Solar system

Article

May 25, 2022

The solar system is a planetary system consisting of a variety of celestial bodies held in orbit by the gravitational force of the Sun, which also includes the Earth: with a diameter of about 120-130 au - 0.0019 light years - (if intended as the area of ​​the space that is subjected to the solar wind, leaving out the immense area subjected only to solar gravity) is located in the Orion arm of the Milky Way, orbiting around the galactic center at a distance of about 26700 light years and a speed of 230 km / s ; it is estimated that the solar system takes about 230 million years to complete one revolution around the galactic center. It consists of the Sun, which alone possesses 99.86% of the power of the entire system, of eight planets (four inner rocky planets and four outer gas giants) and five dwarf planets, their respective natural satellites, and many other bodies minors; this last category includes asteroids, largely divided between two asteroid belts (the main belt and the Kuiper belt), comets (mainly located in the hypothetical Oort cloud), meteoroids and interplanetary dust. distance from the Sun, the eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune; the five dwarf planets are: Ceres, located in the main asteroid belt, Pluto, Haumea, Makemake, and Eris. The solar wind, a flow of plasma generated by the continuous expansion of the solar corona, permeates the entire solar system, creating a bubble in the interstellar medium known as the heliosphere, which extends beyond half of the diffuse disk.

History of observations

Although many of the major celestial bodies in the solar system were already known since ancient times, the concept itself was ignored as there was mostly an idea of ​​a geocentric system with the Earth at the center of the universe. One of the first to imagine a heliocentric system was Aristarchus of Samo, but his ideas did not take hold in the community of philosophers and thinkers of the time. It was only in the sixteenth century that Nicolaus Copernicus proposed the modern vision of the solar system, with the Sun at the center and the planets known then orbiting around. The only known bodies of the solar system, however, were only the four terrestrial planets, Jupiter, Saturn, the Sun and the Moon. In the following century, with the invention of Galileo Galilei's telescope, other minor bodies were discovered, such as the Medici satellites, the rings of Saturn and some comets and for about 200 years it was not thought that there could be other objects in the solar system, in particular was the firm belief that the planets were only those then known. In 1781, William Herschel's discovery of Uranus challenged the preconceptions that the scientific community had, generating doubts about the possibility that transuranic planets existed. A few years later, in 1801, Giuseppe Piazzi declared that he had discovered a new planet, between the orbits of Mars and Jupiter; it was actually Ceres. The conclusion came by excluding that it could be a comet and not knowing other objects other than planets and comets, completely unaware that he had discovered a new type of object, the asteroid. Since then the discoveries of new objects multiplied, in particular many new asteroids were discovered. In 1846 a planet was discovered in a completely revolutionary way: before direct observation, the perturbations of the orbit of Uranus were calculated and it was deduced that a planet had to exist at a precise point in space to justify the discrepancies observed. A few days later, Johann Gottfried Galle and Heinrich Louis d'Arrest confirmed the presence of Neptune less than one degree away from the calculated point. In 1930, the discovery of Pluto increased the number of known planets to nine, then believed to be an object of ma