How Pluto got its moon: The ‘Kiss-and-Capture’ theory

New research suggests that billions of years ago, Pluto (also known as a dwarf planet) may have captured its largest moon, Charon, through a unique "kiss-and-capture" collision. Unlike Earth, where the moon orbits the planet, Pluto and Charon orbit each other. Both are icy bodies located in the Kuiper Belt, beyond Neptune.

The study, led by NASA postdoctoral fellow Adeene Denton at the University of Arizona's Lunar and Planetary Laboratory, proposes that Pluto and Charon were once two icy worlds that collided in the distant Kuiper Belt. Rather than destroying each other, they briefly merged into a spinning "cosmic snowman" before separating. Despite this, they remained gravitationally bound, forming the Pluto-Charon system we see today.

This "kiss-and-capture" event offers a new understanding of how moons are captured and helps scientists learn more about how planetary bodies form and evolve in the cold, icy regions of the solar system.

New theory: How Charon formed 

Scientists presumed for decades that the dwarf planet’s unusually large moon, Charon, formed from a massive collision, similar to Earth's moon. The common idea was that a large object collided with Pluto, causing molten material to form Charon. However, this theory works better for larger, hotter planets like Earth, where the colliding bodies behave like fluids. 

Pluto and Charon are smaller and colder, mainly made of rock and ice. When Denton and her team considered the strength of these materials, they found something completely new. “Pluto and Charon are different—they’re smaller, colder, and made mainly of rock and ice. When we looked at the actual strength of these materials, we discovered something unexpected," Denton explained.

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 The 'Kiss and Capture' model

The research team’s model shows that instead of a massive collision or simple grazing, Pluto and Charon may have briefly collided, stuck together, and then separated, all while remaining gravitationally bound. This new "kiss and capture" mechanism is different from the more common "hit and run" or "graze and merge" collision scenarios.

Also Read: What is inside the moon’s inner core? Here’s what scientists revealed

Findings in journal: Nature Geoscience

The findings published in the journal Nature Geoscience could revolutionise our understanding of how icy bodies in the Kuiper Belt and beyond form and evolve. “The compelling thing about this study is that the model parameters that work to capture Charon end up putting it in the right orbit. You get two things right for the price of one,” said Erik Asphaug, senior author and professor at the Lunar and Planetary Laboratory.

The "kiss and capture" theory could lead to a better understanding of how moons and planets in the solar system, particularly those in the cold interact and form. 

(With inputs from agencies)