Transitional disks , protoplanetary disks with deep and wide central gaps , may be the result of planetary sculpting .
By comparing numerical planet-opening-gap models with observed gaps , we find systems of 3–6 giant planets are needed in order to open gaps with the observed depths and widths .
We explore the dynamical stability of such multi-planet systems using N -body simulations that incorporate prescriptions for gas effects .
We find they can be stable over a typical disk lifetime , with the help of eccentricity damping from the residual gap gas that facilitates planets locking into mean motion resonances .
However , in order to account for the occurrence rate of transitional disks , the planet sculpting scenario demands gap-opening-friendly disk conditions , in particular , a disk viscosity \alpha \lesssim 0.001 .
In addition , the demography of giant planets at \sim 3 - 30 AU separations , poorly constrained by current data , has to largely follow occurrence rates extrapolated outward from radial velocity surveys , not the lower occurrence rates extrapolated inward from direct imaging surveys .
Even with the most optimistic occurrence rates , transitional disks can not be a common phase that most gas disks experience at the end of their life , as popularly assumed , simply because there are not enough planets to open these gaps .
Finally , as consequences of demanding almost all giant planets at large separations participate in transitional disk sculpting , the majority of such planets must form early and end up in a chain of mean motion resonances at the end of disk lifetime .