Mars
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This article is about the planet. For other uses, see Mars (disambiguation).
 Mars in 2001 as seen by the Hubble Space Telescope | ||||||||||
| Designations | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Pronunciation |  i /ˈmɑrz/ | |||||||||
| 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 day 1.8808 Julian years 668.5991 sols | |||||||||
| Synodic period | 779.96 day 2.135 Julian years | |||||||||
| Average orbital speed | 24.077 km/s | |||||||||
| Inclination | 1.850° to ecliptic 5.65° to Sun's equator 1.67° to invariable plane[2] | |||||||||
| Longitude of ascending node | 49.562° | |||||||||
| Argument of perihelion | 286.537° | |||||||||
| Satellites | 2 | |||||||||
| Physical characteristics | ||||||||||
| 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 | 0.005 89 ± 0.000 15 | |||||||||
| Surface area | 144,798,500 km2 0.284 Earths | |||||||||
| Volume | 1.6318 × 1011 km3[4] 0.151 Earths | |||||||||
| Mass | 6.4185 × 1023 kg[4] 0.107 Earths | |||||||||
| Mean density | 3.9335 ± 0.0004[4] g/cm³ | |||||||||
| Equatorial surface gravity | 3.711 m/s²[4] 0.376 g | |||||||||
| Escape velocity | 5.027 km/s | |||||||||
| Sidereal rotation period | 1.025 957 day 24.622 9 h[4] | |||||||||
| Equatorial rotation velocity | 868.22 km/h (241.17 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 | 0.15 (geometric) or 0.25 (bond)[5] | |||||||||
| Surface temp. Kelvin Celsius |
| |||||||||
| Apparent magnitude | +1.8 to −2.91[5] | |||||||||
| Angular diameter | 3.5–25.1"[5] | |||||||||
| Surface pressure | 0.636 (0.4–0.87) kPa | |||||||||
| Composition | 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[8] 2.5 ppm Neon 850 ppb HDO 300 ppb Krypton 130 ppb formaldehyde 80 ppb xenon 30 ppb ozone[citation needed] 18 ppb hydrogen peroxide[9] 10 ppb methane[10] | |||||||||
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, yet of all the planets in the Solar System other than Earth, Mars is the most likely to harbor liquid water, and thus to harbor life.[14] Geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface, while small geyser-like water flows may have occurred during the past decade.[15] In 2005, radar data revealed the presence of large quantities of water ice at the poles,[16] and at mid-latitudes.[17][18] The Phoenix lander directly sampled water ice in shallow martian soil on July 31, 2008.[19]
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 two Mars Exploration Rovers (Spirit and Opportunity) and several 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.[20]
Mars can easily be seen from Earth with the naked eye. Its apparent magnitude reaches −2.91,[5] a brightness surpassed only by Jupiter, Venus, the Moon, and the Sun. Mars has an average opposition distance of 78 million km but can come as close as 55.7 million km during a particularly close approach, such as the opposition of 2003.[5]
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