Made of dust, ice, carbon dioxide,
ammonia and methane, comets resemble dirty snowballs. You may remember them as
blurry smudges in the sky. Comets orbit the Sun, but most are believed to
inhabit in an area known as the Oort Cloud, far beyond the orbit of Pluto.
Occasionally a comet streaks through the inner 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 of dust and gas called a head, or coma. Comets
become visible when sunlight reflects off 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 the solar wind, forming two tails. Dust particles
form a yellowish tail, and ionized gas makes a bluish ion tail. A comet's
tails, like these on comet Halley, always points away from the Sun.
When Earth crosses the path of a
comet, even if the comet hasn't been around for a few years, leftover dust and
ice can create increased numbers of meteors.
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