Mars

This article is about the planet. For the deity, see Mars (mythology). For other uses, see Mars (disambiguation).
Mars Astronomical symbol of Mars
The planet Mars
Mars imaged by the
Hubble Space Telescope in 2003
Designations
Pronunciation UK English: /mɑːz/
US English: Listeni/ˈmɑːrz/
Adjectives Martian
Orbital characteristics [2]
Epoch J2000
Aphelion 1.6660 AU
249.2 Gm
Perihelion 1.3814 AU
206.7 Gm
Semi-major axis
1.523679 AU
227.9392 Gm
Eccentricity 0.0934
Orbital period
1.8808 Julian years
686.971 d
668.5991 sols
Synodic period
779.96 days
2.135 Julian years
Average orbital speed
24.077 km/s
Mean anomaly
19.373°
Inclination 1.850° to ecliptic
5.65° to Sun's equator
1.67° to invariable plane[1]
Longitude of ascending node
49.558°
Argument of perihelion
286.502°
Satellites 2
Physical characteristics
Mean radius
3,389.5±0.2 km[a] [3]
Equatorial radius
3,396.2±0.1 km[a] [3]
0.533 Earths
Polar radius
3,376.2±0.1 km[a] [3]
0.531 Earths
Flattening 0.00589±0.00015
Surface area
144,798,500 km2
0.284 Earths
Volume
1.6318×1011 km3[4]
0.151 Earths
Mass
6.4171×1023 kg[5]
0.107 Earths
Mean density
3.9335±0.0004 g/cm³[4]
Surface gravity
3.711 m/s²[4]
0.376 g
Moment of inertia factor
0.3662±0.0017[6]
Escape velocity
5.027 km/s
Sidereal rotation period
1.025957 d
24h 37m 22s[4]
Equatorial rotation velocity
868.22 km/h (241.17 m/s)
Axial tilt
25.19° to its orbital plane[7]
North pole right ascension
21h 10m 44s
317.68143°
North pole declination
52.88650°
Albedo 0.170 (geometric)[8]
0.25 (Bond)[7]
Surface temp. min mean max
Kelvin 130 K 210 K[7] 308 K
Celsius −143 °C[10] −63 °C 35 °C[11]
Fahrenheit −226 °F[10] −82 °F 95 °F[11]
Apparent magnitude
+1.6 to −3.0[9]
Angular diameter
3.5–25.1″[7]
Atmosphere[7][12]
Surface pressure
0.636 (0.4–0.87) kPa
0.00628 atm
Composition by volume
95.97% carbon dioxide
1.93% argon
1.89% nitrogen
0.146% oxygen
0.0557% carbon monoxide
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is often referred to as the "Red Planet"[13][14] because the iron oxide prevalent on its surface gives it a reddish appearance.[15] 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.
The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. 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. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature.[16][17] Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids,[18][19] similar to 5261 Eureka, a Mars trojan.
There are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers.[20][21][22][23] Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about  6⁄1000 that of the Earth's,[24] except at the lowest elevations for short periods.[25][26] The two polar ice caps appear to be made largely of water.[27][28] The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters (36 ft).[29]
Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91,[7] which is surpassed only by Jupiter, Venus, the Moon, and the Sun. Optical ground-based telescopes are typically limited to resolving features about 300 kilometers (190 mi) across when Earth and Mars are closest because of Earth's atmosphere.[30]