The Ariel ІІ micrometeorite penetration measurements

Abstract

The upper limits of the penetration rates of the thin aluminium foil sensors of the Ariel ІІ satellite are lower by up to four orders of magnitude than the flux measured by microphone detectors in the vicinity of the Earth, if the sensitivity of the two types of sensor is equated in terms of solid impacting particles. It may be postulated that the flux comprises loose agglomerates of low density, and that the depth of penetration is much less than the particle diameter. Although this removes the discrepancy between the microphone and penetration detector flux rates, the postulate may introduce a serious discrepancy between the penetration detectors and the flux of faint radar meteors. This comparison would indicate a particle density of ca . 1 g/cm 3 or greater and would require that the flux of particles of mass 10 -7 and 10 -9 g is respectively 1 and 3 orders of magnitude lower than the flux indicated by many microphone measurements. The penetration results cannot be compatible simultaneously with both microphone and radar meteor data and other information suggests that the validity of some of the microphone data may be in doubt. The penetration lifetime of thin aluminium in space is shown to be much greater than previous estimates.