Look up at the night sky. That tiny, flickering red dot is the focus of billionaires and space agencies alike, but there’s a massive misconception floating around about its size. Honestly, if you asked a random person on the street if Mars is bigger than Earth, a surprising number would say yes. Maybe it’s the "God of War" persona or the fact that we talk about colonizing it as a "second Earth." In reality? Mars is tiny.
It’s small.
To be blunt, Mars is essentially a fixer-upper planet that never quite finished growing. If Earth were the size of a standard basketball, Mars would be roughly the size of a grapefruit. That’s a huge gap. We aren’t talking about a slight difference in diameter; we are talking about a completely different class of planetary scale that dictates everything from how much you’d weigh on its surface to why the planet lost its atmosphere in the first place.
The Brutal Reality of the Mars Bigger Than Earth Myth
Why do we get this wrong? Humans tend to equate importance with size. Since Mars is the most "Earth-like" place we can reach, our brains want to scale it up. But the numbers don’t lie. The radius of Earth is about 3,959 miles. Mars? Only 2,106 miles.
It’s actually the second smallest planet in the solar system. Only Mercury is smaller. You could basically fit six Mars-sized globes inside the volume of one Earth. That is a staggering realization for anyone who grew up imagining sprawling Martian continents.
Mass Matters More Than Surface Area
Surface area is one thing, but mass is where the real story lives. Mars has only about 11% of Earth’s mass. Think about that. Even though it has about 28% of Earth's surface area (which, fun fact, is roughly equal to the total dry land area on Earth), it lacks the "heft." This lack of mass is the primary reason Mars is a frozen desert today.
Without enough mass, a planet can’t hold onto a thick atmosphere. Earth’s core is a churning, hot mess of molten iron that generates a massive magnetic field. Mars, being smaller, cooled down much faster. Its internal engine stalled out billions of years ago. When the magnetic field died, the solar wind—a constant stream of charged particles from the sun—literally stripped the Martian atmosphere away, molecule by molecule.
Gravity: The 38% Rule
If you’ve ever dreamt of being a pro athlete, Mars is your spot. Because the planet is so much smaller and less dense than ours, gravity is significantly weaker. Specifically, Martian gravity is about 38% of Earth’s.
- If you weigh 200 pounds on Earth, you’d step on a scale at Gale Crater and see roughly 76 pounds.
- Your vertical jump would triple.
- Lifting heavy equipment would feel like moving pillows.
But there is a dark side to this. NASA and researchers like those at the Translational Research Institute for Space Health (TRISH) are worried about what this low gravity does to the human body long-term. We evolved for Earth’s 1g. On Mars, your bones start to leak calcium. Your muscles atrophy because they don't have to fight against a heavy "Earth-sized" pull. We don't actually know if a human can live there for ten years without their cardiovascular system essentially forgetting how to pump blood to their head.
Why Size Influences the Search for Water
NASA's "Follow the Water" strategy is directly tied to the planet's size. Because Mars is small, it has a lower "escape velocity." On Earth, you need to go about 11.2 km/s to break free from gravity. On Mars, it’s only 5 km/s. This made it very easy for water vapor to escape into space once the atmosphere thinned.
Curiosity and Perseverance rovers have found clear evidence of ancient riverbeds and deltas. We know Mars used to have a lot of water. But because it couldn't hold onto its heat or its air, that water either froze into the permafrost or drifted off into the vacuum. If Mars were bigger than Earth—say, a "Super-Earth"—it might still have rolling blue oceans today. Instead, we have a dusty orange ball.
The Mount Everest Comparison
Ironically, while the planet is smaller, its features are way bigger. This is one of those weird cosmic paradoxes. Because the gravity is lower, volcanoes can grow much taller without collapsing under their own weight.
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- Olympus Mons: This is the largest volcano in the solar system. It’s about two and a half times the height of Mount Everest.
- Valles Marineris: A canyon system that would stretch from New York to Los Angeles.
- Hellis Planitia: An impact crater so deep you could fit the entire Himalayas inside it.
If Mars were larger, these landmarks wouldn't exist in their current form. Earth’s high gravity and plate tectonics "recycle" the crust, keeping mountains relatively short. Mars is a static, small world where things just... pile up.
Geopolitical and Scientific Implications
When we talk about the Mars bigger than Earth misconception, it impacts how we plan for the future. SpaceX’s Starship is designed with these physics in mind. Aerobraking—using the atmosphere to slow down—is much harder on Mars because the air is 1% as thick as Earth's. You can't just use a parachute and call it a day; you need retro-rockets for almost the entire descent.
Dr. Becky Smethurst, an astrophysicist at the University of Oxford, often points out that our focus on Mars is purely a matter of proximity, not because it’s a "perfect" twin. It's a "failed" twin. Understanding the scale helps us manage expectations for "Terraforming." You can't just "add air" to Mars. Without a magnetic field and more mass, that air would eventually just blow away again.
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Final Reality Check
So, is Mars bigger than Earth? Not even close. It’s a small, frigid, low-gravity world that presents a massive engineering challenge.
If you are following the latest updates from the Artemis missions or the Mars Sample Return program, keep the scale in mind. We are moving from a big, vibrant, protected world to a small, exposed, skeletal one. The fascination isn't that Mars is "great," but that it's just big enough to have once been alive, and just small enough to have lost it all.
Your Next Steps for Understanding Planetary Scale
- Use a Scale Calculator: Head over to an online "Weight on Other Planets" calculator to see exactly how your body would react to the 0.38g environment.
- Visual Comparison: Check out the high-resolution "Blue Marble" Earth photo alongside the "Viking 1" Mars mosaics. The size difference in the curvature of the horizons is noticeable if you look closely.
- Track the Rovers: Follow the raw image feeds from the Perseverance rover. Look at the horizon lines; because the planet is smaller, the horizon is actually closer to the viewer than it is on Earth, which can play tricks on your sense of distance.
- Study the Magnetosphere: Read up on the "Mars Global Surveyor" data which mapped the crustal magnetic remnants. It explains why Mars's small size led to its current atmospheric state.