Space dust might provide insight about the birth of planets

A recent lab experiment shows that electrostatic forces might be the solution to solving the “bouncing barrier” problem.

Typically, planets are born when dust particles gather in a protoplanetary disk in the proximity of a young star.

The problem

One of the main problems of the study of planetary formation is the bouncing barrier, which is a term used for the cumulation of dust particles that ultimately leads to the formation of a new planet. 

However, electric charge provides additional stickiness that is required by such cosmic motes for clumps to continuously grow, according to the scientific report that was published on December 9 in Nature Physics.

Testing the hypothesis

In order to confirm the explanation, vigorous shaking of thousands of small glass beads and catapulting them at over 100 meters was required. These conditions were supposed to mimic the birthplaces of planets, protoplanetary disks.

Protoplanetary disks, which are essentially a mixture of dust and gas, are the place where seeds of planets collide and stick together, gaining more and more mass. Simulations and experiments show that, once the size of such particles reaches about a millimeter, their growth ceases because they begin bouncing off one another instead of sticking, and this prevented the progress of planetary formation simulations.

It turns out that the dust particles can somehow overcome the bouncing barrier, therefore resulting in a cosmos with a great variety of worlds scattered around.

Experimental astrophysicist Tobias Steinpilz of the University of Duisburg-Essen in Germany said:
“We see exoplanets so there must be a way to get bigger particles”.

Steinpilz and his colleagues began the process of forming counterparts of planetary seeds. They used glass beads instead of protoplanetary dust grains, and all of those were less than one millimeter wide. The collision of those beads would simulate colliding dust particles in a makeshift protoplanetary disk. However, Steinpilz evidentiated one potentially fatal issue: Earth’s gravity, which, according to him, “overpowers everything” they want to see.

The experiment

The scientists launched their experiment via catapult inside a 120 meter tall tower (The Bremen Drop Tower in Germany). They let the device that contained the glass beads, a camera and designated measurement equipment fly upwards and then fall. The flight took about nine seconds and the device proved to be approximately weightless.

Before the launch, researchers shook the beads hard, thus simulating the collisions that particles would experience over time in a protoplanetary disk. This movement provoked a buildup of electric charges in the beads, some negative and some positive. The moment the beads went weightless they formed clumps, some of them consisting of more than a thousand beads because of the electric forces between the charged beads, according to the study.

Results

The results of the study “clearly show that electrostatic forces help grow beyond the bouncing barrier in lab conditions,” astronomer Richard Booth of the University of Cambridge said.  “There is a question of trying to extrapolate these lab conditions to what we see in protoplanetary disks,” he added.

Previous experiments

Steinpilz’s team has also previously completed shaking experiments with basalt spheres, which are known to be similar with the particles in an actual protoplanetary disk. The team found that basalt particles have built up a greater charge than the glass beads have.

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