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Piccard Mons
A color-coded topographical map, based on New Horizons data, shows Piccard Mons on the surface of Pluto. The mountain’s structure suggests that it’s an ice volcano. (Credit: NASA / JHUAPL / SwRI)

Scientists with NASA’s New Horizons mission say that at least a couple of the miles-high mountains on Pluto look as if they’re ice-belching volcanoes, providing further evidence that the dwarf planet is geologically active.

Although the case for cryovolcanoes isn’t yet rock-solid, it’s the “least weird explanation” for the observations of 2-mile-high Wright Mons and 3-5-mile-high Piccard Mons, said Oliver White of NASA’s Ames Research Center, a member of the mission’s geology team.

If the mountains’ status is confirmed, “that would be one of the most phenomenal discoveries of New Horizons,” White told reporters. “Whatever they are, they’re definitely weird.”

Pluto’s potential status as a volcanic world was just one of the revelations that came to light on Monday during a review of New Horizons’ latest discoveries at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences in National Harbor, Md.

“The New Horizons mission has taken what we thought we knew about Pluto and turned it upside down,” Jim Green, director of planetary science at NASA Headquarters, said in a news release about the findings.

Like Piccard Mons, Wright Mons has a summit depression that suggests it's an ice volcano on Pluto. (Credit: NASA / JHUAPL / SwRI)
Like Piccard Mons, Wright Mons has a summit depression that suggests it’s an ice volcano on Pluto. (Credit: NASA / JHUAPL / SwRI)

The ice mountains are south of Sputnik Planum, near the edge of the disk that was imaged by the piano-sized New Horizons spacecraft as it sped past on July 14. Piccard Mons could be seen only in the twilight zone just outside the world’s sun-illuminated half of Pluto. Each of the mountains is hundreds of miles wide, and have a structure similar to Mars’ shield volcanoes.

“These are big mountains with a large hole in their summit, and on Earth that generally means one thing – a volcano,” White explained in NASA’s news release. “If they are volcanic, then the summit depression would likely have formed via collapse as material is erupted from underneath. The strange hummocky texture of the mountain flanks may represent volcanic flows of some sort that have traveled down from the summit region and onto the plains beyond – but why they are hummocky, and what they are made of, we don’t yet know.”

New Horizons’ scientists had already determined that Pluto was exhibiting geological activity, based on the uplift of ice mountains as well as the flowing patterns of frozen nitrogen glaciers in crater-free Sputnik Planum. And before the flyby, scientists speculated that they might see places where slush or ice pushed its way through the surface. Such ice could consist of frozen water, nitrogen, ammonia or methane.

On some worlds, such as the Jovian moon Io, volcanic activity arises due to tidal flexing. But the mechanism at work on Pluto is thought to be something different – for example, the heat generated by radioactive decay of minerals within the dwarf planet’s rocky core.

Scientists said the findings could change their perspective on planetary evolution at the solar system’s edge. “After all, nothing like this has been seen in the deep outer solar system,” Ames Research Center’s Jeffrey Moore, the leader of New Horizons’ geology team, said in NASA’s news release.

New Horizons still has to send back about 80 percent of the readings that it collected during the flyby, and some of those readings could provide further evidence of volcanism – or knock down the hypothesis. “What would be nice is to see if we could get to the compositional data there,” White said.

Among Monday’s other revelations:

  • More detailed readings reveal that Pluto’s atmosphere is colder and more compact than they previously thought. That will force them to change their models for the dwarf planet’s loss of its thin but nitrogen-rich atmosphere.
  • By counting craters on the surface, New Horizons’ scientists have determined that some areas of Pluto are geologically recent and that others are ancient, but they also found that still other parts of the surface – for example, east Tombaugh Regio – have an intermediate age, in the range of 1 billion years.
  • At least two of Pluto’s moons, Kerberos and Hydra, show signs that they were formed through the merger of two separate objects. That suggests Pluto once had more moons than the five it has today, with some of those moons smashing together over the course of billions of years. The smaller moons don’t keep the same face oriented toward Pluto, as is the case with Earth and its moon, but wobble chaotically in orbit.
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