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What are meteors and where do they come from?
What are they? Scientists think that between 1,000 tons to more than 10,000 tons of this debris falls on the Earth each day. Most of this stuff is very tiny and takes the form of dust-like grains a few micrometers in size. (These particles are so tiny that the air resistance is enough to slow them sufficiently that they do not burn up, but rather fall gently to Earth.) Where does this stuff come from? Where do they come from? They come from within our own solar system. Their composition gives us clues to their origins. They may share a common origin with the asteroids. Some of this debris is similar to the Earth and Moon and some is quite different. Some evidence suggests an origin from comets. When can we see them? Several shooting stars per hour can usually be seen on any given night. Sometimes the number of objects seen increases dramatically. In fact, some of these showers occur annually or at rather regular intervals. The number is greater in autumn and winter. The number always increases after midnight and is usually greatest just before dawn. Perhaps the most famous are the Perseids which peak around August 12 every year. These showers are usually named after a star or constellation which is close to the radiant (the position from which the debris appear to come). Many of the showers are associated with comets. The Leonids are associated with Comet Tempel-Tuttle; Aquarids and Orionids with Halley, and the Taurids with Encke.
This object is a sample of the crust of the asteroid Vesta, which is only the third solar system object beyond Earth where scientists have a laboratory sample (the other extraterrestrial samples are from Mars and the Moon). What do they look like?
These rocks may look very much like Earth rocks, or they may have a burned appearance. They may be dense metallic chunks or more rocky. Some may have thumbprint-like depressions, roughened or smooth exteriors. They vary in size from micrometer size grains to large individual boulders. The largest individual iron is called Hoba from southwest Africa which has a mass of about 54,000 kg. The stones are much smaller, the largest falling in Norton County, Kansas having a mass of about 1,000 kg. Considering the vast infall of these rocks, one cannot help but wonder if anyone has been hurt or killed by one of them. There are only a few documented cases on record. A shower of stones fell upon Nakhla, near Alexandria, Egypt on June 28, 1911, one of which allegedly killed a dog. On November 30, 1954, Mrs. Hewlett Hodges of Sylacauga, Alabama was severely bruised by an 8 pound stony rock that crashed through her roof. This is the first known human injury. What are they made of? Most samples are either iron, stony,which are predominately rocky-silicates, or stony-iron. While most of them burn up before reaching the Earth's surface, many meteoroids break apart in the upper atmosphere, and become "fluffy meteors". This "fluffy" nature indicates a loose structure or vapor grown crystal aggregates. This gives rise to theories that some meteoroid material was aggregated, some subjected to heating-vaporization-condensation. This contrasts with the idea that meteoroids originated from an exploded planet or planetoid or asteroid. Sixteen meteorites have been found in Antarctica that are believed to have originated on the planet Mars. Gases trapped in these meteorites match the composition of the martian atmosphere as measured by the Viking spacecraft ,which landed on Mars in the mid-1970s. Controversy continues about whether structures found in one of these meteorites, known as ALH 84001, might be fossil bacteria or geologic structures. Much remains to be learned about meteorites and their origins.
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