Facts About Mars, the Red Planet

What kind of planet is Mars?

Mars is the fourth planet from the Sun and the last of the four rocky planets. NASA describes it as a dusty, cold desert world with a very thin atmosphere. It has seasons, polar ice caps, extinct volcanoes, deep canyons and weather, including dust storms that can cover almost the whole planet.

Mars is about half as wide as Earth: if Earth were the size of a nickel, Mars would be about as big as a raspberry. Because it has no oceans, though, its land area is about the same as all of Earth's dry land. It's named after the Roman god of war, because its color reminded people of blood. Ancient Egyptians called it "the red one."

Mars by the numbers

Source: NASA Planetary Fact Sheet and NASA Science.

A day on Mars, called a sol, is only about 40 minutes longer than ours. A year is almost two Earth years. Because Mars is tilted almost exactly like Earth, it has seasons too, but they last about twice as long and are uneven, since its orbit is more stretched out.

Why is Mars red?

Mars's rocks, soil and dust contain a lot of iron. Over billions of years, that iron has combined with oxygen and rusted, just like an old bike left in the rain. Wind lifts the fine rusty dust into the air, so even the sky looks pinkish-orange. NASA notes that up close, the ground is a mix of browns, golds and tans.

Giant volcanoes and the biggest canyon

Mars holds two solar system records.

• Olympus Mons is the largest volcano in the solar system. NASA says it is more than 25 kilometers (16 miles) tall, about three times the height of Mount Everest, with a base about the size of Arizona. It probably grew so big because Mars has no moving plates, so lava kept piling up in one place.
• Valles Marineris is the largest canyon in the solar system: about 3,870 kilometers (2,400 miles) long, up to 600 kilometers wide and up to 9 kilometers deep. It would stretch from California to New York, and it's more than 10 times longer than the Grand Canyon.

Mars also has polar ice caps made of water ice, with a seasonal frosting of frozen carbon dioxide that comes and goes with the seasons.

Water on Mars, then and now

Mars today is bone-dry on the surface, but it wasn't always. Orbiters and rovers have found dried-up river valleys, lake beds, deltas and minerals that only form in water. NASA says huge floods may have rushed across Mars about 3.5 billion years ago.

Most of that water is gone or frozen now. Ice sits in the polar caps and just under the ground near the poles. The air is so thin, less than 1 percent of Earth's surface pressure, that liquid water on the surface would quickly boil or freeze.

What's inside Mars?

Tap the cutaway in the diagram to explore Mars's layers, using NASA's numbers:

1. Crust: 10 to 50 kilometers of rock rich in iron, magnesium, aluminum, calcium and potassium.
2. Mantle: rocky, between about 1,240 and 1,880 kilometers thick.
3. Core: iron, nickel and sulfur, with a radius of about 1,500 to 2,100 kilometers.

NASA's InSight lander, which worked from 2018 to 2022, measured the inside of Mars by listening for marsquakes. Mars has no global magnetic field today, but magnetized rocks in its southern crust show it had one about 4 billion years ago.

Phobos and Deimos

Mars has two small, potato-shaped moons that may be captured asteroids. Their names come from the horses that pulled the chariot of the Greek war god.

• Phobos, the larger, inner moon, circles Mars three times a day. It is slowly spiraling inward and, NASA says, will crash into Mars or break up into a ring in about 50 million years.
• Deimos is about half the size of Phobos and orbits about two and a half times farther away. Loose dust fills its craters, so it looks smoother.

Robots on Mars

Mars is the only planet besides Earth where rovers have driven around.

• Curiosity landed in Gale Crater in 2012 and is still climbing Mount Sharp, studying layers of rock that record Mars's past.
• Perseverance landed in Jezero Crater, an ancient lake bed, in 2021. It's searching for signs of ancient microscopic life and collecting rock samples. It carried the Ingenuity helicopter, which made the first powered flight on another planet.
• Orbiters like the Mars Reconnaissance Orbiter map the surface from above and relay messages to Earth.

Seeing Mars in the night sky

Mars is easy to spot when it's near Earth: look for a bright, steady, orange-red point that doesn't twinkle like the stars. About every 26 months, Earth passes between Mars and the Sun. Mars is then closest and brightest, rising at sunset and shining all night. Those same alignments set the launch windows for missions to Mars.

Fun facts about Mars

• Sunsets on Mars look blue, because fine dust scatters blue light toward the setting Sun.
• If you weigh 80 pounds on Earth, you'd weigh about 30 pounds on Mars.
• Mars has the biggest dust storms in the solar system; some cover the whole planet for months.
• Standing at the equator at noon, your feet might feel about 24 °C while your head is near freezing, NASA says, because the thin air holds so little heat.

Learning about Mars at home

Have kids sprinkle iron-rich steel wool fibers in damp sand and watch them rust over a few days: it's the same chemistry that colors Mars. Take the facts quiz above, then print the labeled Mars diagram.

Compare Mars with Earth and with giant Jupiter next door, or see all eight planets in order.