While the number of exoplanets has surged in recent decades, the exploration of the outer regions of planetary systems has lagged behind, primarily due to the limitations of current detection techniques. A promising, indirect avenue to bridge this gap is offered by debris disks – exoplanetary cousins of our Solar System’s asteroid and Kuiper belts. Debris disks, ubiquitous in planetary systems, encapsulate records of past and ongoing processes, including interactions with planets. Thus, deciphering debris disks serves as a unique lens to unravel the intricacies of planetary system formation, architecture, and evolution, and potentially unveiling hidden planets. In this talk, I review the theoretical landscape of planet-debris disk interactions, tracing its historical evolution and elucidating the diverse methods employed to constrain the presence and parameters of yet-undetected planets within debris-hosting systems. Specifically, I explore the existing theoretical tapestry designed to explicate commonly observed structures in debris disks, highlighting both its strengths and limitations. Emphasizing the often-overlooked role of disk gravity in shaping some of these structures, I then delve deeper into the potential insights that future detections or non-detections of planets, facilitated by instruments such as JWST, can provide regarding planetary systems.

Planetesimal (debris) disks offer valuable insights into the formation, evolution, and architecture of exoplanetary systems. In particular, their substructures – now commonly observed across various wavelengths – provide indirect evidence of dynamical perturbations, such as those from yet-unseen exoplanets. However, most existing studies of planet-debris disk interactions adopt simplified models that treat the disks as swarms of massless planetesimals. This is at odds with observations suggesting that debris disks may contain a few to tens of Earth masses of material. What role do massive debris disks play in their dynamical evolution, and how do they influence interpretations of observed substructures? In this talk, we address these questions using orbit-averaged secular dynamics. We demonstrate that the disk’s gravity can significantly shape both its radial and vertical structure, giving rise to features such as gapped (double-ringed) morphologies, warps, and spiral patterns. Notably, these effects can arise even when the disk is less massive than the perturbing planet, challenging common assumptions. These findings are particularly timely, as JWST observations aim to detect or rule out planetary companions in systems hosting debris disks. Our findings suggest that planetary inferences based on massless disk models may be compromised, underscoring the need for more realistic dynamical treatments.