What is an exoplanet?

The first exoplanet found orbiting a Sun-like star, 51 Pegasi b, was announced in 1995 by Michel Mayor and Didier Queloz, who shared the 2019 Nobel Prize in Physics for it. NASA’s count of confirmed exoplanets passed 5,000 in 2022 and has kept rising, with missions such as Kepler and TESS finding thousands. Most are detected indirectly, by the dip in starlight as a planet passes in front of its star or the wobble it causes. Exoplanets range from scorching “hot Jupiters” to rocky worlds in the habitable zone where liquid water might exist. The James Webb Space Telescope now studies some of their atmospheres.