Here's a breakdown:

* Mercury is the closest planet to the sun. This means it has a much smaller orbital path to travel than Earth.

* Orbital speed is faster for objects closer to the sun. This is due to the sun's gravity being stronger at closer distances.

* Mercury completes one orbit around the sun in just 88 Earth days. This makes a "year" on Mercury significantly shorter than a year on Earth (which is 365.25 days).

While a year on Mercury is short, a day on Mercury is extremely long. It takes 59 Earth days for Mercury to rotate once on its axis. This means that a single day on Mercury is longer than its entire year!