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The direct evidence on the micrometeorite environment near the Earth is obtained from piezoelectric sensors ( essentially microphones ) and from wire gages ; ;

these instruments are installed on rockets, satellites, and space probes.

Statistically, the most significant data have been collected from the sensors on 1958 Alpha ( Explorer 1 ), 1958 Delta 2 ( Sputnik 3 ), and 1959 Eta ( Vanguard 3 ).

These vehicles, with large sensitive areas, have collected data for long enough times to give reliable impact rates for the periods of exposure.

Many other vehicles with smaller sensitive-area exposure-time products contribute some information.