How are planets born?
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To build a planetary system, all you need is a cloud of gas and dust surrounding a young star, and lots of patience. Gravity does the rest.
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Stars are born from collapsing clouds of gas and dust. Most of this material ends up in the central star, but a few percent or so form a flat, rotating disc around the star. Over a few million years, small dust particles within this disc grow into centimetre-sized pebbles — the first building blocks of planets. 4.6 billion years ago, our own planetary system grew from such a disc. Because of their planet-forming potential, these discs are known as protoplanetary discs, or proplyds for short.
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Starting with tiny snowflakes, you can make larger snowballs and giant snowmen. Likewise, small particles of gas and dust can grow into planets.