On August 11 and 12, the annual Perseid meteor shower will peak, filling the sky with streaks of light, commonly known as shooting stars. Such visually stunning showers are actually but the tip of the iceberg when it comes to meteoroids slamming into Earth’s atmosphere: Some 10 to 40 tons of material of invisible meteoric dust enters the atmosphere from interplanetary space every day.
The big showers like the Perseids, and later the Leonids in November, are caused when Earth and its atmosphere travel through a region of the sky filled with leftover debris lost by a particular comet. In the case of the Perseids, the small fragments were ripped off the tail of comet Swift-Tuttle, which orbits the sun once every 130 years.
The fragments light up due to the immense friction created when they plough into the gas surrounding the Earth. Each such fragment is approximately the size of a penny, but the more constant, sporadic meteoroids have been around much longer, breaking down over time into tiny fragments only about as wide as a piece of human hair.
“This is interplanetary dust,” said Diego Janches, who studies micrometeoroids at NASA”s Goddard Space Flight Center in Greenbelt, Md. “The fragments are either remnants from the solar system’s formation, or they are produced by collisions between asteroids or comets from long ago.”