Near earth environment

Planet Earth provides an interface to the interplanetary environment; its atmosphere forms a protective shield against direct impacts and erosion and is a medium in which to observe the approach of meteoroids and even to capture intact smaller meteoroids. The Earth’s gravitational well enhances the flux of interplanetary dust and modifies its velocity distribution. We consider the effect of the Earth on the dynamical properties on the interplanetary dust population, the relative contribution of sporadic meteoroids and annual streams, the efficiency of the atmosphere in capturing and fragmenting meteoroids and the effect of space debris on in situ experimental results. We review the range of modelling tools necessary to interpret the complex interaction of these populations with spacecraft, with particular emphasis on the improved calibration of impact detectors and the application of software models. Analysis of the available data from 30 years of in situ impact experiments, and more recent recovered samples reveals evidence of the relative contributions from space debris and various astrophysical sources. While temporally and spatially averaged fluxes are well represented by existing isotropic interplanetary models for meteoroids responsible for penetrating experimental foils (of thickness F max) greater than approximately 30 μm, at smaller sizes a high degree of anisotropy is apparent in resolved data. An Earth apex component is observed for particles larger than a few microns in size whereas at smaller sizes, β-meteoroids from the solar direction dominate. Space debris forms an increasingly significant proportion of the LEO population at F max < 30 μm in addition to its dominance in the centimetre size range and above.