How planets form is still a very contentious matter and while we have a general idea, the details are still a bit unclear. A French-UK-Australian collaboration created a computer model that might have shone a light on what happens.

Star systems form from giant clouds of dust and gas. The dust turns into pebbles and the pebbles get together to form planetesimals, the primordial cores of planets. In a study, published in the Monthly Notices of the Royal Astronomical Society, the researchers have found a way to go from pebbles to planetesimals.

"Until now we have struggled to explain how pebbles can come together to form planets, and yet we've now discovered huge numbers of planets in orbit around other stars," lead author Dr Jean-Francois Gonzalez, from the Center for Astrophysics Research of Lyon, said in a statement. "That set us thinking about how to solve this mystery."

The simulation shows that turbulent gas clouds create a "dust trap" region where grains of dust slow down and accumulate, allowing pebbles to go from microscopic to asteroid-sized. The researchers thought that these dust traps were only found in a handful of environments, but the simulations have shown these might be very common.

"What we have been able to identify is the key role of the drag of dust on the gas," co-author and Swinburne Dean of Science, Professor Sarah Maddison, stated. “Often in astronomy, the gas tells the dust how to move, but when there is a lot of dust, the dust tells the gas how to move. This effect, known as aerodynamic drag back-reaction, is usually negligible. However, the effect becomes important in dust rich environments, like those found in the planet formation process."

As the dust and gas spin around a star, they move inward under the effect of gravity. The larger dust grains begin to slow down and accumulate, creating the back-reaction seen in the gas that leads to the formation of dust traps.

The researchers are now planning to extend the simulation to see how the dust trap model might explain the subsequent formation of larger and larger objects, including that of planets.