The dwarf planet Pluto, whose surface is dominated by a light heart-shaped feature, is in the foreground. Its moon Charon sits slightly behind and to the left.
New research shows Pluto and its moon Charon had an instant connection. This image of Pluto (lower right) and its large moon Charon (upper left) was taken by the New Horizons spacecraft in 2015. This composite image, made using a combination of photos, is not to scale.
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.
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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.
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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.”
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Pluto may have captured its largest moon, Charon, with a “kiss-and-capture” collision, scientists have found. #space #astronomy #planets #sciencenews
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Power Words
More About Power Words
computer model: A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.
core: Something — usually round-shaped — in the center of an object. (in geology) Earth’s innermost layer. Or, a long, tube-like sample drilled down into ice, soil or rock. Cores allow scientists to examine layers of sediment, dissolved chemicals, rock and fossils to see how the environment at one location changed through hundreds to thousands of years or more.
crust: (in geology) Earth's outermost surface, usually made from dense, solid rock (in planetary science) the outermost surface of rocky planets, dwarf planets and natural satellites.
debris: Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
dwarf planet: One of the solar system’s small celestial objects. Like a true planet, it orbits the sun. However, dwarf planets are too small to qualify as true planets. Prime examples of these objects: Pluto and Ceres.
gas giant: A giant planet that is made mostly of helium and hydrogen, which on Earth are gases. Jupiter and Saturn are gas giants.
geoscience: Any of a number of sciences, like geology or atmospheric science, concerned with better understanding Earth. People who work in this field are known as geoscientists.
Kuiper Belt: An area of the solar system beyond the orbit of Neptune. It is a vast area containing leftovers from the formation of the solar system that continue to orbit the sun. Many objects in the Kuiper Belt are made of ice, rock, frozen methane and ammonia. The best known of the larger Kuiper Belt objects is the dwarf planet Pluto. The belt extends out from the sun at a distance of 30 to 55 astronomical units. (An astronomical unit is equal to Earth’s from the sun.)
mantle: (in geology) The thick layer of the Earth beneath its outer crust. The mantle is semi-solid and generally divided into an upper and lower mantle.
mass: A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.
model: A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.
molten: A word describing something that is melted, such as the liquid rock that makes up lava.
moon: The natural satellite of any planet.
orbit: The curved path of a celestial object or spacecraft around a galaxy, star, planet or moon. One complete circuit around a celestial body.
planet: A large celestial object that orbits a star but unlike a star does not generate any visible light.
Pluto: A distant world that is located in the Kuiper Belt, just beyond Neptune. Known as a dwarf planet, Pluto is the ninth largest object orbiting our sun.
protoplanet: A consolidating celestial object that might one day turn into a planet — but only if its mass is large, it orbits some star, and during that orbiting it eventually sweeps other debris out of its path.
satellite: A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.
simulation: (v. simulate) An analysis, often made using a computer, of some conditions, functions or appearance of a physical system. A computer program would do this by using mathematical operations that can describe the system and how it might change over time or in response to different anticipated situations.
solar system: The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
Citations
Journal: C.A. Denton et al. Capture of an ancient Charon around Pluto. Nature Geoscience. Vol. 18, January 6, 2025, p. 37. doi: 10.1038/s41561-024-01612-0.