Thus, landers that touched down late in the Martian day have begun their sol count at 0, while those that touch down early in the day began their count at 1.Īlthough NASA lander missions have twice occurred in pairs, no effort was made to synchronize the sol counts of the two landers within each pair. Generally speaking, the choice between counting from Sol 0 or Sol 1 has been made so that Sol 1 would be the first sol with 'meaningful' or 'useful' lander operations. Mars Pathfinder and the two Mars Exploration Rovers instead defined touchdown as 'Sol 1'. The two Viking landers, Mars Phoenix, Mars Science Laboratory rover Curiosity, InSight, and Perseverance rover projects all counted the sol of touchdown as 'Sol 0'. When a NASA spacecraft lander begins operations on Mars, the passing Martian days (sols) have been tracked using a simple numerical count. The solar day lasts longer because Mars's rotation is the same direction as its orbital motion. The sidereal rotational period of Mars-its rotation compared to the fixed stars-is 24 hours, 37 minutes and 22.66 seconds. The average duration of the day-night cycle on Mars - i.e., a Martian day - is 24 hours, 39 minutes and 35.244 seconds, equivalent to 1.02749125 Earth days. The sol was adopted in 1976 during the Viking Lander missions and is a measure of time mainly used by NASA when, for example, scheduling the use of a Mars rover.

A Martian year is approximately 668 sols, equivalent to approximately 687 Earth days or 1.88 Earth years.

It is approximately 24 hours, 39 minutes, 35 seconds long. It is one of several units for timekeeping on Mars.Ī sol is slightly longer than an Earth day. A sol is the apparent interval between two successive returns of the Sun to the same meridian (sundial time) as seen by an observer on Mars. Sol (borrowed from the Latin word for sun) is a solar day on Mars that is, a Mars-day.

Sol by Murat Gültekingil