Nov/Dec 2001 Table of Contents
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).
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.
40,000 tons of space dust and rocks, the leftover wreckage of our
solar systems 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. Thats why we go
to the ends of the Earth and beyond to collect it.
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 Earths 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.
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.