September 21, 2009
Take a look at this photograph:
(Photo 1) Taken at 200 times life-size, the semi-transparent line is a human hair, about 100microns wide. (200x)
The metallic spheres above are about 200 to 500+ microns in diameter. Notice that the majority are near-perfect spheres and highly reflective. They are probably NOT micrometeorites, but contamination from man-made sources.
Other images I have show similar microspheres less than 50 microns, the largest are more than 600 microns. Some are colored differently (probably rust) and with rough surfaces. While I cannot confirm (this requires an electron microscope) that these are micrometeorites I do have a photo from the Defense Department showing micrometeorites on page 3 of this article.
As micrometeorites enter the atmosphere at 20,000 miles an hour, they melt into spherical shapes and gradually descend through the atmosphere in the wind, or commonly in water droplets. Likewise do metallic particles when heated to high temperatures in low-gravity environments.
My interest in micrometeorites began with the fact that they have high iron content to which they are easily attracted to magnets. Because rain, snow, and hail need some particle -- a solid particle, dust is typical, micrometeorites or chemical substances in the atmosphere form droplets, and for study, micrometeorites are typically gathered in a wide plastic basin as it rains.
A magnet then is used to sort the extremely small, iron-containing particles from other debris that comes with the rain. What is attracted to the magnet is just barely visible to the naked eye, passed through a filter (I use a plastic-mesh coffee filter) and put it under my 50x and 200x lenses.
When I started this hobby, I wasn't familiar with the "basin-gathering" technique nor just how (un)common they are, so thinking I could find micrometeorites practically anywhere, I went to the recreational area and gathered with a magnet from a surface area of perhaps only two square yards some of what you see above and in images 1, 2, and 3. The six points of light is the light-source for my digital microscope, six LED's (light-emitting diodes) arranged in a circle.
I haven't counted all the spheres from the two square yards at the open, exposed-to-the-sky, football field, but would easily estimate around 100 of these spheres in only one sample.
Upon recommendation from two technicians of the local planetarium, I sent the images to the physics professor at the university who specializes in the analysis of micrometeorites, and was I disappointed -- not from his reply, but as to the likely sources of these spheres"
He wrote (translation below) that 99.9% of these objects are from man-made sources - typically coal-powered electrical generation plants, metal foundries, and high-temperature ovens.