Micrometeorite
A micrometeorite is a tiny particle of space dust, usually smaller than a millimetre, that has reached Earth's surface.
Not every space rock is big enough to hold in your hand. Most extraterrestrial material reaching Earth arrives as tiny grains, usually less than a millimetre across. Those that reach the ground are called micrometeorites. Estimates vary widely, but thousands of tonnes of this dust probably settle on Earth every year.
Some micrometeorites melt completely as they enter the air and cool into tiny balls called cosmic spherules, often with a shiny surface and fine crystal patterns. Others survive partly or fully unmelted and keep the original minerals of their parent asteroids or comets. They give scientists samples from many different sources, including some not found among larger meteorites. Researchers collect them from Antarctic snow and ice, deep-sea mud and desert sands, and in the 2010s scientists confirmed that they can be found among the dust on city rooftops.
Finding them needs a microscope, a magnet and a great deal of patience, because rooftop dust is full of look-alike spherules from industry. Any search on a roof needs the owner's permission and an adult in charge, with safety equipment.
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Level: Explorer Ages 10 and up