Newly formed planets continue to interact with their nascent protoplanetary disk. The result is often the formation of annular dust gaps and rings around the planet's orbit. Coincidentally, gaps and rings are frequently observed in large, bright protoplanetary disks. This motivates the exciting possibility that such observations are witnessing ongoing planet formation. If so, modeling planet gaps offers a method to detect planets that are otherwise difficult with other methods.
However, some of the observed disks indicate that dust grains are settled near the disk midplane (e.g. for the dust rings around HL Tau, Pinte et al., 2016). On the other hand, if these rings and gaps are induced by a planet, can the dust grains remain settled?
We make a first attempt at addressing this conundrum in our new paper led by my former summer student Jiaqing Bi (University of Victoria). To this end, we performed 3D simulations of dusty protoplanetary disks with embedded planets. We found that planets easily stir up the dust grains, especially at the gap edges where dust grains do not settle significantly. We attribute this effect to the 3D gas flows induced by gap-opening planets previously identified by Fung & Chiang (2016).
Our result may challenge the planet interpretation of dust gaps and rings in some of the observed protoplanetary disks that indicate dust to be well-settled, such as the disk around HL Tau. However, a recent study by Doi & Kataoka (2021) found `puffed up' dust rings in the disk around HD 163296. Could these be consistent with a gap-opening planet stirring the disk? Stay tune for the next paper in our series!