- Wed Jul 30, 2025 10:18 am#8817
1. Pluto has a "heart" that drives activity on the planet.
One of the signature features New Horizons observed on approach and imaged in high resolution during the flyby was the planet's heart—a vast, million-square-mile nitrogen glacier. The heart's left ventricle, called Sputnik Planitia, literally forced the dwarf planet to reorient itself so the basin now faces almost squarely opposite Pluto's moon Charon.
"It's a process called true polar wander—it's when a planetary body changes its spin axis, usually in response to large geologic processes," said James Tuttle Keane, a planetary scientist and New Horizons team member at the Jet Propulsion Laboratory in Pasadena, California.
Sputnik Planitia's current position is no accident. It's a cold trap, where nitrogen ices have accumulated to make an ice sheet that's at least 2.5 miles (or 4 kilometers) thick. The constant imbalance of that hefty mass, combined with the tidal yanks and pulls of Charon as it orbited Pluto, literally tipped the dwarf planet so the basin aligned more closely with the tidal axis between Pluto and Charon.
"That event was also likely responsible for cracking Pluto's surface and creating the many gigantic faults in its crust that zigzag over large portions of Pluto," Keane said.
2. There's probably a vast liquid water ocean sloshing beneath Pluto's surface.
Gathered ices may not be the only thing that helped reorient Sputnik Planitia. New Horizons data from the basin indicated there may be a heavier mass beneath it that played a part, and scientists suspect that the heavier mass is a water ocean.
"That was an astonishing discovery," Keane said. "It would make Pluto an elusive 'ocean world,' in the same vein as Europa, Enceladus, and Titan." Several other lines of evidence, including tectonic structures seen in New Horizons imagery, also point to an ocean beneath Pluto's crust.
Sputnik Planitia was likely created some 4 billion years ago by the impact of a Kuiper Belt object 30 to 60 miles (50 to 100 kilometers) across that carved out a massive chunk of Pluto's icy crust and left only a thin, weak layer at the basin's floor. A subsurface ocean likely intruded the basin from below by pushing up against the weakened crust, and later the thick layer of nitrogen ice seen there now was laid on top.
Recent models based on images of the planet suggest that this liquid ocean may have arisen from a rapid, violent formation of Pluto.
3. Pluto may still be tectonically active because that ocean is still liquid.
Enormous faults stretch for hundreds of miles and cut roughly 2.5 miles into the icy crust covering Pluto's surface. One of the only ways scientists reason Pluto got those fissures, though, is by the gradual freezing of an ocean beneath its surface.
Water expands as it freezes, and under an icy crust, that expansion will push and crack the surface, just like an ice cube in your freezer. But if the temperature is low enough and the pressure high enough, water crystals can start to form a more compact crystal configuration and the ice will once again contract.
Models using New Horizons data showed Pluto has the conditions for that type of contraction, but it doesn't have any known geologic features that indicate that contraction has occurred. To scientists, that means the subsurface ocean is still in the process of freezing and potentially creating new faults on the surface today.
"If Pluto is an active ocean world, that suggests that the Kuiper Belt may be filled with other ocean worlds among its dwarf planets, dramatically expanding the number of potentially habitable places in our solar system," Keane said.
But while Pluto's liquid ocean likely still exists today, scientists suspect it's isolated in most places (though not beneath Sputnik) by almost 200 miles (320 kilometers) of ice. That means it probably doesn't contact the surface today; but in the past, it may have oozed through volcanic activity called cryovolcanism.
4. Pluto was—and still may be—volcanically active.
But maybe not "volcanic" in the way you might think.
On Earth, molten lava spits, drools, bubbles, and erupts from underwater fissures through volcanoes sitting miles high in and protruding from the oceans, like on Hawaii. But on Pluto, there are numerous indications that a kind of cold, slushy cryolava has poured over the surface at various points.
Scientists call that "cryovolcanism."
Wright Mons and Piccard Mons, two large mountains to the south of Sputnik Planitia, both bear deep central pits that scientists believe are likely the mouths of cryovolcanoes unlike any others found in the solar system.
5. Glaciers cut across Pluto's surface even today, and they've done so for billions of years.
Pluto joins the ranks of Earth, Mars, and a handful of moons that have actively flowing glaciers.
East of Sputnik Planitia are dozens of mostly nitrogen-ice glaciers that course down from pitted highlands into the basin, carving out valleys as they go. Scientists suspect seasonal and "mega-seasonal" cycles of nitrogen ices that sublimate from ice to vapor waft around the dwarf planet and then freeze back on the surface are the source of the glacier ice.
But these glaciers are not like our own water-ice glaciers here on Earth. For one, any melt within them won't fall toward the bottom of the glacier, it will rise to the top because liquid nitrogen is less dense than solid nitrogen. As that liquid nitrogen emerges on top of the glacier, it potentially even erupts as jets or geysers.
Additionally, there is the fact that some of Pluto's surface is composed of water ice, which is slightly less dense than nitrogen ice. As Pluto's glaciers carve the surface, some of those water-ice "rocks" will rise up through the glacier and float like icebergs. Such icebergs are seen in several New Horizons images of Sputnik Planitia, the largest of Pluto's known glaciers, which stretches more than 620 miles (1,000 kilometers) across—about the size of Oklahoma and Texas combined.
One of the signature features New Horizons observed on approach and imaged in high resolution during the flyby was the planet's heart—a vast, million-square-mile nitrogen glacier. The heart's left ventricle, called Sputnik Planitia, literally forced the dwarf planet to reorient itself so the basin now faces almost squarely opposite Pluto's moon Charon.
"It's a process called true polar wander—it's when a planetary body changes its spin axis, usually in response to large geologic processes," said James Tuttle Keane, a planetary scientist and New Horizons team member at the Jet Propulsion Laboratory in Pasadena, California.
Sputnik Planitia's current position is no accident. It's a cold trap, where nitrogen ices have accumulated to make an ice sheet that's at least 2.5 miles (or 4 kilometers) thick. The constant imbalance of that hefty mass, combined with the tidal yanks and pulls of Charon as it orbited Pluto, literally tipped the dwarf planet so the basin aligned more closely with the tidal axis between Pluto and Charon.
"That event was also likely responsible for cracking Pluto's surface and creating the many gigantic faults in its crust that zigzag over large portions of Pluto," Keane said.
2. There's probably a vast liquid water ocean sloshing beneath Pluto's surface.
Gathered ices may not be the only thing that helped reorient Sputnik Planitia. New Horizons data from the basin indicated there may be a heavier mass beneath it that played a part, and scientists suspect that the heavier mass is a water ocean.
"That was an astonishing discovery," Keane said. "It would make Pluto an elusive 'ocean world,' in the same vein as Europa, Enceladus, and Titan." Several other lines of evidence, including tectonic structures seen in New Horizons imagery, also point to an ocean beneath Pluto's crust.
Sputnik Planitia was likely created some 4 billion years ago by the impact of a Kuiper Belt object 30 to 60 miles (50 to 100 kilometers) across that carved out a massive chunk of Pluto's icy crust and left only a thin, weak layer at the basin's floor. A subsurface ocean likely intruded the basin from below by pushing up against the weakened crust, and later the thick layer of nitrogen ice seen there now was laid on top.
Recent models based on images of the planet suggest that this liquid ocean may have arisen from a rapid, violent formation of Pluto.
3. Pluto may still be tectonically active because that ocean is still liquid.
Enormous faults stretch for hundreds of miles and cut roughly 2.5 miles into the icy crust covering Pluto's surface. One of the only ways scientists reason Pluto got those fissures, though, is by the gradual freezing of an ocean beneath its surface.
Water expands as it freezes, and under an icy crust, that expansion will push and crack the surface, just like an ice cube in your freezer. But if the temperature is low enough and the pressure high enough, water crystals can start to form a more compact crystal configuration and the ice will once again contract.
Models using New Horizons data showed Pluto has the conditions for that type of contraction, but it doesn't have any known geologic features that indicate that contraction has occurred. To scientists, that means the subsurface ocean is still in the process of freezing and potentially creating new faults on the surface today.
"If Pluto is an active ocean world, that suggests that the Kuiper Belt may be filled with other ocean worlds among its dwarf planets, dramatically expanding the number of potentially habitable places in our solar system," Keane said.
But while Pluto's liquid ocean likely still exists today, scientists suspect it's isolated in most places (though not beneath Sputnik) by almost 200 miles (320 kilometers) of ice. That means it probably doesn't contact the surface today; but in the past, it may have oozed through volcanic activity called cryovolcanism.
4. Pluto was—and still may be—volcanically active.
But maybe not "volcanic" in the way you might think.
On Earth, molten lava spits, drools, bubbles, and erupts from underwater fissures through volcanoes sitting miles high in and protruding from the oceans, like on Hawaii. But on Pluto, there are numerous indications that a kind of cold, slushy cryolava has poured over the surface at various points.
Scientists call that "cryovolcanism."
Wright Mons and Piccard Mons, two large mountains to the south of Sputnik Planitia, both bear deep central pits that scientists believe are likely the mouths of cryovolcanoes unlike any others found in the solar system.
5. Glaciers cut across Pluto's surface even today, and they've done so for billions of years.
Pluto joins the ranks of Earth, Mars, and a handful of moons that have actively flowing glaciers.
East of Sputnik Planitia are dozens of mostly nitrogen-ice glaciers that course down from pitted highlands into the basin, carving out valleys as they go. Scientists suspect seasonal and "mega-seasonal" cycles of nitrogen ices that sublimate from ice to vapor waft around the dwarf planet and then freeze back on the surface are the source of the glacier ice.
But these glaciers are not like our own water-ice glaciers here on Earth. For one, any melt within them won't fall toward the bottom of the glacier, it will rise to the top because liquid nitrogen is less dense than solid nitrogen. As that liquid nitrogen emerges on top of the glacier, it potentially even erupts as jets or geysers.
Additionally, there is the fact that some of Pluto's surface is composed of water ice, which is slightly less dense than nitrogen ice. As Pluto's glaciers carve the surface, some of those water-ice "rocks" will rise up through the glacier and float like icebergs. Such icebergs are seen in several New Horizons images of Sputnik Planitia, the largest of Pluto's known glaciers, which stretches more than 620 miles (1,000 kilometers) across—about the size of Oklahoma and Texas combined.
- By mousumi