Mars was named by the ancient Romans for their god of war because its reddish color was reminiscent of blood. Other civilizations also named the planet for this attribute; for example, the Egyptians called it "Her Desher," meaning "the red one." Even today, it is frequently called the "Red Planet" because iron minerals in the Martian dirt oxidize, or rust, causing the surface to look red.

​Mars is the fourth planet from the Sun – a dusty, cold, desert world with a very thin atmosphere. Mars is also a dynamic planet with seasons, polar ice caps, canyons, extinct volcanoes, and evidence that it was even more active in the past.

Mars is a cold desert world. It is half the size of Earth. Mars is sometimes called the Red Planet. It's red because of rusty iron in the ground.

Like Earth, Mars has seasons, polar ice caps, volcanoes, canyons, and weather. It has a very thin atmosphere made of carbon dioxide, nitrogen, and argon.

There are signs of ancient floods on Mars, but now water mostly exists in icy dirt and thin clouds. On some Martian hillsides, there is evidence of liquid salty water in the ground.

WHY MARS?

At an average distance of 140 million miles, Mars is one of Earth's closest habitable neighbors. Mars is about half again as far from the Sun as Earth is, so it still has decent sunlight. It is a little cold, but we can warm it up. Its atmosphere is primarily CO2 with some nitrogen and argon and a few other trace elements, which means that we can grow plants on Mars just by compressing the atmosphere. Gravity on Mars is about 38% of that of Earth, so you would be able to lift heavy things and bound around. Furthermore, the day is remarkably close to that of Earth.

Diameter 6,791 km / 4,220 mi
Day Length 24 hrs 37 min
Force of Gravity 38% of Earth
Avg Distance from Earth 225Mkm / 140Mmi
Age 4.5 billion years

MONTHS TO GET TO MARS

MOONS

ORBITING SATELLITES

Northern summer on Mars
Clear day on rock covered Mars
Pathfinder's Ares Vallis landing site
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Northern Summer on Mars

This mosaic comprises about 50 red-, green-, and violet-filter Viking Orbiter images, mosaiced in an orthographic projection at a scale of 1 km/pixel. The images were acquired in 1980 during late northern summer on Mars. Image Credits: NASA/JPL/USGS

02
Clear day on rock covered Mars

On a clear day on Mars, you can see tens of thousands of rocks. Two high-resolution scans by one of Viking 2's cameras were mosaiced to create this scene looking northeast to the horizon some three kilometers (two miles) away. Image Credit: NASA/JPL

03
Pathfinder's Ares Vallis landing site

A panoramic view of Pathfinder's Ares Vallis landing site, featured on the cover of the Dec. 5 issue of Science, reveals traces of this warmer, wetter past, showing a floodplain covered with a variety of rock types, boulders, rounded and semi-rounded cobbles and pebbles. These rocks and pebbles are thought to have been swept down and deposited by floods which occurred early in Mars' evolution in the Ares and Tiu regions near the Pathfinder landing site. Image Credit: NASA/JPL

10 Need-to-Know Things About Mars

SMALL PLANET

If the Sun were as tall as a typical front door, Earth would be the size of a dime, and Mars would be about as big as an aspirin tablet.

FOURTH ROCK

Mars orbits our Sun, a star. Mars is the fourth planet from the Sun at an average distance of about 228 million km (142 million miles) or 1.52 AU.

LONGER DAYS

One day on Mars takes a little over 24 hours. Mars makes a complete orbit around the Sun (a year in Martian time) in 687 Earth days.

RUGGED TERRAIN

Mars is a rocky planet. Its solid surface has been altered by volcanoes, impacts, winds, crustal movement and chemical reactions.

BRING A SPACESUIT

Mars has a thin atmosphere made up mostly of carbon dioxide (CO2), argon (Ar), nitrogen (N2), and a small amount of oxygen and water vapor.

TWO MOONS

Mars has two moons named Phobos and Deimos.

RINGLESS

There are no rings around Mars.

MANY MISSIONS

Several missions have visited this planet, from flybys and orbiters to rovers on the surface.The first true Mars mission success was the Mariner 4 flyby in 1965.

TOUGH PLACE FOR LIFE

At this time, Mars' surface cannot support life as we know it. Current missions are determining Mars' past and future potential for life.

MANY MISSIONS

Mars is known as the Red Planet because iron minerals in the Martian soil oxidize, or rust, causing the soil and atmosphere to look red.