Leonids Meteor Shower: What are Meteors and Meteorites?

What are Meteors and Meteorites?

The Solar System is not a tidy place and there are literally countless chunks of leftover planet making stuff floating around between planets. Some are smaller than a grain of sand, others are much larger. Many of them orbit within the asteroid belt between Mars and Jupiter. Others have highly elliptical orbits which carry them far out into the outback of the Solar System. Still others have stranger orbits which sometimes come close enough to cross Earth's orbit. And some of those which cross Earth's orbit actually enter the Earth's atmosphere and burn up. We call these meteorites.

Meteor jargon is thus: The streak seen as the particle burns up in the atmosphere, is called a meteor. Especially brilliant, or exploding meteors are called bolides or fireballs. If there is anything left after the trip through the atmosphere and it strikes the ground, it is called a meteorite. And, finally, the chunk of rocky debris which causes the meteor, is called a meteoroid. However, it's really ok to just called them meteors!

Meteorites are old, very old, some maybe as old as the Solar System itself. They are much older than any rocks on Earth. Studying them can tell us things about the early Solar System and how the planets formed.

There are generally three classes of meteorites, stony, iron and stony-iron. Stony are the most common and make up about 93 percent of all meteorites. Iron meteorites only account for six percent, and stony-iron are the rarest yet. The funny part about this is that it is most often the iron meteorites which are found, mostly because they look most different from Earth rocks.

Most meteorites are recovered in Antarctica, where the constant snow covers the native rocks and makes the meteorites much easier to spot.

Most stony meteorites are of a type called chondrites, so named because they containe small spherical inclusions called chondrules. Chondrules are mineral deposits formed by rapid cooling. They look like tiny pea sized bits of glassy rock. The origins of chondrules is unknown but since melting would have destroyed them, they are evidence that chondrites have never fully melted.

Chondrites have been heated slightly however. The rock in which the chondrules are embedded is very old but it does not contain volatiles. What this means is that they have been heated enough to rid themselves of any volatiles, but not hot enough to melt the chondrules. Chondrites formed in the early Solar System when the very first solid material condensed.

Carbonaceous chondrites contain both chondrules and volatiles. Even slight heating would have driven off the volatiles, so these meteorites have never been heated and are the least altered. Very few of these have ever been recovered. One fascinating thing about carbonaceous chondrites is that in at least one case, amino acids, the building blocks of life, were found in a sample. Some of the ingredients for life on Earth may have come from space.

Iron meteorites have varying amounts of nickel in them. Some show a crystalline structure called Widmanstatten Lines which indicates a very slow cooling process, perhaps only a few degrees per million years. These meteorites provide other clues to the early Solar System.

Origin of Meteorites

What are Meteors and Meteorites?

Constellations

The Solar System