Mars

Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmosphere, and has a crust primarily composed of elements similar to Earth's crust, as well as a core made of iron and nickel. Mars has surface features such as impact craters, valleys, dunes, and polar ice caps. It has two small and irregularly shaped moons: Phobos and Deimos.

Mars
Mars seen by the Mars Orbiter Mission space probe in true color with a regular Bayer filter[1]
Designations
AdjectivesMartian
Orbital characteristics[2]
Epoch J2000
Aphelion249261000 km
(154884000 mi; 1.66621 AU)[3]
Perihelion206650000 km
(128410000 mi; 1.3814 AU)[3]
227939366 km
(141634956 mi; 1.52368055 AU)[4]
Eccentricity0.0934[3]
686.980 d
(1.88085 yr; 668.5991 sols)[3]
779.94 d
(2.1354 yr)[4]
24.07 km/s
(86700 km/h; 53800 mph)[3]
19.412°[3]
Inclination
49.57854°[3]
2022-Jun-21[6]
286.5°[4]
Satellites2
Physical characteristics
Mean radius
3389.5 ± 0.2 km[lower-alpha 1][7]
(2106.1 ± 0.1 mi)
Equatorial radius
3396.2 ± 0.1 km[lower-alpha 1][7]
(2110.3 ± 0.1 mi; 0.533 Earths)
Polar radius
3376.2 ± 0.1 km[lower-alpha 1][7]
(2097.9 ± 0.1 mi; 0.531 Earths)
Flattening0.00589±0.00015[6][7]
144.37×106 km2[8]
(5.574×107 sq mi; 0.284 Earths)
Volume1.63118×1011 km3[9]
(0.151 Earths)
Mass6.4171×1023 kg[10]
(0.107 Earths)
Mean density
3.9335 g/cm3[9]
(0.1421 lb/cu in)
3.72076 m/s2[11]
(12.2072 ft/s2; 0.3794 g)
0.3644±0.0005[10]
5.027 km/s
(18100 km/h; 11250 mph)[12]
1.02749125 d[13]
24h 39m 36s
1.025957 d
24h 37m 22.7s[9]
Equatorial rotation velocity
241 m/s
(870 km/h; 540 mph)[3]
25.19° to its orbital plane[3]
North pole right ascension
317.68143°[7]
21h 10m 44s
North pole declination
52.88650°[7]
Albedo
Surface temp. min mean max
Celsius −110 °C[15] −60 °C[16] 35 °C[15]
Fahrenheit −166 °F[15] −80 °F[16] 95 °F[15]
Surface absorbed dose rate8.8 μGy/h[17]
Surface equivalent dose rate27 μSv/h[17]
−2.94 to +1.86[18]
3.5–25.1″[3]
Atmosphere[3][19]
Surface pressure
0.636 (0.4–0.87) kPa
0.00628 atm
Composition by volume

    Some of the most notable surface features on Mars include Olympus Mons, the largest volcano and highest known mountain on any planet in the Solar System, and Valles Marineris, one of the largest canyons in the Solar System. The Borealis basin in the Northern Hemisphere covers approximately 40% of the planet and may be a large impact feature.[20] Days and seasons on Mars are comparable to those of Earth, as the planets have a similar rotation period and tilt of the rotational axis relative to the ecliptic plane. Liquid water on the surface of Mars cannot exist due to low atmospheric pressure, which is less than 1% of the atmospheric pressure on Earth.[21][22] Both of Mars's polar ice caps appear to be made largely of water.[23][24] In the distant past, Mars was likely wetter, and thus possibly more suited for life. However, it is unknown whether life has ever existed on Mars.

    Mars has been explored by several uncrewed spacecraft, beginning with Mariner 4 in 1965. NASA's Viking 1 lander transmitted in 1976 the first images from the Martian surface. Two countries have successfully deployed rovers on Mars, the United States first doing so with Sojourner in 1997 and China with Zhurong in 2021.[25] There are also planned future missions to Mars, such as a Mars sample-return mission set to happen in 2026, and the Rosalind Franklin rover mission, which was intended to launch in 2018 but was delayed to 2024 at the earliest, with a more likely launch date at 2028.

    Mars can be viewed from Earth with the naked eye, as can its reddish coloring. This appearance, due to the iron oxide prevalent on its surface, has led to Mars often being called the Red Planet.[26][27] It is among the brightest objects in Earth's sky, with an apparent magnitude that reaches −2.94, comparable to that of Jupiter and surpassed only by Venus, the Moon and the Sun.[18] Historically, Mars has been observed since ancient times, and over the millennia, has been featured in culture and the arts in ways that have reflected humanity's growing knowledge of it.


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