An exoplanet is any planet that orbits a star other than the Sun. Over 5,700 exoplanets have been confirmed as of 2026, ranging from gas giants larger than Jupiter to rocky worlds smaller than Earth. JWST is revolutionising exoplanet science by directly imaging them and analysing their atmospheres.
Understanding Exoplanet
How Exoplanets Are Found
The transit method detects the tiny dip in a star's brightness (typically 0.01–1%) when a planet passes in front of it. This reveals the planet's size and orbital period. The radial velocity method measures the star's back-and-forth motion caused by the planet's gravity, revealing the planet's mass. Combining both gives density, which indicates whether a planet is rocky, gaseous, or icy.
JWST's Role
JWST transforms exoplanet science in two ways. First, its NIRSpec and NIRISS instruments perform transit spectroscopy — analysing starlight that passes through a planet's atmosphere during transit to identify molecules (H₂O, CO₂, CH₄, NH₃). Second, NIRCam's coronagraph can directly image young, hot exoplanets by blocking the parent star's light. In 2022, JWST directly imaged HIP 65426 b, a gas giant 385 light-years away.
Notable Exoplanets
| Planet | Distance | Type | Significance |
|---|---|---|---|
| Proxima Centauri b | 4.24 ly | Rocky, habitable zone | Nearest known exoplanet |
| TRAPPIST-1 system | 40 ly | 7 rocky planets | 3 in habitable zone — JWST priority target |
| K2-18 b | 124 ly | Sub-Neptune, habitable zone | JWST detected CO₂ and possible biosignatures |
| HIP 65426 b | 385 ly | Gas giant | First exoplanet directly imaged by JWST |