Meteorites


A meteorite is an object which has fallen to Earth from space. Meteors are the flashes of light ('falling stars') produced when meteorites pass through Earth's atmosphere. Other, smaller, pieces of extraterrestrial debris also cause meteors, including grains of dust from comets. While some meteorites are found immediately after their fall, many, called 'finds', have lain on the Earth for many tens of thousands of years prior to their discovery.

Meteorites are either stony, in which case they are only slightly heavier than a typical terrestrial rock of the same size, or they are metallic, in which case they are much heavier and ring like a bell when struck with a metallic object. Meteorites that have fallen recently have a distinctive black coating called fusion crust that looks glassy and smooth. Older meteorites are typically weathered and seem to be covered with a fairly smooth dark brown coating. Most meteorites are magnetic, some strongly, some weakly. If a corner is broken off and polished, most meteorites will contain numerous small flecks of metal.

Contrary to the image sometimes given to them in movies and fiction, meteorites are generally no more radioactive than typical terrestrial rocks, and they do not glow or feel unusually warm to the touch. They are not poisonous and thus there is no danger in touching or even ingesting a piece of meteorite (the latter not, however, being recommended). While some cultures have made meteorites a focus of worship (A few are still housed in temples in Japan and Asia), there is no evidence that they give their possessors any superhuman powers.

Positive identification of a meteorite can be difficult and may require an expert. While many meteorites are magnetic, not all are, and some terrestrial rocks and certain 'rock-like' manufactured materials are also magnetic. The best way to confirm the meteoritic nature of a possible meteorite is to send a small piece (about the size of a fingernail) to one of many meteorite experts, many of whom are members of the Meteoritical Society, including members at universities and museums. These analyses are usually provided free of charge. In the United States and most countries of the western world individuals can own and trade meteorites, original ownership usually going either to the finder or to the owner of the fall site. Some countries, however, claim ownership of all meteorites found in their boundaries as national treasures.

Meteorites are important because most are as old as the Earth and the entire solar system and have compositions very similar to the Sun's. It is widely thought that they formed at the same time as the planets. Unlike most solids in the solar system, they did not form into planets but formed the smaller bodies known as asteroids that now circle the Sun between Mars and Jupiter. Unlike most of the planets, these bodies have been essentially 'dead' since their formation, and thus are one of our few unaltered windows back to the beginning of our solar system. A few meteorites have come planetary bodies, namely from our own Moon, and perhaps from Mars.

Some of our members maintain homepages with more specific information on meteorites and related materials. The American Meteor Society has information about meteor falls. Many local and regional museums have meteorite specimens on public display. Three of the largest meteorite collections open to the public are curated by the National Museum of Natural History (Smithsonian, Washington DC); the American Museum of Natural History (New York); and the Natural History Museum (London).

There are many fine books and encyclopedia articles about meteorites, including many written by our members. Derek Sears' book Thunderstones is an introduction to meteorite studies with special emphasis on those that fell in the state of Arkansas (University of Arkansas Press, 1988). Robert Dodd's Thunderstones and Shooting Stars (Harvard University Press, 1986), Hap MacSween's Meteorites and their Parent Bodies (Cambridge University Press, 1987) and John Wood's Meteorites and the Origins of the Planets (McGraw-Hill, 1978) are all excellent books on meteorites, and there are also excellent articles in Encyclopedia Britannica and the McGraw-Hill Encyclopedia of Science and Technology.

The photos below are from the November 1995 issue of Meteoritics (Volume 30, number 6). The top photo is of a meteorite as discovered on the Plain of Oman (Libya). The rocks nearby are no more than a couple cm across. The bottom photo is of the Baszkowka (Poland) meteorite, which fell in 1994. Note the flow texture of the fusion crust, formed as the front (uppermost) portion of the stone melted and poured off the stone as it entered the atmosphere. The stone is about 30 cm across.