When you look up at the night sky from a dark location, what do you see? On average, you can expect to see perhaps seven meteors per hour and considerably more during a meteor shower. What you’re actually witnessing is the fiery descent of a small particle through the Earth’s atmosphere. Most meteors simply burn up in the atmosphere, but some survive to strike the Earth as meteorites. By finding these space rocks and analyzing their composition, we’ve learned a great deal about the origins of the Earth and the evolution of the solar system.
Meteor Facts: What’s in a Name?
The terms meteor, meteorite, meteoroid, micrometeoroid and asteroid all refer to space rocks in one form or another. What’s the difference between them? Meteoroids and micrometeoroids refer to the vast number of relatively small rocks and particles in orbit around the sun. If a meteoroid encounters the Earth’s atmosphere and vaporizes, the visible trail we see in the sky is referred to as a meteor. They are sometimes called falling stars or shooting stars, though they aren’t stars at all. Sometimes a meteor survives its fiery descent and strikes the ground. Meteors that have hit Earth are referred to as meteorites. There are also fireballs and bolides, which refer to very bright meteors that often explode as they descend.
What’s the difference between meteoroids and asteroids? It’s largely a matter of size but not all that well-defined. According to the American Meteor Society, the vast majority of meteoroids range in size from small pebbles down to a grain of sand. Micrometeoroids are dust-sized particles. The largest meteoroids are those space rocks up to one meter or perhaps several meters in size. Anything larger is generally considered an asteroid. Asteroids can be as large as hundreds of kilometers in diameter. The largest, such as Ceres at about 952 km (592 miles) in diameter, are considered dwarf planets.
What Have We Learned?
According to National Geographic, approximately 50 tons of space debris falls onto the Earth’s surface every day. The vast majority of these particles are dust-sized micrometeorites. Occasionally, meteorites as large as boulders strike the Earth and a few impressive examples have survived the impact event and have been found intact. The largest of these is the Hoba meteorite in Namibia, discovered in 1920. This 54,000 kilogram-monster is too large to move. Other large meteorites are mostly destroyed on impact, leaving behind huge craters such as the Barringer Meteorite Crater near Winslow, Arizona.
Here’s a case where the distinction between asteroids and meteorites is somewhat blurred. The object that created the Barringer Meteorite Crater about 50,000 years ago was a nickel-iron meteorite about 50 meters across that massed about 270,000 metric tons. This huge rock is clearly large enough to be considered an asteroid but is still commonly referred to as a meteorite. Of course, there have been actual asteroid strikes in the distant past, such as the 10 kilometer asteroid that formed the Chicxulub Crater in Yucatan, Mexico. Chicxulub is one of the largest impact craters ever discovered on the Earth. That violent event is believed to have triggered the extinction of the dinosaurs and other animal and plant life some 65 million years ago.
Meteor’s and the Earth’s Origins
Most meteorites appear to come from large asteroids that broke up, or never completely formed, billions of years ago. Studying them helps scientists understand the processes taking place deep inside the Earth. Although the center of the Earth has never been directly seen or examined, meteorite studies have enabled us to determine that the Earth’s core is composed mostly of nickel and iron metal. This is true for the other planets as well. When the Earth was in the process of being formed and still molten, the metals sank to the center while the lighter materials formed the mantle and rocky crust on the exterior.
Evolution of the Solar System
The scientific study of meteors that have hit Earth, or meteorites, is crucial to the understanding of the solar system’s history and origin. Researchers have determined the age of certain ancient meteorite materials and have used that to establish the age of the solar system to be almost 4.6 billion years. The study of these primitive meteorites has yielded clues to the conditions present during planetary formation, as well as the composition and proportion of elements present in the entire solar system. This kind of information supports the process of mission planning for asteroid visits and will ultimately help identify the resources necessary to enable human spacefaring into the solar system.
Meteorite or “Meteorwrong”?
Meteorites are extremely rare and there are those dedicated to hunting for them. As you pursue your own adventures, you might come across an unusual rock. Did you actually find a meteorite or the much more common “meteorwrong”?Geoffrey Notkin, star of TV’s Meteorite Men and National Space Society president certainly knows his meteor facts and offers an excellent Comprehensive Guide To Meteorite Identification to help you. Happy hunting!
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