Liquid nitrogen may have recently flowed across Pluto’s heart-shaped glacier

Pluto’s heart-shaped glacier may be leaking. Along the northern edge of Sputnik Planitia, the frozen nitrogen plain that forms the western lobe of Pluto’s heart, dark streaks and smudges look like the stains left where liquid has recently wetted an ice surface. A team led by Alan Stern, principal investigator of NASA’s New Horizons mission, argues that the best explanation is liquid nitrogen rising through cracks from a melted layer at the base of the glacier.

If that holds up, it would be the first evidence of recently flowing liquid on Pluto. NASA’s summary of the study notes that Pluto’s atmosphere and temperatures make liquid nitrogen rain physically impossible, so any liquid has to come from below. That would mean the dwarf planet’s interior is still shaping its surface today.

“Pluto never stops surprising us, and this new result certainly does that,” Stern said in the Southwest Research Institute announcement.

What the dark marks look like

The features sit on the northern part of Sputnik Planitia, a glacier of nitrogen ice roughly 1,200 by 2,000 kilometers across, larger than Texas and Oklahoma combined. The glacier’s surface is broken into polygons that mark city-sized convection cells, where ice wells up in the middle and sinks at the edges, very slowly, like the wax in a lava lamp.

The team describes two kinds of dark feature. One is narrow, dark lines that trace the borders between cells. The other is broader, more diffuse dark aprons. Both look like the wetting patterns seen on Earth’s glaciers, and both appear in the north of the plain.

How they did it

The researchers worked from images New Horizons captured during its flyby, then compared them with satellite pictures of the Greenland ice sheet from NASA’s Landsat 9. On Earth, meltwater and rain leave dark stains on glacier surfaces, and the Pluto features resemble those patterns.

Orkan Umurhan of the SETI Institute then built computer models of the ice. They show that nitrogen at the base of the glacier can melt under Pluto’s present-day internal heat. Liquid nitrogen is less dense than the solid ice above it, so it can rise through narrow channels, in the way magma climbs through cracks on Earth. Once at the surface, it flows downhill and darkens the ice as it goes.

The models favor short bursts over a steady trickle. Summaries of the paper put each event at roughly 100,000 to 1 million cubic meters of liquid, released over hours to days. An Olympic swimming pool holds about 2,500 cubic meters, so a single burst would fill somewhere between 40 and 400 of them.

Why nitrogen can melt on Pluto

Nitrogen turns from solid to liquid at about minus 210 degrees Celsius, only some 20 degrees above the temperature of Pluto’s surface. In the models, the melting happens kilometers below the surface, where heat rising from Pluto’s interior is enough to tip the bottom of the glacier into liquid. That is the “basal” flow in the paper’s title.

The age of the surface makes the idea more plausible. Sputnik Planitia is probably less than one million years old, which is at most about 0.02 percent of the age of the Solar System. A surface that young is still being renewed, and something has to be renewing it.

What it doesn’t settle

The paper calls its own evidence “possible,” and the word matters. Nobody has watched anything flow on Pluto. New Horizons passed the dwarf planet once, so the data are a single snapshot. The team argues that solar heating and other ordinary explanations fall short, but the melting itself is a model result, not a measurement.

The Greenland comparison has limits too. Kelsi Singer, a principal scientist at the Southwest Research Institute and a co-author, acknowledged that “Pluto has many unique terrains seen nowhere else,” with surface conditions unlike Earth’s. What wets an ice sheet in Greenland is not what would wet a nitrogen glacier at minus 230 degrees.

The team also points out that more than half of Pluto has never been mapped at high resolution, so the same features could be common elsewhere on the planet, or rare.

Common questions about liquid on Pluto

Is there liquid on Pluto right now?

Not confirmed. The study infers that liquid nitrogen recently reached the surface in the north of Sputnik Planitia, and the models suggest it happens in short episodes rather than continuously. No one has seen it happen.

Could it rain on Pluto?

No. NASA’s summary says Pluto’s atmosphere and surface temperatures make liquid nitrogen rain physically impossible. That is why the team looks for liquid rising from below the glacier instead of falling from the sky.

What is Sputnik Planitia?

It is the smooth, bright plain that forms the western lobe of Pluto’s heart-shaped region, a glacier of nitrogen ice larger than Texas and Oklahoma combined. Its surface is estimated at less than one million years old.

Could other worlds have liquid nitrogen flows?

Possibly. The researchers suggest similar processes could operate on other Kuiper Belt objects with nitrogen ice, and summaries of the work point to Neptune’s moon Triton, where geysers have been seen, and the dwarf planet Eris as candidates.

What comes next

The team recommends additional high-resolution observations to find out whether similar features exist elsewhere on Pluto, on other Kuiper Belt objects, and on Triton. The paper was published on July 31, 2026, in The Planetary Science Journal, and it is based on New Horizons images taken in 2015 and 2016. NASA published its own summary of the result in August 2026.

Reference: Stern et al., “Evidence for Possible N2 Basal Flow beneath Pluto’s Northern Sputnik Planitia,” The Planetary Science Journal, 2026. DOI: 10.3847/PSJ/ae7e85

Tags: astronomy, Kuiper Belt, PLUTO, Alan Stern, liquid nitrogen, New Horizons