METEORITES IN YOUR OWN BACK YARD
If you have searched and searched for meteorites, but they continue to elude you, or if you simply can't find the time to spend the days or weeks in the field necessary to recover these rare objects, perhaps it's time to look closer to home.
Each day, millions of microscopic particles of burnt space debris, byproducts of ablation, and space dust rain down on our homes, streets, and on us. Collecting these can be a fun 'little' hobby.
While meteorites of visible size are quite rare, and masses of over a gram are not likely to fall on your house in a lifetime, these microscopic particles drift down with great frequency, making collection comparatively easy. Sorting them from the windblown dust, pollen, trash, and leaf litter that falls with them is another matter altogether. We'll come to that later, though. Let's start with how to collect them.
How do I find micrometeorites?
All you really need to begin collecting micrometeorites is a clean open container aimed at the sky for a significant period of time, a magnet, and a small plastic bag. The hobby is a lot more fun if, in addition to this, you have a microscope.
I have heard of people collecting micrometeorites amidst other small particles by coating microscope slides with a thin layer of Vaseline and leaving them out for a few days, but it seems a needlessly challenging method to me. It does, however, potentially allow you to count the fall rates of various kinds of microscopic particles per area in a given amount of time. An easier method is to partially fill a large glass dish with water (distilled might be best, but isn't necessary) and then place the dish outside under the open sky. The water is simply to keep anything that falls into the dish from blowing away. It also helps to raise your dish away from the ground to minimize wind blown dust and debris. After a few days, a week, or a month if you feel so inclined, place your magnet inside a small plastic bag that has been turned inside out and sweep it around in the bottom of your dish. Your prizes will not be immediately visible to the unaided eye unless you are a very unusual person or are extraordinarily lucky. Turn your bag right side out and put away your magnet for the moment. This process will leave your magnet outside the bag and your small treasures now safely inside. Allow the material you have thus collected to dry
The larger your collection area, the more material you will accumulate. Many houses have gutters which make ideal meteorite sluice boxes.
My favorite micrometeorite collecting process involved an enameled metal roof and mis-installed backsloping gutters that came with a house I once owned. (The gutters were subsequently reinstalled at a correctly directed, but less than normal slope to slow the flow rate of the water sluicing through them). I permanently installed magnets at intervals on the bottom of the gutter to hold all possibly meteoritic dust particles for later retrieval, sorting, and examination. This elaborate setup was augmented by lack of contamination since the roof has no composite material to shed, no overhanging trees, no nearby cities or industry to create manmade fallout, and clean high mountain air. If you look around hard enough, you will find similar ideal unintentional micrometeorite traps such as old tin roofed barns with gutters filled with 50 years worth of debris, glass roofed sunrooms with channels along the edges that haven't been cleaned in 10 years, or old buckets or watering cans that you've left sitting in the yard for months. The possibilities are endless. (I've long had a secret desire to place heavy duty magnets on the gutter down spouts of several acre stadiums, glass topped malls, and tiled or slate roofed auditoriums.) I would love to hear about the results if anyone ever sets something like this up. (with permission from the appropriate management of course)
So what do I do with this mess?
The end product of your collection will look like anything ranging from a few specks of dust to a fist sized wad of muck depending upon your approach to collecting. If what you have gathered is a small amount of dust-like particles, simply empty them into a plate or onto a slide and have a look with a microscope. If what you have is a big wad or bag of goop that your magnet pulled out of a gutter, read on. This mess will be made up, as mentioned above, mostly of terrestrial dust and organic debris. The most demanding part of gathering micrometeorites is the sorting and screening. A few tools that will help are your handy magnet (I recommend small Neodium Iron Born magnets available from: http://www.wondermagnet.com or similar sources), a piece of window screen, a fine meshed tea infusing ball (yes, the thing you use to make tea from loose type teas - it is very fine mesh and already cup shaped... very handy), a couple of plastic food storage type containers that you don't mind messing up, a fine artists brush (the smallest you can get), and a small clear glass or plastic container (I actually use the little plastic drawers that are made for storing loose nuts, bolts, and other shop debris.)
Put your material to be washed into one of your plastic dishes with water. Hold a strong magnet against the bottom and stir it up good so that all of the magnetically attracted material sticks to the magnet. Pour of the muddy water and bits of leaves and such. Repeat. Repeat. Repeat. Now let your remaining material dry. (this may take a day or so) Repeat the process without the water (dry washing) in the following manner. Holding the magnet firmly against the bottom of the container, turn it upside down and tap it against a surface covered with paper. This will dislodge a lot of the terrestrial dust. By doing it over a surface covered with paper, you can retrieve your sample if you accidentally dump the entire mess out of the container. This really beats fishing it out of the bottom of a garbage can.
Next just filter your dust through the larger screen and then the smaller screen. Any micrometeorites, along with other magnetic debris, will fall through both screens along with a bunch of very small pieces of iron stained silicate matter, terrestrial magnetite dust (black angular particles), and miscellaneous magnetically attracted junk. Make a quick microscopic scan of the larger material that you have sorted with your screens before discarding... you never know. The trick to collecting micrometeorites is really in this washing, drying, and sorting procedure. Collecting a glob of muck is easy. Ideally, over several evening you will reduce the entire pound or so to a few grams of concentrate.
What will the meteorites look like?
Micrometeorite, or ablation spherules, look for the most part like small black metallic or glassy spheres. Place you meteorite dust concentrate in a dish and shake aside the larger stuff. Look at the result under a microscope. These are about the smallest things in the sample except for a few natural magnetite grains. I'm always amazed at what I find. Not all of the small metallic spheres that you see will be extraterrestrial, but a small portion of them will.
Sorting the spheres from the concentrate can be done with a fine paint brush with all but 2 hairs removed. the process is simple: Dip hairs in alcohol, pick up sphere, tap into other container. This process is very tedious.
A few last notes. Because part of what you will find is the result of ablation (meaning the burning away of meteorites in the atmosphere) or the upper atmospheric destruction of gram sized masses, frequency of falls might be greater after meteor showers such as the Leonids and Perseids. Recent research seems to be indicating that some of this material is not ablation products, but rather relatively unaltered materials that tell us a lot about the local environment of space. Some particles known as 'cosmic dust' are so small upon entering the atmosphere that they don't experience ablation in the manner of larger meteorites. These 'cosmic dust' particles are much smaller and quite scarce, however, and will not typically be the metallic or glassy spheres you are observing though your microscope. Microspherules might also be found in greater abundance during snow and rainstorms since precipitation helps to carry the material out of atmospheric winds that might otherwise keep them aloft.
Contamination and Man-made Materials
It would be very cool and romantic if ever tiny sphere that you found was a micro-meteorite. Sadly, however, only a tiny portion are. The remainder are a broad class of objects originating from coal combustion and other human activites. It is extremely difficult to distinguish between micrometeorites and microspherules that result from people burning things. Even so, it is neat to know that a fraction of what you are looking at came from space. A list of articles and links providing examples of science relating to both micrometeorite ablation spherules and other fascinating types of microspherules that result from human and natural processes is below.
Where can I learn more about the science of microspherules?
Meteorite Microspherule Science
Have fun and good luck.
This article is adapted and updated from one that was originally published in a meteorite magazine called Voyage. Though it was a great magazine, it is no longer in print, so I'm re-posting this here for those who are interested. I've had some great feedback from people who have used this information to put together educational programs or science projects. I'd love to hear what you have done with it. As with anything I write, please correct me if you notice anything wrong.