Liquid Nitrogen on Pluto: In 2015, NASA’s New Horizons spacecraft flew by Pluto and captured detailed images of its frozen surface. More than a decade later, scientists revisited the images and found evidence that liquid nitrogen may have once flowed across the dwarf planet.
This result does not mean that scientists saw a liquid stream moving across Pluto. Instead, researchers combined unusual surface features, comparisons with Greenland and computer models to build a possible explanation for what happened. The study is entitled “Evidence of possible basal N2 flow beneath Pluto’s northern Sputnik Planitia“, was published in Planetary science magazine.
What did scientists find on Pluto?
Sputnik Planitia is the bright western section of Pluto’s famous heart-shaped region. Its nitrogen glacier is larger than the Texas and Oklahoma Rivers combined, and New Horizons has imaged large convection cells across its surface.
Among these features are thin dark lines and broader fuzzy spots.
Since Pluto’s surface is too cold for nitrogen rain to create such marks, researchers considered another possibility. Their models suggest that nitrogen ice found deep within the glacier could melt under the unusual pressure, stress and strain found there.
The fluid can then be forced upward through narrow passages, somewhat similar to geyser or lava channels. Once it reached the surface, it may have remained liquid long enough to travel down the hill and wet the nearby ice. This process could explain the dark trails seen in the New Horizons images.
As Alan Stern, New Horizons principal investigator and lead author of the study, said: “Pluto never ceases to surprise us.”
Can liquid nitrogen really move under ice?
Computer modeling provides the main support for the idea.
Sputnik Planitia contains a glacier several kilometers deep. Under the right conditions, nitrogen ice can melt near its base. Buoyancy or pressure from below can push the fluid upward.
The proposed process is particularly striking because Pluto appears frozen and inactive at first glance. However, models indicate that nitrogen ice can still move, melt at depth, and potentially reach the surface.
Researchers are cautious about what the evidence proves. The dark marks correspond to ice that has been temporarily wetted from below, but they are not a direct record of liquid flow.
The New Horizons spacecraft made only one close pass of Pluto in 2015. Its images cannot pinpoint exactly when a particular jet occurred or how often such events occur.
What does Greenland have to do with it?
Earth provided an unexpected comparison. The research team examined Landsat 9 images of the Greenland ice sheet, and found narrow dark contours in places where liquid water reached the surface of the snow and ice.
Some of these patterns are similar to the markings observed north of Sputnik Planitia.
The comparison is not evidence in itself. But when combined with the fact that nitrogen rain can’t explain the features and with computer model results, it supports the possibility that liquid nitrogen emerged from the bottom of Pluto’s glacier and temporarily wetted its surface.
This makes the Greenland comparison useful as a visual guide rather than a direct confirmation.
How soon could this happen?
Sputnik Planitia’s surface is believed to be relatively small. According to modeling, its surface may be less than a million years old, because convection constantly turns over the nitrogen ice. If the dark features were created by liquid nitrogen flows, they formed during that relatively early period.
The research also raises the possibility that liquid nitrogen exists beneath the glacier today.
However, there is no way to attach a specific date to an individual event. New Horizons imaged Pluto during a single flyby, leaving scientists with snapshots rather than continuous observations.
Is this liquid water?
No, the suggested liquid is nitrogen, not water. The study does not indicate the existence of an underground river like those found on Earth, nor does it provide evidence of the existence of life on Pluto.
The distinction is important because Pluto is extremely cold. The water ice there behaves like rock, while nitrogen is the substance most likely to melt and move under the conditions the researchers designed.
The importance of this discovery lies in what it suggests about volatile ice and how it could reshape the surfaces of distant planets.
Why are scientists still studying ancient images of Pluto?
New Horizons made history on July 14, 2015, when it became the first spacecraft to closely explore the planet Pluto. It passed about 7,800 miles above the surface, revealing glaciers, mountains, fog and possible signs of continued activity.
But the mission did not answer every question. Scientists keep returning to the images with new models and comparisons. In this case, images taken during one flyby became the starting point for a subsequent investigation into whether Pluto’s icy glacier is active below the surface.
Researchers now want to conduct laboratory experiments to examine how solid nitrogen behaves under Pluto-like cold, pressure, stress and strain. More work is needed to understand when melting begins, how long the liquid can remain, and how efficiently it moves upward. There are also significant limitations to the images available: more than half of Pluto has not been imaged at high resolution.
What could this mean for Pluto?
The potential nitrogen fluxes add another layer to a world that has already turned out to be much more complex than expected. Sputnik Planitia may not just be a giant frozen storehouse of nitrogen. Alternatively, the ice can rotate and melt at depth, sometimes releasing liquid at the surface.
This possibility also raises questions about whether similar processes could help explain activity elsewhere, including geysers observed on Neptune’s moon Triton. This association remains an open possibility and is not a firm conclusion.
Frequently asked questions
Did scientists see liquid flow on Pluto?
No, the evidence comes from photos and computer models.
Was the water liquid?
No, researchers suggest it was liquid nitrogen.
