The formation of the Solar System

Some of the planets in our solar system (© Arteclick).

We live on planet Earth, which orbits around the Sun, the star in our Solar System, which in turn is located inside the Orion Arm of our galaxy, the Milky Way.

The Solar System was formed 4.5 billion years ago. It contains many astronomical bodies of all kinds and sizes. The 8 planets that orbit the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The Solar System

The Italian astronomer, Galileo Galilei, perfected the telescope and discovered that the Earth revolved around the Sun. (© Arteclick).

The Solar System is defined as the collectenion of astronomical objects that are subject to the Sun’s gravitational field.

It is part in the Orion Arm, a minor spiral arm of our Milky Way galaxy.

At the centre of the Solar System is the Sun. Around our star gravitate, in order of increasing distance, the 4 rocky planets Mercury, Venus, Earth, Mars; an asteroid belt composed of small rocky bodies, 4 gaseous planets, Jupiter, Saturn, Uranus, Neptune; a second belt called the Kuiper belt, composed of icy objects. Far beyond this belt is the Oort cloud, made up of scattered objects.

It also includes satellites and rings that orbit these different planets, dwarf planets, asteroids, comets, meteorites and dust particles.

The planets of the Solar System

The other bodies of our solar system

There are several other types of objects, some smaller and some larger, that orbit around the Sun. Some of these bodies also orbit around the planets, these are the satellites or the moons. There are also asteroids and comets as well as dwarf planets.

Asteroids They are rocky and/or metallic bodies, varying in size from one centimetre to 800 kilometres. They come from an unformed planet. They occur mainly between the orbits of Mars and Jupiter. Some asteroids leave this area and may take trajectories that approach the Earth. They are then called: Earth-Crossing Asteroids (ECA). Meteorites These are rocky and/or metallic bodies that arrive on the earth's surface after passing through the atmosphere. A meteorite 15 kilometres in diameter struck the Earth 65 million years ago destroying dinosaurs. During their journey through the atmosphere, we call them shooting stars.	Comets A comet is a small body that can reach 10 kilometres in diameter. It is made of ice and dust. As it approaches the Sun, it begins to melt and develops a dust tail several million kilometres long. This reflects sunlight and makes the comet visible from Earth.	Satellites and dwarf planets Satellites or moons are spherical bodies. They are not massive enough to be included in the category of planets. They orbit the planets. For example, Phobos and Deimos are the two satellites of the planet Mars, while the Moon is the satellite of the Earth. In contrast the dwarf planets orbit the Sun. There are 5 dwarf planets: Eris, Pluto, Ceres, Makemake and Haumea.

The Sun, the central star of our Solar System.

The Sun is the star closest to the Earth. The Earth-Sun distance is about 150 million kilometres and defines the astronomical unit (1 AU).

The mass of the Sun represents the majority of the mass of the solar system. It is used as a unit of mass for stars.

Solar energy, of vital importance to the Earth and especially to life, is produced by the nuclear reactions that take place in the heart of the Sun.

The Sun is about 5 billion years old and will continue to shine for another 5 billion years before evolving into a red giant and then dying.

A solar flare seen in ultraviolet with false colors (© Nasa).