7 January 2005
Collecting Micrometeorites
Richard Haynes
Micrometeorites (1) are incredibly small bits of iron or nickel-iron of four general shapes: rounded rod, raindrop, sphere or pear as seen in Fig. 1. They range in size from a fraction of a micrometer to several hundreds of micrometers.
Micrometeorites are formed when material from space is violently incinerated in the upper atmosphere (~100 km altitude) to become meteor debris (2). As the solids are seared, any metals they contain are melted and spewed into the cold atmosphere, where they generally condense into one of the four basic shapes in Fig. 1 and become micrometeorites (or micromets).
Because they are so tiny and may weigh only about 1 x 10-6 grams, micrometeorites do not usually fall straight to the earth. Instead, they may be carried by winds aloft, from which they gradually escape via rain, snow or surface winds and come to rest on the earth, a majority of them falling into the oceans.
You can collect micrometeorites with the help of surprisingly simple equipment. The following items are needed:
(A) Clean 8 to 20 liter (or 2 to 5 gallon) plastic bucket(s) or other large, non-metallic container(s).
(B) Plastic sandwich bag.
(C) Magnet (I use a very strong, 2.5 cm (1 inch) diameter neodymium disk magnet. See reference 3.)
(D) Microscope.
For collecting micromets, a large-area roof equipped with a gutter system is nearly ideal. Other possibilities include a child’s swimming pool, a large satellite dish antenna, or a large plastic sheet.
Micrometeorites deposited on a roof will be dislodged by rain or melting snow and will find their way to the gutter system, where the runoff water is collected in plastic buckets placed beneath one or more drain spouts.
After a rain, a significant quantity of water, along with dirt, wood, leaves, insects and other debris, will be in the bucket. The micromets must now be separated from the rest of the solids.
(A) Carefully decant the water from the bucket so that most solids are left behind.
(B) Place the magnet in the sandwich bag and lower it to the bottom of the bucket. Swirl it through the watery solids and then lift the bag and inspect it. Any fragments of iron that might have been attracted to the magnet will be clinging to the outside of the plastic bag.
(C) Remove the magnet from the bag, being careful that the iron particles remain with the plastic bag.
(D) Lay several clean microscope slides on a white sheet of paper; over them shake loose the wet particles from the sandwich bag.
(E) Examine the slides at 30X to 100X with the microscope. Any micromets present will be tiny, glossy shapes resembling those shown in Fig.1. At least 100X will probably be required to see them clearly.
(F) Continue sweeping with the magnet until you believe most of the iron has been collected from the bottom of the bucket. Mount several slides for future reference.
Figures 2-5 are microphotographs that provide a good idea of what you might see at various magnifications.
Collecting micrometeorites can be a fun way to introduce a young person to the wonders of astronomy, meteorology and microscopy.
Collecting and studying bits of dust from outer space can also lead to various research projects with genuine scientific value. Here are just some of the possibilities:
- Study the rate of fall of micrometeorites over a geographical area over a period of time.
- Compare the number of micrometeorites you find with weather information, such as winds aloft, surface winds, precipitation types, rates and amounts. Are there differences in the numbers of micrometeorites over months and seasons?
- Study differences in fall rates before, during and after meteor showers, such as the Perseids, Draconids, Leonids and others. Are there differences in micrometeorite types and numbers? Dedicated amateur Charles Kapral made such a study in 1995 (4).
Projects like these will require you to know the concentration of micrometeorites falling onto a measured surface over a known time. Therefore, you will need to carefully plan your study. You will also need to use an open water container to collect your specimens.
[Figure 6, for example, shows a cosmic dust collector made from a satellite dish that was used for several years at Hawaii’s Mauna Loa Observatory (3,400 km or 11,200 feet elevation). The water was continuously recirculated to cause particles to descend toward the bottom of the dish. Iron particles were attracted by a powerful magnet at the center of the bottom. This experiment proved to be an excellent place to see the latest assortment of insects blown up to the observatory from far below. Editor.]
Amateur scientists are sure to discover other reasons for collecting and studying micrometeorites—while enjoying the process.
1. Cambridge Atlas of Astronomy, third edition, Cambridge University Press (1996).
2. A news release about a study of the origins of micrometeorites conducted at Penn State University may be seen at www.psu.edu/ur/NEWS/news/micrometeorites.html
3. Neodymium-iron-boron magnets are available from www.wondermagnet.com
4. Charles Kapral, Astronomy with a Microscope, The Practical Observer 6, 2 (1995). 
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