“Dirty snowballs” have joined together since the planets formed

Across cosmic time and space, stellar systems form.

Molecular gas clouds contract, fragment, and portions of it collapse.

Some fragmented regions form protostars, surrounded by a protoplanetary disk.

After the star’s birth, imperfections within the disk rapidly grow and evolve.

After another few million years, a planetary system typically results.

At a variety of locations, “frost lines” enable ice-rich objects to develop.

This leads to “belts” of material accumulating, with small, sub-planetary objects inside.

In our own Solar System, we have two such belts: the asteroid and Kuiper belts.

Approximately 4.6 billion years have elapsed since those belts first formed.

Over time, many objects have gravitated and merged: growing quite massive.

But most objects remain small, only experiencing random, chance encounters.

These ice-rich objects are sometimes called dirty snowballs: composed of rock and ice mixes.

In theory, when these snowballs collide, they should fuse together: forming contact binaries.

We’ve now discovered many objects that appear as contact binaries, including:

• Donaldjohanson, visited by Lucy,

• Torifune, visited by Hayabusa 2,

• Arrokoth, visited by New Horizons,

• and Churyumov-Gerasimenko, visited by Rosetta.

Asteroid Nysa, discovered in 1857, is our first trilobed object: a contact trinary.

These relics provide compositional glimpses into our pre-solar nebula.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.

This article “Dirty snowballs” have joined together since the planets formed is featured on Big Think.