1.3 Terrestrial and Jovian Planets: Geology of the Solar System

1.3 Terrestrial and Jovian Planets: Geology of the Solar System

The planets fall quite nicely into two groups: the terrestrial, Earth-like planets, Mercury, Venus, Earth, and Mars, and the Jovian, Jupiter-like planets, Jupiter, Saturn, Uranus, and Neptune. Pluto was recently demoted to a dwarf planet, a new class of solar system objects that have an orbit around the Sun but share their space with other celestial bodies.

The most obvious difference between the terrestrial and the Jovian planets is their size. The largest terrestrial planets, Earth and Venus, have diameters only 1/4 as great as the diameter of the smallest jovian planet, Neptune. Also, their masses are only 1/17th as great as Neptune’s. Hence, the Jovian planets are often called Giants. Because of their relative locations, the four Jovian planets are also referred to as the outer planets whereas the terrestrial planets are called the inner planets. As we shall see, there appears to be a correlation between the location of these planets within the solar system and their sizes.

Other dimensions in which the terrestrial and the Jovian Planets differ include density, chemical makeup, and rate of rotation. The densities of the terrestrial planets average about five times the density of water, whereas the Jovian planets have densities that averaged only 1.5 times that of water. One of the outer planets, Saturn, has a density only 0.7 times that of water which means that Saturn would float if placed in a large enough water tank. Differences in the chemical compositions of the planets are largely responsible for these density differences.


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