Exoplanet

An exoplanet is a planet orbiting a star beyond the Sun or a stellar remnant. Exoplanets range from rocky worlds to gas giants and can orbit in systems unlike our own.

Transit method: A method that detects a planet when it passes in front of its star and dims the star’s light. Repeated dips in starlight reveal a planet’s orbital period and relative size.
Planetary system: A star or stellar remnant together with the planets and other bodies gravitationally bound to it. An exoplanet is one member of a planetary system beyond the Solar System.
51 Pegasi b: An exoplanet orbiting the Sun-like star 51 Pegasi, announced in 1995 as the first confirmed planet around a main-sequence star. Its discovery established that giant planets could orbit close to ordinary stars.
Exoplanet atmosphere: The gaseous envelope surrounding an exoplanet, whose composition and structure can be studied through its light. Atmospheric spectra provide clues to a planet’s temperature, chemistry, and clouds.
Solar System: The Sun and the objects gravitationally bound to it, including eight planets and smaller bodies. Its planets provide the nearby baseline against which exoplanet systems are compared.
Radial velocity method: A method that detects a planet through the periodic motion it induces in its star, measured by Doppler shifts. The star’s wobble provides evidence for planets too small or distant to image directly.
Orbital period: The time an orbiting body takes to complete one revolution around another body. Its measured period helps characterize an exoplanet’s orbit and distance from its star.
Michel Mayor: A Swiss astronomer who co-discovered 51 Pegasi b with Didier Queloz using radial-velocity measurements. His work helped establish the first widely accepted exoplanet around a Sun-like star.
Transmission spectroscopy: A technique that analyzes starlight filtered through a planet’s atmosphere during a transit. It can identify atmospheric molecules by their wavelength-dependent absorption.
Free-floating planet: A planetary-mass object that does not orbit a star or stellar remnant. Unlike an exoplanet as defined here, it has no host star or remnant.

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