⛄ Where do these space snowmen come from?

Snowmen floating in space: far from being a fantasy, this shape appears on some icy objects at the far reaches of the Solar System. How can such particular structures come into being?

These objects, named planetesimals, are the remnants of the early ages of our planetary system. They form from disks of dust surrounding young stars, where small pebbles gradually clump together under the influence of gravity. Like snowflakes assembling, they give birth to more massive bodies, essential for building planets.


In 2019, NASA's New Horizons mission offered a first close-up look at these curiosities. The images of Arrokoth, a planetesimal composed of two connected spheres, confirmed their presence. This observation immediately raised questions about the mechanisms at work in these distant regions, beyond the orbit of Neptune.

A recent study, published in Monthly Notices of the Royal Astronomical Society, provides some answers using an innovative approach. The researchers modeled planetesimals not as perfect spheres, but as clouds of interacting particles. This more detailed method allows tracking the individual behavior of each pebble within the system.

In these simulations, rotating clouds can sometimes split into two distinct sets that orbit each other. The elements clump together and, under the effect of their mutual attraction, slowly approach each other until they come into contact gently. This merger creates various shapes, ranging from spheres to elongated structures or snowman shapes, depending on the speed and cohesion of the particles.

The results show that only 4% of the simulated planetesimals become contact binaries, a rate lower than previous estimates. Scientists attribute this discrepancy to the limitations of computer models, particularly in terms of the number and size of particles used. Improving these parameters could increase the proportion of these particular objects in future simulations.


Researchers are now exploring the possibility of more elaborate formations, such as triple systems where three planetesimals orbit together. This work could help understand the diversity of objects observed in the Kuiper belt. Without collisions to destabilize them, these structures can persist for billions of years.