Do all gaps in protoplanetary discs host planets?

Vol. 677
10. Planets and planetary systems

Do all gaps in protoplanetary discs host planets?

The Atacama Large Millimeter/submillimeter Array (ALMA) has unveiled numerous protoplanetary disks with a multi-ringed structure, indicating the presence of gaps. Traditionally, these gaps were thought to host young, growing planets that interact with the disk.

This study challenges this assumption by simulating the evolution of such systems over 100 million years. The authors employed N-body simulations, initially assuming the presence of three to seven planets. They took into account pebble and gas accretion, migration, damping of eccentricities and inclinations, disk-planet interactions, and disk evolution, while exploring different values of viscosity.

Interestingly, the results obtained from these simulations are inconsistent with the observed planetary systems. Systems initially containing more than four young planets became unstable, while those with three or four planets ended up with final eccentricities much smaller than what was observed. Additionally, these simulations show the presence of giant planets that orbit too far from the central star.

Consequently, this leads to the conclusion that alternative explanations for the observed gaps are required. They could include pebble growth near condensation zones, zonal flows, self-induced dust traps, or gravitational instabilities.