Where do the tons of “space dust” that arrive yearly come from?

Many types of space dust are floating around the universe, but the most common kind in our solar system comes from asteroid collisions and comets. Every so often, two asteroids smack into one another, pulverizing into tiny grains of dust. In addition, when a comet (basically a big ball of ice and dust) passes close to the sun, the ice melts, leaving a dusty trail behind. This trail of melted ice and dust forms the comet’s tail.

Asteroids and comets (like the rest of the solar system) were formed out of the large cloud of gas and dust that condensed down to form the sun and planets. A cloud like this is called a nebula. Many nebulae similar to the one that gave birth to the solar system are visible on a clear night with binoculars.

Tracing the dust’s origins back one more step, this nebula formed when an old star ran out of fuel and exploded in a violent supernova. The resulting ash from the explosion drifted out into space and became our mother nebula. On average, a grain of dust anywhere in space has gone through this cycle-nebula, star, supernova, and then nebula again-about 20 times.

Every day, about 40 tons of space dust falls on Earth. Scientists have been studying this cosmic debris for many years now, using dust collectors (essentially space-age flypaper) mounted on high-altitude aircraft like the U-2, and now on satellites that make up NASA’s Stardust mission. Questions still linger about exactly what the stuff is made of, but most astronomers can agree on one thing: Chicken Little was right-as a matter of fact, the sky is falling.