Orbital period

The orbital period of an exoplanet is the time it takes to complete one full orbit around its star, usually measured in days. Most of the exoplanets discovered so far have orbital periods of less than one year.

It’s often one of the first characteristics astronomers determine when a planet is discovered, especially through the transit or radial velocity methods. In the transit method, a planet regularly passes in front of its star from our perspective, causing slight dips in brightness at consistent intervals — these intervals reveal the orbital period. In the radial velocity method, astronomers detect small shifts in the star’s light caused by the planet’s gravitational pull; the timing of these "wobbles" also indicates how long the planet takes to orbit.

The orbital period helps estimate the distance between the planet and its star. In general, shorter orbital periods mean the planet is closer to the star, while longer periods suggest greater distance. This distance directly influences the planet’s temperature. Planets with short periods are typically hotter due to more intense radiation, while those with longer periods tend to be colder.

Exoplanets with orbital periods shorter than one day are called ultra-short-period planets. These worlds are exposed to extreme heat and radiation.