Meteoroid stream
A trail of dust and small particles spread along the orbit of a comet or asteroid, which produces a meteor shower when Earth passes through it.
When a comet nears the Sun, escaping gas drags out dust and small particles, called meteoroids. They leave at slightly different speeds, so they drift ahead of and behind the comet, gradually spreading out along its orbit. Over many returns this builds a meteoroid stream, a tube of debris that can eventually fill the whole orbit. Within it, younger, denser strands known as dust trails can still be traced to particular returns of the parent comet.
If Earth's orbit crosses a stream, we get an annual meteor shower on about the same dates each year. The Perseids come from Comet 109P/Swift–Tuttle, and both the Orionids and Eta Aquariids come from Comet Halley. Not every stream comes from an obvious comet. The Geminids come from 3200 Phaethon, an object that looks like an asteroid, and the Quadrantids may be linked to asteroid 2003 EH1, possibly a dormant or broken comet.
Streams evolve: planetary gravity shifts them, so showers can strengthen, weaken or produce outbursts. Stream meteoroids are typically millimetres in size and fragile, and no meteorite has been reliably linked to a shower. You recognise a stream from the sky by meteors sharing a radiant and speed.
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