The outer reaches of our solar system are filled with icy rock formations that look like snowballs.

Exactly why many of these distant objects look like snowmen, one large spherical object attached to another, remains a mystery.

But a team of astronomers thinks they may have solved the mystery and discovered the cause of the formation of these strange structures.

Understanding the edge of the solar system

Far beyond Neptune, at the edge of the solar system, lies a large ring of rocky icy debris. kuiper belt.

This ring is made up of leftover material from which the planets and moons of our solar system formed around young stars.

The region is home to the building blocks of the universe known as “planetary bodies,” and astronomers say about one in 10 of these objects is a contact binary star.

The Kuiper Belt object named Arrokoth is famous for being observed by. NASA’s New Horizons spacecraft.

New Horizons’ primary mission was a flyby of Pluto, which it accomplished on July 14, 2015.

Since then, the spacecraft has continued its journey into the outer regions of the solar system, providing astronomers with great views of some of the strange “snowball” objects that lurk there.

These planetesimals form from two connected spheres, but exactly how they form is something of a mystery.

But a team of researchers at Michigan State University say the answer may be relatively simple: a process called gravitational collapse.

“Given that 10% of planetesimals are contact binaries, the process that forms them is not unusual,” says Seth Jacobson, professor of Earth and Environmental Sciences and senior author of the paper.

“Gravitational collapse matches well with what we observed.”

Explanation of gravitational collapse

Newly formed stars are usually surrounded by a rotating disk of dust and gas made from the material that formed the star.

The same is true for our young Sun, and remnants of its host star’s formation 4.6 billion years ago can still be found in the Kuiper Belt.

These debris include dwarf planets like Pluto, as well as comets and planetesimals.

Planetesimals are collections of pebble-sized objects pulled together by gravity over time from small clouds of material.

Astronomers say these clouds could rotate and collide, tearing themselves apart and forming two separate planetesimals orbiting each other.

In the computer simulations used by the researchers, the orbiting pairs spiraled toward each other and touched each other, forming the shape of a two-lobed snowman.

Burns said these newly formed objects are less likely to encounter other nearby objects, allowing them to remain intact.

“We were able to test this hypothesis in a legitimate way for the first time,” Burns said. “That’s what’s so interesting about this paper.”

The research team says the model should also help scientists better understand systems involving three or more objects.

Cosmic snowmen like this may be common in the outer reaches of the solar system, and it appears that many more are waiting to be discovered.

To read the full paper, go to Royal Astronomical Society monthly notices.