/images/transform/v1/crop/frm/XBxJDq6WLub2UphQ8wEq23/ba6aa038-f8e6-4508-8bb5-8dfc40528a76.jpg/r0_318_5431_3387_w1200_h678_fmax.jpg The Moon is the Earth’s constant companion, with us every step of the way as we orbit our Sun. But have you ever wondered how it got there, or how the other planets get their multitudes of moons?
The building of planets happens at the same time as the building of stars, in a chaotic and messy process. A giant cloud of dust and gas collapses and forms a star and through this collapse, a disc of dust and gas forms around the star – very similar to what happens when someone tosses a ball of pizza dough in the air. And from this disc, planets can grow. The collision meant that all the bits making up the baby Earth and Theia got mixed together, and for a very short time there was a ring around the Earth, which the Moon grew from. From that chance collision we got something beautiful, our Moon.
From simulations of this crash, it seems that Theia didn’t collide head-on with the baby Earth, but that it knocked the side of the baby Earth off. However, not all moons had such destructive beginnings.
It was from this chaos and destruction that our Moon was born. The baby planet that would become the Earth suffered a collision with a Mars-sized object called Theia. The building of planets is a messy process filled with chaos, crashes, and collisions. Sometimes the building blocks of planets stick together and continue to grow, other times the crashing together of these building blocks can lead to devastating destruction.
This is the case for Mars’ two moons – Deimos and Phobos – which are captured asteroids. This means that as the asteroids were travelling past Mars they got caught in its gravity, becoming bound to Mars. Some planets capture passers by in their web of gravity and gain moons that way.
This is especially the case for the larger moons of the giant planets, like Jupiter’s moons – Io, Europa, Ganymede and Callisto – or Saturn’s largest moon – Titan. But the smaller ones can be captured as they wander past, just like the moons of Mars. The giant planets – Jupiter, Saturn, Uranus and Neptune – are a different story altogether. Giant planets form in much the same way as stars do, from a cloud with a big disc around them, and so their moons can grow from the planet’s disc in the same way that the planets grow from the star’s disc. So just like planets growing around stars, moons can grow around the giant planets.
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- Headline: SPACE SUNDAY: The magic of the moon a bit like making a pizza | The examiner
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