ALMA continuum emission observations of the two systems we used as testbeds for our numerical models, as shown in Huang et al. (2018). Solid and dotted white arcs mark the location of bright rings and dark gaps, respectively, along with their distance from the host star in au. It is likely that a planet is responsible for one or more of the gaps observed in either system. Left: HD 163296, a 12.6 Myr old likely isolated system that features at least two clearly visible gaps at 48 and 86 au. Our models focus on the 20–60 au range, with a planet carving a gap at 48 au. Right: AS 209, a 1 Myr old system in the Ophiuchus region that is rich in annular structures, boasting five rings between 20 and 130 au. This source has been modeled by Zhang et al. (2018), who found that a fit with a single planet at 99 au could reconstruct all five of these rings.