Space Dust and Helium 3

Asteroid Breakup Covered the Earth in Extraterrestrial Dust

Boulder, Colorado -- Scientists from the California Institute of Technology
(Caltech), Southwest Research Institute (SwRI), and Charles University in
the Czech Republic have made the first positive link between a breakup event
in the main asteroid belt and a large quantity of interplanetary dust
particles deposited on Earth.

Sediments found in oceanic core samples indicate that millions of years ago,
the Earth was blanketed by extraterrestrial dust. Computer simulations
indicate these particles are fallout from the breakup of a large asteroid in
the main asteroid belt, a population of interplanetary bodies ranging from
tiny pebbles to Texas-sized rocks located between the orbits of Mars and
Jupiter. These findings appear in the Jan. 19 issue of the journal Nature.

Interplanetary dust is composed of bits of rock -- from a few to several
hundred microns in diameter -- produced by asteroid collisions or ejected
from comets. Interplanetary dust migrates toward the Sun, and en route some
of this dust is captured by the Earths gravitational field and deposited
on its surface. Presently, more than 20,000 tons of this material
accumulates on Earth each year, but the accretion rate should fluctuate with
the number of asteroid collisions and active comets. By looking at ancient
sediments that include both interplanetary dust and ordinary terrestrial
sediment, it should be possible to detect major dust-producing solar system
events in the past.

Because interplanetary dust particles are so small and rare in sediment --
significantly less than a part per million -- they are difficult to detect
using direct measurements. However these particles are extremely rich in a
rare isotope of helium -- helium 3 -- compared with terrestrial materials.
Over the past decade, Professor Ken Farley of Caltech has measured helium 3
concentrations in sediments formed over the last 75 million years to create
a record of the interplanetary dust flux.

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