Planet populations inferred from debris discs

Insights from 178 debris systems in the ISPY, LEECH, and LIStEN planet-hunting surveys

¹ Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität Jena, Schillergäßchen 2-3, 07745 Jena, Germany
e-mail: timothy.pearce@uni-jena.de
² Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁴ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁵ Space Telescope Science Institute, 3700 San Martin Drive Baltimore, MD 21218, USA
⁶ ETH Zurich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
⁷ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁸ Observatoire de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁹ Institut für Astrophysik, Friedrich-Hund Platz 1, 37077 Göttingen, Germany
¹⁰ Naval Research Laboratory, Remote Sensing Division, 4555 Overlook Ave. SW, Washington, DS, USA

Received: 22 November 2021
Accepted: 17 January 2022

Abstract

We know little about the outermost exoplanets in planetary systems because our detection methods are insensitive to moderate-mass planets on wide orbits. However, debris discs can probe the outer-planet population because dynamical modelling of observed discs can reveal properties of perturbing planets. We use four sculpting and stirring arguments to infer planet properties in 178 debris-disc systems from the ISPY, LEECH, and LIStEN planet-hunting surveys. Similar analyses are often conducted for individual discs, but we consider a large sample in a consistent manner. We aim to predict the population of wide-separation planets, gain insight into the formation and evolution histories of planetary systems, and determine the feasibility of detecting these planets in the near future. We show that a ‘typical’ cold debris disc likely requires a Neptune- to Saturn-mass planet at 10–100 au, with some needing Jupiter-mass perturbers. Our predicted planets are currently undetectable, but modest detection-limit improvements (e.g. from JWST) should reveal many such perturbers. We find that planets thought to be perturbing debris discs at late times are similar to those inferred to be forming in protoplanetary discs, so these could be the same population if newly formed planets do not migrate as far as currently thought. Alternatively, young planets could rapidly sculpt debris before migrating inwards, meaning that the responsible planets are more massive (and located farther inwards) than debris-disc studies assume. We combine self-stirring and size-distribution modelling to show that many debris discs cannot be self-stirred without having unreasonably high masses; planet- or companion-stirring may therefore be the dominant mechanism in many (perhaps all) debris discs. Finally, we provide catalogues of planet predictions and identify promising targets for future planet searches.