The moon has a lower density because it didn't originate from the metal core of the earth but from the mantle which has a lower density. This theory gives an explanation of the different densities of the earth and the moon. Because of the tidal forces two huge bulges raised one at the side nearest to the sun and the other at the opposite side.The fluid mass oscillated in a very short time and resonance caused the height of the bulge to increase until a mass separated from the earth and cooled to become the moon. In the beginning the earth and moon were one body which rotated very fast. This theory suggests that the moon was removed from the earth. The first one is called the fission hypothesis and was developed by Sir George Darwin (1880). Only Pluto's moon Charon is larger relative to its planet. Our moon is very special not only because it can be seen without telescope but it is also very large compared with the earth. Let us first take a look at our own moon. Usually the moons are divided in two groups by the properties of their orbits: the regular with almost circular orbits and the irregular satellites, with elliptical orbits and inclination.ĭifferent theories have been developed in explaining the forming of moons. There are different kinds of satellites and the moons of one group probably formed in the same way. In examining the origin of the natural satellites it seems necessary to classify the satellites by their characteristics. The following picture (from "Encyclopedia of the Solar System" page 436) shows all the known natural satellites of the gaseous planets in our Solar System. Eight satellites are about the size of our moon, whereas the other moons are much smaller. The total mass of the satellites is only 0,1 times the mass of the earth. The gaseous planets have together at least 60 moons, much more then the terrestrial planets which possess only 3 moons. In fact all the gaseous planets, Jupiter, Uranus, Neptune (and Saturn) are known to have a ring-system. These days we know that Saturn is not the only planet with rings. In 1857 Maxwell theoretically demonstrated that rings consist of numerous tiny masses in independent orbits. In the nineteenth century there were again many discoveries because of the more resolving power of the new telescopes. The next century no new discoveries of moons and rings were made. Later Giovanni Cassini observed the other four large satellites of Saturn. In 1655 Huygens also discovered Titan, the largest moon of Saturn. It was Cassini who first came with the idea that the ring was not solid but composed of particles of ice and rock. In 1655 Christiaan Huygens proposed that the appandages were a disk of matter in the equatorial plane of the planet. At first he thought they were also moons, but then he discovered the earlike structures didn't change position with respect to Saturn. A few months later he observed the 'strange appendages' of Saturn. In 1610 Galileo Galilei discovered with his telescope the four large satellites of Jupiter, which are also known as the Galilean satellites. Some facts about planetary rings and satellitesīefore the invention of the telescope none of the moons of the outer planets was known. Origin of the planetary rings of Jupiter, Uranus and Neptune Some facts about planetary rings and satellites How did planetary rings and satellites form?
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