by George Wilkinson
Every year, the Earth captures thousands of tons of interplanetary particles, with objects in the micron size range striking every thirty microseconds. Because of their small size, some of them waft to the surface with minimal heat damage—thus their interiors preserved traces of their interplanetary origins. Although micrometeories fall in over the earth’s entire surface(and can be collected from rainspouts), scientists try to collect them in isolated environments, away from both natural and anthropogenic contaminants. An ongoing program in Antarctica makes use of the extremely clean, dry environment to collect micrometeorites from the icepack. Scientists melt ice by the ton and sieve the meltwater to recover a fine grit very rich in micrometeorites. Because of the heterogeneity of the collected particles, they have to be analyzed individually, by electron microscopy and specialized spectroscopy.
But how faithfully does the dust collected on earth reflect its interplanetary reservoir? The STARDUST space mission collected dust from the coma of the comet Wild-2, a Jupiter family comet recently deflected nearer to earth, making use of an aerogel as a high-tech butterfly net to capture dust particles with relative velocities approaching that of a rifle bullet. STARDUST returned to Earth bringing back thousands of small (<30 μm) solid particles. The examination of Wild 2 samples made it possible to explore the connection between micrometeorites recovered on earth and cometary and asteroidal objects as they exist in the interplanetary space.

