Some exoplanets’ orbits are aligned such that they appear to pass in front of their host stars. This is referred to as an exoplanet transit and results in its host star appearing to become temporarily dimmer. By carefully observing the brightness of exoplanet host stars, it is possible to accurately determine the times of exoplanet transits.
Most exoplanets have constant orbital periods, meaning that their transits always occur at regular intervals. However, some exoplanets have varying orbital periods, resulting in their transits occurring at variable intervals. These variations can be caused by gravitational interactions between planets orbiting the same star, which allow the planets’ masses to be determined. However, variations can also occur if an exoplanet’s orbit is decaying due to tidal interactions with its host star.
Therefore, the study of transit timing variations can teach us much about the architecture and evolution of planetary systems.