A breathtaking image, captured at the dawn of the new year, reveals the clearest view yet of a celestial enigma – ancient objects in the solar system’s distant reaches, strikingly resembling snowmen. For decades, astronomers have puzzled over these peculiar shapes, and now, a breakthrough from an American student is rewriting our understanding of the solar system’s origins.
Beyond the familiar asteroid belt, lies the Kuiper Belt, a frigid realm beyond Neptune teeming with icy relics from the solar system’s birth. These ancient building blocks, known as planetesimals, have endured for billions of years, largely untouched by time. Surprisingly, roughly one in ten of these objects are “contact binaries” – two connected spheres, evoking the image of a cosmic snowman.
The mystery lay in their formation. How could these delicate structures survive the violent collisions common in the early solar system? Jackson Barnes, a graduate student, tackled this question with a novel approach: the first computer simulation demonstrating how these two-lobed shapes can arise naturally through gravitational collapse – the very force that births stars and planets.
Previous models treated these objects as fluid, quickly merging into single spheres. Barnes’ simulations, powered by high-performance computing, allowed the objects to retain their strength, gently settling against one another. This subtle difference proved crucial, revealing a surprisingly simple explanation for a long-standing puzzle.
“If we think 10% of planetesimal objects are contact binaries, the process that forms them can’t be rare,” explains Seth Jacobson, a senior author of the study. “Gravitational collapse fits nicely with what we’ve observed.” The theory suggests these snowmen aren’t the result of improbable events, but a common outcome of the solar system’s formation.
The first detailed glimpse of a contact binary came in 2019, when NASA’s New Horizons spacecraft flew past a Kuiper Belt object nicknamed Ultima Thule. The stunning images sparked a re-examination of distant bodies, revealing that about 10% share this distinctive shape. In the vast emptiness of the Kuiper Belt, these objects drift undisturbed, shielded from frequent impacts.
The early Milky Way was a swirling disc of gas and dust, and remnants of this era persist in the Kuiper Belt, including dwarf planets like Pluto, comets, and these fascinating planetesimals. These planetesimals formed as dust and pebbles coalesced under gravity, much like snowflakes compressing into a snowball – loose aggregates pulled from clouds of tiny particles.
Barnes’ simulation reveals that as these rotating clouds collapse, they can split into two separate bodies, orbiting each other. Over time, their orbits tighten, leading to a gentle fusion that preserves their rounded forms. The survival of these fragile structures, Barnes explains, is a matter of chance – in the remote Kuiper Belt, collisions are rare, leaving the snowmen largely unscathed.
For years, scientists suspected gravitational collapse played a role, but lacked the tools to test the hypothesis effectively. “We’re able to test this hypothesis for the first time in a legitimate way,” Barnes states, highlighting the significance of this research. He believes this model could unlock further understanding of even more complex systems involving multiple bodies.
As future missions venture deeper into the outer solar system, the snowman shape may prove to be far more prevalent than previously imagined. This discovery isn’t just about understanding distant objects; it’s about unraveling the very processes that shaped our solar system and the universe beyond.
