Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury.
The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly.
A planet is an astronomical object orbiting a star or stellar remnant that
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Named after the Roman god of war, it is often referred to as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance.
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Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth.
An impact crater is an approximately circular depression in the surface of a planet, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity impact of a smaller body.
Earth is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.
An atmosphere is a layer of gases surrounding a planet or other material body, that is held in place by the gravity of that body.
The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons.
In astronomy, the rotation period of a celestial object is the time that it takes to complete one revolution around its axis of rotation relative to the background stars.
Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System.
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
Valles Marineris is a system of canyons that runs along the Martian surface east of the Tharsis region.
The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature.
The North Polar Basin, more commonly known as the Borealis Basin, is a large basin in the northern hemisphere of Mars that covers 40% of the planet.
Mars has two moons, Phobos and Deimos, which are small and irregularly shaped.
These may be captured asteroids, similar to 5261 Eureka, a Mars trojan.
The Mars trojans are a group of Trojan objects that share the orbit of the planet Mars around the Sun.
Until the first successful Mars flyby in 1965 by Mariner 4, many speculated about the presence of liquid water on the planet's surface.
Mariner 4 was the fourth in a series of spacecraft intended for planetary exploration in a flyby mode.
This was based on observed periodic variations in light and dark patches, particularly in the polar latitudes, which appeared to be seas and continents; long, dark striations were interpreted by some as irrigation channels for liquid water.
In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface.
These straight line features were later explained as optical illusions, though geological evidence gathered by uncrewed missions suggests that Mars once had large-scale water coverage on its surface at an earlier stage of its existence.
In 2005, radar data revealed the presence of large quantities of water ice at the poles and at mid-latitudes.
The Mars rover Spirit sampled chemical compounds containing water molecules in March 2007.
A chemical compound is an entity consisting of two or more atoms, at least two from different elements, which associate via chemical bonds.
The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.
On September 28, 2015, NASA announced the presence of briny flowing salt water on the Martian surface.
The National Aeronautics and Space Administration is an independent agency of the executive branch of the United States federal government responsible for the civilian space program as well as aeronautics and aerospace research.
The United States of America, commonly referred to as the United States or America, is a federal republic composed of 50 states, a federal district, five major self-governing territories, and various possessions.
Mars is host to seven functioning spacecraft: five in orbit—2001 Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, MAVEN and Mars Orbiter Mission—and two on the surface—Mars Exploration Rover Opportunity and the Mars Science Laboratory Curiosity.
Mars Science Laboratory is a robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed Curiosity, a Mars rover, in Gale Crater on August 6, 2012.
Mars Atmosphere and Volatile EvolutioN mission was developed by NASA to study the Martian atmosphere while orbiting Mars.
The Mars Orbiter Mission, also called Mangalyaan, is a space probe orbiting Mars since 24 September 2014.
Observations by the Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars.
In 2013, NASA's Curiosity rover discovered that Mars's soil contains between 1.5% and 3% water by mass.
There are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life.
In situ investigations have been performed by the Viking landers, Spirit and Opportunity rovers, Phoenix lander, and Curiosity rover.