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Mars
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Mars
Pronunciation
i/'m?rz/
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
Average 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 perihelion
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
1.6318×1011 km3
0.151 Earths
Mass
6.4185×1023 kg
0.107 Earths
Mean 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 (241.17 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
0.170 (geometric)
0.25 (Bond)
Surface temp.
Kelvin
Celsius
min
mean
max
186 K
210 K
293 K
-87 °C
-63 °C
20 °C
Apparent magnitude
+1.6 to -3.0
Angular diameter
3.5–25.1"
Surface 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
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 successful 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 Jupiter, Venus, the Moon, and the Sun. Optical ground based telescopes are typically limited to resolving features about 300 km (186 miles) across when Earth and Mars are closest, because of Earth's atmosphere.
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