The discovery provides the first evidence of relatively recent liquid flow on Pluto. The study is based on observations from NASA’s New Horizons spacecraft and was led by SwRI Vice President Alan Stern, Ph.D., principal investigator for the New Horizons mission.

“Pluto never ceases to amaze us,” said lead author Stern. “This new result certainly shows that. In addition to suggesting that liquid has recently appeared on Pluto’s surface, it also suggests a new type of time-varying feature for Pluto.”

Dark Features in Pluto’s Giant Nitrogen Glacier

Sputnik Planitia is a vast glacier made primarily of frozen nitrogen. It is larger than Texas and Oklahoma combined. Images collected by New Horizons in 2015 and 2016 revealed city-sized geological convection cells in its northern region, along with thin dark lines and more diffuse dark spots.

A new examination of these features suggests that they may occasionally become temporarily wet. The most likely source is liquid nitrogen rising from beneath Pluto’s surface. The results were published in the peer-reviewed Planetary Science Journal.

Liquid nitrogen cannot fall as rain on Pluto because the dwarf planet’s temperature and atmospheric conditions do not allow it. However, parts of northern Sputnik Planitia have darkened in patterns similar to those found on terrestrial glaciers after exposure to rainwater or fluids flowing from beneath the ice.

Clues from Greenland’s Ice Sheet

To investigate the similarities, the SwRI-led team compared New Horizons images with NASA Landsat 9 images of icy regions on Earth, including the Greenland ice sheet.

In Greenland, narrow dark patterns appear where liquid water is present on ice or snow. A similar pattern appears on Sputnik Planitia, where researchers propose that subsurface fluids—particularly nitrogen—may be rising to wet Pluto’s frozen nitrogen surface.

“The surface of Sputnik Planitia is very young, perhaps less than a million years old based on models of surface overturning, so these landforms we’re looking at must have formed since then,” said SwRI Principal Scientist Dr. Kelsi Singer, one of the study’s co-authors.

“Pluto has many unique landforms found nowhere else in the solar system, including this region of Sputnik Planum. Its surface offers a different set of conditions than the Earth we are used to, and exploring it can help us better understand how materials behave in environments that are difficult to produce on Earth.”

Previous studies, including one led by Stern, proposed that Pluto had liquid flowing in the distant past. The new discovery goes further, suggesting that liquid nitrogen may be present beneath Sputnik Planitia or may have existed there until very recently.

How Could Liquid Nitrogen Reach Pluto’s Surface?

A computer simulation led by Dr. Orkan Umruhan, principal investigator at the SETI Institute, provides a possible explanation.

The model shows that liquid nitrogen could form when nitrogen ice melts at the bottom of Sputnik Planum, several kilometers beneath the surface. The liquid could then rise through narrow channels, similar to material moving through lava or geyser tubes. Buoyancy or pressure from below may help push the liquid upward.

Once it reaches the surface, liquid nitrogen may remain liquid long enough to travel downhill across the glacier. As it moves, the surrounding nitrogen ice could become wet, creating the dark patterns observed by New Horizons.

“I think the great significance of these discoveries and the fascinating picture they promote is a great motivation and reason to further study the physics of solid nitrogen at cryogenic temperatures,” Umruhan said. “It’s important to study the physical phenomena that occur within solid nitrogen materials, especially since solid nitrogen materials can dissolve when subjected to stress and strain. These processes have never really been studied in detail in the laboratory.”

What Pluto’s Possible Liquid Flow Could Mean for the Solar System

Researchers have not yet identified clear evidence of this type of basal fluid flow elsewhere on Pluto. However, more than half of the dwarf planet has never been mapped at high resolution, leaving open the possibility that similar processes are occurring in other regions.

The same mechanism, involving melting and the upward movement of liquid, may also help explain activity elsewhere in the solar system. One possible example is Triton, Neptune’s largest moon, where NASA’s Voyager 2 spacecraft observed geysers erupting from the surface.

Scientists say additional high-resolution observations of Pluto and other Kuiper Belt objects will be needed to determine whether similar processes are occurring elsewhere in the distant solar system.

The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, designs, manufactures, and operates the New Horizons spacecraft and mission for NASA’s Science Mission Directorate. The Planetary Mission Program Office at Marshall Space Flight Center (MSFC) in Huntsville, Alabama, provides oversight of New Horizons for NASA. San Antonio-based Southwest Research Institute is leading the mission through Principal Investigator Dr. Alan Stern, who leads the science team, payload operations, and science planning. New Horizons is part of the New Frontiers program managed by NASA’s MSFC.