Pluto and Charon formed through a 'kiss and capture' collision

Billions of years ago, in the icy outskirts of our solar system, two celestial bodies collided. Instead of a catastrophic destruction, they united briefly, spinning together like a cosmic snowman. This “kiss and capture” scenario led to the formation of Pluto and its moon, Charon, as we know them today.

A recent study from the University of Arizona has challenged long-held assumptions, shedding light on how these two icy worlds became a binary system.

Adeene Denton, a NASA postdoctoral fellow at the U of A Lunar and Planetary Laboratory, led the research. Her team revealed an overlooked factor in planetary collision models: the structural strength of rock and ice in small, cold worlds like Pluto and Charon.

“Pluto and Charon are different – they’re smaller, colder, and made primarily of rock and ice. When we accounted for the actual strength of these materials, we discovered something completely unexpected,” Denton explained.

Pluto and Charon’s unique collision

For many years, scientists thought Charon, Pluto’s largest moon, formed in a way similar to Earth’s moon. They believed a massive collision caused the bodies to deform and stretch, behaving like molten or fluid materials.

This model worked for Earth and its moon because of the high temperatures and larger masses involved, which allowed the materials to flow and reshape easily.

However, Pluto and Charon are smaller, colder, and primarily composed of ice and rock, which are much more rigid than molten material.

Kiss and capture mechanism

Using advanced computer simulations, the researchers discovered that when Pluto and proto-Charon collided, they didn’t behave like fluids. Instead, they temporarily stuck together, forming a snowman-shaped structure.

Over time, they separated but remained gravitationally linked, creating the binary system we observe today. This unique “kiss and capture” process differs significantly from traditional models of moon formation.

“Most planetary collision scenarios are classified as ‘hit and run’ or ‘graze and merge.’ What we’ve discovered is something entirely different – a ‘kiss and capture’ scenario,” said Denton.

Unlike traditional models, this mechanism placed Charon in a stable orbit around Pluto, perfectly matching observations.

Preserved integrity and internal heating

The study also revealed that Pluto and Charon remained mostly intact during their collision. This preservation of original composition challenges older models suggesting extensive mixing and deformation.

Additionally, the collision generated tidal forces that deposited significant heat into both bodies. This heating may have enabled Pluto to develop a subsurface ocean without requiring early solar system conditions that troubled past theories.

“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,” noted Erik Asphaug, senior author of the study.

Implications for planetary science

This discovery paves the way for new research into Pluto and Charon’s formation and evolution. The team plans to study how tidal forces – created as the two bodies separated after their collision – affected their early development.

The experts aim to understand how this impact influenced Pluto’s surface features, such as its mountains and plains, and whether it contributed to the formation of a subsurface ocean.

Additionally, researchers want to explore whether similar “kiss and capture” processes could explain the creation of other binary systems in the universe.

According to Denton, understanding how the collision’s aftermath shaped Pluto’s geology could reveal more about its surface and internal structure.

This work may shed light on the broader mechanisms driving planetary formation and evolution in icy, distant regions of the solar system.

Pluto and Charon reshape planetary system theories

The “kiss and capture” origin story of Pluto and Charon challenges older theories about how planetary systems form. It introduces a new way to think about collisions in space, showing how two bodies can briefly stick together before settling into a stable orbit.

This discovery changes how we understand not only Pluto and Charon’s history but also how similar systems might have formed throughout the universe.

By exploring this idea further, scientists hope to uncover more about the processes that shape planets, moons, and other celestial bodies – offering fresh insights into the mysteries of our solar system and beyond.

The study is published in the journal Nature Geoscience.

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