Researchers used New Horizons images to identify evidence that liquid nitrogen may have flowed from beneath Pluto’s famous heart-shaped glacier. Dark markings across part of Pluto’s enormous heart-shaped glacier may record something unexpected beneath its frozen surface: liquid nitrogen moving upward and briefly flowing across the ice. Using observations from NASA’s New Horizons spacecraft, researchers [...]
Pluto's atmosphere appears to be freezing out as the dwarf planet moves ever further away from the sun, according to careful observations of Pluto astronomers made as it was seen passing in front of stars in the sky.
Pluto is already cold. Its surface temperature is about –382 degrees Fahrenheit (–230 degrees Celsius), while its upper atmosphere is a little warmer at –333 degrees Fahrenheit (–203 degrees Celsius). As Pluto moves away from the sun it will grow even colder and its nitrogen-rich atmosphere should start to collapse and freeze out, condensing as frost on the frigid surface.
Now, a team led by Amanda Sickafoose of Arizona's Planetary Science Institute believe they have seen the onset of this process. "We're at a particularly interesting point for Pluto," said Sickafoose in a statement. "Our work suggests that the atmosphere has recently started decreasing in pressure."
Pluto's orbit is highly elliptical and very oblique to the ecliptic plane of the solar system. In fact, so eccentric is Pluto's orbit that for ten years either side of its perihelion in 1989 (when Pluto was closest to the sun), it was actually closer to the sun than Neptune was.
However, ever since 1989 Pluto has been moving away from the sun on its 248-year-long orbit – we've not even seen Pluto complete half of its orbit yet since its discovery in 1930. Pluto will reach its furthest point from the sun – called aphelion – in the year 2114 when it will be about 49 astronomical units (7.3 billion kilometers/4.6 billion miles) distant.
When NASA's New Horizons mission flew past Pluto in July 2015, it measured Pluto's atmospheric pressure to be 10 microbars. This is a tiny amount, millions of times lower than the atmospheric pressure on Earth, resulting from Pluto's thin nitrogen atmosphere that also contains hazes made from organic molecules including methane and carbon monoxide.
An image taken by NASA's New Horizons spacecraft that offered scientists the first look at Pluto's atmosphere in infrared wavelengths when it was taken in July 2015. (Image credit: NASA/JHUAPL/SwRI)
With New Horizons now having flown past Pluto and deeper into the Kuiper Belt, astronomers have to instead rely on more distant and less direct means of keeping tabs on Pluto's atmosphere. From our point of view on Earth, Pluto is sometimes seen to pass in front of a distant star. This is called a stellar occultation. When an airless body, such as an asteroid, occults (or hides) a background star the star's light winks out in an instant, before suddenly reappearing. When there is an atmosphere involved, however, the light of the star doesn't go out all at once when blocked by Pluto, but steadily fades as the atmosphere scatters and refracts the starlight before the star vanishes behind the dwarf planet's solid body.
Between 2017 and 2023, Sickafoose's team probed Pluto's atmosphere during ten occultations of stars ranging in brightness from about magnitude 12 to magnitude 18, far below naked-eye visibility.
Observing stellar occultations is not always a simple matter. They are not visible from everywhere on Earth, but only along narrow tracks, often in difficult to reach areas. The tracks, which are just a few kilometers wide, are effectively Pluto's shadow falling on the Earth. By spacing observers across the width of the track, it is possible to measure the extent of Pluto's atmosphere (there usually also has to be an unlucky observer just outside the track to confirm that is indeed the edge of the shadow track).
"I'm constantly amazed at how the simple technique of watching starlight dim and reappear allows us to study a thin atmosphere – a few millionths of the Earth's – on a world two-thirds the size of our moon and 30 times farther from the sun," said Sickafoose.
Of the ten occultations, four could be seen from observatories in multiple locations, which meant that the different observatories could confirm each other's results.
"We often prefer to observe predicted occultations that have shadow paths over large observatories because that equipment and data have proven successful," said Sickafoose. "Then, we try to improve those datasets by collaborating with local observers in the shadow paths."
Light curve from the June 1, 2026 occultation, observed from Savannah Skies Observatory in Chillagoe, Queensland, Australia. The gray vertical lines indicate different stages of the occultation. The baseline flux level contains combined light from the star and the Pluto system (Pluto plus all of its moons). The flux drops gradually as the starlight bends and scatters in Pluto's atmosphere, reaching nearly zero flux as defined by only light coming from the Pluto system. As the star appears on the other side of Pluto, the light gradually reappears in the atmosphere before returning to full strength. (Image credit: A. Sickafoose/Planetary Science Institute)
Previous work had suggested that Pluto's atmosphere began freezing out in 2018, but Sickafoose's team found that actually, Pluto's atmosphere remained constant from 2015 to midway through 2021. However, between mid-2021 and the last occultation that Sickafoose's team observed in 2023, Pluto's atmospheric pressure dropped by 16 per cent.
The pressure drop was deduced from the light curves, which show how the star's brightness changed with time during an occultation. The light curves revealed that while the structure of Pluto's upper atmosphere remained fixed, the lower atmosphere changed.
Sickafoose's team interprets this as being the haze particles settling towards lower latitudes. This is what is expected to happen when the atmospheric pressure drops.
"I am hopeful that we'll be able to get more data in the next years to decades to specifically confirm or refute this trend," said Sickafoose.
It is thought that Pluto's atmosphere won't have completely frozen onto the dwarf planet's surface by the time it reaches aphelion, and then as Pluto begins moving in towards the sun once more the feeble solar heating that Pluto receives will slowly begin to increase, causing nitrogen frost to sublimate from the surface and thicken the atmosphere once more.
Planetary researchers analyzing images from NASA’s New Horizons spacecraft have found evidence that liquid nitrogen may still be seeping up from beneath the dwarf planet’s giant glacier, Sputnik Planitia, marking the first suggested case of recently flowing liquid on Pluto’s surface.
According to the researchers behind the detection, the liquid nitrogen evidence captured by NASA’s New Horizons Spacecraft is the first evidence of any liquid flowing on Pluto. They also suggest that the discovery could help scientists better understand other solar system features such as the geysers on Neptune’s moon Triton.
New Horizons Mission Gave First Hint of Liquid Nitrogen on Pluto
When New Horizons captured images of Pluto’s surface between 2015 and 2016, it gathered extensive imagery of a massive surface feature called Sputnik Planitia. Larger than Texas and Oklahoma combined, the frozen nitrogen lake has long fascinated planetary scientists.
When examining the spacecraft’s photos, researchers spotted thin, dark, linear features separating the city-sized geologic convection cells on Sputnik Planitia’s northernmost portions. Critically, the thinner, separating features were more diffuse than the larger ones. Although some previous studies suggested that Pluto may have a liquid water ocean beneath its frozen outer shell, the surface temperatures would prevent any of that water from flowing on the surface long enough to cause the features.
Some theories proposed a liquid nitrogen explanation for the thinner features, even though the research team behind the discovery said that Pluto’s atmospheric and thermal conditions make liquid rain physically impossible. Still, the team notes, the surface patterns on Pluto’s northern Sputnik Planitia “have been darkened in ways that resemble glacial features on Earth that have been wetted by water rain or the subsurface emergence of liquids to the surface.”
To better understand the data, SwRI Associate Vice President and principal investigator on the New Horizons mission, Dr. Alan Stern, reexamined the data, focusing on similar features on Earth.
Sputnik Planitia Evidence “Very Similar” to Greenland Ice Sheet Features
To start, Dr. Stern and colleagues compared the New Horizons images with Earth imagery collected by NASA’s Landsat 9. The researchers focused on the Greenland Ice Sheet, since similar surface features caused by liquid water separating ice and snow have been previously observed.
When focusing on topography, the team said the two regions appeared “very similar.” This similarity suggested that subsurface liquids in the form of nitrogen were rising to the surface and wetting areas of Sputnik Planitia’s nitrogen ice.
Pluto’s northern Sputnik Planitia glacier (in the western or left side of Pluto’s brightheart) is shown here in a color mosaic made from New Horizons imagery. The direction of north is shown on the image. The image is ~ 700 x 350 kilometers across. The red box has been added to show most of the region containing dark features attributed to the wetting of the glacier by liquid nitrogen sourced from a “basal melting” process beneath the glacier. (2026). Image Credit: NASA/John Hopkins APL/Southwest Research Institute.
SwRI Principal Scientist Dr. Kelsi Singer, one of the study’s co-authors, said Sputnik Planitia’s surface is “quite young” in geological terms, with most estimates placing it at less than one million years. As a result, the dark, thin surface features must have formed during that short window of time.
“Pluto has many unique terrains seen nowhere else in the solar system, and this area of Sputnik Planitia is one of them,” Dr Singer explained. “Its surface provides a different set of conditions compared to what we are used to on Earth, and exploring that allows us to better understand how materials behave in environments that are difficult to produce on Earth.”
To support the visual evidence of liquid nitrogen on Pluto, Dr. Orkan Umurhan, a senior research scientist at the SETI Institute, oversaw the creation of computer models designed to simulate the dwarf planet’s local environment. According to the study authors, the models “show that nitrogen ice at the base of Pluto’s kilometers-deep Sputnik glacier can melt, forming liquid nitrogen.”
Dark, narrow surface features have been identified here in areas in Greenland where liquid water darkens the ice and snow in a manner analogous to what is now believed to perhaps be occurring on northern Sputnik Planitia on Pluto due to present or recent liquid nitrogen there. Image Credit: NASA/Johns Hopkins /Southwest Research Institute.
The same models also revealed that buoyancy and pressure from underneath can cause liquid nitrogen to migrate to Pluto’s surface via a series of small conduits that resemble lava or geyser tubes. Although the dwarf planet’s distance from the Sun makes it an extremely frigid environment, the models also suggested that once liquid nitrogen reaches Pluto’s surface, it can maintain liquid form long enough to flow down the nitrogen glacier slopes and cause the features seen in the images.
“Pluto Never Stops Surprising Us”
When discussing the significance of the findings, Dr. Umurhan pointed to the study’s “tantalizing picture that it promotes,” including potentially motivating a further examination of 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,” the study author explained, adding that these processes “have never been studied in real detail in the laboratory.”
The SwRI-led team also noted that over half of Pluto remains unmapped in high resolution, meaning there is still a lot of room for future discoveries. This includes further mapping of the other Kuiper Belt planets “to determine if similar processes are occurring elsewhere in that region of the solar system.”
Finally, the SwRI-led team said the findings could offer some assistance in explaining other events across the solar system, such as the geysers observed by NASA’s Voyager 2 on Neptune’s moon Triton.
“Pluto never stops surprising us, and this new result certainly does that,” Stern concluded. “In addition to suggesting that liquids have recently expressed themselves on Pluto’s surface, it also suggests a new kind of time-variable feature on Pluto.”
Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org
Pluto’s tenuous atmosphere appears to have begun contracting after years of holding steady, according to a new study published in the Planetary Science Journal.
The aftermath of landslides have been found in images of Pluto's surface taken when the New Horizons mission flew past the dwarf planet in 2015. The landslides are evidence that the icy world is still active, albeit on geological timescales.
A team led by geologist Marco Emanuele Discenza pored over images taken by New Horizons' LORRI (Long-Range Reconnaissance Imager) instrument, which was capable of detecting surface features as small as 984 feet (300 meters). They found convincing evidence for six landslides in total that have taken place down the inner walls of three craters on the western edge of Sputnik Planitia, the heart-shaped feature that characterizes Pluto's appearance.
Previously, geological features left behind by landslides have been found on a host of bodies in the solar system, including Mars, Ceres in the asteroid belt, some of the icy moons of the gas giants, and even Pluto's companion, Charon. However, these are the first to be found on Pluto.
A landslide that fell 1.4 miles (2.2 kilometers) was identified in Pluto's Coughlin crater, close to a secondary crater on Coughlin's rim that may have triggered the landslide in the first place. Two further landslide features were seen in Giclas crater, and another three were spotted in a third, unnamed, crater.
The landslides were identifiable by their large debris aprons that spilled out onto the crater floors, the distance the landslide material travelled ranging being between 6.3 and 9 miles (10.1 and 14.5 km). Some of these debris aprons appeared bumpy, as if they contain large boulders of solid ice, while the areas around the source of the landslides feature well-defined, concave-shaped cliffs where material has broken away and tumbled down the craters' steep walls.
The great lengths that the debris rolled means that Pluto's landslides are among the most mobile in the solar system, a product of low gravity and low-friction icy rubble. The largest of the debris aprons covers 50 square miles (130 square kilometers), which would be large enough to bury a small city or a large town.
Landslides are important processes in shaping planetary surfaces, enabling the transport of material across great distances. The trigger for Pluto's landslides, however, is not yet clear. While the landslide in Coughlin appears to have been caused by a smaller impact nearby, the other five have less certain origins. One possibility is thermal stresses in the surface ice caused by the slight temperature changes that cause Pluto's volatile materials – among them molecular nitrogen, carbon monoxide and methane – to periodically sublimate and then condense again. These temperature changes are the result of Pluto subtly heating up and cooling down as its elliptical orbit brings it slightly closer to the sun, crossing inside Neptune's orbit, and then moving farther away again.
There is also evidence for more landslides in other craters, but New Horizons' coverage of Pluto's surface was limited as it hurriedly flew past on July 4, 2015, and the imagery required to confirm these other landslides is lacking.
The findings were published in the journal Icarus.
New research indicates that Pluto’s largest moon, Charon, may continue to lose rotational energy despite the pair’s long-standing tidal lock, offering scientists a rare glimpse into the hidden interiors of distant icy worlds.
My biblical creation model of the solar system expects the presence of icy materials forming the outer planets and celestial bodies. Recent findings of water and ice in bodies like Ceres, and moons of Jupiter and Saturn support this theory, confirming the Genesis account of creation.
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