Mars

Mars is the fourth planet from the Sun and the outer neighbor of Earth. It is a terrestrial, rocky planet with a thin atmosphere composed mainly of carbon dioxide. Because of its orange-red appearance, Mars is often called the “Red Planet”; the color comes from iron oxide dust on its surface.

With a diameter of about 6,800 km, Mars is roughly half the size of Earth and is the second-smallest planet in the Solar System after Mercury (planet). Its surface gravity is about 38% of Earth’s, and its year lasts 687 Earth days. Mars also has a rotation period similar to Earth’s, so its day is only slightly longer than an Earth day, and its axial tilt produces seasons. The planet’s orbit is more eccentric than Earth’s, which makes its seasonal pattern more asymmetric between the hemispheres.

Mars has a varied and dramatic surface. The northern hemisphere is dominated by broad lowlands, while the southern hemisphere is more heavily cratered and mountainous. It contains the tallest volcano in the Solar System, Olympus Mons, and the vast canyon system Valles Marineris. Small dust particles are widespread on the surface and in the atmosphere, and the planet experiences dust storms. Although Mars retains water as ice, frost, clouds, and subsurface deposits, it has no stable liquid water on the surface today.

The planet has two small moons, Phobos (moon) and Deimos (moon). Mars has long been visible to the naked eye and has been associated with war in many cultures, including in the naming of the planet after the Roman god Mars (mythology). Modern exploration began in the 1960s, and since the 1990s Mars has been continuously studied by orbiters and landers. It remains a major target in the search for past or present life and for future crewed exploration.