Debris Disks in Multi-Planet Systems: Are Our Inferences Compromised by Unseen Planets?

TL;DR

This study examines how the presence of multiple planets in a system can lead to inaccuracies when inferring planetary properties from debris disk features modeled under the assumption of a single planet, highlighting potential misinterpretations.

Contribution

It introduces a two-planet modeling approach to assess the reliability of single-planet inferences from debris disk features in multi-planet systems.

Findings

Single-planet models can misinterpret planet properties by orders of magnitude in extreme cases.

Disk warps are highly susceptible to misinterpretation under single-planet assumptions.

Certain disk features like host star-disk offsets are less affected by multiple planets.

Abstract

Resolved debris disk features (e.g., warps, offsets, edges and gaps, azimuthal asymmetries, radially thickened rings, scale heights) contain valuable information about the underlying planetary systems, such as the posited planet's mass, semi-major axis, and other orbital parameters. Most existing models assume a single planet is sculpting the disk feature, but recent observations of mature planetary systems (e.g., by radial velocity surveys or \textit{Kepler}) have revealed that many planets reside in multi-planet systems. Here we investigate if/how planet properties inferred from single-planet models are compromised when multiple planets reside in the system. For each disk feature, we build a two-planet model that includes a planet b with fixed parameters and a planet c with a full range of possible parameters. We investigate these two-planet systems and summarize the configurations for which assuming a single planet (i.e., planet b) leads to significantly flawed inferences of that planet's properties. We find that although disk features are usually primarily dominated by a single planet, when using single-planet models we are at risk of misinterpreting planet properties by orders of magnitude in extreme cases. Specifically, we are at high risk of misinterpreting planet properties from disk warps; at moderate risk from disk edges and gaps, radially thickened rings, and scale height features; and at low risk from host star-disk center offsets and azimuthal asymmetries. We summarize situations where we can infer the need to use a multi-planet model instead of a single-planet one from disk morphology dissimilarities.