Far beyond Neptune, in the frigid expanse of the Kuiper Belt, a peculiar population of icy bodies has long puzzled astronomers. These objects, remnants from the solar system’s formation, often exhibit a striking resemblance to snowmen – two distinct lobes connected to form a bi-lobed shape. Now, researchers at Michigan State University (MSU) believe they’ve cracked the code, demonstrating through sophisticated computer simulations that this unusual morphology can arise from a surprisingly simple process: gravitational collapse.
The Kuiper Belt, a region beyond the orbit of Neptune, is populated with planetesimals – the building blocks of planets that never fully coalesced. Approximately 10 percent of these planetesimals are classified as contact binaries, meaning they consist of two connected lobes. For decades, the question of how these contact binaries formed without being torn apart by collisions remained unanswered. Previous models struggled to explain their existence, often treating collisions as events that would result in a single, spherical body.
Jackson Barnes, a graduate student at MSU, developed a new simulation that challenges those earlier assumptions. Using the high-performance computing resources at MSU’s Institute for Cyber-Enabled Research (ICER), Barnes’ model allowed objects to retain their strength and interact more realistically. Unlike previous simulations that treated colliding objects as fluid blobs, Barnes’ work allowed for objects to remain solid and gently adhere to one another.
The simulation reveals that the formation of these “snowmen” isn’t necessarily driven by dramatic events, but rather by the fundamental force of gravity. In the early stages of the solar system, a vast cloud of dust and gas began to coalesce under its own gravitational pull. However, this process wasn’t always smooth. As the cloud rotated, instabilities arose, causing portions of the material to collapse inward. In some instances, this collapse wasn’t uniform, leading to the formation of two distinct, rotating masses.
These two masses then entered a slow, spiraling dance toward each other. Instead of a violent collision, they gently touched, remaining connected due to their mutual gravitational attraction. This delicate interaction allowed them to maintain their individual shapes, resulting in the characteristic bi-lobed structure observed in Kuiper Belt objects like 2014 MU69, informally known as Ultima Thule, which was famously imaged by NASA’s New Horizons spacecraft in 2019.
“For years, astronomers have tried to understand why so many icy bodies in the outer solar system resemble snowmen, with two rounded sections joined together,” explained researchers at MSU. The new simulation provides compelling evidence that this shape can emerge naturally from gravitational collapse, eliminating the need for more complex and less probable formation scenarios.
The significance of this finding lies in its simplicity. Previous theories often invoked rare or exotic events to explain the formation of contact binaries. Barnes’ simulation demonstrates that the process can occur relatively frequently, simply as a consequence of the physics governing the early solar system. This suggests that contact binaries may be far more common than previously thought.
The research builds on decades of observations of these unusual objects. NASA’s New Horizons mission provided the first close-up view of a contact binary, Ultima Thule, revealing its remarkably well-preserved structure. This image, captured during a flyby on , served as a crucial benchmark for validating the simulation results.
The implications extend beyond understanding the formation of these specific objects. The process of gravitational collapse is fundamental to the formation of many celestial bodies, from stars and planets to smaller objects like planetesimals. By gaining a better understanding of how this process works in the extreme conditions of the outer solar system, scientists can refine their models of planet formation and gain insights into the origins of our own solar system.
The research, published in the Monthly Notices of the Royal Astronomical Society, represents a significant step forward in our understanding of the outer solar system. It demonstrates that even in the vastness of space, simple physical processes can give rise to complex and beautiful structures, like the cosmic snowmen that populate the distant Kuiper Belt.
