Interactions between planets and debris disks: the role of disk gravity

Planetary systems generally contain not only planets, but also belts of debris similar to the Solar System's asteroid and Kuiper belts. High-resolution observations of such exo-Kuiper belts, or debris disks, frequently reveal complex morphologies such as gaps or double-ringed structures, spirals, and warps. Most existing dynamical models for explaining such morphologies focus on the role of (invoked) massive perturbers such as planets and stellar companions, ignoring the gravitational effects of the disk itself. This assumption, however, may not always be justified, especially in view of observations that debris disks could contain tens of Earth masses in large planetesimals. Here, I will present results showing that the (self-)gravitational potential of debris disks can be important for producing some of the observed disk structures. Namely, I will demonstrate that the long-term (i.e., secular) interaction between a single planet and an external, self-gravitating debris disk can lead to the formation of a wide gap within the disk. The proposed mechanism is based on the occurrence of secular resonances within the disk, which is found to be quite robust even when the disk is less massive than the planet (contrary to what may be naively expected). I will also show that the same mechanism may lead to the launching of a long, one-armed spiral arm beyond the gap, while at the same time the planet's orbital eccentricity is damped. This circularization occurs in the absence of planet-planetesimal scattering. Applications of these results for explaining observations will be discussed at length, focusing on three systems: HD 107146, HD 92945, and HD 206893. I will also discuss the implications of these findings for inferring the dynamical masses of debris disks, as well as the orbital parameters and evolution of planets in debris disk-hosting systems.