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Where do they come from?
Most meteorites come from asteroids, rocky bodies orbiting between Mars and Jupiter. Recently we have learned that a few meteorites have been blasted off the Moon and the planet Mars. |
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10. The solar system
Although people have seen meteorites fall since the earliest times, it was only about 1800 when scientists finally became convinced that rocks really did fall from the sky. Since then, we've discovered that most meteorites come from the asteroid belt, the area of the solar system between the orbits of Mars and Jupiter where many asteroids orbit the sun. (Artist's conception, NASA JSC photo S79-29468)
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11. Asteroid Ida
Asteroids are small planets, fragments of rock and iron left over from the formation of the solar system or the breakup of larger fragments. Many asteroids probably look like Ida, the asteroid in this picture taken by the Galileo spacecraft in 1993. Ida is about 30 kilometers long, is made of rock, and has many craters. (NASA Jet Propulsion Laboratory)
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12. Comet Giacobini-Zinner
Comets are small bodies made of rock, dust and ice, formed in the distant reaches of the solar system. Some comet orbits take them near the Sun. Then solar radiation heats the comet's surface, causing part of the ice to boil off into space and carry some of the dust with it. When this happens the comet can develop a "tail" millions of kilometers long, and leave a dust trail behind in solar orbit. (NASA Jet Propulsion Laboratory)
When the Earth crosses a comet's trail some of the dust enters our atmosphere and burns, making bright streaks called meteors in the sky. Some of the particles do not burn, but stay in the upper atmosphere, where we can collect them with high-flying aircraft. Scientists call these "interplanetary dust particles," or more simply "cosmic dust."
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13. Asteroid in space
Larger meteorites, though, don't come from comets but from asteroids. It's a long way from the asteroid belt to the Earth, and very few asteroid pieces get the chance to travel that far. Most asteroids never do, and spend eternity in space, quietly orbiting the Sun. (Artist's conception, NASA JSC photo S79-29481)
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14. Asteroid collision
Every now and again, though, the orbits of asteroids cross and their quiet times end. Then the asteroids collide and shatter, and the pieces fly into different orbits around the sun. Some of these pieces orbit closer and closer to the sun. Eventually some of their orbits cross the Earth's orbit, and the piece of asteroid can hit the Earth. (Artist's conception, NASA JSC photo S79-29478)
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15. Meteor
As the asteroid fragment approaches the Earth, it passes through our atmosphere where friction heats it white hot. We see this moving flame as a meteor crossing the sky. If the asteroid fragment is big enough, fist-sized or so, it won't burn up completely and will fall to the Earth as a meteorite. These small meteorites do not explode or make craters when they hit. They just hit like an extra large hailstone or a rock thrown from across the street. Newly fallen meteorites are usually found sitting on the ground, a rock that wasn't there the day before. (Artist's conception, NASA JSC photo S79-29471)
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