Mars

American  

[mahrz] / mɑrz /

noun

1. the ancient Roman god of war and agriculture, identified with the Greek god Ares.

2. Astronomy. the planet fourth in order from the sun, having a diameter of 4,222 miles (6,794 km), a mean distance from the sun of 141.6 million miles (227.9 million km), a period of revolution of 686.95 days, and two moons.

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adjective

1. (often lowercase) of or relating to any of various pigments used in painting that are artificially made from an iron oxide base.

   Mars color; Mars pigments.

Mars ¹ British  

/ mɑːz /

noun

1. Also called: the Red Planet.  the fourth planet from the sun, having a reddish-orange surface with numerous dark patches and two white polar caps. It has a thin atmosphere, mainly carbon dioxide, and low surface temperatures. Spacecraft encounters have revealed a history of volcanic activity and running surface water. The planet has two tiny satellites, Phobos and Deimos. Mean distance from sun: 228 million km; period of revolution around sun: 686.98 days; period of axial rotation: 24.6225 hours; diameter and mass: 53.2 and 10.7 per cent that of earth respectively

2. the alchemical name for iron

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Mars ² British  

/ mɑːz /

noun

1. Greek counterpart: Ares.  the Roman god of war, the father of Romulus and Remus

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Mars Scientific  

/ märz /

1. The fourth planet from the Sun and the second smallest in the solar system, with a diameter about half that of Earth. Mars is the last of the terrestrial or inner planets and has notable similarities to Earth, including polar ice caps and a tilted axis that gives it seasons. However, it is significantly less dense than Earth and has no magnetic field, suggesting that it lacks a metallic core, and its atmosphere, made up mostly of carbon dioxide, is much thinner than Earth's. Mars has no surface water apart from a layer of permanent ice that underlies the seasonally changing caps of frozen carbon dioxide at its poles; there is, however, clear evidence of earlier water flows in the form of channels, outwashes, and canyons. Other surface features include numerous craters, especially in the southern hemisphere, along with very large volcanoes and extensive windblown dunes. Mar's reddish color is due to the abundance of hematite in its surface rocks. Its two small, irregular moons, Phobos and Deimos, may be asteroids captured earlier by gravitational attraction.

2. See Table at solar system

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Mars ¹ Cultural  

1. The Roman name of Ares, the Greek and Roman god of war.

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Mars ² Cultural  

1. In astronomy, the fourth major planet from the sun. Mars was named after the Roman god of war because of its red color. (See solar system; See under “Mythology and Folklore.”)

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Discover More

The month of March is named after Mars.

The fourth planet from the sun (the Earth is third) is named Mars, possibly because its red color is reminiscent of blood.

Smaller than the Earth, Mars has polar ice caps and a surface that includes red sands.

Mars has been, and remains, the focus of space research by NASA. Voyages to Mars, including multiple landings, are scheduled through the first decade of the twenty-first century.

The Viking space mission, which placed landers on the surface of Mars, did not discover any signs of life.

Compare meaning

How does mars compare to similar and commonly confused words? Explore the most common comparisons:

• Mars vs. Ares

Example Sentences

There, Lowell convinced himself that alien-built canals crisscrossed the Martian surface, though anyone who has observed Mars with a similar telescope knows it’s hard to see much detail at all.

From The Wall Street Journal • Apr. 23, 2026

Rovers currently are trundling on Mars, attempting to learn whether life existed more than three billion years ago when the planet was warmer and wetter.

From The Wall Street Journal • Apr. 23, 2026

"The same stuff that rained down on Mars from meteorites is what rained down on Earth, and it probably provided the building blocks for life as we know it on our planet," Williams said.

From Barron's • Apr. 21, 2026

The Perseverance rover, which is on Mars collecting rock and soil samples, could face spending reductions.

From Los Angeles Times • Apr. 19, 2026

I mean, I know you’ve been on Mars for almost two years now, and she’d been working on you for like a billion years before that, but still.

From "A Rover's Story" by Jasmine Warga

Related Words

• earth