Do you know Mars has more leap years than regular years?

Leap years occur when a planet's orbit around the Sun (year) and rotation on its axis (day) do not precisely align. 

Leap years are necessary to ensure that our calendar year corresponds to the solar year, which is the length of time it takes for Earth to complete one orbit around the sun.

This is true for nearly every other planet in our solar system. But Mars experiences more leap years than regular years.

A year on Mars is 668 sols (Martian days) and it takes 668.6 sols to complete one full orbit around the Sun. 

As a result, you would occasionally need to add a sol to help the calendar catch up. 

In ten years, four years would have 668 sols, while six would be leap years with 669 sols.