An exoplanet is any planet found orbiting a star outside our solar system. The first confirmed exoplanets were discovered in the 1990s, and since then astronomers have found several thousand more, ranging from scorching gas giants huddled close to their star to small, rocky worlds sitting in their star’s habitable zone.
Most exoplanets are found indirectly rather than by seeing them outright, since they are far too faint and too close to their bright host stars to photograph easily. The two most productive methods are the transit method, watching for a tiny dip in a star’s brightness as a planet passes in front of it, and the radial velocity method, detecting the slight wobble a planet’s gravity causes in its star.
Missions like Kepler and TESS have turned exoplanet hunting into one of astronomy’s most active fields, and the search has increasingly shifted from simply finding planets to studying their atmospheres for signs of water, and eventually, for signs of life.