Final answer:
To differentiate exoplanet transit depth results from those caused by asteroids or comets, astronomers rely on multiple consistent transit observations, Doppler shift detections, and the possible discovery of additional planets in a multi-planet system.
Step-by-step explanation:
To ensure that transit depth results are from exoplanets and not asteroids/comets, astronomers typically measure three or four evenly spaced transits. These observations, showing a slight drop in a star's brightness, must be consistent in depth and timing to suggest a planet. Further confirmation of an exoplanet can come from detecting a Doppler shift with the same period as the transits using ground-based telescopes. Additionally, discovering a planetary system around the same star could corroborate the transit data.
However, confirming Earth-sized planets remains challenging due to limitations in ground-based telescopic technology. The use of space-based observatories like the NASA Kepler space telescope, however, has greatly enhanced the capability to discover smaller exoplanets. The transit technique also provides information about the size of the planet relative to the star, especially if the star's size is known. Repeated transits can reveal the planet's orbital period and distance from the star through Kepler's laws, which is more easily observed for larger planets.
In summary, multiple consistent transits, detection of variations in stellar velocity (Doppler shifting), and finding additional planets within the same system are keys to differentiating between exoplanet transits and those caused by other objects like asteroids or comets.