Pluto’s Heart Bleeds Like a Greenland Glacier

A July 31 paper says dark streaks on Pluto’s heart glacier Sputnik Planitia are stains from liquid nitrogen that rose through the ice. NASA called the result the first evidence of recently flowing liquid on Pluto.

The match that sold the team was not a cryovolcano. It was wet ice on Greenland, read onto a 2015 flyby image of a world too cold for rain.

The Dark Lines Look Like Wet Greenland Ice

New Horizons flew past Pluto on July 14, 2015, and the northern edge of Sputnik Planitia has been sitting in those frames ever since. City-size convection cells cover the nitrogen ice, and along their rims the ice is marked by thin dark lines and wider, softer dark patches. Early ideas blamed wind, frost, or ice sliding around buried bumps. The new reading is wetness.

NASA’s August 5 science note said the surface has been darkened in ways that resemble glacial ice on Earth after rain, or after liquid reaches the surface from below. Pluto’s air and temperatures make liquid nitrogen rain physically impossible, so the liquid, if it is real, has to come from underneath.

https://x.com/NASASolarSystem/status/2085056679641563250

The SwRI-led team compared the New Horizons frames with NASA Landsat 9 images of the Greenland ice sheet, where dark narrow features mark places liquid water has reached snow and ice. The Pluto marks look, in that comparison, very similar. Mashable’s Elisha Sauers, writing on August 8, put the same finding in plainer language: the heart may be slowly leaking liquid onto the surface.

Sci.News, reporting the paper, described Sputnik Planitia as a 1,200 by 2,000 km nitrogen-ice basin filling the western lobe of Tombaugh Regio, the bright heart. NASA’s shorter yardstick is that the glacier is larger than Texas and Oklahoma combined. The mosaic used in the new work is about 700 by 350 km across, with a red box around most of the stained northern ground.

How Liquid Nitrogen Reaches Pluto’s Surface

The paper, published in The Planetary Science Journal as Evidence for Possible N2 Basal Flow, keeps the word “possible” in the title. The chain it offers is still specific. Heat from Pluto’s interior, plus pressure at the base of a thick glacier, can melt solid nitrogen. Liquid nitrogen is less dense than the ice around it, so it can rise through narrow cracks and tubes, the way the authors compare to lava, geysers, or volcanic dikes on Earth.

HOW A NITROGEN PULSE WOULD MOVE

• The melt: Models led by Orkan Umurhan of the SETI Institute show nitrogen ice at the base of the kilometers-deep Sputnik glacier can melt.
• The rise: Buoyancy or pressure then drives that liquid upward through small conduits toward the surface.
• The pulse: Sci.News said the team calculated the eruptions would have to come as short bursts, on the order of 100,000 to 1 million cubic meters over hours to days, because a slow underground trickle is too weak to make the flows.
• The stain: Once on top, the liquid can stay wet long enough to run downslope, darken the ice, and then freeze or evaporate in Pluto’s near-vacuum cold.

NASA said those dark linear and more diffuse features may be wetted only from time to time. That is a stain record, not a live stream. The 2015 encounter lasted hours, and the spacecraft has not gone back.

Solid nitrogen on Pluto was already known to creep. In 2015, New Horizons found flowing nitrogen ices photographed in 2015 in the same basin, with swirl-shaped light and dark patterns that Bill McKinnon of Washington University in St. Louis compared to glaciers on Earth at minus-390 degrees Fahrenheit. The new claim is a step past that slow solid flow: actual liquid, at least briefly, on the surface.

A Surface Younger Than One Million Years

“Recently,” in this paper, is not last winter. SwRI principal scientist Kelsi Singer, a co-author, said the surface of Sputnik Planitia is quite young, probably less than one million years based on modeling of the surface overturn, so the dark features must have formed since then. Mashable noted the same clock and added that, by geological standards, the activity could still be going on.

The plain has looked young since the flyby. It is strangely smooth and almost crater-free, which is why teams argued it is being resurfaced on short timescales. The ice is divided into those broad cells that resemble a very slow boiling pot, with nitrogen ice thought to rise in the middle of each cell and sink at the edges.

New Horizons principal investigator Alan Stern, who led the study from Southwest Research Institute, said the result also suggests a new kind of time-variable feature on Pluto. The paper does not clock a pulse. It argues that whatever darkened those rims did so on a surface that convection keeps turning over, so the stains cannot be ancient fossils.

Earlier work, some of it also led by Stern, had already pointed to ancient liquid flows. The August 5 SwRI release said the new analysis suggests there is currently, or recently, liquid nitrogen beneath the glacier. That “or” is doing a lot of work, and some posts recapping the NASA note flattened it into liquid flowing right now.

Earth Glacier Scientists Share the Author List

NASA’s own write-up flagged a staffing detail most Pluto recaps skipped: the authors include planetary scientists and experts in terrestrial glaciology. SciTechDaily listed the full names as S. A. Stern, Orkan Umurhan, Gary D. Clow, Robert S. Anderson, Alan Howard and Kelsi N. Singer. The Earth ice names are not decoration. The load-bearing method is a Landsat 9 reading of Greenland, then a transfer of that wet-ice pattern onto Sputnik Planitia.

Singer said Pluto has many unique terrains seen nowhere else in the solar system, and that this part of Sputnik Planitia is one of them. Exploring it, she said, helps show how materials behave in environments that are difficult to produce on Earth. That is the honest limit of the analog. Greenland supplies the stain language. It cannot supply Pluto’s temperature, gravity, or nitrogen physics.

Umurhan’s models are the other half of the case, because a pretty match to Greenland is not enough if the glacier’s base cannot melt. His comment after the modeling is the least slogan-like line in the rollout, and it points at a gap the headlines did not.

I think the great significance of these findings, and the tantalizing picture that it promotes, is a great motivation and reason to further examine solid state nitrogen physics at very low temperatures. Specifically, it’s important to examine the physics taking place in solid nitrogen materials under stress and strain, which can cause them to melt. These processes have never been studied in real detail in the laboratory.

Orkan Umurhan, senior research scientist, SETI Institute, in the Southwest Research Institute release

The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, designed, built, and operates New Horizons. Stern’s SwRI team directs the science. Marshall Space Flight Center’s Planetary Missions Program Office provides NASA oversight. Eleven years after closest approach, that same 2015 dataset is still the only close look anyone has.

Voyager 2 Left Triton’s Geysers Unsolved

SwRI said no other region of Pluto shows evidence of basal flow, and that the same upward movement of melt could help explain geysers Voyager 2 saw on Neptune’s moon Triton in 1989. Triton is the older open file. Its plumes have been argued for decades, and one long-running idea has been basal melting of a nitrogen polar cap. The Pluto paper does not close that file. It offers a mapped, photographed cousin.

Sci.News quoted the authors saying Eris could be a good candidate to show basal melt or liquid flows at the surface, because it appears to host thick nitrogen ice. They also said that, for Eris and for any later dwarf planet with a deep nitrogen reservoir, proof would have to wait for high-resolution mapping of the sort New Horizons did at Pluto. Presently, they said, no other Kuiper Belt dwarf planet has shown nitrogen ice on its surface.

NASA’s August 5 post was quickly pulled into the old argument over whether Pluto should still be called a planet. The paper does not address the IAU vote. The grouping that actually sits in the text is chemical: worlds with thick nitrogen ice and some internal heat, of which Pluto is the only one with a New Horizons-class map.

Half of Pluto Still Lacks a Close-Up Map

The SwRI release is blunt about the hole in the map. Over half of Pluto remains unmapped in high resolution. The stained cells are in the northern part of the left lobe of the heart, inside that 700-by-350 km mosaic, not a global survey. A second flyby does not exist, and an orbiter was never flown.

WHAT WE KNOW

• The stains: Thin dark lines and more diffuse dark patches run along convection-cell boundaries on northern Sputnik Planitia in the 2015 images.
• The rain ban: NASA says Pluto’s air and temperatures make liquid nitrogen rain physically impossible, so any wetting has to come from below.
• The age cap: Singer said modeling of surface overturn puts the plain at probably less than one million years, so the marks formed after that.

WHAT IS UNCONFIRMED

• Today versus the last million years: The paper and NASA describe recent and occasional wetting; they do not time a pulse to the flyby hour.
• The rest of Pluto: SwRI said no other mapped region shows basal flow, while more than half the world still lacks a close-up map.
• Triton and Eris: The same plumbing is offered as a possible explanation, not as a detection on those bodies.

Stern said Pluto never stops surprising us. The surprise this time is a familiar one from Earth ice sheets, rewritten in nitrogen, on a glacier photographed once. SwRI closed its release by saying further high-resolution mapping of Pluto and other Kuiper Belt planets is needed to tell whether the same process is running elsewhere.

Frequently Asked Questions

What camera on New Horizons photographed Sputnik Planitia?

Sci.News said the mosaic was made from New Horizons LORRI frames taken on July 14, 2015, from 80,000 km (49,700 miles), looking northeast over dark Cthulhu Regio toward the bright nitrogen plain, with color overlaid from the Ralph mapper. LORRI is the Long Range Reconnaissance Imager; Ralph is the color and composition instrument. Those are the stills the 2026 team went back to, not a new spacecraft pass.

Who operates the New Horizons spacecraft for NASA?

The Johns Hopkins Applied Physics Laboratory designed, built, and operates the spacecraft and mission for NASA’s Science Mission Directorate. The Planetary Missions Program Office at Marshall Space Flight Center in Huntsville, Alabama, provides NASA oversight, and Southwest Research Institute directs the science through principal investigator Alan Stern, who leads the science team, payload operations, and science planning. New Horizons is part of NASA’s New Frontiers Program, managed by Marshall.

Why can nitrogen ice flow on Pluto when water ice would stay rigid?

After the 2015 flyby, New Horizons compositional data from Ralph showed the center of the plain is rich in nitrogen, carbon monoxide, and methane ices. At Pluto’s temperatures of minus-390 degrees Fahrenheit, Bill McKinnon said those ices can flow like a glacier, while the crust underneath is mostly much more rigid water ice. The 2026 paper is about a further step, melting at the base, not that slower solid creep.

Has any other Kuiper Belt dwarf planet shown nitrogen ice like Pluto’s?

The authors said that, at present, no other Kuiper Belt dwarf planet has shown evidence for nitrogen ice on its surface, though they flagged Eris as a good candidate because it appears to host thick nitrogen deposits. They added that if such ice is found on other dwarf planets later, the basal-melt mechanism described for Sputnik Planitia might operate there too, but only high-resolution maps on the Pluto scale could show it.