A planetary system, such as our Solar System, includes a star, planets that orbit the star, their moons, and all the other objects whose movements are affected by the gravity of the star.

In the outer regions of the vast Milky Way Galaxy, around 4.5 billion years ago, perhaps caused by a shockwave of an exploding star somewhere in the distance, a dense cloud of stardust began to spin and whirl. At the centre of the vortex, gravity¹ began to pull more and more matter together – a yellow star we have named the Sun came into being. It grew bigger and bigger, eventually amassing more than 99 per cent of available matter.

The remnants also began to clump up, clumps smashing into one another, becoming larger and larger. Some grew big enough, forming planets, dwarf planets, and moons, while smaller leftover pieces became asteroids, comets, and meteoroids.

Since only rocky material could withstand the heat of the Sun, the closest planets – Mercury, Venus, Earth, and Mars – became small and solid with rocky surfaces. The materials we are used to seeing as ice, liquid, or gas settled in outer regions of our solar system. Therefore, gas giants Jupiter and Saturn and ice giants Uranus and Neptune formed further away from the Sun.

Hence, our Solar System consists of our star, the Sun; planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets such as Pluto, dozens of moons, and millions of asteroids, comets, and meteoroids.

¹ Gravity is an invisible force by which a body draws objects toward itself. Anything with mass has gravity, and objects with more mass have more gravity. Besides, gravity is greater closer to the body. Gravity explains, for example, how stars and planets form, why planets orbit stars, and why you and I can walk on Earth.

Bibliography

Boyle, R. 2024. Our Moon a Human History. London, United Kingdom: Hodder & Stoughton. 313 p. ISBN 9781529342789. Pages 15-16, 22-23.

Rutherford, A. 2014. Creation The Origin of Life. London, United Kingdom: Penguin Books. 272 p. ISBN 9781780229072. Page 55-56.

NASA Science (2021). Solar System Exploration. Available at: https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth (Accessed: 1 September 2022).

Cohen, A. & Cox, B. 2023. The Universe. Dublin, Ireland: HarperCollinsPublishers. 272 p. ISBN 9780008389352. Pages 100-102, 127, 154-155.

Kilpua, E. & Koskinen, H. 2023. Aurinko Tuttu ja Tuntematon Tähtemme. Helsinki, Finland: Gaudeamus. 318 p. ISBN 9789523452329. Pages 64-65, 68.

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