Micrometeorites

From JacobAllred

I haven't tried collecting micrometeorites yet (I don't have a microscope) but it looks like it could be fun.

Instructions 1

On a clear, dark night, far from city lights and with no Moon in the sky, one can see about 6 meteors per hour. Meteors are often called “falling stars” or “shooting stars,” because that’s what they look like. They are not stars: they are rocks from space, heating up as they plunge into Earth’s atmosphere, often at speeds of over 100,000 miles per hour. (A rifle bullet travels at about 3,000 miles per hour.)

During meteor showers, the hourly rate can be much greater. Meteor showers happen when Earth crosses the path of where a comet orbits the Sun. Comets are big, dirty snowballs: they spend most of their time in the Outer Solar System. Every so often, a comet comes in close to the Sun. When they do, the ice melts (actually sublimates, or turns directly into gas). This makes the long, gaseous tails for which comets are famous. Comets leave behind plenty of debris, the dust particles and rocks that used to be in the ice. When Earth crosses one of these trails of debris, we get a meteor shower, as the dust particles and rocks plunge into Earth’s atmosphere.

Meteor showers appear to come from one point in the sky, called the radiant. Meteor showers are named after the constellations in which their radiants appear. For example, the Perseid shower appears to come from the constellation Perseus. The Perseids happen every year, in August: their average rate is about 60 meteors per hour. This may be too slow for some people, but watching meteors under a dark sky is a delight. The best time to see a meteor shower is after midnight, as Earth moves into the stream. Most people, therefore, aren’t impressed by meteor showers, because they often do exactly the wrong things when trying to observe them: they try observing them in the early evening, which is the wrong time of night, and under the glare of city lights, which never helps.

Meteor showers can turn into meteor storms, with much higher hourly rates. The highest this author has seen is 3,000 meteors per hour, in the 2001 Leonids. (The Leonids happen in November, although they won’t peak again for another 33 years.) The 2001 Leonids looked like a good Fourth-of-July show. The 1966 and 1833 Leonid showers had over 100,000 meteors per hour: some people who saw them thought the world was ending!

Bits of meteors that survive the passage through Earth’s atmosphere and hit Earth are called meteorites. Meteors may be common, but meteorites are quite rare. What happens to the materials that make up the bulk of the observed meteors? As early as the 19th century some people speculated that the smaller objects left behind small, microscopic materials that came to be known as micrometeorites These small particles are worn off (or ablated from) larger meteors, which plunge through the atmosphere and melt as a result of the heat generated when the meteors are slowed by Earth’s atmosphere. These small pieces quickly cool into spherical shapes and, over a few days, slowly settle to Earth. You can collect your own micrometeorites, and examine them with a microscope.

COLLECTING MICROMETEORITES

In order to increase your chances of finding any micrometeorites, you need to collect material which is likely to have a higher than average concentration of micrometeorites. The roof of a house or building makes a good collector of micrometeorites, since they are continuously falling from the sky. When it rains, the dust, pollen, micrometeorites, and other debris will be washed from the roof and carried to the rain gutters and downspouts by the rushing water. If you check these areas, you will find a very fine powdery material. This fine dust is likely to be rich in micrometeorites. Ordinary dirt does not work as well: it should be fine dust.

Follow the instructions of your lab supervisor in collecting the dust. You can look around the downspouts, in the cracks of the sidewalks, or on the roof of McLane Hall. Use a magnet to pick up this fine dust, to collect any micrometeorites that are high in iron. Smear this dust onto the sticky part of a sticky-note card. Once back in the lab, use a microscope to examine the on the sticky-note card. The micrometeorites will be shiny and spherical, because they were once melted. Other than in meteors, few processes in nature (volcanoes or lightning) are hot enough for long enough to vaporize iron. Any naturally occurring spheres of iron are therefore micrometeorites. Once you find one, try to separate it from the other material using a straight pin or tweezers. Look for more micrometeorites in your sample.

The micrometeorites collected with a magnet are high in iron. A significant fraction of micrometeorites are stony and are therefore not magnetic, so we can’t collect them reliably with this method.

Instructions 2

Meteors are small bits of rock and other matter within the solar system. Occasionally these meteors enter our atmosphere. Their surfaces are heated, causing the "shooting stars" we see occasionally. Most are small and burn up completely in the atmosphere. Occasionally they do pass through, or at least bits of them, and strike the earth's surface. These are meteorites, and can either be rocky or metallic. They are usually very small, but every so often (geologically speaking) a really big one hits, leaving a large crater like the mile wide one in Arizona.

Some meteors are so tiny that they fall through the atmosphere without burning up. They are so small in fact that they float around in the atmosphere, eventually reaching the ground with rain droplets or heavier dust particles. The best times to collect micrometeorites are after meteor showers.

Stuff you need:

• Two glass or Pyrex dishes or pans
• a magnet
• hot plate
• microscope and slides
• distilled water
• needle or pin
• small plastic or cellophane bag

Use a small glass dish, such as a glass pie pan, to collect rainwater. The dish needs to be very clean. Let it sit outdoors long enough to fill. If you don't live where it rains very much, fill the pan with distilled water and let it sit outside for a few days.

Metallic micrometeorites are usually iron or iron and nickel and can be collected with a magnet. Use a small but strong magnet and cover it with a small plastic or cellophane bag. The idea is to provide a barrier around the magnet that can be immersed in water. Sweep the covered magnet slowly through the water along the sides and bottoms of the dish. Remove the covered magnet, and place it into a second clean dish filled with distilled water. Remove the magnet from its cover, and shake the cover in the water to loosen the particles that have (hopefully) gathered there. Evaporate the water by placing the dish on a hotplate or in a warm oven (making certain that the dish is oven safe!) Once evaporated, magnetize a straight pin or sewing needle by rubbing it one way across a magnet for a minute or so. Drag the needle across the sides and bottom of the dish. Tap the needle on to a clean microscope slide. Check the slide with the microscope to determine if a large number of particles have been gathered. If so, glue down a cover glass over the particles and examine the particles more carefully. Not everything on your slide will be a micrometeorite. In fact, it is possible that there won't be any at all. Any jagged shaped particles are likely not micrometeorites. Any rounded metallic particles may very well be.

You can also separate out non-metallic particles, though not as easily. Evaporate the original dish of water and scrape it out with a needle. Tap the needle on to a microscope slide, cover, and examine it with the microscope. Most, if not all, of the particles you see will not be micrometeorites. There may be pollen, ash, and other "dust" of terrestrial origin. If you are fortunate, you will come across a rounded stony object, which is likely to be a micrometeorite.

Sal D'Ambra adds:

"I did this as a kid and had good success collecting and melting clean fresh snow. The micromet's form nuclei for crystallization of the snow flakes. Also a magnet in a plastic bag worked great for collecting. The bag was placed inside-out around the magnet, dragged through the water from the melted snow, and turned rightside out trapping the little devils."

Thanks, Sal!

The major yearly meteor showers are approximately:

• January 2-3 - Quadrantids
• April 20-22 - Lyrids
• May 4-6 - Aquarids
• July 28 - Aquarids
• August 10-13 (one of the best) - Perseids
• October 8-10 - Draconids
• October 18-23 - Orionids
• November 4-6 - Taurids
• November 15-17 - Leonids
• December 10-13 (the other best) - Geminids
• December 22 - Ursids

The International Meteor Organization publishes a more thorough schedule along with observation tips.