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Scientists Prove a 50-Year-Old Theory About How Planets Form

For decades, astronomers have traced the broad outlines of planetary birth: a young star surrounded by a swirling disk of gas and dust, where tiny particles somehow collide, clump, and grow into worlds.

The earliest, most critical step in that story has remained frustratingly opaque. No telescope can zoom in close enough to watch dust grains aggregate into the first solid blobs, called planetesimals, that eventually become planets.

Now, a Swiss research team has taken a different approach—by recreating the conditions of a protoplanetary disk inside a small chamber aboard a specially configured aircraft, and watching what happens when gravity essentially disappears.

The TEMPusVoLa Experiment

The team, based at the University of Bern and led by researchers including Holly L. Capelo, built an instrument called TEMPusVoLa in 2020 specifically to study a theoretical process called shear-flow instability.

The idea is this: within a protoplanetary disk, gas and dust don't simply drift passively. Instead, layers of material slide past one another at different speeds, and under the right conditions, that shearing motion can trigger instabilities that cause dust particles to concentrate and collide more frequently.

The process has been modeled mathematically for years, but no one had actually demonstrated that it could occur in the ultra-thin gas and minuscule particle densities found in real disks around newborn stars.

Why Microgravity Was Essential

Earth's gravity masks the delicate interactions Capelo's team wanted to observe. On our planet, heavier particles settle quickly, and buoyancy forces distort the behavior of dust suspended in gas.

To isolate the true physics, the researchers needed something close to weightlessness—which they found aboard parabolic flight aircraft, the same aircraft popularly known as the "Vomit Comet" that astronauts use for training.

These planes execute steep climbs and dives at roughly 45-degree angles, and during each dive, everything inside experiences about 20 to 25 seconds of microgravity. That's precisely the regime where gas and dust behave the way they do in a protoplanetary disk.

The Methodology

Implications and Next Steps

The team recreated the conditions that arise in the planet-forming regions of protoplanetary disks, and demonstrated that this theoretically proposed shear-flow instability can actually occur in reality.

Only microgravity allows scientists to probe the dilute flow regime that mirrors the gas and dust swirling around young stars.

The findings come with a caveat: parabolic flights provide only fleeting windows of weightlessness. Once the instability initiated, the team observed characteristic patterns forming in the particle flow, but they couldn't watch those patterns evolve into fully developed turbulence within the 20-second windows.

That's the next frontier. Capelo's group is now designing an improved experiment intended for the International Space Station, where microgravity persists indefinitely, allowing researchers to observe the complete lifecycle of these instabilities and their role in dust concentration.

Why This Matters

By confirming that shear-flow instabilities can genuinely operate in protoplanetary environments, the experiments give modelers a firmer foundation for simulating planet formation.

Only experiments can reveal the details of dust and gas movement at scales too small to observe directly in nature. The ultimate goal is understanding how our own Solar System—and Earth—crystallized from a simple cloud of gas and dust billions of years ago. This Swiss team just proved a critical chapter of that story is physically real.

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Based on: Scientists Prove a 50-Year-Old Theory About How Planets Form; University of Bern and University of Zurich; Communications Physics (Nature journal).