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 |