If you moved to Mars tomorrow, your birthday would suddenly become a rare event. You’d have to wait nearly two Earth years just to blow out the candles once. It sounds like a sci-fi trope, but the actual mechanics of Martian timekeeping are a headache for NASA engineers and a fascination for anyone looking at the night sky. So, how many days are in a year in Mars? The short answer is 687 Earth days. But honestly, that’s where the simplicity ends.
Mars doesn’t follow our rules. On Earth, we’ve got it easy with our 24-hour cycle and a 365-day lap around the Sun. Mars is a different beast entirely. It’s further out in the solar system, meaning it has a much longer track to run.
The Sol vs. The Day: Why Martian Time is Tricky
You can’t just say "days" when you’re talking about the Red Planet. Scientists at the Jet Propulsion Laboratory (JPL) use the term Sol. A Sol is a Martian solar day. If you were standing on the surface of Gale Crater, a Sol is the time it takes for the Sun to return to the exact same spot in the sky.
It’s longer than an Earth day. Specifically, a Sol lasts about 24 hours, 39 minutes, and 35 seconds.
That 40-minute difference feels like nothing at first. It’s a long lunch break. But for the teams operating rovers like Curiosity or Perseverance, it’s a logistical nightmare. Because the Martian day is longer, "noon" on Mars drifts later and later against Earth time every single day. Eventually, the rover drivers find themselves starting their shifts in the middle of the night in Pasadena just to align with the sunlight on Mars.
When we calculate how many days are in a year in Mars, we have to decide which "day" we mean. If you count by Martian Sols, a year is roughly 668 Sols. If you count by standard 24-hour Earth days, it’s about 687.
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The Elliptical Wobble: Mars Isn't a Perfect Circle
Our orbit around the Sun is pretty close to a circle. It’s not perfect, but it’s consistent enough that our seasons are relatively balanced. Mars is eccentric. Not "quirky" eccentric—mathematically eccentric. Its orbit is an elongated oval.
This eccentricity means Mars’s distance from the Sun changes drastically. At its closest point (perihelion), it’s about 128 million miles away. At its furthest (aphelion), it swings out to 154 million miles.
This has a massive impact on the length of the seasons. On Earth, seasons are roughly 90 days each. On Mars, they are wildly lopsided. The Martian spring in the northern hemisphere lasts about 194 Sols, while autumn is a measly 142 Sols. If you’re planning a colony there, you’d better hope you like the long winters.
Why the 687 Figure Matters for Space Travel
When NASA planners talk about how many days are in a year in Mars, they aren’t just doing a trivia exercise. This number dictates every "launch window." Because Earth and Mars are moving at different speeds on different tracks, they only get close to each other once every 26 months. This is called "opposition."
If you miss that 26-month window? You're stuck waiting. You can’t just point a rocket at Mars and fire; you have to aim for where Mars will be nearly 700 days into its journey.
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The Math Behind the Martian Calendar
We use the Gregorian calendar. Mars doesn't have an official one yet, but several have been proposed by experts like Michael Allison of the Goddard Institute for Space Studies. The most common "academic" calendar is the Darian calendar.
Instead of 12 months, the Darian calendar suggests 24 months. Each month would be about 27 or 28 Sols. Imagine trying to keep track of that on your iPhone.
Actually, the "leap year" situation on Mars is even more complex than ours. On Earth, we add a day every four years because our year is roughly 365.25 days. On Mars, the year is about 668.6 Sols. To keep the calendar from drifting, you’d need a complex pattern of leap years—specifically, six leap years in every ten-year cycle.
Gravity, Speed, and Kepler’s Laws
Why is it so much longer? It’s basically down to Johannes Kepler’s Third Law of Planetary Motion. The law states that the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
Basically: The further away you are, the slower you travel and the longer the path you have to take.
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Mars travels at an average speed of about 53,979 miles per hour. Earth zips along at about 66,615 miles per hour. So Mars is slower and has a bigger loop to complete. That’s the recipe for a 687-day year.
Living on Martian Time: The Human Factor
We’ve seen what happens when humans try to live on Martian time. During rover missions, staff often wear "dual-time" watches. One shows Earth time, the other shows the Sol.
Psychologically, the 24-hour, 40-minute cycle is brutal. It’s just long enough to mess with your circadian rhythm. It’s like living in a permanent state of jet lag where you move one time zone west every single day. Within two weeks, your "daytime" has flipped entirely.
Essential Takeaways for Your Martian Curiosity
If you're tracking the Red Planet or just curious about the celestial mechanics, here are the raw numbers you need to remember:
- One Martian Year = 687 Earth Days.
- One Martian Year = 668.6 Martian Sols.
- One Sol = 24 hours, 39 minutes, 35 seconds.
- The seasons on Mars are nearly double the length of Earth's but vary in duration due to the orbital oval.
Understanding how many days are in a year in Mars is the first step in grasping just how alien our neighbor really is. It’s not just a "smaller Earth." It’s a world that operates on a fundamentally different clock.
If you want to track where Mars is in its current year right now, you can check the Mars24 Sunclock provided by NASA. It gives you the current "Mission Time" for various landing sites. It’s a great way to see just how out of sync our two worlds are at any given moment. For those interested in the future of colonization, looking into the Darian Calendar proposals offers a fascinating glimpse into how we might one day structure a Martian society.
Next Steps for Enthusiasts:
- Download the NASA Mars24 software to see real-time Sol tracking.
- Research the 2026 Mars Launch Window to see when the next fleet of explorers is scheduled to depart based on the 687-day orbital cycle.
- Compare the "eccentricity" of Mars to other planets like Venus to see why Mars has such unique seasonal shifts.