The PAIRS project: a global formation model for planets in binaries

I. Effect of disc truncation on the growth of S-type planets

¹ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
² Instituto de Astrofísica de La Plata, CCT La Plata-CONICET-UNLP, Paseo del Bosque S/N (1900), La Plata, Argentina
³ Department of Space Research & Planetary Sciences, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 15 September 2025
Accepted: 9 January 2026

Abstract

Binary stars are as common as single stars. The number of detected planets orbiting binaries is rapidly increasing thanks to the synergy between transit surveys, Gaia, and high-resolution direct-imaging campaigns. However, global planet formation models around binary stars are still underdeveloped, which limits the theoretical understanding of planets orbiting binary star systems. We introduce the PAIRS project, which aims to build a global planet formation model for planets in binaries and to produce a planet population synthesis to statistically compare theory and observations. In this first paper, we present the adaptation of the circumstellar disc to simulate the formation of S-type planets. The presence of a secondary star tidally truncates and heats the outer part of the circumprimary disc (and vice versa for the circumsecondary disc), limiting the material to form planets. We implemented and quantified this effect for a range of binary parameters by adapting the Bern Model of planet formation in its pebble-based form and for in situ planet growth. We find that disc truncation has a strong impact on reducing the pebble supply for core growth and steadily suppresses planet formation for binary separations below 160 a when all the formed planets more massive than Mars are considered. Moreover, S-type planets tend to form close to the central star with respect to the binary separation and disc truncation radius. Our newly developed model will be the basis of future S-type planet population synthesis studies.