Densities terrestrial bodies

Table I. Observed and Zero-Pressure Densities of Terrestrial Bodies...

The terrestrial planets and the Moon are differentiated, with dense iron-rich cores and rocky mantles. The uncompressed densities of Earth and Venus are similar. Mercury has a high density which suggests it has relatively large core. Conversely, the Moon has a low density, indicating a very small core. There is little observational evidence that asteroids are differentiated except for Vesta and Ceres (Thomas et al. 2005). However, iron meteorites from the cores of differentiated asteroids are quite common, and the irons found to date come from several dozen different parent bodies (Meibom Clark 1999). Most meteorites come from asteroids that never differentiated. These chondritic meteorites consist of intimate mixtures of heterogeneous material millimeter-sized rounded particles that were once molten, called chondrules, similarly sized calcium-aluminum-rich inclusions (CAIs), and micrometer-sized matrix grains. 

It is a metallic body of a bluish colour with a dark mddy tinge it is igneous and fusible, and occupies a middle position between Sol and Luna, gold and silver. It is composed of quicksilver, but impure, unfixed, terrestrial, combustible, mddy, and not clear and, in like manner, of sulphur wanting in fixity, purity, and density. Bad and feeble sulphur, like a father of ill complexion and disposition, copulates with a noble mother, that is, with quicksilver, and generates copper of good quality, a son of bluish colour, tinged with dark red. 

It was at one time thought that even the terrestrial planets themselves formed directly by condensation from a hot solar nebula. This led to a class of models called heterogeneous accretion models, in which the composition of the material accreting to form the Earth changed with time as the nebula cooled. Eucken (1944) proposed such a heterogeneous accretion model in which early condensed metal formed a core to the Earth around which silicate accreted after condensation at lower temperatures. In this context the silicate-depleted, iron-enriched nature of Mercury makes sense as a body that accreted in an area of the solar nebula that was kept too hot to condense the same proportion of silicate as is found in the Earth (Lewis, 1972 Grossman and Larimer, 1974). Conversely, the lower density of Mars could partly reflect collection of an excess of silicate in cooler reaches of the inner solar nebula. So the... 

The Earth s Moon is the fifth largest satellite in the solar system. Its distance from the Earth is only 30 times the diameter of the Earth, the orbit is elliptical. The nearest distance to Earth (perigee) is 363 104 km, the largest distance (apogee) is 405 696 km. The semi major-axis is 384 399 km. The orbital period is 27 d 7 h 43.1 min which exactly corresponds to its rotational period. The orbit of the Moon is inclined to the plane of the ecliptic by about 5.1°. The mean radius of the Moon is 1737.1 km which is 0.273 that of the Earth s radius. The surface area is about 37 X 10 km. The density is relatively high and corresponds more to that of terrestrial planets and is 3.34 gcm . Our Moon is a relatively dark body with a surface albedo of 0.12. 

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