Meteor head echo
A meteor head echo is a radar reflection from the cloud of plasma moving with a meteoroid, used to measure its speed.
When a meteoroid enters the atmosphere, it produces a small cloud of ionised gas, or plasma, travelling with it. Powerful radars can detect a reflection from this moving plasma, called a head echo. The radar measures how the echo's distance changes over time, giving the meteoroid's speed and deceleration with great precision.
Head echoes are different from the more common trail echoes, which come from the long column of plasma left behind. Head echo observations require very large radars, such as the Arecibo telescope in Puerto Rico before it collapsed in 2020 or high-power systems in Peru, Norway and elsewhere.
These radars detect meteoroids far smaller than those visible to the eye, down to tiny grains of micrograms. They show that a large share of the dust hitting Earth comes from fast, often retrograde orbits linked to comets. Head echo studies help estimate the total amount of space dust reaching Earth each day.
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Level: Expert Advanced