Why does one year on earth have 365 days and one year on Mercury have only 88 days?

One year on Earth has 365 days because it takes that long for the Earth to complete one full orbit around the Sun. In contrast, Mercury is much closer to the Sun and has a shorter orbital path, allowing it to complete a full revolution in just 88 Earth days. Additionally, Mercury's rotation period is very slow, leading to a unique day-night cycle, but the primary reason for the shorter year is its proximity to the Sun and the speed of its orbit.