![]() Mercury in true color (by MESSENGER in 2008) | |||||||||||||
Designations | |||||||||||||
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Pronunciation | /ˈmɜːrkjʊri/ ⓘ | ||||||||||||
Adjectives | Mercurian /mərˈkjʊəriən/,[1] Mercurial /mərˈkjʊəriəl/[2] | ||||||||||||
Symbol | ![]() | ||||||||||||
Orbital characteristics[3] | |||||||||||||
Epoch J2000 | |||||||||||||
Aphelion | 0.466697 AU (69.82 million km) | ||||||||||||
Perihelion | 0.307499 AU (46.00 million km) | ||||||||||||
0.387098 AU (57.91 million km) | |||||||||||||
Eccentricity | 0.205630[4] | ||||||||||||
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115.88 d[4] | |||||||||||||
Average orbital speed | 47.36 km/s[4] | ||||||||||||
174.796° | |||||||||||||
Inclination |
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48.331° | |||||||||||||
29.124° | |||||||||||||
Satellites | None | ||||||||||||
Physical characteristics | |||||||||||||
Flattening | 0.0009[4] | ||||||||||||
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Volume |
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Mass |
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Mean density | 5.427 g/cm3[6] | ||||||||||||
3.7 m/s2 (0.38 g0)[6] | |||||||||||||
0.346±0.014[9] | |||||||||||||
4.25 km/s[6] | |||||||||||||
176 d[10] | |||||||||||||
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Equatorial rotation velocity | 3.026 m/s | ||||||||||||
2.04′ ± 0.08′ (to orbit)[9] (0.034°)[4] | |||||||||||||
North pole right ascension | |||||||||||||
North pole declination | 61.41° [11] | ||||||||||||
Albedo | |||||||||||||
Temperature | 437 K (164 °C) (blackbody temperature)[14] | ||||||||||||
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−2.48 to +7.25[16] | |||||||||||||
−0.4[17] | |||||||||||||
4.5–13″[4] | |||||||||||||
Atmosphere[4][18][19] | |||||||||||||
Surface pressure | trace (≲ 0.5 nPa) | ||||||||||||
Composition by volume | |||||||||||||
Mercury is the first planet from the Sun. It is a rocky planet with a trace atmosphere. While it is the smallest and least massive planet of the Solar System, its surface gravity is slightly higher than that of Mars. The surface of Mercury is similar to Earth's Moon, heavily cratered, with expansive rupes system, generated from thrust faults, and bright ray systems, formed by ejecta. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi), which is about one-third the diameter of the planet (4,880 km or 3,030 mi). Being the most inferior orbiting planet it appears in Earth's sky, always close to the Sun, either as a "morning star" or an "evening star". It stays most of the time the closest to all other planets and is the planet with the highest delta-v needed to travel to from all other planets of the Solar System.
Mercury's sidereal year (88.0 Earth days) and sidereal day (58.65 Earth days) are in a 3:2 ratio. This relationship is called spin–orbit resonance, and sidereal here means "relative to the stars". Consequently, one solar day (sunrise to sunrise) on Mercury lasts for around 176 Earth days: twice the planet's sidereal year. This means that one side of Mercury will remain in sunlight for one Mercurian year of 88 Earth days; while during the next orbit, that side will be in darkness all the time until the next sunrise after another 88 Earth days. Above the planet's surface is an extremely tenuous exosphere and a faint magnetic field that is strong enough to deflect solar winds. Combined with its high orbital eccentricity, the planet's surface has widely varying sunlight intensity and temperature, with the equatorial regions ranging from −170 °C (−270 °F) at night to 420 °C (790 °F) during sunlight. Due to the very small axial tilt, the planet's poles are permanently shadowed. This strongly suggests that water ice could be present in the craters.
Like the other planets in the Solar System, Mercury formed approximately 4.5 billion years ago. There are many competing hypotheses about Mercury's origins and development, some of which incorporate collision with planetesimals and rock vaporization, as of the early 2020s, many broad details of Mercury's geological history are still under investigation or pending data from space probes. Its mantle is highly homogeneous, which suggests that Mercury had a magma ocean early in its history, like the Moon. According to current models, Mercury may have a solid silicate crust and mantle overlying a solid outer core, a deeper liquid core layer, and a solid inner core.
Mercury is a classical planet, therefore observed throughout history and recognized as a planet (or wandering star). In English, it is named after the ancient Roman god Mercurius (Mercury), god of commerce and communication, and the messenger of the gods. The first space probe reached Mercury March 29, 1974 (Mariner 10), and has been visited and explored by other probes.
horizons
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nasa
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MallamaMercury
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