What is the term for a Martian solar day?

A Martian solar day is called a sol. It lasts about 24 hours, 39 minutes, and 35 seconds, making it slightly longer than an Earth day.

The word sol is derived from the Latin word for Sun and describes the interval between two successive times when the Sun reaches the same position in the Martian sky. It is therefore a solar day, rather than Mars's slightly shorter rotation period measured against distant stars.

NASA uses sols to organize rover and lander operations. Mission teams refer to the day of landing as Sol 0, then count upward as the spacecraft conducts science, drives, drills, and communicates. This system was especially important during the Viking missions and remains standard for missions such as Curiosity, InSight, and Perseverance.

Mars takes about 668.6 sols to complete one orbit around the Sun. A sol is not the same as a Martian year, and “sun” is only the source of the term, not the name of the day itself.