The solar system formed about 4.6 billion years ago, when part of a giant molecular cloud experienced a gravitational collapse. The centre became the Sun, which comprises more than 99 per cent of the solar system’s total mass. The rest of the cloud became a dense, flat rotating disk of gas from which planets formed, called a protoplanetary disk. In our solar system, most of that disk became the eight planets, each of which orbits the Sun.
There are two different categories of planets: gas giants and terrestrials. The gas giants are the four outer planets: Jupiter, Saturn, Uranus and Neptune. They are much bigger than the terrestrial planets and are mostly made of helium and hydrogen, although Uranus and Neptune also contain ice. All of the outer planets have ring systems made of cosmic dust. These planets comprise more than 90 per cent of the rest of the solar system’s mass.
The four inner planets are very close to the Sun. To grant perspective, for example, the distance between Jupiter and Saturn is larger than the radius of all the inner planets put together. These terrestrials are made up from rocks and metals, have no ring systems and have a low number of satellites (moons). They include Mercury, Venus, Earth and Mars. Except for Mercury, the inner planets also have recognisable weather systems operating in their atmospheres.
In addition to the eight main planets, there are also dwarf planets such as Pluto. The five dwarf planets are Ceres, Pluto, Haumea, Makemake and Eris. In addition, the solar system is home to numerous small solar system bodies, which include all minor planets, asteroids and comets.
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Hypothetically speaking, Saturn is so light that if it were placed in a galactic sized swimming pool it would float. Hard experiment to carry out though!
2) Binary system
Due to the size and short orbital distance between Pluto and its largest moon Charon, it is often treated as a binary system as its centre of mass lies with neither.
3) Dust bowl
Mars, often referred to as the ‘red planet’, is actually red thanks to its coating of iron dust, which prevails in its carbon dioxide-rich atmosphere.
4) Gas giant
Jupiter is so large that over 1,300 Earths could fit inside it and it has a mass which is 2.5 times larger than the total of all other eight planets combined.
During the day on Mercury, the closest planet to our Sun in the solar system, the temperature reaches up to a positively scorching 430 degrees Celsius.
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