An exoplanet, or extrasolar planet, is a planet that orbits a star outside of our solar system. The discovery of exoplanets has revolutionized our understanding of the universe, confirming that planets are common throughout the galaxy. These distant worlds come in a wide variety of sizes and compositions, from massive gas giants larger than Jupiter to small, rocky planets similar to Earth. Some exoplanets, known as 'rogue planets,' do not orbit a star at all and wander through space on their own.
While the idea of other worlds has been speculated about for centuries, the first confirmed detection of an exoplanet occurred in 1992, with the discovery of planets orbiting a pulsar. The first exoplanet found orbiting a sun-like star, 51 Pegasi b, was detected in 1995. The field of exoplanet science exploded in the 2000s and 2010s, largely thanks to space-based observatories that could detect the faint signals of these distant worlds. These discoveries have transformed exoplanet studies from a niche field into a major area of astronomical research.
The discovery of thousands of exoplanets has been driven by dedicated space missions, most notably NASA's Kepler Space Telescope and its successor, the Transiting Exoplanet Survey Satellite (TESS). These missions have primarily used the transit method, which detects the slight dimming of a star's light as a planet passes in front of it. Other detection methods include radial velocity (detecting the 'wobble' of a star caused by a planet's gravitational pull) and direct imaging. The ongoing study of exoplanets, particularly with the advanced capabilities of the James Webb Space Telescope, is a key part of the search for habitable worlds and signs of life beyond Earth.