How does the transit method detect extrasolar planets?

The transit method detects extrasolar planets by measuring periodic drops in a star's brightness. This occurs when a planet’s orbit is oriented in space such that the planet passes directly between its host star and a telescope, effectively occulting a small portion of the star's disk.123

These observations, often analyzed via a light curve, provide critical data about the planet, including its size and orbital period. When combined with radial velocity measurements, astronomers can determine the planet's mass and density, which helps identify its likely composition. Furthermore, spectroscopic studies of the transit can reveal the presence of specific gases in the planet's upper atmosphere.124

The transit technique is most sensitive to large planets orbiting close to their stars. This method has been instrumental in major discovery missions, such as the Kepler mission and the Transiting Exoplanet Survey Satellite (TESS), which have identified thousands of planetary candidates.123