# New Frontiers for Terrestrial-sized to Neptune-sized Exoplanets In the Era of Extremely Large Telescopes

## TL;DR

This paper discusses how upcoming extremely large telescopes (ELTs) will revolutionize the detection and characterization of small exoplanets, addressing key questions about their prevalence, composition, and atmospheres around nearby stars.

## Contribution

It provides an overview of the technological challenges and potential of ELTs to detect and study terrestrial to Neptune-sized exoplanets in the coming decade.

## Key findings

- ELTs will enable diffraction-limited imaging of small exoplanets.
- Adaptive optics will improve contrast and stability for exoplanet observations.
- ELTs will facilitate multi-wavelength and all-sky surveys of nearby exoplanets.

## Abstract

Surveys reveal that terrestrial- to Neptune-sized planets (1 $< R <$ 4 R$_{\rm{Earth}}$) are the most common type of planets in our galaxy. Detecting and characterizing such small planets around nearby stars holds the key to understanding the diversity of exoplanets and will ultimately address the ubiquitousness of life in the universe. The following fundamental questions will drive research in the next decade and beyond: (1) how common are terrestrial to Neptune-sized planets within a few AU of their host star, as a function of stellar mass? (2) How does planet composition depend on planet mass, orbital radius, and host star properties? (3) What are the energy budgets, atmospheric dynamics, and climates of the nearest worlds? Addressing these questions requires: a) diffraction-limited spatial resolution; b) stability and achievable contrast delivered by adaptive optics; and c) the light-gathering power of extremely large telescopes (ELTs), as well as multi-wavelength observations and all-sky coverage enabled by a comprehensive US ELT Program. Here we provide an overview of the challenge, and promise of success, in detecting and comprehensively characterizing small worlds around the very nearest stars to the Sun with ELTs. This white paper extends and complements the material presented in the findings and recommendations published in the National Academy reports on Exoplanet Science Strategy and Astrobiology Strategy for the Search for Life in the Universe.