Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury. In English, Mars carries the name of the Roman god of war.
Mars is a terrestrial planet with a thin atmosphere, and has a crust primarily composed of elements similar to Earth's crust, as well as a core made of iron and nickel. Mars has surface features such as impact craters, valleys, dunes, and polar ice caps. It also has two small and irregularly shaped moons, Phobos and Deimos.
Some of the most notable surface features on Mars include Olympus Mons, the largest volcano and highest known mountain on any Solar System planet, and Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the Northern Hemisphere covers 40% of the planet and may be a giant impact feature.
The days and seasons on Mars are comparable to those of Earth as the planets have a similar rotation period and tilt of the rotational axis relative to the ecliptic plane. Liquid water on the surface of Mars cannot exist due to low atmospheric pressure, which is less than 1% of the atmospheric pressure on Earth.
Both of Mars's polar ice caps appear to be made largely of water. Multiple lines of evidence suggest that Mars was wetter in the distant past, and thus possibly more suited for life. However, whether life ever did exist there, and if it could have survived to the present day, remain unanswered questions.
Mars has been explored by several uncrewed spacecraft, beginning with Mariner 4 in 1965. NASA's Viking 1 lander transmitted the first images from the Martian surface in 1976. Two countries have successfully deployed rovers on Mars, the United States first doing so with Sojourner in 1997 and China with Zhurong in 2021.
There are also planned future missions to Mars, such as a Mars sample-return mission set to happen in 2026, and the Rosalind Franklin rover mission, which was intended to launch in 2018 but was delayed to 2024.
Mars can easily be seen from Earth with the naked eye, as can its striking reddish coloring. This appearance, due the iron oxide prevalent on its surface, has led to Mars often being called the Red Planet. It is among the brightest objects in Earth's sky, with an apparent magnitude that reaches −2.94, comparable to that of Jupiter and surpassed only by Venus, the Moon and the Sun.
Historically, Mars has been observed since ancient times, and over the millennia, has been featured in culture and the arts in ways that have reflected humanity's growing knowledge of it.