High-Contrast Imaging of Forming Protoplanets: VLTs, JWST, and the Promise of ELT

TL;DR

This paper reviews recent high-contrast imaging efforts to directly observe forming protoplanets, discusses the importance of upcoming ELT instruments, and proposes methods to better understand planetary formation and evolution.

Contribution

It synthesizes current observational strategies, emphasizes the potential of ELT, and introduces a new approach to estimate the planet mass-to-radius ratio for formation models.

Findings

Low direct detection rate of protoplanets in disks.

Upcoming ELT instruments will significantly enhance observational capabilities.

Proposed method to estimate planet mass-to-radius ratio ($M_p/R_p$).

Abstract

Planet formation remains a fundamentally important yet poorly understood process. Protoplanetary disks, the birthplaces of planetary systems, exhibit a wide range of substructures that are increasingly interpreted as signatures of interactions with forming planets. However, the direct detection rate of protoplanets within these disks remains low, leaving critical gaps in our understanding of the physical mechanisms driving their formation and early evolution. In this chapter, we review recent efforts by the high-contrast imaging community to directly observe forming protoplanets and their immediate environments. These observations aim to provide key constraints on thermal and accretion processes, planetary growth, and the formation of circumplanetary disks and satellite systems. We also propose a path forward for deriving observational estimates of the planet mass-to-radius ratio ($M_p/R_p$), a crucial parameter for distinguishing between competing formation models and understanding the thermal evolution of young planets. Finally, we highlight how upcoming instruments on the Extremely Large Telescope (ELT), with their unprecedented combination of high spatial and spectral resolution, will transform our ability to probe planet formation at the smallest and most critical scales.