Mars

Mars (astronomical symbol: ♂) 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 and is often referred to as the "Red Planet". The latter refers to the effect of the iron oxide prevalent on Mars's surface, which gives it a reddish appearance (as shown in the picture), that is distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, with surface features reminiscent of the impact craters of the Moon, and the valleys, deserts and polar ice caps of Earth.

The days and seasons are comparable to those of Earth, because the rotation period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. A year on Mars is 687 Earth days, almost two times longer as a year on Earth. A day on Mars is 24 hours 37 minutes and 22.7 seconds, about 2.7% longer than a day on Earth. A day on Mars is called a sol, named after a Latin word for Sun. Mars is the site of Olympus Mons, the largest volcano and highest known mountain on any planet in the Solar System, and of 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. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped compared to Earth's Moon. These may be captured asteroids by Mars' larger gravity, similar to 5261 Eureka, a Mars trojan, at some point in the past.

Mars has been explored by several uncrewed spacecraft. Mariner 4 was the first spacecraft to visit Mars; launched by NASA on 28 November 1964, it made its closest approach to the planet on 15 July 1965. Mariner 4 detected the weak Martian radiation belt, measured at about 0.1% that of Earth, and captured the first images of another planet from deep space. The latest spacecraft to successfully land on Mars are CNSA's Tianwen-1 lander and Zhurong rover, landed on 14 May 2021. Zhurong rover was successfully deployed on 22 May 2021, which makes China the second country to successfully deploy a rover on Mars, after the United States.