A new study suggests that billions of years ago, Pluto may have captured its largest moon, Charon, in a very brief icy “kiss.” This theory could explain how a dwarf planet (yes, I wish Pluto was still a planet) could capture a moon about half its size.
The team behind the study believes that two frigid worlds in the Kuiper belt, a ring of icy bodies at the edge of the solar system far from the sun, collided billions of years ago. Rather than annihilate each other, the two bodies merged into a rotating “cosmic snowman.” These objects separated relatively quickly, but remained joined in orbit, forming the Pluto/Charon system we see today.
This “kiss and capture” process represents a new theory of moon capture and cosmic collisions. It could also help scientists better investigate the structural strength of the Kuiper Belt’s frigid ice worlds.
About supporting science journalism
If you enjoyed this article, please consider supporting our award-winning journalism. Currently subscribing. By subscribing, you help ensure future generations of influential stories about the discoveries and ideas that shape the world today.
“Assuming that Pluto and Charon are objects with material strength, we found that Pluto could indeed capture Charon from a giant collision,” said team leader Adeen, a lunar and planetary researcher at the University of Arizona.・Denton told Space.com. “This collision-and-capture process is called ‘kiss-and-capture’ because Pluto and Charon briefly join together into a ‘kissing’ element before separating to form two separate objects. It will be. ”
Most planetary collision scenarios fall into the category of “hit and run” or “grazing merger,” meaning this “kiss and capture” scenario is entirely new.
“We were absolutely Denton continued, “I was surprised by the ‘kiss’ part in Kiss and Capture. I’ve never really seen an impact where two bodies briefly come together and then separate again! ” he continued.
The team’s study was published in the journal Nature Geoscience on Monday (6 January).
Pluto charmed Charon with a 10-hour kiss
The reason the relationship between Pluto and Charon is difficult for scientists is because the difference in size and mass between the two icy objects is relatively small.
“Charon is so massive compared to Pluto that it’s actually a binary star,” Denton explained. “It is half the size of Pluto and has 12% of the mass of Pluto, so it is much more similar to Earth’s moon than any other moon in the solar system.”
For comparison, our moon is only a quarter the size of Earth, while Ganymede, the solar system’s largest moon, is about 1/28th the size of its parent planet Jupiter.
The University of Arizona researcher, who is also a NASA postdoctoral fellow, added that such relatively large satellites are difficult to acquire using “normal” methods. (“Normal” means capturing satellites by gravity, such as the moons of Mars, Phobos and Deimos, and the moons of the giant planets Jupiter and Saturn.)
So the general theory for the formation of the Pluto-Charon system is that a giant celestial body is thought to have collided with Earth and ejected material, similar to what our planet captured to give birth to our moon. It is based on the idea of collision capture.
“Something big will hit Pluto and we’ll get Charon, but like the Earth-moon system, we don’t fully understand how it works or the conditions under which it happens,” Denton said. he said. “This is a pretty big question because many other large Kuiper belt objects also have large moons. So this seems to be something that happens with some frequency in the Kuiper belt, but how and why? I don’t know if that will happen.”
The screenshot shows the Pluto/Charon system during its linked “snowball” phase.
Robert Merrican and Adeen Denton
In a standard “collision capture”, a large collision occurs, causing the two bodies to stretch and deform like a fluid. This process well explains the formation of the Earth-Moon system. This is because the intense heat generated in the collisions and the greater mass of the objects involved make them fluid.
There are additional factors to consider when considering Pluto and Charon in the collision capture process. It’s the colder ice and the structural strength of the rock. This is something that has been ignored in the past when researchers considered Charon’s collisional creation.
To incorporate this into the simulation, the team turned to the University of Arizona’s high-performance computing cluster. When Denton and colleagues factored in the strength of these materials in their simulations, they discovered something completely unexpected.
“Because both objects have material strength, Charon did not penetrate deep enough to merge with Pluto. This would not be the case if the objects were fluid,” Denton explained. “In the same collision conditions, assuming Pluto and Charon are inert, they would actually merge into one large body and Charon would be absorbed. However, if there was strength, Pluto and Charon would be in a short-term merger remains structurally intact.”
In this scenario, Charon would not be able to sink into Pluto, leaving it beyond the so-called “co-rotation radii” of both objects. As a result, it could not rotate as fast as Pluto, and the two bodies could not remain fused. When they parted and this cold kiss ended, the researchers think Pluto would have brought Charon closer to a higher circular orbit, from which the moon would have moved outward.
“The ‘kissing’, or merging, in this kiss-and-capture is geologically speaking very brief, lasting 10 to 15 hours before both bodies separate again,” Denton said. “Charon then begins to slowly move outward toward its current location.”
The researchers believe that the first collision occurred very early in the solar system’s history, perhaps tens of millions of years after the solar system formed, or billions of years ago.
“Typical large-scale collisions are simple mergers where objects join together or both objects remain independent,” Denton said. “So this was something very new to us. It also raised a lot of interesting geological questions that we wanted to test, because whether kiss-and-capture would work or not. Because it depends on Pluto’s thermal conditions, and we can connect that to Pluto’s modern conditions.” Test Geology.
“We hope to find out how the initial Pluto-Charon collision will affect whether and how Pluto and Charon develop oceans.”
Denton explained that there are two paths the team can follow to advance this development.
“The first is to see how this applies to other large Kuiper belt objects with large moons, such as Eris and Dysnomia, Orcus and Vance,” Denton explained. “Our initial analysis suggests that kiss-and-capture may be the source of these other systems, but they all differ in their composition and mass, making kiss-and-capture a likely source. It is important to know how the capture worked throughout Kuiper’ belt. “
The second path the team plans to take involves examining Charon’s long-term tidal evolution to confirm theories of its formation.
“To be really confident that this is the formation process of Pluto and Charon, we need to see Charon move to its current position, about eight times the width of Pluto,” Denton said. “But this is a process that occurs on a much longer timescale than the initial collision, so our model is not well-suited to tracking it.
“We plan to study this more closely in the future to determine what conditions not only recreate Pluto and Charon as objects, but also place Charon in its current correct position.”
Copyright 2025 space dot comthe company of the future. Unauthorized reproduction is prohibited. This material may not be published, broadcast, rewritten or redistributed.
