Why the outer solar system is filled with giant cosmic “snowmen”
Science Daily
February 23, 2026
AI-Generated Deep Dive Summary
The outer solar system’s mysterious “snowman” shapes, found among icy objects in the Kuiper Belt, have long puzzled scientists. These two-lobe structures, resembling giant snowmen made of ice and rock, make up about 10% of all planetesimals—ancient remnants from the solar system's formation. For years, researchers struggled to explain how these delicate forms could naturally form without violent collisions breaking them apart. Now, a groundbreaking simulation by Jackson Barnes, a graduate student at Michigan State University, reveals that gravitational collapse is the key process behind their creation.
Barnes’ computer model demonstrates that as two orbiting planetesimals spiral inward, they gently settle against each other rather than colliding violently. This slow merging preserves their rounded shapes, resulting in the distinctive double-lobe structure. Previous simulations often oversimplified the process by treating colliding bodies as fluid masses that merged into smooth spheres, which failed to replicate the snowman-like appearance. Barnes’ more realistic approach retained the structural integrity of the objects, allowing them to form stable contact binaries through gravitational forces.
The discovery is significant because it explains why these unusual shapes are relatively common in the Kuiper Belt. While earlier theories relied on rare cosmic events or unique conditions, this new model shows that gravitational collapse is a natural and efficient process. The simulation also aligns with observations from NASA’s New Horizons mission, which captured images of a contact binary in 2019 and revealed that roughly one in ten planetesimals share this shape.
The survival of these structures over billions of years is due to the sparsity of collisions in the Kuiper Belt. Without frequent impacts to disrupt them, the snowman-shaped objects remain intact. This stability highlights how gravitational collapse provides a reliable mechanism for forming contact binaries, offering new insights into the early solar system’s history and the formation of planetary building blocks.
This research not only solves a long-standing mystery but also deepens our understanding of how planets and other celestial bodies formed from smaller particles in the early solar system. By revealing the role of gravitational collapse, scientists gain a powerful tool for explaining similar structures across the universe, making this discovery a major advancement in planetary science.
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Originally published on Science Daily on 2/23/2026