Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake. How do Planetary Systems Form?

TL;DR

A 30-40 meter telescope in the northern hemisphere is crucial for advancing our understanding of planet formation by enabling detailed observations of protoplanets and disks in key star-forming regions, complementing existing facilities.

Contribution

This paper advocates for a large northern hemisphere telescope to fill observational gaps and fully exploit synergies with other astronomical facilities in studying planet formation.

Findings

Current facilities lack comprehensive census of forming planets.

Northern hemisphere access is essential for observing key star-forming regions.

A large northern telescope would significantly advance planet formation science.

Abstract

The detection and characterization of protoplanets in protoplanetary disks around young stars is emerging as a transformative field that will redefine our understanding of how planetary systems form. While current facilities have revealed the diversity of mature exoplanets and the complex structures of disks, we still lack the crucial observational link between them: a statistically meaningful census of planets caught in the act of formation. This white paper argues that such a breakthrough requires access to the nearest and most informative star-forming regions, roughly half of which are poorly accessible or entirely unreachable from Cerro Armazones. Although the ELT alone will strongly impact our knowledge of planet formation, its location prevents Europe from fully exploiting the necessary parameter space. A 30-40 m telescope in the northern hemisphere is therefore essential for obtaining diffraction-limited imaging of protoplanets and disks across the entire sky, enabling robust demographics, exploiting synergies with ngVLA, Gaia, and other facilities covering the north, and ensuring that Europe remains at the forefront of the planet-formation revolution in the coming decades.