How long is a Martian day (sol) in Earth hours?

A Martian day, called a sol, lasts about 24.6 Earth hours. More precisely, Mars’s average solar day is 24 hours, 39 minutes, and 35 seconds—roughly 2.75% longer than an Earth day.

The word “sol” was adopted during NASA’s Viking missions in 1976 to distinguish a Martian solar day from an Earth day. Mars rotates at a similar rate to Earth, but its day is slightly longer because of the planet’s rotation and orbital motion relative to the Sun.

A sol is not exactly the same length every day. Mars has a more eccentric orbit than Earth, so the apparent solar day varies somewhat over the Martian year. Mission teams operating Pathfinder, Spirit, Opportunity, Curiosity, and other spacecraft have worked on Mars time, with their schedules shifting about 40 Earth minutes later each day.

A common mix-up is confusing a sol with Mars’s sidereal day, which is about 24 hours, 37 minutes, and 23 seconds. The solar day is the standard used for sunrise-to-sunrise timekeeping.