Why do different planets have different orbital periods?

Different planets have different orbital periods due to their varying distances from the Sun and their orbital speeds.

The orbital period of a planet, which is the time it takes for it to complete one orbit around the Sun, is determined by two main factors: its distance from the Sun and its orbital speed. The further a planet is from the Sun, the longer its orbital path is, and therefore the longer it takes to complete one orbit. This is due to Kepler's Third Law of Planetary Motion, which states that the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit (the average distance from the Sun).

In addition to distance, the speed at which a planet orbits the Sun also affects its orbital period. Planets closer to the Sun are pulled by a stronger gravitational force, causing them to move at higher speeds. Conversely, planets further away experience a weaker gravitational pull and therefore move more slowly. This is explained by Newton's Law of Universal Gravitation, which states that the force between two objects decreases as the distance between them increases.

For example, Mercury, the planet closest to the Sun, has an orbital period of about 88 Earth days, while Neptune, the furthest planet, takes approximately 165 Earth years to complete one orbit. This is because Neptune is much further from the Sun than Mercury and therefore has a much longer orbital path and a slower orbital speed.

In conclusion, the orbital period of a planet is determined by its distance from the Sun and its orbital speed. The further a planet is and the slower it moves, the longer its orbital period will be.