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Elusive Micrometeorites May Come From Dawn of Solar System

The Pennsylvania State University

Contact:
A'ndrea Elyse Messer (814) 865-9481 (office) (814) 867-1774 (home)
aem1@psu.edu
Vicki Fong 814-865-9481 (o) 814-238-1221 (h) vyf1@psu.edu

5-27-97

Elusive Micrometeorites May Come From Dawn of Solar System

Baltimore, Md. -- Millions of incredibly old, minute, previously
undetected invaders enter the Earth's atmosphere every day and
until recently, no one has been able to track, count or
investigate them, according to a Penn State researcher.

These micrometeorites are so small that even when they
disintegrate in the atmosphere, they are presently only recordable
at high-resolution using the very sensitive 430 megahertz radar
system at Arecibo Observatory in Puerto Rico.

"Radio and radar telescopes have always seen meteors and generally
considered them noise," says Dr. John D. Mathews, professor of
electrical engineering and director of Penn State's Communications
and Space Sciences Laboratory. "It has only been with recent
technology that we can observe these micrometeorites at extremely
high velocity resolution."

Another reason to look at meteors is the expected peak in November
1999 of the Leonid Meteor Shower. Both the U.S. Air Force and NASA
are concerned with an increase in potential damage to their
satellites and spacecraft. Historical pictures of the Leonids
shows a sky painted with multiple meteor trails, indicating that
the visible meteors were numerous.

While Mathews and his collaborators observed the Leonid Shower
from Arecibo in 1995 and 1996 and plan to observe the Leonids
every year until 2001, observations suggest that these
micrometeorites are not associated with the cometary debris
streams that cause meteor showers, but are entering the earth's
atmosphere all the time and from all directions accessible from
Arecibo.

"We can track the micrometeorites' orbits back through time, and
most of these tiny rocks appear to originate on the edges of our
solar system and not in the trails left by comets," Mathews told
attendees today (May 27) at the spring meeting of the American
Geophysical Union in Baltimore. "We think that the material in
much of the micrometeorites that we see is left over from the
formation of the solar system.

"We do have one candidate that might prove to come from outside
the solar system," Mathews added. "It moved too fast not to be
interstellar in origin."

The researchers have not accurately traced its possible stellar
origins yet because that requires a complex back tracking of both
the micrometeorites and the solar system as it moves through
space.

While micrometeorites disintegrate at about 60 miles above the
earth and weigh only about one microgram, they carry the energy of
a 22-caliber bullet.

"Spacecraft always become pitted, and it is attributed to dust or
space junk, these micrometeorites are probably the dust that pits
the surface of satellites," says Mathews. "They are also fairly
abundant. An object the size of the new Space Station would be
struck by one of these micrometeorites about once every orbit."

At Arecibo, one micrometeorites crosses through the 990-diameter
radar beam every minute. These events are not rare, just small and
illusive.

Mathews and his collaborators, Professor D.D. Meisel, Department
of Physics and Astronomy, State University of New York Geneseo,
and Qihou Zhou, staff scientist, Arecibo Observatory and a 1991
Penn State doctoral recipient, are also interested in these
micrometeorites because of the way they interact with the upper
atmosphere and the way they appear on radar.

"Regardless of the radar wavelength we use, we get the same
signature," says Mathews. "This appears to mean that we see a
shell of free electrons just surrounding the meteor, not the
meteorite itself."

The researchers don't know how the micrometeorites generate these
electrons. The particles are so small that when they enter the
upper atmosphere, they travel between air molecules.

"The interaction between the particles and the air before the
particles burn up or disintegrate is very interesting and not
understood," says Mathews. "Air molecules numbering only one
percent of the molecules in the particles are apparently
sufficient to destroy the micrometeorites."

**aem**

EDITORS: Dr. Mathews may be reached at (814) 865-2354 or
JDMathews@psu.edu
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