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