Four years of dust particle measurements in cislunar and selenocentric space from Lunar Explorer 35 and OGO 3.

Since July 1967, knowledge concerning the distributions of picogram size particulate matter in selenocentric space has been obtained from the Lunar Explorer 35 dust particle experiment. For almost 40% of the time, the mean sporadic cumulative flux is quite similar to the flux in interplanetary space. However, there are fluctuations of an order of magnitude during major meteor showers. The coincident increase of the flux in selenocentric space during the shower periods has been observed for the fourth year. The 100-picogram sensor does not show an increase during shower times, indicating a mass threshold of less than 100 picograms for particles with velocities equal to or greater than lunar escape velocity. The flux values from Lunar Explorer 35 are compared to other long-lifetime measurements in selenocentric, cislunar and interplanetary space with excellent agreement for masses less than one nanogram.