Types of Metal Detecting Activities, page 36:


(CONTINUED from previous page)

Meteorite Detecting Technique

To find a meteorite, you have to go where they have been found before - at a strewnfield which is also called a distribution ellipse field. Your goal is to locate this zone where multiple meteorites from the same fall landed.

A distribution ellipse field has a considerable number of small meteorites at one end - the "small end," and fewer numbers of larger meteorites at the far end - the "big end." The nature of these two "ends" of the elliptical zone can be explained by the following process.

When a large meteoroid enters the earth's atmosphere at about 26 miles per second (42 kilometers per second), it brakes into debris at altitudes of 30 to 60 miles (50 to 95 kilometers). The smallest fragments have less mass and inertia than large pieces, so they are the first to slow down and hit the earth at the "small end." The largest fragments travel further and fall at the "big end." If you can figure out the trajectory of the fall, you will be able to locate and harvest either "end" at your choice.

The same concept applies to a spectacular fireball, also called bolide - an exceptionally bright fireball, particularly one that explodes, and meteor - colloquially a shooting star or falling star. Fireballs can be seen in the sky a few times every year. However, not only cosmic bodies can create such fireballs. The rocket fuel tanks, old satellites and their parts (over 10,000 tons of junk is orbiting the earth) may create similar fireballs while burning up upon returning to Earth.

While meteors get completely burnt out, bolides explode and split into numerous pieces which rain down upon the earth. Fireball chasing relates to these fireball events and is an extremely difficult type of meteorite hunting because one has to determine the location where the meteor debris landed, race to the site, and be the first to recover meteorites if possible.

In the areas without bare terrain, a strewnfield may encompass many different types of ground, including plowed farm fields with black earth, planted fields or abandoned fields with overgrown vegetation, grasslands, and forests. Such conditions will impose on you a great difficulty, if not an imposiibility, in finding small, dark-colored stones.

Usually meteorites may be found lying on the surface. Some meteorites may be partially buried into the ground if they fell at high velocity. And several specimen may create small impact depressions on the ground upon hitting it, then bounce, and come to rest a short distance away.

The rule of thumb is that when you find one meteorite, focus on this area and expect to find more pieces. If a meteorite you have found is a "cold find" - a meteorite that is discovered where none have been found before, you are extremely lucky to be the first to search a brand new strewnfield. In most cases, you will be dealing with old strewnfields and recovering meteorites missed by others unless you conduct a "fireball chase."

To conduct a thorough coverage of the area where you found a meteorite, you should use a linear gridding pattern of search (see details here - how_to_metal_detect_p2). When you discover a "cold find," you should use the spiral pattern of search first. This search pattern begins at the spot where you recovered your find, then you metal detect while moving around this spot and widening every new circle as much so you could still overlap your previous track.

The spiral search pattern would let you see in which direction meteorite finds continue to occur. This way, you can determine the long axis of the distribution ellipse field, i.e. the trajectory of the fall, and your position in relation to either "big" or "small end" of it.

Then you begin using a linear pattern of search to recover as many meteorites as possible. Although this method sounds easy in theory, in reality it might be quite difficult if the meteorites spread thin over a vast area, and you may find only one meteorite per acre. You also may come across many false targets, and recognizing them would require some skills as well.

The same search coil discipline applies to meteorite hunting as to any metal detecting activity conducted on land. You can find more details on Search Coil Discipline here.

Do not forget to use your eyes as well as your metal detector. As it was mentioned before, meteorites do not look like regular rocks. While metal detecting, try to eyeball those stones that are out of place or just look odd for the area you are searching. Look for the rocks with dark black or brown fusion crust. The long-weathered meteorites typically have a red-brown color and sometimes are shiny due to erosion of the wind-blown sand.

