Pluto may be far colder than any place on Earth, but scientists have discovered evidence that something surprising may still be moving beneath its frozen surface.
A new study suggests that liquid nitrogen may have recently flowed across part of Pluto’s famous heart-shaped glacier, making it the first evidence of recent liquid activity on the distant dwarf planet.
The discovery comes from scientists led by researchers at the Southwest Research Institute, who studied images collected by NASA’s New Horizons spacecraft during its historic flyby of Pluto in 2015.
Their findings were published in The Planetary Science Journal.
The area of interest is Sputnik Planitia, a massive glacier made mostly of frozen nitrogen.
It forms the western half of Pluto’s iconic heart-shaped feature and covers an area larger than Texas and Oklahoma combined.
Although the glacier looks frozen solid, researchers now believe that liquid nitrogen may occasionally rise from beneath its surface.
When New Horizons photographed the northern edge of Sputnik Planitia, it revealed giant convection cells—slow-moving patterns in the ice that are each about the size of a city. Between these cells were dark streaks and patches that puzzled scientists for years.
To better understand these unusual markings, the research team compared them with satellite images of Greenland taken by NASA’s Landsat 9 mission. On Earth, similar dark patterns appear when liquid water reaches the surface of ice or snow, either from melting or from underground sources.
While rain is impossible on Pluto because of its extremely thin atmosphere and frigid temperatures, the similarities suggest that liquid nitrogen may have seeped onto the surface in much the same way.
The researchers believe the dark markings are relatively young because Sputnik Planitia itself is thought to be less than one million years old. This means the liquid activity that created them likely happened recently in geological terms.
Computer simulations provided another important clue. The models showed that deep beneath the glacier, where thick layers of nitrogen ice are under pressure, the ice can melt into liquid nitrogen.
That liquid could then slowly rise through narrow cracks or channels, driven upward by pressure or buoyancy, much like magma moving through volcanic rock or water rising through a geyser.
Once the liquid reaches the surface, it may stay in liquid form long enough to flow downhill along gentle slopes before freezing again. As it spreads across the surface, it could temporarily darken the ice, creating the mysterious streaks seen in the spacecraft images.
Scientists say this discovery opens a new chapter in understanding Pluto. Previous studies hinted that liquid nitrogen may have flowed there in the distant past, but this is the strongest evidence yet that the process may still be happening today.
Many questions remain unanswered because more than half of Pluto has never been photographed in high resolution.
Researchers also think similar underground nitrogen flows might help explain the icy geysers seen on Triton, Neptune’s largest moon. Future missions to the outer solar system could reveal whether these hidden liquid processes are more common than anyone expected.
