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Mercury, Nov/Dec 2001 Table of Contents

This scanning electron microscope image shows an interplanetary dust particle known as a "cosmic sphere." It measures 300 microns across, about three times the width of a human hair. It is made of glass and crystals of olivine and magnetite. Courtesy of Don Brownlee (University of Washington).

Scientists go to Antarctica, the stratosphere, and the seafloor to collect material more precious than gold, dust that tells how the stuff of life was brought to Earth.

by Monika Kress

About 40,000 tons of space dust and rocks, the leftover wreckage of our solar system’s birth, fall to Earth each year. Even though this debris could fill an Olympic-size swimming pool in a single month, it is insignificant compared to the mass of Earth. But it is extremely significant to scientists like myself who are doggedly pursuing answers to these questions: How did the solar system form? How did life on Earth begin? How likely is it that life exists elsewhere in the Galaxy? The cosmic debris that falls to Earth holds clues that will help us answer these questions. That’s why we go to the ends of the Earth – and beyond – to collect it.

Meteorites are bits and pieces of asteroids, the Moon, and Mars that have fallen to Earth. Components of certain types of meteorites are more than 4.5 billion years old – over half a billion years older than the oldest rocks in Earth’s crust. Such ancient meteorites have changed very little since the birth of the solar system, and they are believed to represent the building blocks of Earth itself. These ancient meteorites hold clues that tell us what the solar system was like when the planets were just starting to form, and what kind of materials went into building them.

Macroscopic meteorites constitute a small fraction of the total mass that falls to Earth each year. The vast majority of incoming extraterrestrial matter is far too small to make good paperweights or even earrings, because it arrives in the form of microscopic dust grains. These micrometeorites, also known as "interplanetary dust particles," are shed by asteroids banging into one another, and by comets evaporating as they wander too close to the Sun. Most micrometeorites are only a few hundred micrometers across – about the diameter of a human hair. They are utterly dwarfed by the grains of sand you shake out of your shoe after a walk on the beach. But the total amount of micrometeorites that scientists collect in one year (despite their valiant efforts) would not even begin to fill your shoe.