What is the length of a year on Mars in Earth days?

A year on Mars lasts 687 Earth days because that is the approximate time Mars needs to complete one orbit around the Sun. This is about 1.88 Earth years, so the seasons on Mars last nearly twice as long as those on Earth.

Mars takes longer to orbit the Sun because it travels farther from the Sun than Earth does. Its average distance is about 228 million kilometers, compared with Earth’s roughly 150 million kilometers. Mars also follows a more noticeably elliptical orbit, which makes its seasons unequal in length.

The 687-day figure refers to an Earth-day comparison, not the length of a Martian day. A Martian solar day, called a sol, lasts about 24 hours, 39 minutes, and 35 seconds. One Martian year contains approximately 668.6 sols, which add up to about 687 Earth days.

This difference matters for spacecraft and rovers. NASA missions track operations by sols, while mission anniversaries and orbital milestones are often described in Earth days. Curiosity, for example, completed one Martian year after 687 Earth days on the surface. Mars’s longer year also means its seasonal climate cycles unfold much more slowly than Earth’s.