We’ve known for a while that Earth is under a constant rain of space dust, and that it’s copious. Given its microscopic size, however, it’s been very hard to obtain an accurate estimate of the quantity.

Such micrometeorites are no bigger than a fraction of a millimeter, shed like space dander from passing comets and asteroids.

After two decades of collecting the stuff in Antarctica, an international team of scientists now has a number: around 5200 tons of micrometeorites smaller than 700 micrometers (0.7 millimeters), every year.