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Other names none
Orbital Characteristics
Adjective Mercurian
Aphelion 69,816,900 km
Semimajor axis 57,909,100 km (0.387 098 AU)
Orbital Period 87 earth days
Average orbital speed 107,082.14 mph (47.87 km/s, 172,332 km/h)
Satellites None
Physical Characteristics
Surface area 7.48×107 km (0.147 earths)
Volume 6.083×1010 km (0.056 earths)
Mass 3.3022×1023 (0.055 earths)
Axial tilt 2.11′ ± 0.1
Surface temperature (min) 80 K (-315 °F, -193 °C)
Surface temperature (avg) 452 K (354 °F, 178 °C)
Surface temperature (mean) 340 K (66 °F, 18 °C)
Surface temperature (max) 700 K (800 °F, 426 °C)
Other information
Population 0
Surface Pressure ~10-15 bar (0.001 picobar)
Composition 42% Molecular oxygen

29.0% sodium 22.0% hydrogen 6.0% helium 0.5% potassium

Habitable No, far too hot, far too cold, also too close to Sun

Mercury is the the smallest planet in the Solar System and the closest planet to the Sun, with an orbital period of 87 earth days. Seen from the Earth, it appears to orbit every 116 days, faster then any other planet in the Solar System. It was named after the Roman god Mercury, the fast-flying messenger to the gods. Mercury does not have a surface to retain heat and therefor has a greater temperature variation then any other planet in the Solar System, with an average temperature of 106 K (-268 °F, -167 °C) during night and around 700 K (800 °F, 426 °C) during the day. The poles of Mercury are usually below 180 K (-135 °F, -93 °C). Mercury's axis has the smallest tilt of any other planet in the Solar System. Mercury has the highest Orbital eccentricity. Mercury's surface has a similar appearance to the Moon, and is heavily cratered, meaning it may have been geologically inactive for billions of years.

Mercury is gravitationally locked and rotates in a way which is unique in the Solar System. As seen relative to the fixed stars, it rotates exactly three times for every two revolutions it marks around its orbit. As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefor see only one day every two years.

As Mercury, along with Venus, lies within the Earth's orbit, it can sometimes appear in Earth's sky during the morning and the evening, but not during night.

Structure of MercuryEdit


The internal structure of Mercury: 1. Crust - 100 -300 km thick 2. Mantle - 600 km thick 3. Core: 1800 km radius

Mercury is one of the fourth terrestrial planets in the Solar System, which means it has a solid, rocky surface like Earth. It is the smallest planet in the Solar System, with an equatorial radius of 2,439.7 km. Mercury is smaller, though more massive, then the largest natural satellites in the Solar System, Ganymede and Titan. Mercury consists of approximately 70% metallic and 30% silicate material. Mercury's density is the second highest in the Solar System. Mercury's density is 5.427 g/cm3, which is slightly less than Earth's density of 5.515 g/cm3. If the effect of gravitational compression were to be factored out, the materials of which Mercury is made would be denser, with an uncompressed density of 5.3 g/cm3 versus Earth's 4.4 g/cm3.

Mercury's density can be used to infer details of its inner structure. Although Earth's high density results appreciably from gravitational compression, particularly at the core, Mercury is much smaller and its inner regions are not compressed. Therefore, for it to have such a high density, its core must be large and rich in iron.

Geologists estimate that Mercury's core occupies around 42% of its volume; for Earth this proportion is 17%. Research published in 2007 suggests that Mercury has a molten core.

Mercury's core has a higher iron content than any other planet in the Solar System. Surrounding this core is a 500-700 km mantle consisting of silicates. Based on data from the Mariner 10 mission and Earth-based observation, Mercury's crust is believed to be 100-300 km thick. One distinctive feature of Mercury's surface is the presence of numerous narrow ridges, extending up to several hundred kilometers in length. It is believed that these were formed as Mercury's core and mantle cooled and contracted at a time when the crust had already solidified.

Mercury's core has a higher iron content than that of any other major planet in the Solar System, and several theories have been proposed to explain this. The most widely accepted theory is that Mercury originally had a metal-silicate ratio similar to common chondrite meteorites, thought to be typical of the Solar System's rocky matter, and a mass approximately 2.25 times its current mass. Early in the Solar System's history, Mercury may have been struck by a planetesimal of approximately 1/6 that mass and several thousand kilometers across. The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component. A similar process, known as the giant impact hypothesis, has been proposed to explain the formation of the Moon.

Alternatively, Mercury may have formed from the solar nebula before the Sun's energy output had been stabilized. It would have initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2500 K (4040 °F, 2226 °C) and 3500 K (5840 °F, 3226 °C) and possibly even as high as 10,000 K (17540 °F, 9726 °C). Much of Mercury's surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapor" that could have been carried away by solar wind.

Surface geologyEdit

Mercury's surface is very similar to that of our Moon, showing extensive mare-like plains and heavy cratering, indicating that Mercury has been geologically inactive for billions of years. It is the least understood of all terrestrial planets due to our knowledge of Mercury's geology being based only on the 1975 Mariner flyby and terrestrial observations.

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