Mars gets more attention than almost any other planet, and for good reason, it’s the world humanity actually plans to send astronauts to next. Before any of that happens, here’s what the numbers actually say about the Red Planet’s size, its distance from the Sun, and the two strange little moons that orbit it.
About Half of Earth’s Size
Mars is the fourth planet from the Sun and roughly half of Earth’s diameter, small enough that its total surface area is close to Earth’s total land area once you subtract our oceans. Like the other rocky planets, Mars has a central iron, nickel, and sulfur core, a rocky mantle, and a solid crust. Its signature reddish color comes from iron oxide, essentially rust, coating much of its dusty surface.
Despite being smaller, Mars still manages some genuinely oversized features, Olympus Mons, the largest volcano in the solar system, stands nearly three times taller than Mount Everest.
A Long, Cold Trip From the Sun
Mars orbits the Sun from an average distance of about 142 million miles, or 1.5 astronomical units, meaning it’s roughly 50 percent farther from the Sun than Earth is. Sunlight that reaches Earth in about 8 minutes takes closer to 13 minutes to arrive at Mars. That extra distance, combined with a thin atmosphere unable to trap much heat, keeps Mars a genuinely cold world, temperatures can swing from a relatively mild 90 degrees Fahrenheit down to a brutal minus 190 degrees Fahrenheit.
Phobos (left) and Deimos, Mars’ two small, irregularly shaped moons, are believed to be either captured asteroids or debris left over from an ancient impact on Mars. (Image: NASA/JPL-Caltech/University of Arizona)
A Day Almost Like Ours, a Year Nearly Twice as Long
One of Mars’s more Earth-like traits is its rotation, a single Martian day, called a sol, lasts just 24.6 hours, barely longer than our own. Its axial tilt of 25 degrees is also remarkably close to Earth’s 23.4 degrees, which means Mars experiences seasons in a similar way to Earth, just stretched out considerably longer.
That stretching comes from Mars’s orbit, which takes 687 Earth days, nearly two full Earth years, to complete a single trip around the Sun. Combine the longer year with the Earth-like day length, and a single Martian year works out to about 669 sols.
Two Tiny, Doomed Moons
Unlike Earth’s single, round Moon, Mars hosts two small, lumpy moons named Phobos and Deimos, named for the sons of the Greek god of war. Neither is large enough for its own gravity to pull it into a sphere, Phobos measures roughly 17 by 14 by 11 miles across, while Deimos is smaller still, at about 9 miles across. Both are thought to be either captured asteroids or debris from an ancient impact, and their composition closely resembles that of dark, carbon-rich asteroids rather than typical planetary material.
Phobos orbits remarkably close to Mars, just 3,700 miles out, completing a full orbit in under 8 hours, fast enough that it actually rises and sets twice a day as seen from the Martian surface. That closeness comes at a cost, Phobos is slowly spiraling inward and is expected to either crash into Mars or break apart into a ring within the next 50 million years. If you’re curious how Mars stacks up against other worlds nearby, our full profile of Mercury, the actual closest planet to the Sun, covers how that innermost planet’s orbit compares.
Why the Numbers Matter
Mars’s distance and orbit aren’t just trivia, they directly shape every mission NASA plans there. Because Earth and Mars orbit the Sun at different speeds, the two planets only line up for an efficient transfer window roughly once every 26 months, which is exactly why Mars missions tend to launch in clusters rather than whenever convenient.
For more detailed data straight from the source, check out NASA’s Mars Facts page and the additional overview from Astronomy.com.
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