By Mari Hansen 
The solar system retains some of its oldest secrets far beyond Neptune, where sunlight is weak and time appears to move at a different pace. Things that appear oddly familiar are floating through the darkness out there. Not smooth spheres, not craters. Something completely different.
Two rounded shapes combined to form one. similar to cosmic peanuts. Or snowmen, as astronomers occasionally say with a hint of humor.
| Category | Information |
|---|---|
| Region | Kuiper Belt |
| Location | Beyond Neptune in the outer Solar System |
| Type of Objects | Icy planetesimals (remnants from solar system formation) |
| Notable Example | Arrokoth (nicknamed “Ultima Thule”) |
| Typical Shape | Bilobate or “contact binary” — two lobes fused together |
| Estimated Frequency | About 10% of Kuiper Belt objects |
| Key Research | Michigan State University simulations explaining formation |
| Key Scientists | Jackson Barnes, Seth Jacobson |
| Discovery Boost | NASA’s New Horizons spacecraft flyby in 2019 |
| Reference | https://science.nasa.gov |
Researchers were baffled by the shape for years. The majority of small bodies are beaten into roughly spherical lumps because space is full of collisions and chaos. However, a startlingly large number of objects in the Kuiper Belt—that far-off halo of icy debris—appear to be two snowballs gently pressed together.
The 2019 photo taken by NASA’s New Horizons spacecraft is sure to make you stop. As the probe passed Arrokoth, it revealed a delicate, nearly handcrafted double-lobed structure. One spherical lobe. One more, a little bigger. Carefully joined, as though gravity had been extra forgiving that day.
How such shapes could exist at all was a topic of discussion among scientists at the time. Fragile geometry is often erased by violent impacts. In most simulations, when you smash two rocks together, you get a lumpy sphere rather than a neat snowman.
According to a recent study that was published in the Monthly Notices of the Royal Astronomical Society, the solution may be less complicated than anticipated.
The explanation starts about 4.6 billion years ago, when the young Sun was surrounded by a whirling disk of gas and dust. Tiny grains drifted apart, clumped together, and then collided once more. These grains eventually grew into loose clouds of debris and pebble-sized pieces. Within those clouds, gravity started working quietly.
Michigan State University researcher Jackson Barnes created computer simulations that try to replicate this early chaos. A pattern became apparent as the models were run on powerful computing clusters. A revolving cloud of debris may not always collapse into a single body. Rather, it splits. There are two tiny planetesimals. Slowly, they go around one another. Then a soft thing occurs.
The two drift in closer. It was more of a cautious approach than a disastrous crash. The surfaces come into contact. They are slowed by friction. They eventually become a single unit, solidifying into that characteristic double-lobed shape. A snowman from space.
Even the researchers who ran the simulations might have been taken aback by the process’s elegance. In previous models, collisions were handled as though the objects were fluid blobs that instantly merged into round shapes. However, Barnes’ simulation preserved the bodies’ rigidity, demonstrating how two whole worlds could just lean into one another. The story essentially ends when they first meet.
The emptiness of the Kuiper Belt is astounding. Beyond Neptune, the area is home to millions of ice artifacts, but they are separated by vast distances. Accidents do occur, but they are rare. That seclusion is important.
In a few million years, a delicate contact binary drifting in the asteroid belt would most likely be destroyed. However, the atmosphere is almost peaceful out here. Slowly moving objects follow patient orbits in the dark. Those delicate shapes can endure for billions of years in the absence of frequent impacts.
According to current estimates, roughly 10% of objects in the Kuiper Belt might have this structure. The debate’s tone is altered by that statistic alone. Chance explanations become unsatisfactory when a shape appears that frequently.
As Seth Jacobson, another scientist involved in the study, noted, if ten percent of planetesimals are contact binaries, the process forming them can’t be rare. Suddenly, gravitational collapse—quiet, slow, and frequent—seems like the clear suspect. The story isn’t completely resolved, though.
There are new questions as you watch these simulations play out. Some things seem more intricate than basic snowmen with two lobes. Some might entail the merging of three bodies. Long after formation, others may have undergone partial collisions that slightly altered their outlines.
Furthermore, there is still much to learn about the Kuiper Belt itself. The area goes well beyond Pluto’s orbit and into areas where telescopes have difficulty picking up any signals at all. The outskirts of the solar system still seem to have a lot of surprises in store.
There might be dozens more of these frozen snowmen floating in the dark, according to future observations and possibly another deep-space mission. The physics of that ancient dust disk would be preserved in each one, which would be a tiny fossil from the early stages of planetary formation.
As you watch this story develop, it’s hard not to get a weird sense of curiosity. At one time, the outer solar system appeared to be a cemetery of icy rocks. However, every few years, a new strange orbit or shape indicates that the location is more complex than that.
In a sense, even playful. After all, it seems almost poetic to think that gravity, the most powerful cosmic force, spent the solar system‘s dawn silently creating snowmen in the dark.