school energy&environment

The planets

Though the Sun is the main actor, the planets are also protagonists, but an important fact must be highlighted: since the mass of the Sun alone makes up 99% of the mass of the entire Solar System, the planets are like crumbs respect to our star. In addition to this, these particles orbit around the Sun at enormous distances respect to their own size. A proportion could be calculated between the size of the Sun and that of Jupiter, the biggest planet in the Solar System and the distances between them could be scaled down by the same factor. If the Sun were the size of a grapefruit, then Jupiter would be the size of a grape about 100 metres away, the length of a football pitch. There is a void space between them, with the exception of some other “grapes”, and darkness, because out in space it is absolutely dark, if one is not looking directly at the Sun.
Since they are not stars, planets cannot produce their own light, but only reflect it. Some appear to be the brightest objects in the sky after the Moon and are visible even at dawn and dusk when the sky is not dark, the last to disappear when the Sun rises and the first to reappear when night falls.
Planets are often accompanied by satellites, or moons, bodies that rotate around them and with which they form a single structure that revolves around the Sun. Moreover, the bigger planets have a ring system, probably the remains of satellites that in ancient times disintegrated and that the force of gravity has kept suspended around the planet.
In the Solar System, planets have been classified in two categories: rocky planets and gas planets. There are four rocky planets and they form the inner Solar System: in order of their distance from the Sun, they are Mercury, Venus, Earth and Mars. They are called rocky planets because their surface is made up mainly of solid material and they are surrounded by a thin atmosphere respect to the size of the planet itself. Moreover, they have moderate sizes and few or no satellites. The gas giants, instead, are part of the outer Solar System; they are Jupiter, Saturn, Uranus and Neptune. They are mainly made up of gas that becomes denser and denser as you move towards the centre. Some hypotheses claim that there is a very small solid nucleus at the centre. These planets have ring systems that can be more or less complex and bright and numerous small satellites that orbit around them.