Space dust on your roof

Not all space rocks are big. Most of the bits that reach Earth are tiny, smaller than a grain of sand.

They are called micrometeorites. Because they are so small, the air slows them down gently. Many survive and float down to the ground.

Scientists think thousands of tonnes of this space dust reach the ground every year. It lands everywhere: on oceans, deserts, fields and rooftops.

Most micrometeorites that are found are tiny balls. They melted as they fell through the air, then cooled into little round beads, some shiny and dark.

Scientists collect them from Antarctic snow and from the bottom of the sea, where they have been piling up for a long time. Some people have found them in dust from gutters on city roofs.

Sorting real space dust from ordinary dust is hard. It needs a microscope, a lot of patience and careful checking by experts.