Mars and Earth are dramatically different planets in many respects, including size, atmosphere, and surface conditions. Despite these major differences, the time it takes for the Red Planet to complete a single rotation is surprisingly similar to our own planet’s diurnal cycle. This near-synchronicity in rotation periods makes Mars a fascinating object for both astronomical study and future human exploration.
The Length of the Martian Day
The precise time it takes for Mars to spin once depends on the reference point used for measurement. The true rotational period, known as the sidereal day, is the time required for Mars to rotate 360 degrees relative to the fixed background stars. The Martian sidereal day is 24 hours, 37 minutes, and 22.663 seconds long. This value represents the fixed physical spin rate of the planet itself.
The measurement most relevant to daily life is the solar day, which is the time from noon to noon, and on Mars, this is officially called a “Sol.” A Sol is slightly longer than the sidereal period because the planet is also moving along its orbit around the Sun. During the time it takes to rotate once, Mars has moved a short distance, meaning it must rotate an extra fraction of a degree to bring the Sun back to the same position in the sky. The average length of a Martian Sol is 24 hours, 39 minutes, and 35.244 seconds.
Comparing Mars and Earth Rotation
The solar day (Sol) on Mars is only about 40 minutes longer than the 24-hour average solar day on Earth. This similarity in rotational speed is unusual when considering the other planets in our solar system. Earth’s sidereal day, the time it takes to complete one true rotation, is 23 hours, 56 minutes, and 4.09 seconds. Mars’s sidereal period is only about 41 minutes longer than Earth’s.
This comparable rotation rate yields similar effects on the two planets, such as the Coriolis force, which influences the circulation patterns of the atmosphere. The rotational period also affects a planet’s oblateness. Planets that spin much faster, like Jupiter, are significantly more flattened than both Mars and Earth. The rotational axis of Mars is tilted at 25.2 degrees, a value very close to Earth’s 23.5 degrees, which is why both planets experience seasons.
Timekeeping on Mars
The measurement of the Sol is of practical significance for scientists and engineers managing robotic missions on the Martian surface. Space agencies like NASA adopt the Sol as the primary unit of time for planning rover and lander operations. Mission logs track events by the Sol count, with Sol 0 typically marking the day the spacecraft successfully lands. Using the Sol ensures that mission activities, such as driving or collecting solar power, are synchronized with the local Martian daylight hours.
Because the Martian day is nearly 40 minutes longer than an Earth day, ground control teams must adjust their work schedules daily to remain on “Mars time.” This means that the teams start their shifts approximately 40 minutes later each successive Earth day, allowing them to communicate with the rover during its active period. This practice, often referred to as “Mars-shifting,” can be disruptive to the personal lives of the personnel, who essentially experience a form of perpetual jet lag. Despite the logistical challenges, synchronizing operations to the Sol is the most efficient way to maximize data collection and mission efficiency.