The spacecraft made a flyby of the dwarf planet and its moons in July 2015, and the ideas collected after that are still rewriting almost everything scientists understand about Pluto.
The dwarf planet is at the edge of our solar system in the Kuiper Belt, the largest number of icy bodies out there that orbit far from the Sun. The icy world, which has an average temperature of minus 387 degrees Fahrenheit (minus 232 degrees Celsius), is home to mountains, valleys, glaciers, plains, and craters. If you were to stand on the roof, you would see a blue sky with red snow.
A new analysis of images has revealed a bumpy region on Pluto unlike any other part of the small world — or the rest of our cosmic neighborhood.
“We found a field of very large ice volcanoes that is unlike anything else we’ve seen in the solar system,” said study author Kelsey Singer, a senior researcher at the Southwest Research Institute in Boulder, Colorado.
The area is located southwest of the Sputnik Planitia ice sheet, which covers an ancient basin extending for 621 miles (1,000 km). It consists largely of bumpy water ice, and is dotted with volcanic domes. Two of the largest are known as Wright Mons and Piccard Mons.
Wright Mons is about 13,123 to 16,404 feet (4 to 5 km) high and spans 93 miles (150 km), while Piccard Mons is about 22,965 feet (7 km) high and 139 miles (225 km) wide.
Wright Mons is similar in size to Mauna Loa volcano in Hawaii, one of the largest volcanoes on Earth.
Singer said that some of the domes observed in the photos are merging together to form larger mountains. But what can create it? Ice volcanoes.
Ice volcanoes have been observed elsewhere in our solar system. They transport materials from the subsurface to the surface and create new terrain. In this case, the water quickly turned to ice once it reached the freezing temperatures of Pluto’s surface.
“The way these features look is very different from any volcanoes across the solar system, whether they are ice examples or rock volcanoes,” Singer said. “They formed as mountains, but there are no calderas at the top, and they have big outcrops all over. They are.”
While Pluto has a rocky core, scientists have long believed that the planet lacks a lot of internal heating, which is necessary to stimulate volcanic activity. To create the area that Singer and her team studied, there would have been many volcanic eruption sites.
The research team also noted that the area had no archaeological craters, which can be seen across the surface of Pluto, indicating that the ice volcanoes have been active relatively recently — and that the interior of Pluto has more residual heat than expected, Singer said.
“This means that Pluto has more internal heat than we thought, which means we don’t fully understand how planetary bodies work,” she said.
Singer added that ice volcanoes likely formed “in multiple rings” and were likely active as recently as 100 million to 200 million years ago, which is a little geologically recent.
If you were to witness an ice volcano erupting on Pluto, it might look a little different than you expect.
“The icy material may have been a mixture of ice and water or more like toothpaste as it flowed out of a volcanic vent on the surface of Pluto,” Singer said. “It’s so cold on the surface of Pluto that liquid water can’t stay there for long. In some cases, the flow of material has formed the massive domes we see, as well as the lumpy terrain that is ubiquitous in this region.”
When New Horizons flew near this area, the team saw no current glacial volcano activity, but they were able to see the area for about a day. It is possible that ice volcanoes are still active.
“It can be like volcanoes on Earth that lie dormant for some time and then activate again,” she said.
Pluto was once a subsurface ocean, and the finding of these ice volcanoes could indicate that a subsurface ocean still exists — and that liquid water could be close to the surface. Combined with the idea that Pluto has a much warmer interior than previously thought, the results raise intriguing questions about the habitability of the dwarf planet.
“There are still a lot of challenges for any organisms trying to survive out there,” Singer said. “They will still need some continuous source of nutrients, and if the volcanoes are episodic and so the available heat and water is variable, that is sometimes difficult for living things as well.”
Investigating Pluto’s intriguing surface requires sending an orbiter to the distant world.
“If we send in a future mission, we can use ice-penetrating radar to head straight to Pluto and maybe even see what the volcanic plumbing looks like,” Singer said.
“Devoted student. Bacon advocate. Beer scholar. Troublemaker. Falls down a lot. Typical coffee enthusiast.”