To calculate Mercury's orbital period, we can use Kepler's Third Law of Planetary Motion, which states that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun. Mathematically, this is represented as P² = a³, where P is the orbital period in Earth years and a is the average distance in astronomical units (AU). In Mercury's case, its orbital period is approximately 0.24 Earth years, or about 88 Earth days.