Mars is the fourth planet after the sun and the second smallest planet in the solar system after mercury. In English, Mars bears the name of Roman god of war, which is often called "red planet", because the red iron oxide on its surface makes its surface look reddish, which is a unique eye in the naked celestial body. Mars is an earth planet with a thin atmosphere. Its surface features are reminiscent of moon craters and valleys, deserts and earth's polar ice caps.

The rotation and seasonal cycles of Mars are similar to those of earth, and so are the tilts that produce the seasons. Mars is the site of Olympus Mons, the largest volcano and the second highest mountain range in the solar system, and Valles Marineris, one of the largest canyons in the solar system. The smooth Arctic basin in the northern hemisphere covers 40% of the earth, which may be a huge impact feature. Mars has two moons, Phobos and demons, which are small and irregular in shape. These may be captured asteroids, similar to the Mars Trojan 5261 Eureka.

Investigations are being conducted to assess Mars's past habitability and the potential for existing life. Future astrobiology missions are planned, including Mars 2020 and ExoMars Mars. Because of the low atmospheric pressure, liquid water cannot exist on the surface of Mars, and the atmospheric pressure is less than 1% of the earth's unless it is at the lowest elevation in a short period of time. Two polar ice sheets seem to be made mainly of water. If the Antarctic ice sheet melts, the amount of water ice in the Antarctic ice sheet will be enough to cover the entire planet's surface to a depth of 11 meters (36 feet). In November 2016, NASA reported that a large amount of underground ice had been found in the utopian Planitia area of Mars. It is estimated that the amount of water detected is equal to the amount of water in Lake Superior.

The naked eye can easily see Mars from the earth, and its red color can also be seen. Its apparent magnitude is 2.91, only Jupiter, Venus, the moon and the sun surpass it. When the earth and Mars are closest to each other due to the earth's atmosphere, optical based ground-based telescopes usually can only analyze features of about 300 kilometers (190 miles).