Ever looked up at that tiny orange dot in the night sky and wondered why we haven't just moved there yet? Well, one of the biggest headaches for NASA isn't just the lack of oxygen—it's the calendar.
If you moved to the Red Planet tomorrow, you’d basically stop aging. Okay, not literally, but you’d only get to blow out birthday candles once every two Earth years. That’s because Mars takes 687 Earth days to orbit the Sun.
Honestly, that’s a long time to wait for a "Happy Birthday" text. It’s about 1.88 Earth years, to be precise. But "687 days" is just the short answer. The reality of how Mars moves through space is a lot more chaotic and, frankly, kind of fascinating.
Why Mars is Such a Slowpoke Compared to Earth
Basically, it comes down to distance and speed. Mars is the fourth rock from the Sun, sitting at an average distance of about 142 million miles (228 million kilometers). For context, Earth is only 93 million miles away.
Because Mars is further out, it has a much longer "track" to run. But there's a second reason it takes so long: gravity.
Johannes Kepler figured this out back in the 1600s with his Laws of Planetary Motion. The Sun's gravitational pull gets weaker the further away you get. Since the pull is weaker on Mars, the planet doesn't need to move as fast to stay in orbit. While Earth zips through space at roughly 67,000 mph, Mars is a bit more chill, cruising at about 54,000 mph.
Combine a longer path with a slower speed, and you get a year that feels like it’s dragging its feet.
Sols vs. Days: Keeping Time on a Different World
When we talk about "687 days," we are talking about Earth days (24 hours). But if you’re a rover like Curiosity or Perseverance sitting on the surface, you’re measuring time in Sols.
A "Sol" is a Martian solar day. Since Mars rotates on its axis slightly slower than Earth, a Sol is about 24 hours and 39 minutes long. Those extra 39 minutes might not sound like much, but they add up.
In a single Martian year, there are only about 668 Sols.
Scientists at the Jet Propulsion Laboratory (JPL) actually have to live on "Mars time" during the start of missions. They wear special watches and shift their sleep schedules by 40 minutes every day. It’s like living in a permanent state of jet lag. Imagine your lunch break moving from 12:00 PM to 12:40 PM, then 1:20 PM, and so on. It’s a mess.
The Weirdness of Martian Seasons
Because a Mars year is nearly double ours, the seasons are stretched out, too. But they aren't even.
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On Earth, our orbit is almost a perfect circle, so our seasons are roughly the same length. Mars is different. Its orbit is an ellipse—more like a squashed egg. This is called "orbital eccentricity."
- Northern Spring: This is the marathon runner of seasons, lasting about 194 Sols.
- Northern Autumn: This one is a sprint, lasting only 142 Sols.
When Mars is at perihelion (its closest point to the Sun), it moves much faster than when it’s at aphelion (its furthest point). This means that in the southern hemisphere, summers are short but incredibly hot, while winters are long and brutal.
The "Launch Window" Problem
You’ve probably heard people talk about "launch windows" to Mars. These only happen because of how the two planets orbit the Sun at different speeds.
Every 26 months, Earth and Mars end up on the same side of the Sun, relatively close to each other. This is called Opposition. Because Earth is on the "inside track," we essentially lap Mars like a faster runner on a track.
If you miss that 26-month window? You're stuck waiting another two years for the planets to align again. This is why you see "fleets" of spacecraft leaving for Mars all at once, like the 2020 rush when the US, China, and the UAE all launched missions within weeks of each other.
How This Impacts Future Humans
If we ever actually put boots on the ground, the 687-day orbit changes everything about how we live.
- Agriculture: You can't just plant crops and expect a harvest in three months. Greenhouses will have to deal with seasons that last half a year.
- Solar Power: During that long, slow trek away from the Sun (aphelion), solar panels get less "juice." Plus, that’s usually when the massive dust storms kick up.
- Mental Health: Imagine being "stuck" in a winter that lasts nearly six months. The psychological toll of the Martian calendar is something researchers are still trying to wrap their heads around.
Actionable Insights for Space Enthusiasts
If you want to track the Martian year yourself, you don't need a PhD. Here is how you can stay in the loop:
- Check the Ls (Solar Longitude): Astronomers use "Ls" to track Mars seasons. $Ls = 0°$ is the spring equinox in the north. If you see a news report saying it’s $Ls = 270°$ on Mars, you know the north is entering a long, dark winter.
- Watch for Opposition: The next time Mars will be closest to Earth is January 2025. That's your best chance to see it through a backyard telescope as more than just a blurry dot.
- Follow the Sols: NASA's mission websites for the Perseverance rover always list the current "Sol" of the mission. It's a great way to get a feel for the rhythm of a world that takes its sweet time going around the Sun.
Basically, Mars doesn't care about our 365-day calendar. It moves to its own beat, governed by the cold math of orbital mechanics and its lonely, distant path around our star. Knowing that 687-day number is just the start; the real trick is learning to live with the 40-minute lag.