The James Webb Space Telescope (JWST) is a large, space-based infrared observatory that was launched on December 25, 2021. It is a general-purpose observatory designed to answer wide-ranging questions about our cosmic origins. One of its key science goals is to discover and characterize exoplanets, planets orbiting other stars. Due to its immense light-gathering power and infrared sensitivity, JWST promises to revolutionize our understanding of planetary systems outside our own solar system.

JWST has several capabilities that make it uniquely suited for exoplanet observations. Firstly, its 6.5-meter diameter primary mirror and concert of advanced infrared detectors and instruments give it about 100 times the light-gathering power of Hubble. This increased sensitivity allows it to detect fainter objects like exoplanets much further away. Secondly, its infrared vision allows it to peer through the dust clouds that often obscure young planetary systems. Infrared also happens to be the wavelength regime where differences between a planet’s own infrared glow and the infrared light reflected from its star are largest, making exoplanets much easier to distinguish from their parent stars.

With these strengths, JWST opens up entirely new possibilities for exoplanet science. Firstly, it will directly image young, giant exoplanets still in the process of formation around other stars. By studying their atmospheres, temperatures and other characteristics at this crucial stage, we can gain insights into how planets like our own Earth formed in the ancient past. It will search for telltale signs like water vapor, methane and carbon dioxide that could indicate the presence of habitable environments on some exoplanets.

JWST also has the sensitivity to detect and study planets only a few times the mass of Earth, including the discovery and spectroscopy of temperate, Earth-sized exoplanets in the habitable zones of their parent stars. Characterizing the atmospheres of Earth-sized temperate exoplanets is considered the “holy grail” in the search for life elsewhere. Any detection of potential biosignatures like oxygen, ozone or methane not in photochemical equilibrium could suggest biological activity on these distant worlds.

Another important application is JWST’s ability to study exoplanet atmospheres in detail. By observing planets as they transit, or pass in front, of their stars, it can collect starlight that has filtered through their atmospheres. The wavelengths where certain molecules absorb can then be identified in the planet’s transmission spectrum. This technique has already been used by Hubble and Spitzer to analyze the atmospheres of hot Jupiters, but JWST’s greater light-gathering power means it can analyze smaller, more Earth-like planets. Important molecules like water, carbon dioxide and methane can thus be detected, providing insights into the planets’ compositions and climates.

By tracking an exoplanet as it orbits its star and watching how its brightness varies over time, JWST can obtain its thermal emission spectrum. This reveals characteristics like temperature profiles and abundances of different gases in an exoplanet’s atmosphere. Combined with transmission spectroscopy, a more complete understanding of the exoplanet’s atmospheric structure and ingredients can emerge. Precisely characterizing many exoplanet atmospheres is a primary goal of JWST and will revolutionize our understanding of exoplanet diversity.

Another exoplanet technique JWST will advance is direct imaging of young, wide-orbit exoplanets. Hubble has already imaged a handful of massive planets actively forming, but JWST’s greater clarity will allow detection of smaller, cooler planets further from their stars where our own outer planets formed. By studying many such systems, valuable clues about how our own solar system assembled could be uncovered. In short, the James Webb Space Telescope’s tremendous light-gathering power and infrared sensitivity make it uniquely equipped to revolutionize the study of exoplanets. From the first steps of planet formation to the climates and compositions of Earth-sized worlds, JWST promises to transform our understanding of planets beyond our solar system.