Astronomers have long debated why so many icy objects in the outer solar system look like snowmen. Michigan State University researchers now have evidence of the surprisingly simple process that may be responsible for their creation.

Far beyond the violent, chaotic asteroid belt between Mars and Jupiter lies what’s known as the Kuiper Belt. There, past Neptune, you’ll find icy, untouched building blocks from the dawn of the solar system, known as planetesimals. About one in 10 of these objects are contact binaries, planetesimals that are shaped like two connected spheres, much like Frosty the Snowman. But just how these objects came to be without the help of a magic silk hat has been an open question.

Jackson Barnes, an MSU graduate student, has created the first simulation that reproduces the two-lobed shape naturally with gravitational collapse, which refers to matter shrinking into itself because its own gravity pulls it together more strongly than any force acting to expand. His work is published in the Monthly Notices of the Royal Astronomical Society.