A young gas giant and hidden substructures in a protoplanetary disk

TL;DR

This study uses high-resolution ALMA and Gaia data to indirectly detect a young gas giant planet in the MP Mus protoplanetary disk, revealing hidden substructures and suggesting such features are more common than previously thought.

Contribution

It provides the first indirect detection of an exoplanet in a protoplanetary disk through combined ALMA and Gaia observations, unveiling hidden substructures at longer wavelengths.

Findings

Detection of an inner cavity and a ring at 10 au in the disk

Hydrodynamic simulations support a gas giant at 1-3 au

Substructures are more prevalent than previously observed

Abstract

The detection of planets in protoplanetary disks has proven to be extremely challenging. In contrast, rings and gaps, usually attributed to planet-disk interactions, have been found in virtually every large protoplanetary (Class II) disk observed at 0.9-1.3 mm with sufficient spatial resolution (5 au). The nearby disk around MP Mus (PDS 66) stands as an exception to this rule, and its advanced age (7-10 Myr) is particularly difficult to reconcile with its apparent lack of substructures. Despite the disk's smooth appearance, Gaia data of MP Mus show a significant proper motion anomaly, signalling the presence of a companion. Here we present ALMA 3 mm observations of the system with comparable high spatial resolution to previous 1.3 mm data. The new observations pierce deeper into the disk midplane and reveal an inner cavity (<3 au) and a ring at 10 au. The disk structure inferred from ALMA observations narrows down the properties of the companion to a gas giant orbiting at 1-3 au, and hydrodynamic simulations further confirm that such a planet can produce the observed cavity. These independent pieces of evidence constitute an indirect but compelling detection of an exoplanet within a protoplanetary disk using Gaia astrometry. MP Mus is the first system in which undetected substructures are revealed thanks to the lower optical depths at longer wavelengths, suggesting that rings and gaps are even more abundant than what is currently believed.