Mars

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.

Mars 

Mars in natural colour in 2007[a]
Designations
Pronunciation	UK English: /mɑːz/ US English: i/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[b] [3]
Equatorial radius	3,396.2±0.1 km[b] [3] 0.533 Earths
Polar radius	3,376.2±0.1 km[b] [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

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  ⁶⁄₁₀₀₀that 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] In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior.^[30][31][32]

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.^[33]