Mars
Americannoun
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the ancient Roman god of war and agriculture, identified with the Greek god Ares.
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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.
adjective
noun
noun
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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
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the alchemical name for iron
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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.
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See Table at solar system
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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.
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Example Sentences
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NASA’s Mars Sample Return mission was supposed to do that in the 2030s, but the mission grew too bloated and expensive.
From The Wall Street Journal • Apr. 23, 2026
The project fits into Musk's long-term ambition to build colonies on the Moon and Mars and is "a first step towards becoming a Kardashev II-level civilization," he wrote.
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
The ultimate demise of the pinball era is dated by the author to 1999, when Williams released two final games, Star Wars Episode I and Revenge From Mars.
From The Wall Street Journal • Apr. 15, 2026
My navigation tools tell me that we are rapidly approaching Mars.
From "A Rover's Story" by Jasmine Warga
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
