Mars in 1980 as seen by the Viking 1 Orbiter
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Name | Mars | Pronunciation | c-enen-us-Mars.oggˈmɑrz | Adjective | Martian | Epoch | J2000 | Aphelion | 249,209,300 km
1.665 861 AU | Perihelion | 206,669,000 km
1.381 497 AU | Semi-major axis | 227,939,100 km
1.523 679 AU | Eccentricity | 0.093 315 | Orbital period | 686.971 days
1.8808 Julian years
668.5991 sols | Synodic period | 779.96 days
2.135 Julian years | Avg orbital speed | 24.077 km/s | Mean anomaly | 19.3564° | Inclination | 1.850° to ecliptic 5.65° to Sun's equator 1.67° to invariable plane | Longitude of ascending node | 49.562° | Argument of peri | 286.537° | Satellites | 2 | Equatorial radius | 3,396.2 ± 0.1 km
0.533 Earths | Polar radius | 3,376.2 ± 0.1 km
0.531 Earths | Flattening | 0.005 89 ± 0.000 15 | Surface area | 144,798,500 km2
0.284 Earths | Volume | 1.6318 km3
0.151 Earths | Mass | 6.4185 kg
0.107 Earths | Density | 3.9335 ± 0.0004 g/cm³ | Equatorial surface gravity | 3.711 m/s2
0.376 g | Escape velocity | 5.027 km/s | Sidereal rotation period | 1.025 957 day
24.622 9 h | Equatorial rotation velocity | 868.22 km/h (241.2 m/s) | Axial tilt | 25.19° | North pole right ascension | 21 h 10 min 44 s
317.681 43° | North pole declination | 52.886 50° | Albedo | 0.170 (geometric)
0.25 (Bond) | Apparent magnitude | +1.6 to −3.0 | Angular diameter | 3.5 � 25.1" | Pressure | 0.636 (0.4 � 0.87) kPa | Composition | (mole fractions)
95.32% carbon dioxide
2.7% nitrogen
1.6% argon
0.13% oxygen
0.08% carbon monoxide
210 ppm water vapor
100 ppm nitric oxide
15 ppm molecular hydrogen
2.5 ppm neon
850 ppb HDO
300 ppb krypton
130 ppb formaldehyde
80 ppb xenon
30 ppb ozone
18 ppb hydrogen peroxide
10 ppb methane |
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Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, 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 highest known mountain within the Solar System, and of Valles Marineris, the largest canyon. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature.
Until the first flyby of Mars occurred in 1965, by Mariner 4, many speculated about the presence of liquid water on the planet's surface. 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. These straight line features were later explained as optical illusions, though geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface. 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. The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.
Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Martian trojan asteroid. Mars is currently host to three functional orbiting spacecraft: Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. On the surface are the Mars Exploration Rover Opportunity and its recently decommissioned twin, Spirit, along with several other inert landers and rovers, both successful and unsuccessful. The Phoenix lander completed its mission on the surface in 2008. Observations by NASA's now-defunct Mars Global Surveyor show evidence that parts of the southern polar ice cap have been receding. Observations by NASA's Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars.
Mars can easily be seen from Earth with the naked eye. Its apparent magnitude reaches −3.0[ a brightness surpassed only by Venus, Jupiter, the Moon, and the Sun. ]
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