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Why is the snowman shape so common in the outer solar system?
The outer region of the solar system is home to a slew of snowman-shaped objects. One famous example is Arrokoth, a member of the Kuiper Belt, which is a region beyond Neptune that contains Pluto and other icy objects such as planetesimals. In fact, one in 10 Kuiper Belt objects is snowman-shaped, or what astronomers call a contact binary. On February 19, 2026, researchers at Michigan State University said the reason for all these snowman-shaped objects might be surprisingly simple.
Lead author Jackson Barnes of Michigan State University (MSU) created computer simulations that show gravitational collapse can naturally produce these snowman-shaped objects. Barnes used MSU’s Institute for Cyber-Enabled Research’s High-Performance Computing Center to create simulations that show the formation of dual-lobed objects doesn’t rely on chance collisions or unusual encounters.
Co-author Seth Jacobson of MSU said:
If we think 10% of planetesimal objects are contact binaries, the process that forms them can’t be rare. Gravitational collapse fits nicely with what we’ve observed.
Our first closeup look at a contact binary was Arrokoth. The New Horizons spacecraft flew past the rocky snowman on New Year’s Day in 2019.
The researchers published their peer-reviewed paper in the journal Monthly Notices of the Royal Astronomical Society on February 19, 2026.
Modeling the collapse process
The simulations needed to find an explanation that allowed the contact binaries to happen fairly regularly. And they needed to assure that these objects could retain their shapes over the years. Other computer models ended up with something that eventually morphed into a single, blob-like shape. Barnes’ simulations allow the snowmen to retain their characteristic shape.
In the early solar system, the sun and planets formed out of a swirling disk of gas and dust. On the outer edges of our solar system were remnants of this disk that didn’t become incorporated into the larger bodies. These Kuiper Belt objects live placid lives in the spacious regions of the solar system’s outskirts. Scientists say few collisions occur here.
In Barnes’ simulations, planetesimals form out of the dusty disk into loose aggregations of material. Gravity can then cause the objects to collapse inward, which can rip the object into two parts that then orbit each other until they are once again pulled into a single snowman-shaped object. In a sparsely populated environment, there’s nothing to knock into the objects and separate them again. The scientists note:
Most binaries aren’t even pocked with craters.
The MSU scientists are now working to create even more accurate modeling of the collapse process.
Watch a simulation of a snowman-shaped object after its collapse into 2 and as it reconnects.
Bottom line: Scientists at MSU have modeled the process of gravitational collapse that they say creates the snowman shape that is so common in the outer solar system.
Source: Direct contact binary planetesimal formation from gravitational collapse
Via Royal Astronomical Society
Read more: A new Earthlike planet in the distant Kuiper Belt?
Rare Kuiper Belt triplet might be one of many