How long is a comet s tail

A.� It’s the tail that makes a comet such an impressive sight. The tail, a trail of dust particles driven from the comet by escaping gases, can extend as far as 10,000,000 kilometres long.

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Q.� What causes the escaping gas

A.� Comets are made up largely of ice that melts as it nears the sun, along with dust. Because liquid cannot exist in the vacuum of space the ice moves straight into the gas state: steam. The steam builds up into a huge cloud around the comet, known as the coma.

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The solar winds then blow this coma behind the comet, forming a huge trail of dust and gas.

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Q.� What are comets

A.� They're basically balls of dirty ice that are left over from when our solar system formed, around 4.5 billion years ago. Each comet has a relatively small solid part, the nucleus, which is often no more than a few kilometres in diameter. The nucleus is made up of icy chunks, frozen gases, rock and dust.

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Q.� Ice, but surely the beginning of our solar system was very hot, where did the ice come from

A.� It was certainly very hot in the centre of the hot disk of gas that orbited the sun as the solar system was forming. But on the outer rim of this disk it was much cooler and this is where ice grains formed from the H2O molecules that are readily abundant in space. Over time these ice grains would have collided and formed larger icy bodies, which are now the outer planets of our solar system. The left over chunks of ice became the nuclei of comets, along with other space debris.

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Q.� Where do comets 'live'

A.� Most of them come from the ice regions beyond Neptune where they would have originally formed, in a region known as the Kuiper Belt.

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by Lisa Cardy