What are micrometeorites and can I collect them?
Micrometeorites are tiny particles of space dust, smaller than about 2 mm, that survive their fall to Earth. Thousands of tonnes land every year, and with patience and a microscope you can search for them.
Most of the space material reaching Earth arrives as micrometeorites: particles generally smaller than about 2 mm, most of them a fraction of a millimetre. They come from comets and from collisions between asteroids. Because they are so small and light, many are slowed gently by the upper atmosphere instead of vaporising.
They come in several kinds. Cosmic spherules melted completely during entry and froze into tiny balls, often with a shiny surface patterned with crystals, a bit like a minuscule golf ball, or with a bright metal bead. Others, called unmelted or partly melted micrometeorites, kept their original texture and are especially valuable because they preserve pristine material from space.
Scientists collect them from places where they accumulate and are not mixed with too much Earthly dust, such as Antarctic ice and snow and deep-sea sediments. In the mid-2010s, a study confirmed that micrometeorites can also be found in sediment from city rooftops and gutters, opening up a hobby for anyone patient.
To try it, collect sediment from gutters or flat roofs, wash it through fine sieves, dry it, and pull out magnetic particles with a magnet in a plastic bag. Then examine them under a microscope. The hard part is identification: the vast majority of magnetic spheres are industrial or from fireworks, welding and vehicles. Genuine micrometeorites show particular textures and compositions, so confirming one usually needs a powerful microscope and expert help. Safety matters. Adults should do any work on roofs or ladders, use gloves when handling gutter dirt, and wash hands afterwards. Children can help with sieving and looking, but should never taste samples, heat them or use chemicals. Always ask permission before collecting from someone else's roof.