Exoplanet detection

Exoplanet detection is the use of observations to identify planets orbiting stars beyond the Solar System. Its methods infer planets from their effects on starlight or from light they emit or reflect.

Transit method: A method that detects a planet by measuring the dip in a star’s brightness as the planet passes in front of it. Repeated brightness dips reveal a planet’s orbital period and relative size.
Kepler's laws of planetary motion: Three laws describing how planets orbit the Sun, including their elliptical paths and orbital periods. They connect a planet’s measured period to the scale and shape of its orbit.
Planetary radius: The distance from a planet’s center to its surface or, for a gas giant, its defined atmospheric boundary. Transit depth gives a planet’s radius relative to its star.
51 Pegasi b: An exoplanet orbiting the Sun-like star 51 Pegasi, announced in 1995 as the first planet found around a Sun-like star. Its discovery demonstrated that radial velocity could reveal a close-orbiting giant planet.
Detection bias: A systematic distortion in observed data caused by some objects being easier to detect than others. Short-period, large planets are overrepresented in many surveys.
Radial velocity method: A method that detects a planet through periodic shifts in its star’s spectral lines caused by motion toward and away from Earth. The star’s reflex motion supplies evidence independent of a transit.
Doppler effect: The change in observed wavelength or frequency caused by relative motion between a source and an observer. Radial-velocity measurements use wavelength shifts to track stellar motion.
Minimum mass: The lower bound on a planet’s mass inferred from radial velocity when orbital inclination is unknown. A stellar wobble alone generally measures mass multiplied by an inclination factor.
HD 209458 b: A hot Jupiter that was the first known exoplanet observed transiting its star. Its transit made a planet’s radius measurable and opened a new observational route.
False positive: A result that appears to indicate a phenomenon but is produced by another cause. Eclipsing binary stars and instrumental artifacts can imitate planetary signals.

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