exoplanet

An exoplanet, or extrasolar planet, is a planet that orbits a star other than the Sun. Since the first confirmed detections in the 1990s, thousands of exoplanets have been identified, revealing a remarkable diversity in size, composition, and orbital configurations. Exoplanet science seeks to understand how planets form, evolve, and produce the wide range of environments observed across the galaxy, including those that might harbor life.

Most exoplanets are discovered indirectly, through methods such as radial velocity, which measures the star’s wobble due to a planet’s gravity; and the transit method, which detects periodic dips in starlight as a planet passes in front of the star. Other techniques include direct imaging, gravitational microlensing, and timing variations in pulsars or eclipsing binaries. Space missions like Kepler and its successor K2, and the Transiting Exoplanet Survey Satellite (TESS), have driven the exponential growth in known exoplanets, while ground-based spectrographs such as HARPS have refined mass measurements.

Exoplanets vary widely in size and composition, from Earth-sized rocky worlds to gas giants larger than Jupiter. Early discoveries included hot Jupiters—large planets in very close orbits—which surprised theories of planet formation. The Kepler mission showed that small, rocky planets are common, and systems with multiple planets are common as well. Notable systems include the TRAPPIST-1 chain of seven rocky planets, and Proxima Centauri b, which orbits the nearest star to the Sun and lies in its star’s habitable zone.

Research continues with atmospheric characterization, using transmission spectroscopy to detect chemical signatures in planet atmospheres. Biosignature detection remains a key goal but has not yet produced a confirmed result. Future facilities, including the James Webb Space Telescope, the Roman Space Telescope, and next-generation ground-based observatories, aim to further characterize exoplanets and their potential habitability.