Pluto and its largest moon’s meet-cute may have started with a kiss.
New research shows the dwarf planet and Charon may have paired up in a “kiss-and-capture” collision. That’s when two bodies briefly collide before settling into their current positions.
Let’s learn about Pluto
Pluto and Charon had an instant connection, says Adeene Denton. “They kiss and they say: ‘Yeah, this is it. I want to build a system together with you.’ And then they do.”
Denton is a planetary scientist at the Southwest Research Institute in Boulder, Colo. She was part of the team that shared these results January 6 in Nature Geoscience.
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Origin story plot holes
Of Pluto’s five moons, Charon is unusually large. It’s half Pluto’s size and has a little less than one-ninth as much mass. Since the 1990s, planetary scientists have thought that Charon could have formed in a way similar to Earth’s moon. Some impact on Pluto might have splashed out hot, molten material, which then began orbiting around it. Eventually that debris could have come together, forming a large moon.
But, just as with Earth’s moon, details of that possible scenario have been fuzzy. “It goes: Something hit Pluto,” Denton says. Then “question mark, question mark, question mark — Charon is now there.”
Past computer models of such collisions seemed to yield a system like Pluto and Charon. But those models treated the rocky, icy bodies as fluids. They ignored their material strength. And that would have been a decent assumption for large objects, such as gas giants or galaxies. When something hits them, those do behave like fluids. But Pluto and Charon are ice-wrapped rocks. And, it turns out, you can’t ignore that.
The real Charon-forming collision would have been a lot less splashy, Denton says. So in her team’s models, the researchers included Pluto’s and Charon’s rocky cores and icy mantles and crusts. And then it turned out that the protoplanets had an instant connection.
Touch and go
In the new models, Pluto and Charon joined up and rotated together, with each body remaining basically intact. After about 30 hours of contact, Charon would have separated from Pluto. Then, it likely would have migrated into the orbit it has around Pluto today.
The researchers found that two other pairs of Kuiper Belt objects could also be explained by such “kiss-and-capture” collisions. One is the dwarf planet Eris and its moon Dysnomia. The other is the dwarf planet Orcus and its moon Vanth.
Denton plans to extend her team’s new work to other objects with different masses and makeups. “Can this still work? I’m pretty confident that it does,” she says.
“If that’s true,” she adds, “kiss-and-capture happened all over the Kuiper Belt in the solar system’s history.” And that, she concludes, would seem “very romantic.”
