Made of dust, ice, carbon dioxide, ammonia and methane, comets resembledirty snowballs. You may remember them as blurry smudges in the sky. Cometsorbit the Sun, but most are believed to inhabit in an area known as the OortCloud, far beyond the orbit of Pluto. Occasionally a comet streaks through theinner solar system; some do so regularly, some only once every few centuries.
Heads and tails
As a comet nears the Sun, its icy core boils off, forming a cloud ofdust and gas called a head, or coma. Comets become visible when sunlight reflectsoff this cloud. As the comet gets closer to the sun, more gas is produced.
The gas and dust is pushed away by charged particles known as thesolar wind, forming two tails. Dust particles form a yellowish tail, andionized gas makes a bluish ion tail. A comet's tails, like these on cometHalley, always points away from the Sun.
When Earth crosses the path of a comet, even if the comet hasn't beenaround for a few years, leftover dust and ice can create increased numbers ofmeteors.
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