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Raining space rocks: a scientist looks to meteorites for clues about our solar system's birth.

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As Earth whirls through space, debris like dust and rocks slam into its atmosphere like bugs on a windshield. If one of these space rocks makes it to the ground, it's called a meteorite.

"At least three fist-sized meteorites hit the Earth every day," says Denton Ebel. He is the curator of meteorites at the American Museum of Natural History in New York City. While it's impossible to find every meteorite that crashes into Earth, Ebel and other experts are busy studying the ones they're lucky enough to collect. These space rocks carry clues about the beginning of our solar system.

Blast From the Past

When space rocks fall to Earth, scientists get a window into the past. Our solar system developed from microscopic dust and gas. The sun and other bodies formed as gravity, a force that pulls objects toward each other, drew these particles of dust and gas together. As the particles got larger, each clump's gravity increased, attracting more particles. Some of these clumps grew into massive objects like planets and moons. Some formed into smaller objects like asteroids and comets (see "Space Rock Who's Who").

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Rock Science

Each meteorite contains different amounts of chemical elements that act like the space rock's fingerprint. When scientists find a meteorite, they study the amounts and types of elements they contain. The measurements can reveal the meteorite's age, where it came from, and how long it's been since it fell to Earth.

Most meteorites contain tiny droplets of solidified rock from the earliest days of the solar system. These space rocks are called chondrites. "They are what's leftover from the formation of the planets and the sun," says Ebel. The oldest chondrites include droplets that are more than 4.5 billion years old!

Finding Meteorites

So how do you know if you've found a rock from space? Most meteorites have telltale markings from their trip through Earth's atmosphere. As the rock plunges toward the ground, its outer layer melts. Air scrapes most of this layer off. "It's like getting a rug burn as you slide across the carpet," says Ebel. Before the rock hits the ground, the last melted layer hardens into a thin, black crust. Meteorites also tend to be rounded. Some are magnetic. Meteorites can land anywhere at any rime, so it's no surprise that people sometimes stumble upon them. It's possible that a cool-looking rock you've picked up could have come from the other side of the solar system.

check it out

Nearly a mite wide, Arizona's Barringer Crater formed when an iron meteorite as wide as an 9-story building is tall slammed into the desert. The impact created one of 200 known craters on Earth. See a diorama of Barringer and learn more about meteorites at the Arthur Ross Hall of Meteorites at the American Museum of Natural History (www.amnh.org), or ask your teacher.

SPACE ROCK WHO'S WHO

There are many different kinds of space rocks. Here's how to tell the difference.

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ASTEROIDS: Asteroids are space rocks. They can be as small as a pebble or as large as Texas. Most come from the asteroid belt between Mars and Jupiter.

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COMETS: These icy dirt balls come from the solar system's outer regions. When comets near the sun, dust and vapor escape, making trademark tails.

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METEORS: These small asteroids burn up as they enter Earth's atmosphere. At night, they can be seen as "shooting stars" streaking across the sky.

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METEORITES: If an asteroid makes it through Earth's atmosphere without burning up, the rock that lands on the ground is called a meteorite.

BEFORE READING

Set a Purpose

Learn why scientists study meteorites and what these rocks can tell us about Earth and our solar sytem.

Background

* Why do asteroids, comets, and meteors collide with other objects? All objects in the universe--including asteroids, planets, and stars--exert a pulling force, called gravity, on every other object. Because these objects are constantly tugging on each other, they gradually change each other's paths. Sometimes this causes two objects to move toward the same place at the same time.

* Thousands of asteroids and comets, scattered all over the solar system, are traveling in paths that bring them near Earth. That's why astronomers scan the sky every night to make sure that a large asteroid isn't headed out way anytime soon. The chance that Earth will be struck by a large asteroid or comet during our lifetimes is almost zero.

Discussion Question

* Have you ever seen a shooting star while gazing at the night sky? What did it look like? What did you think it was? (Answers will vary.)

AFTER READING

Discussion Question

* Denton Ebel has called meteorites "fossils of the early solar system." What do you think he means by this? (Answers will vary.)

RESOURCE

* For more information about meteorites and the origins of the solar system, visit: http://www.omnh.org/exhibitions/permonent /meteorites
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Title Annotation:earth science
Author:Hamalainen, Karina
Publication:SuperScience
Geographic Code:1USA
Date:Mar 1, 2011
Words:827
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