jeudi 6 mars 2014

Asteroids, Comets, and Meteors

Asteroids, Comets, and Meteors


Most people lump asteroids, meteors, and comets together and consider that the terms are interchangeable. But that is a bit of a misconception. Although asteroids, comets, and meteors do share the fact that they are all bits of rock or ice that aren't part of a major planet, they really are quite different.

Asteroids:  
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Asteroids are amazingly diverse. Some asteroids, like Mathilde, are more like piles of rubble that are just loosely held together. Other asteroids, like Kleopatra, are metallic in nature and are solid rock. The largest asteroid is Ceres, which is 580 miles across, and the smallest asteroids (that we know of) are only one-tenth of that size. Most of the known asteroids orbit the sun between Mars and Jupiter in the Asteroid Belt.

Comets: 

Comets are made up mostly of ice and dust. Comets have a nucleus and grow tails when they get close enough to the sun. When a comet gets close to the sun, the heat from the sun heats up the ice and vaporizes it. The gases fly off the comet and cause dust to fly up, too. A cloud of the gases and dust forms around the nucleus, and as the comet speeds through space, some of the gases are stripped of neutrons and blown back by the solar wind, forming the tail of the comet.

Meteors: 
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Meteors are sometimes called "shooting stars." They are not, of course, "stars." Meteors are small pieces of interplanetary dust that burn up when they slam into the atmosphere of the earth. What's called a "meteor shower" happens when the earth passes through a field of dust that a comet has left behind. Most of the time these little pieces of rock or dust burn up completely but occasionally one will survive the impact with the earth's atmosphere and crash into the earth. These are called "meteorites."

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