How Astronomers Find Exoplanets

Five main techniques dominate exoplanet discovery. Each one catches a different corner of the parameter space, and none finds every kind of planet.

1. Transit method

When a planet crosses in front of its star from our viewpoint, the star's light dips slightly. Repeated dips at a fixed period reveal the planet's radius and orbital period. Kepler and TESS have found most confirmed exoplanets this way. Read the deep-dive on the transit method.

2. Radial velocity

A planet's gravity tugs its star into a small, rhythmic orbit. Precise spectrographs measure the resulting Doppler shift in the star's spectral lines to reveal the planet's period and a minimum mass. See our full radial velocity article.

3. Direct imaging

Coronagraphs and starshades suppress the star's overwhelming glare so that light from a nearby planet can be photographed directly. It works best on young, wide-orbit giant planets that still glow warmly in the infrared. Explore direct imaging.

4. Gravitational microlensing

When a foreground star and its planet pass in front of a more distant background star, their gravity bends and briefly magnifies the background light. The shape of the brightening curve reveals a planet's mass and separation. Learn more about microlensing.

5. Astrometry

The very small looped path a star traces on the sky as a planet tugs it can be measured directly. Because astrometry pins down orbital inclination, it can yield a true planet mass. See our astrometry article for the Gaia era.