How old is the solar system believed to be

Before it was moulded into a neat set of planets, every scrap of matter in the solar system was part of a gigantic nebula - a floating interstellar cloud. This giant cloud was made up of dust, hydrogen, and other gases. It began to collapse in on itself after becoming gravitationally unstable.

This was possibly because of a nearby supernova - an exploding star - sending shock waves rippling through space. Gravity then caused dust and gas to be continually tugged to the centre of the cloud, making its core very hot and dense. Gregory says, 'It became a snowball effect. As more matter got pulled in, the centre got denser, increasing the gravity and pulling even more dust inwards. Once the centre became hot and dense enough it triggered nuclear fusion. Then visible light flooded the solar system for the first time.

This flat disc, called the protoplanetary disc, was where the planets formed. As this rotating disc span around the Sun, it began to cool and form different types of solid material. Gregory says, 'Near to the Sun, the temperature was very high, so minerals and metals formed. And on the edge of the disc, far away from the heat of the Sun, less volatile solids like ice and ammonia formed.

Gradually they got larger and larger, sweeping up all the leftover dust, until they grew into the planets we recognise today. Part of a chondrite found in the Sahara desert, showing the formation of chondrules. The hot, rocky material near the centre of the solar system was sculpted into terrestrial planets with metal cores: Mercury, Venus, Earth and Mars.

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The the Allende meteorite of was the first to show inclusions that were extremely rich in calcium and aluminum. As a red giant, our Sun will become about 2, times brighter than it is now! How Old Is the Sun?

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