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New Theory on Pluto’s Formation and Its Relationship with Charon

The diminutive dwarf planet Pluto and its notable satellite Charon present an intriguing binary system that has perplexed scientists for many years. Central to the debate is the question of how Charon, which is roughly half the size of Pluto, ended up in orbit around the dwarf planet. Recent research proposes a novel explanation dubbed the “kiss and capture” mechanism, offering a fresh perspective on their celestial relationship.

The findings were published in the journal Nature Geoscience by a team of researchers who suggest that the two celestial bodies may have collided billions of years ago in the cold edges of the solar system. Rather than being completely destroyed by the impact, Pluto and Charon allegedly conjoined briefly in a spinning, snowman-like formation for ten to fifteen hours before separating but remaining in a locked gravitational relationship.

“Most planetary collision models fall into categories like ‘hit and run’ or ‘graze and merge.’ We’ve discovered an entirely new scenario—a ‘kiss and capture’ where the bodies briefly stick together and then split while remaining gravitationally bound,” explained Adeene Denton, a NASA postdoctoral fellow and the study’s lead author, in a statement.

David Rothery, a planetary geoscientist at the Open University in England, noted that he had previously assumed that a collision of this magnitude would typically destroy the smaller body involved. His comments point to a significant shift in understanding the dynamics of large celestial impacts.

Historically, scientists have theorized that Charon formed from a massive collision with another celestial body, resembling how Earth’s moon is believed to have originated. This earlier model posited that the intense heat generated by such an impact allowed the materials involved to behave like a fluid, facilitating the formation of Charon from debris. However, Pluto and Charon differ markedly from the Earth-moon system, as they are more akin to a binary system where both bodies orbit each other.

“Charon is significantly large compared to Pluto, reaching about half its size and 12 percent of its mass,” Denton noted. This contrasts sharply with our moon, which is approximately 27 percent of Earth’s size, emphasizing the uniqueness of the Pluto-Charon duo. Additionally, the researchers argue that these two bodies did not exhibit fluid characteristics during their collision due to their smaller size and their predominately rocky and icy composition, which lends them structural integrity that has often been overlooked.

The team employed sophisticated computer simulations to explore the dynamics of the Pluto-Charon collision. By incorporating the new understanding of their material properties, the researchers were able to unveil the “kiss and capture” mechanism for the first time.

“We discovered that if we consider Pluto and Charon as bodies with material strength, the possibility exists for Pluto to capture Charon from such an impact,” said Denton, adding that the surprise element of their findings was the brief merger before re-separation of the two celestial bodies. “This kind of impact scenario had never been proposed previously,” she remarked.

The computational model accurately reflects the current orbit of the Pluto-Charon system, lending credibility to the hypothesis. Denton further explained that because Pluto spins rapidly prior to the collision, it can exert a gravitational influence that causes Charon to migrate outward slowly after their encounter.

This collision may have also initiated a new geological era for Pluto, which was extensively observed by the New Horizons spacecraft in 2015. Researchers are now eager to explore how this new understanding might shed light on the geological features of both bodies, including the possible existence of subsurface oceans and whether the “kiss and capture” scenario could apply to other binary systems across the universe.

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