![]() ![]() Several theories have been proposed to explain Mercury's high metallicity. Mercury has a higher iron content than any other major planet in our solar system. It is believed that these were formed as Mercury's core and mantle cooled and contracted after the crust had solidified. One very distinctive feature of Mercury's surface is numerous ridges, some extending over several hundred kilometers. Mercury's crust is thought to be about 100–200 km thick. It is generally thought that early in Mercury's history, a giant impact with a body several hundred kilometers across stripped the planet of much of its original mantle material, resulting in the relatively thin mantle compared to the sizable core (alternative theories are discussed below). (Earth's core occupies about 17% of its volume.) Geologists estimate that Mercury's core occupies about 42% of its volume. Therefore, for it to have such a high density, its core must be large and rich in iron. While the Earth's high density results partly from compression at the core, Mercury is much smaller and its inner regions are not nearly so compressed. Mercury's high density can be used to infer details of its inner structure. Internal structure: core, mantle and crust When corrected for gravitational compression, Mercury is in fact denser than Earth, with an uncompressed density of 5.3 g/cm³ versus Earth's 4.4 g/cm³. The density of the planet is the second-highest in the solar system at 5.43 g/cm³, only slightly less than Earth's density. ![]() Mercury consists of approximately 70% metallic and 30% silicate material. It is the smallest of the four, with a diameter of 4879 km at its equator. ![]() ![]() Mercury is one of the four terrestrial planets, meaning that like the Earth it is a rocky body. The Hebrews named it Kokhav Hamah (כוכב חמה), "the star of the hot one" ("the hot one" being the Sun). The Chinese, Korean, Japanese, and Vietnamese cultures refer to the planet as the water star, based on the Five Elements. In India, the planet was named Budha (बुध), after the son of Chandra (the Moon). Before the 5th century BC, Greek astronomers believed the planet to be two separate objects: one visible only at sunrise, the other only at sunset. The astronomical symbol for Mercury, displayed at the top of the infobox, is a stylized version of the god's head and winged hat atop his caduceus, an ancient astrological symbol. The Romans named the planet after the fleet-footed messenger god Mercury, probably for its fast apparent motion in the twilight sky. Surface temperatures on Mercury range from about 90 to 700 K (-180 to 430☌), with the subsolar point being the hottest and the bottoms of craters near the poles being the coldest. The planet has a large iron core which generates a magnetic field about 1% as strong as that of the Earth. It has no natural satellites and no substantial atmosphere. Physically, Mercury is similar in appearance to the Moon as it is heavily cratered. Comparatively little is known about the planet: the only spacecraft to approach Mercury was Mariner 10 from 1974 to 1975, which mapped only 40%–45% of the planet's surface. It ranges in brightness from about −2.0 to 5.5 in apparent magnitude, but is not easily seen - its greatest angular separation from the Sun (greatest elongation) is only 28.3° (it can only be seen in twilight). Mercury ( IPA: /ˈmɛːkjəri/) is the innermost and smallest planet in the solar system, orbiting the Sun once every 88 days. Note: This article contains special characters. ![]()
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