Facebook
Twitter
Pocket
Reddit
Email
The secret to the formation of planets may lie in ordinary static electricity—the same phenomenon that can make your hair stand on end or give you an electric shock after walking across a carpet.
A new study, published in Nature Astronomy, suggests that static electricity allows tiny dust particles in protoplanetary disks—the rotating platters of gas and dust that form around young stars—to clump together into “pebbles” that are large enough to play a role in the formation of planets.
The image above shows basaltic beads, each measuring 0.55 millimeters, that were used in an experiment, which took place aboard a suborbital rocket.
The findings help resolve a mystery that has shrouded something called the bouncing barrier—the size threshold that particles must reach in order to rely on gravity to join with other particles—says lead author of the study Jens Teiser, an astrophysicist at the University of Duisburg-Essen in Germany.
The dust particles need static electricity to make them “sticky” enough to cluster into pebbles that can form planets.
Only when particles grow larger than this threshold size—roughly a quarter of an inch, depending on conditions—can they eventually join to form rocky “planetesimals,” from about half a mile to 100 miles across, that scientists think then collide within protoplanetary disks to create planets like Earth.
Smaller “dust particles don’t stick together,” Teiser says, unless they have an electrostatic charge.
Static electricity is produced when different objects with an imbalance of positive and negative charges make contact, which results in an electrostatic charge. In this case, the electrostatic charge is generated by collisions between tiny dust particles, which can cause them to either gain electrons or lose electrons, resulting in a negative or a positive charge, respectively. Oppositely charged particles will then attract each other—according to the law of electrostatics—and can clump together to create even larger charged particles, Teiser says.
Teiser and his colleagues suspected this was the case after conducting “tower drop” experiments with tiny basalt particles, in which they observed the behavior of these particles during nine seconds of near-weightlessness. But that wasn’t enough time to reach a conclusion, so in 2022 the researchers performed an experiment onboard a suborbital rocket that launched from Kiruna in northern Sweden, to observe how the particles behaved during six minutes of weightlessness.
During the 2022 launch, described in the latest study, the rocket reached an altitude of about 160 miles, and weightlessness kicked in as the rocket’s payload fell back to Earth. At that point, a particle reservoir aboard the vessel opened, releasing the particles. In some cases, the reservoir was shaken to give the particles electrostatic charge, but in other cases, it was not. Only those particles that had been shaken began to assemble into an aggregate. The largest cluster, shown in the image, was a little more than an inch in length. Teiser says his team of researchers sent four versions of their experiment aloft in the rocket, each with different starting conditions.
The researchers believe their findings suggest that the dust particles in protoplanetary disks need static electricity to make them “sticky” enough to cluster into pebbles that can form planets. They were also able to calculate the maximum average speeds the tiny particles can travel when they collide if they are to create clumps: about a foot and a half per second. Collisions at greater speeds tended to erode the surfaces of large clusters.
The results will be used in models that try to explain how massive planets like our own arise from mere dust. 
Lead image: University of Duisburg-Essen (UDE)
Get the Nautilus newsletter
Cutting-edge science, unraveled by the very brightest living thinkers.
