Have You Seen a Meteorite?

Center for Meteorite Studies - Arizona State University - Tempe

ORIGIN

Where Meteorites Come From -- Most scientists believe meteorites are part of our solar system derived from the asteroid belt located between Mars and Jupiter. Meteorites may be captured by the Earth when they are pulled from their orbits by the gravitational attraction of the sun or planets or collide with each other.

Definitions -- A meteor is an object in the sky that produces light upon entering the Earth’s atmosphere. These bodies are usually quite small and are sometimes called "shooting" or "falling stars." Large, extremely bright meteors are called "fireballs" or "bolides" and can be as bright as the moon or sun. A meteorite is a solid body that has fallen on the Earth’s surface from outer space.

Falls and Finds -- A fall is a meteorite that was picked up after it was actually seen to fall. A find is a meteorite that was not seen to fall, but was recognized by the diagnostic features described in this booklet.

Sight -- When a meteor enters the Earth’s atmosphere the resulting fireball produces light, due to the friction between its surface and the air. A smoke or dust trail is produced in the sky by the fireball caused by the removal of material from the surface of the meteorite.

Sound -- Because the fireballs are traveling at high speeds, they sometimes produce a sonic boom or whistling heard over 30 miles or more from where the meteorite lands. Several booms may be succeeded by irregular sputtering sounds, comparable to an automobile backfiring.

Fig. 1 An iron meteorite showing "thumbprints."

Composition -- Iron meteorites are composed of almost 100% metal, a nickel-iron alloy. Stony meteorites contain about 75-90% silicate (stony) minerals and 10-25% nickel-iron metal and iron sulfide. A few meteorites are the in-between types called stony-irons with about 50% iron and 50% silicates.

Size -- Meteorites vary from pieces of microscopic size to large masses measuring several feet or more in diameter. The average person is most likely to find a meteorite that measures from two inches to two feet.

Weight -- Meteorites are generally heavier than ordinary rocks. Iron meteorites are very heavy, usually weighing about three times as much as ordinary rocks of the same size. Stony meteorites are not quite one and a half times as heavy as ordinary Earth rocks.

Shape -- In most cases meteorites are very irregular in shape. Some meteorites take the shape of flat cones. They are seldom round.

Fig. 2 The black crust and grainy interior of a stony meteorite.

Crust -- The surface of many freshly fallen meteorites is usually fairly smooth and featureless. Some meteorites show flow lines, furrows, shallow depressions, deep cavities, and smooth pits (thumbprints). The iron meteorites show characteristic smooth pits or thumbprints, resembling imprints of fingers on soft clay (Fig. 1).

Tests — The best single test for an object suspected to be a meteorite is to grind off a small corner on a carborundum wheel. Inspect the ground surface for evidence of metallic specks. Iron meteorites will give an appearance of freshly cut iron (Fig.3). A strong magnet will attract the surface of an iron meteorite.

A stony meteorite will show silvery appearing flecks scattered in a compact stony mass (Fig. 4). These stony meteorites will be attracted only slightly by a strong magnet. A few stony meteorites will not be attracted by a magnet.

Interior -- It is not advisable to break, hammer, or cut open a possible meteorite, as this rough treatment destroys some of the material and lessens its scientific value. Only a small corner should be ground off in order to test the specimen (as described in the preceding section on "Tests"). DO NOT USE AN ACETYLENE TORCH FOR CUTTING, the extreme heat destroys the meteorite’s interior.

Fig 3. Iron meteorite. Polished and etched section and uncut specimen.

Objects Mistaken For Meteorites -- Objects commonly confused with meteorites include furnace and smelter slag, iron oxide concretions, and pieces of manufactured iron.

Fig 4. A polished section of a stony meteorite showing the silvery specks
scattered in a compact stony mass.

Why Study Meteorites -- Meteorites are scientifically important and worthy of careful study because they have come from the solar system beyond our own planet. They are becoming increasingly important as our country engages in its space program.

Our Collection -- The Center for Meteorite Studies at Arizona State University has one of the world’s best meteorite collections. This collection contains specimens of more than 1200 meteorite falls. The collection is being actively used for space-oriented research scientists of Arizona State University and many other investigators throughout the United States. We are always interested in adding new specimens to the collection by gifts, purchases or exchanges.

Field Information — If you are fortunate enough to see a meteorite fall and can recover it, or if you find one in the field, do the following: note carefully its location, take photographs of the meteorite and its location, then contact us immediately. We will examine the specimen and estimate its value.

1. Is the specimen heavy?  Yes / No 

2. Is the specimen solid and compact?   Yes / No 

3. Is the specimen attracted by a magnet?   Yes / No 

4. Is the specimen black or brown and rather smooth on the outside?  Yes / No  

5. Does the specimen show metallic iron specks on a cut surface?  Yes / No 

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