Tentative co-orbital submillimeter emission within the Lagrangian region L₅ of the protoplanet PDS 70 b

¹ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
e-mail: obalsalobre@cab.inta-csic.es
² European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Vitacura, Santiago, Chile
³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ Laboratoire Lagrange, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
⁵ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁶ Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
⁷ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
⁸ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Received: 23 March 2023
Accepted: 14 June 2023

Abstract

Context. High-spatial resolution Atacama Large Millimeter/submillimeter Array (ALMA) data have revealed a plethora of substructures in protoplanetary disks. Some of those features are thought to trace the formation of embedded planets. One example is the gas and dust that accumulated in the co-orbital Lagrangian regions L₄/L₅, which were tentatively detected in recent years and might be the pristine material for the formation of Trojan bodies.

Aims. This work is part of the TROY project, whose ultimate goal is to find robust evidence of exotrojan bodies and study their implications in the exoplanet field. Here, we focus on the early stages of the formation of these bodies by inspecting the iconic system PDS 70, the only confirmed planetary system in formation.

Methods. We reanalyzed archival high-angular resolution Band 7 ALMA observations from PDS 70 by doing an independent imaging process to look for emission in the Lagrangian regions of the two detected gas giant protoplanets, PDS 70 b and c. We then projected the orbital paths and visually inspected emission features at the regions around the L₄/L₅ locations as defined by ±60° in azimuth from the planet position.

Results. We found emission at a ~4-σ level (~6-σ when correcting from a cleaning effect) at the position of the L₅ region of PDS 70 b. This emission corresponds to a dust mass in a range of 0.03–2 M_Moon, which potentially accumulated in this gravitational well.

Conclusions. The tentative detection of the co-orbital dust trap that we report requires additional observations to be confirmed. We predict that we could detect the co-orbital motion of PDS 70 b and the dust presumably associated with L₅ by observing again with the same sensitivity and angular resolution as early as February 2026.