Have you ever wondered how those strange, floating “snowmen” survive in the deep cold of the Kuiper Belt beyond Neptune’s orbit? These oddly shaped, double-lobed rocks, called contact binaries, look as fragile as the famous Arrokoth, yet they have survived billions of years without breaking. Astronomers have been searching for the answer for centuries.Enter Jackson Barnes, a flamboyant graduate student at Michigan State University. He created the first computer simulation proving that these strange planetesimals formed naturally from swirling pebble clouds that collapsed under their own gravity. No magic required, just physics doing its thing in cosmic dust. Mystery solved.
How gravity created ‘snowman’ worlds in space
Beyond the asteroid belt lies a frozen wonder: the Kuiper Belt, a huge ring of icy remnants from the birth of our solar system. Among many “snowman” planetesimals are delicate, double-lobed contact binaries, such as Arrokoth. These strange shapes, interconnected like a cosmic snowball, have baffled astronomers. How do they last for billions of years without disintegrating? This mystery persisted for years. Then, Jackson Barnes, a graduate student at Michigan State University, cracked it. Their pioneering computer simulations showed that these objects formed naturally from pebble clouds in the early Solar System. Gravity causes the clouds to collapse, giving rise to these lumpy, binary structures without naturally occurring collisions. This breakthrough rewrites our understanding of planetary formation. It shows that gentle gravitational processes can craft resilient survivors in the cold void, pointing to similar worlds orbiting other stars. The mysteries of the Kuiper Belt continue to be revealed, one simulation at a time.
Michigan State University’s success; Jackson Barnes leads the charge
Researchers at Michigan State University (MSU) have revealed the simple but fascinating phenomenon behind it: gravitational collapse. Graduate student Jackson Barnes developed the first computer simulation showing how these two-legged ‘contact binaries’ arise naturally from pebble clouds.Older models treated colliding planetesimals as fluid-like blobs that merged into smooth spheres, failing to recreate contact binaries. Barnes, taking advantage of high-performance computing, simulated objects maintain their structural integrity and settle gently upon contact.
Expert Insights from Professor Seth Jacobson
“If we think that 10% of planetary objects are contact binaries, then the process that creates them cannot be that rare,” said the paper’s senior author Seth Jacobson, MSU assistant professor of Earth and environmental sciences. “Gravitational collapse fits well with what we’ve seen.”
The science behind floating ‘snowmen’: Understanding the gravitational collapse that defines the process
As described in the Dictionary of Astrobiology, gravitational collapse is “the collapse of a region of material under its own gravity, for example, the dense core of an interstellar cloud on its way to star formation.” This occurs when local self-gravity overpowers restoring forces such as thermal gas pressure or turbulence.In the protoplanetary disk, millimeter-sized pebbles concentrate through streaming instabilities in the pebble cloud. Self-gravity then triggers collapse, giving rise to planetesimals. Barnes’s model reflects this precisely.
Real-world observations: Arrokoth and New Horizons
Contact binaries came to prominence in January 2019 when NASA’s New Horizons spacecraft flew past one in the Kuiper Belt. Named ‘Ultima Thule’ (later officially Arrokoth), its two-lobed ‘snowman’ shape stunned scientists. Scattered throughout the Kuiper Belt, these globules neither break on impact nor fall alone, indicating benign formation.
Details of unprecedented simulation publication in monthly notice
Writing in Monthly Notices of the Royal Astronomical Society, Barnes and colleagues detail 54 simulations of an early pebble cloud containing 105105 particles, each with a radius of about 2 km (1.25 mi). This low-resolution setup mirrors reality, where real pebble clouds are likely to contain particles 10241024 millimeters in size.
Key Takeaways: Orbital Dance for Spiraling
The team found that, in some cases, two minor planets from the pebble cloud entered mutual orbit. They slowly moved inward, reaching speeds of 5 meters per second or less before touching down. Upon contact, the particles become truly organized, forming a double-lobed shape, merging into a double-lobed planetoid or ‘contact binary’. “Some of the contact binaries in our model bear a strong resemblance to Arrokoth,” Barnes commented.Earlier gravitational collapse simulations had ignored particle-interaction physics, predicting that collisions between small planetesimals would yield a single, spherical object. Barnes’ innovative modeling of how pebbles rest and stick explains the intact ‘snowman’ shapes.
Implications for the origin of the Solar System
This work represents a transformative view of planetary formation. Contact binaries, which comprise 10% of Kuiper Belt objects, suggest that gravitational collapse is common in pebble clouds, creating ‘rubble piles’ that last for eons. This aligns with the low-density, loosely bound structure of Arrokoth observed by New Horizons.Similar patterns are also seen among near-Earth asteroids, suggesting that this process operates throughout the Solar System. Future missions could test these predictions.
Future simulations and observations
High-resolution Pebble Cloud models powered by advanced computing promise deeper insights. Telescopes like the James Webb Space Telescope may see more contacting binaries in the distant disk in the coming days.Jackson Barnes’ simulation not only solves the ‘snowman’ puzzle but also redefines how planetesimals and ultimately planets emerge from cosmic dust.