Mars sol facts for kids
A sol is what we call a day on the planet Mars. It's like saying "Mars-day" instead of "Earth-day." The word "sol" comes from the Latin word for sun.
A sol is measured by how long it takes for the Sun to appear in the same spot in the Martian sky. This is similar to how we measure a day on Earth.
A Mars-day is a little bit longer than an Earth-day. It lasts about 24 hours, 39 minutes, and 35 seconds. A Martian year is much longer than an Earth year. It has about 668 sols. This is equal to about 687 Earth days, or almost two Earth years.
Scientists at NASA started using the term "sol" in 1976. This was during the Viking Lander missions to Mars. They use it to keep track of time for Mars rovers and other spacecraft.
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How Long is a Mars Day?
The average length of a day and night cycle on Mars is 24 hours, 39 minutes, and 35.244 seconds. This is just a bit longer than an Earth day. It's about 1.027 Earth days.
Mars also spins around itself, just like Earth. This spin, compared to distant stars, takes 24 hours, 37 minutes, and 22.66 seconds. The solar day is longer because Mars spins in the same direction it moves around the Sun.
Keeping Time for Mars Missions
When a NASA spacecraft lands on Mars, scientists start counting the Martian days. They use a simple number count for each sol.
For example, the Viking landers, Mars Phoenix, Mars Science Laboratory rover Curiosity, InSight, and Perseverance rover all started counting from "Sol 0." This means the day they landed was Sol 0.
However, the Mars Pathfinder and the two Mars Exploration Rovers started counting from "Sol 1." The choice depends on when the lander arrived. If it landed late in the Martian day, they used Sol 0. If it landed early, they used Sol 1. This way, Sol 1 was always the first day with important work.
Even when two missions landed around the same time, their sol counts were not matched. For example, Spirit and Opportunity both started at "Sol 1." This meant their calendars were about 21 sols apart.
Special Words for Mars Time
Scientists working on Mars missions have made up some new words. "Yestersol" means the day before on Mars. It's like saying "yesterday" on Earth. This word became very popular during the Mars Exploration Rover Mission.
Other new words include "tosol," which means "today" on Mars. For "tomorrow" on Mars, they might say "nextersol," "morrowsol," or "solmorrow." Scientists also use "soliday" for days off. This helps them adjust to the different Martian schedule.
Converting Mars Time to Earth Time
If people ever live on Mars, they will need to figure out how to use Earth time. In some science fiction stories, like the Mars trilogy by Kim Stanley Robinson, Mars settlers use special watches. These watches stop for about 39 minutes and 40 seconds at midnight. This helps them adjust to the longer Martian day. This idea was also used by Philip K. Dick in his book Martian Time-Slip.
For the Spirit mission, a special watchmaker made mechanical watches for the crew. These watches kept Mars time very accurately. In 2022, the watch company Omega started selling similar digital-analog watches to the public.
See also
In Spanish: Día marciano para niños
