Final answer:
The discovery of transiting exoplanets involves observing three transits where an exoplanet passes in front of its host star, causing a consistent dip in the star's brightness. Comprehensive observations by telescopes like Kepler, especially from space, validate these transits and aid in measurements of the exoplanet's characteristics when combined with other methods like the Doppler technique.
Step-by-step explanation:
The discovery of transiting exoplanets is confirmed by observing a series of three transits, which show a slight drop in the brightness of a host star due to a planet crossing in front of it. Initial transits require confirmation because other factors may imitate a transit signal. Once a third transit is observed, with similar depth and consistent timing with the previous two, the existence of an exoplanet is confirmed. This method benefits greatly from space-based observatories such as the Kepler Space Telescope, which operated above the distortions of Earth's atmosphere.
The transit method also provides the size of the exoplanet relative to the host star, and when combined with the Doppler technique, which estimates the planet's mass, scientists can calculate the exoplanet's average density. This provides insights into the composition of the exoplanet. For example, the exoplanet orbiting the star HD 209458 was discovered to be similar to Jupiter or Saturn given its size and mass.