Mars is the fourth planet from the sun, sitting just beyond Earth in the solar system’s lineup. The order goes Mercury, Venus, Earth, then Mars. It orbits at an average distance of about 228 million kilometers (142 million miles) from the sun, though that number shifts significantly as Mars travels its slightly oval-shaped path through space.
How Far Mars Actually Is From the Sun
Because Mars doesn’t orbit in a perfect circle, its distance from the sun changes throughout the Martian year. At its closest approach, Mars comes within 206.7 million kilometers (128.4 million miles) of the sun. At its farthest point, that gap stretches to 249.3 million kilometers (154.9 million miles). That’s a swing of more than 42 million kilometers between the two extremes.
For comparison, Earth sits roughly 150 million kilometers from the sun. So Mars is about 1.5 times farther out than we are. That extra distance means Mars receives less sunlight and heat, which is one reason the planet averages a brutally cold surface temperature around minus 60 degrees Celsius.
How Long a Martian Year Takes
Being farther from the sun means Mars has a longer path to travel and moves more slowly through its orbit. A full trip around the sun takes 687 Earth days, nearly twice as long as our year. On Mars itself, that works out to 669.6 Martian days (called “sols”), since a Martian day is about 37 minutes longer than an Earth day.
Why Mars Looks Red From Earth
Mars is sometimes called the Red Planet, and its color comes from iron-rich minerals coating its surface. For decades, scientists attributed the reddish hue to a form of iron oxide similar to rust. More recent research published in Nature Communications points to a specific mineral called ferrihydrite, a poorly crystalline iron compound that forms in the presence of water, as the dominant iron-bearing material in Martian dust. This finding suggests Mars was once cold and wet rather than the bone-dry desert we see today.
A Thin, Carbon Dioxide Atmosphere
Mars and Earth couldn’t be more different when it comes to their atmospheres. Earth’s air is 78% nitrogen and 21% oxygen. Mars flips the script entirely: its atmosphere is 95% carbon dioxide, with just 3% nitrogen and tiny traces of oxygen. It’s also incredibly thin, with surface pressure less than 1% of what you experience at sea level on Earth. That thin atmosphere can’t trap much heat, which compounds the cooling effect of Mars’s greater distance from the sun.
Size, Gravity, and Moons
Mars is the seventh largest planet in the solar system, roughly half the diameter of Earth. Surface gravity is only 38% of what we feel here, so a person who weighs 100 pounds on Earth would weigh just 38 pounds standing on Mars.
Two small, irregularly shaped moons orbit the planet: Phobos and Deimos, named after the mythological sons of the Greek god of war. Both are lumpy, cratered, and dark, likely captured asteroids made of carbon-rich rock mixed with ice. Phobos is the larger of the two and orbits remarkably close to Mars, just 6,000 kilometers above the surface. No known moon in the solar system orbits closer to its planet. It circles Mars three times per day and is gradually spiraling inward, drifting about 1.8 meters closer to the planet each century. Deimos, the smaller moon, takes a more leisurely 30 hours to complete one orbit.