The Dust Cloud about the Earth

Abstract

THE existence of a high concentration of interplanetary dust near the Earth has recently been demonstrated from rocket, satellite and space-probe observations of acoustical impact. Suspected by Beard¹, the concentration has been proved by me² and by Hibbs³. To a distance of approximately 10⁵ km., the concentration falls off roughly as the inverse 1.4 power of the distance from the Earth's surface (Fig. 1). The impact-rates on randomly oriented surfaces include all particles greater than mass 10⁻⁹ gm. and are adjusted for the differing sensitivities of the equipment. Data are from six U.S. rocket firings; from satellites Explorer I (1958 Alpha), Sputnik III (1958 Delta) and Vanguard III (1959 Eta) ; and from the space probes Explorer VI (1959 Delta) and Pioneer I. At some distance greater than 10⁵ km., the impact-rates approximate those expected from calculations on the zodiacal cloud ; the maximum concentration with respect to the interplanetary medium is perhaps as high as 10⁵.