Final answer:
The light curve dips twice per orbit due to both the transit of an exoplanet across its host star and the subsequent eclipse of the exoplanet by the star, which are observed as decreases in the star's brightness. Confirmed discoveries require repeated observations of these dips at regular intervals, possibly complemented by a Doppler shift in the star's spectrum corroborating the exoplanet's presence.
Step-by-step explanation:
The light curve of a transiting exoplanet can often show two dips per orbit because the exoplanet transits its star, and the star eclipses the exoplanet. This occurrence is seen when the orbital plane of the planet is such that it crosses in front of its host star, causing a slight dimming of the star's brightness. This event, known as a transit, is observed as the first dip in the light curve. The second dip can happen when the exoplanet is eclipsed by the star during its orbit. These events are evidence of an exoplanet's presence as they cause a temporary decrease in the star's observed light intensity and are typically of similar depth if caused by the same planet. Astronomers consider a transiting exoplanet discovered when repeated light curve dips of similar depth and regular intervals are observed, eliminating the chance of false positives from other astronomical or instrumental sources. Also, the discovery can be further confirmed through other methods such as the detection of a Doppler shift in the star's spectrum that matches the transit period, especially in multi-planet systems. The light curve of a transiting exoplanet, which represents the brightness of the star over time, typically shows a dip when the exoplanet passes in front of its host star. This is known as a transit event. If there are two dips per orbit, it suggests that the star itself is also eclipsing the exoplanet, causing an additional decrease in brightness. This phenomenon is referred to as a secondary eclipse or occultation, where the exoplanet is temporarily hidden by its host star. Therefore, option (c) accurately describes the situation where the exoplanet transits its star, and the star also eclipses the exoplanet, leading to two dips in the light curve.