🪐 Exoplanet Discovery Calculator

Detecting Exoplanets by Transit

The transit method detects exoplanets by measuring the tiny dip in a star’s brightness as a planet passes in front of it. The transit depth — the fraction of starlight blocked — is (R_planet/R_star)², since the planet blocks an area proportional to its radius squared relative to the star’s disk area.

Not every planet’s orbit is aligned to transit as seen from Earth; the geometric transit probability is approximately R_star / a, where a is the orbital semi-major axis. Larger planets around smaller stars produce deeper, easier-to-detect transits, while planets in wider orbits are both less likely to transit and transit less frequently.