The IGY artificial earth satellite, 1959 Eta (Vanguard III), carried several sensors for determining the environmental conditions of the satellite. Among these sensors was a microphone for detecting individual impacts of interplanetary dust particles onto selected portions of the metallic shell of the satellite. In addition to contributing to the knowledge gained from direct measurements of interplanetary dust particles with rockets and other satellites about the model average mass and space distributions of small interplanetary dust particles, the dust‐particle sensor on 1959 Eta has revealed an interval of unusual interplanetary dust particle activity. This letter is a report of the important details of the observed interplanetary dust‐particle event, together with some tentative conclusions reached while analyzing the data.

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