Abstract

We know little about the outermost planets in exoplanetary systems, because current detection techniques are insensitive to moderate-mass planets on wide orbits. However, insight can be gained by using debris discs (extrasolar equivalents of our Asteroid and Kuiper Belts) as indirect probes of planetary systems. This approach has been widely applied over the past few decades, allowing us to infer the presence and properties of unseen planets from their gravitational influence on observed debris. Now, with the advent of modern equipment such as JWST , we are finally in the era where direct detections of these long-predicted planets should be possible. In this talk I review the rich and exciting field of planet-debris interactions, outlining its historical evolution, the diverse techniques for constraining planets from debris, and how it is likely to develop in future. I discuss what the approach teaches us about planet populations, debris discs, and planet formation and evolution mechanisms (including my own work), as well as the insights that we would gain from future detections (or non-detections) of expected planets. The talk should be accessible to those without detailed knowledge of planetary system dynamics or debris-evolution mechanisms; instead I aim to summarise what we can infer about planets from debris observations, as well as the strengths and limitations of this approach.