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The Learning Kingdom's Cool Fact of the Day for April 9, 1999
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How much cosmic dust falls to Earth?
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Every year, about 33,000 tons (30 million kilograms) of dust falls
into Earth's atmosphere and settles down to the surface of the planet.
The largest of these particles would just barely be visible without a
microscope, and most are far smaller.
Most of the dust comes from a belt called the zodiacal cloud, which is
formed by evaporation from comets, colliding asteroids, and a few other
sources. This diffuse band of dust is the cause of the "zodiacal
light," a faint glow of reflected sunlight that can sometimes be seen
just before dawn or after sunset, if the sky is very dark and clear.
A small amount of cosmic dust comes from outside the solar system.
Although they are rare, particles of extra-solar dust are important to
science because they reveal what conditions are like in interstellar
space.
Cosmic dust is collected in the stratosphere by NASA:
http://www-curator.jsc.nasa.gov/curator/dust/dust.htm
Another Cool Fact about things that fall from space:
http://www.cool-fact.com/archive/1997/03/20.html
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