Every day, Earth accumulates more than 100 tons of space dust. The space dust is smaller than one-tenth the width of a human hair. About 75% of the dust comes from the collisions of asteroids in the Asteroid Belt just beyond Mars. The other 25% gushes from icy comets when they spew material into space as they heat up when nearing the sun. There is a small amount of space dust that floats through the galaxy, called virginal space dust, that is part of the mix too.

On the average, every square yard of the planet receives one speck of space dust each day. They float around in the air with regular terrestrial or Earth-based dust. The space dust is breathed and eaten, in every home and in every carpet. Everyplace where dust is found, space dust is mixed in it.

As the dust is freed from the asteroids or comets, the sun’s gravity pulls it to the center of our solar system. If the dust passes within 60 miles of Earth, it slows down from traveling ten of thousands of miles per hour when it collides with the gas atoms in our atmosphere. After a mile or two, the dust stops completely and is trapped in our atmosphere. Our atmosphere moves the trapped dust all around. In one cubic inch of atmosphere there are a million times more pieces of space dust than in outer space. Slowly the dust slips through the gas atoms and toward Earth. In one month, the dust will reach Earth’s surface and add its weight to the planet.

For scientists to study space dust, they have to capture it before it gets mixed in with Earth-based dust. In 1974, NASA began mounting sticky fly tape on the highest-flying planes to capture space dust. The Large Area Collector (LAC) is an instrument that attaches to the wing of NASA’s ER-2 plane. The LAC has 8-inch silicon-oiled plastic plates. Each plate can capture about 10 extraterrestrial particles per hour. Spacecraft have been sent to capture the space dust. In February 1999, NASA launched the Stardust spacecraft. Its mission is to collect dust from the inner solar system. In 2004, Stardust will approach a comet and take a sample of the dense haze of gas and dust surrounding the nucleus. Three other spacecraft are scheduled to sample or analyze comet dust too.

After the dust is returned, special care is given to keep the space dust laboratories free of any Earth-based dust to avoid contamination. There is an actual library of space dust at the Johnson Space Center in Houston.

So far, the space dust analysis shows that they are composed of common Earth elements, rocks and minerals. Some examples are sapphire, diamond, graphite, carbon, olivine, glass embedded with metal and sulfides, and micropebbles coated in thick layers of carbon-rich material.