This would be the first evidence of recently flowing liquid on Pluto's surface.
How Can a Frozen World Have Liquid?
Pluto's surface temperature hovers around a frigid -230°C, so the idea of liquid seems impossible. Rain is considered physically impossible in Pluto's thin atmosphere. This means the liquid isn't coming from above, but from below. Computer models suggest that, deep beneath the kilometres-thick nitrogen ice of Sputnik Planitia, the immense pressure could be enough to melt the nitrogen at its base. This liquid nitrogen could then be forced up through cracks and fissures in the ice, briefly flowing across the surface like a temporary spring in the deep freeze.
Unpacking a Decade of Data
The New Horizons spacecraft sped past Pluto in 2015, but the treasure trove of data it collected is so vast that scientists are still making discoveries more than a decade later. These latest findings came from comparing the complex patterns on Pluto to more familiar glacial features here on Earth, such as those in Greenland. By applying knowledge of how liquid water darkens and stains ice sheets on our own planet, researchers could interpret the mysterious dark streaks on Sputnik Planitia. The features suggest this activity is recent, geologically speaking, happening within the last million years—a blink of an eye in cosmic time.
A New Kind of Active World
This discovery fundamentally changes our view of Pluto. It's not a dead, inert world, but a geologically active body. The presence of these time-variable features suggests Pluto has its own unique version of 'plumbing'. Finding signs of flowing liquid and cryovolcanism—ice volcanoes that spew a slurry of water ice—shows that there is enough residual heat in Pluto's interior to power complex planetary processes. It challenges our assumptions about what is required for a celestial body to be active, showing that even in the frigid outer reaches of the solar system, dramatic geological events can unfold.
