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Main idea and Supporting details This article has many details about objects in space and how they affect Earth. What main idea can you discover from these details?

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As the sun rises on February 15, 2013, the people of chelyabinsk, russia, start their mornings as usual, eating breakfast, driving to work, and heading to school. But the 1.1 million residents of this busy city are in for a very unusual day. this morning, a space rock 55 feet across—as wide as a 5-story building is tall—is headed directly for

chelyabinsk. and nobody has any idea.this rock has been circling close to Earth for thousands of years.

Finally, this morning, it enters our atmosphere—the layer of gases that surrounds our planet.

Zooming toward Earth’s surface, the rock gets hotter and hotter. the heat is so intense that it starts to crumble as it travels 40,000 miles an hour—more than twice as fast as a space shuttle at launch. Now it’s about 15 miles above the ground, and it won’t be long until . . . it explodes!

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A huge fireball from space exploded above a Russian city, injuring more than a thousand

people, and no one saw it coming. can we protect ourselves next time?

By Justin o’Neill

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light produced when a rock burns up in Earth’s atmosphere. Our solar system includes millions of rocks, such as asteroids (large space rocks), comets (part rock and part ice), and meteoroids (smaller space rocks). Especially large and bright meteors, like the one in Chelyabinsk, are called fireballs. Any pieces that land on Earth are called meteorites.

Mentions of sacred rocks from the sky appear in writings from ancient civilizations. It wasn’t until 1794, though, that German physicist Ernst Chladni proposed that meteorites came from outer space. But no one took him seriously. The common belief at the time was that rocks that fell from the sky came from Earth; they had first been swept up by strong winds. Then, in April 1803, thousands of meteorites fell on the French town of L’Aigle. A physicist named Jean-Baptiste Biot went to investigate. Biot’s research finally convinced scientists that rocks can—and do—fall from space.

The residents of Chelyabinsk gawk, puzzled, as a brilliant fireball streaks across the blue-pink morning sky and disappears in a blinding flash of light brighter than the sun. An eerie trail of smoke is left behind. Some people run outside or go to the windows for a better look. Others pull their cars over, alarmed.

What was that? A missile? A plane crash? Aliens?!

Two uneasy minutes pass. And then—BOOM! SMASH!Thunderous bangs echo as invisible shock

waves shake Chelyabinsk. Walls collapse. People are knocked to the ground. Windows shatter, flinging razor-sharp shards of glass into homes, schools, and offices throughout the city. In a single instant, 1,200 people are injured.

They are lucky. It could have been worse.

Rocks From the SkyEver look up at the night sky and see a

shooting star? Beautiful, yes? Don’t let the name confuse you, though—a shooting star is not really a star; it’s a meteor, the stream of

Above and top right: The Chelyabinsk fireball was captured by many people using cell phones and cameras. Their images have greatly aided scientists. Bottom right: A large hole where a meteorite crashed into a frozen lake.

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Now we know that space rocks are leftovers from when the planets of our solar system formed about 4.5 billion years ago. Like the planets, the rocks move around the sun in circles called orbits. Generally they stay in the asteroid belt between Mars and Jupiter, but sometimes they knock into their neighbors, bouncing around like bumper cars, and stray close to us. Each day, Earth is bombarded by some 100 tons of debris, most of which burns up in the atmosphere without causing any harm.

But if an asteroid larger than a mile across were to hit Earth, it would mean catastrophe. Sixty-five million years ago, an asteroid likely led to the extinction of the dinosaurs. That asteroid was six miles across. It crashed off the coast of what is now Mexico. Scientists believe dust clouds from the explosion blocked out the sun—perhaps for months—causing plants and animals to die.

Could that happen again?

Another close callThe last time a meteoroid caused as much

damage as the one in Chelyabinsk did was more than 100 years ago—by chance, also in Russia.

On the morning of June 30, 1908, a farmer named S.B. Semenov was sitting on the porch of a trading post in Siberia, a vast area in eastern Russia. Suddenly the sky lit up, and a shock wave knocked him to the ground. He felt fierce heat, writing later, “It almost burned the shirt off me.”

Semenov was more than 40 miles away from the center of what has become known as the Tunguska event. Tunguska is a remote region of the Siberian wilderness. With the force of nearly 200 atomic bombs, the explosion felled 80 million trees in an area more than twice the size of New York City.

But because Tunguska is so remote, it took decades for scientists to piece together what happened. The mystery inspired bizarre theories—a UFO explosion, a science experiment gone wrong, a black hole passing through the planet.

In fact, what happened in Tunguska was just like what happened in Chelyabinsk, except the Tunguska meteor was much larger and much closer to the ground. These events are extremely rare; few of today’s scientists ever imagined

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This photograph of a flattened forest shows the destruction caused by the Tunguska event. Fortunately, no one lived in Tunguska. If the explosion had occurred above Paris or London, the city would likely no longer exist.

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they would live to see anything like it. Very large asteroid events, like the one that probably doomed the dinosaurs, are even more rare. They happen only once every 100 million years or so. Now a group of experts is working feverishly to ensure that such an event never happens again.

Spaceship earthThe B612 Foundation, founded by former

astronauts, is devoted to protecting the planet from asteroids. NASA, America’s space research agency, has already found most of the very largest asteroids. But it has other important projects (like exploring Mars) and can’t devote all its time and money to asteroids. So B612 is building a special satellite—called Sentinel—that will serve as our planet’s eyes, orbiting the sun and hunting for asteroids.

“Right now, we’re on Spaceship Earth, and we’re flying through the universe without any windows,” says Diane Murphy, a spokesperson

for B612. “We’re creating windows for Spaceship Earth.”

But even if we could see a large asteroid coming toward us, is there anything we could do? The experts at B612 say yes. We could alter an asteroid’s course away from Earth by crashing an unpiloted spacecraft into it. If we couldn’t do that, we might at least have time to evacuate a city like Chelyabinsk before an explosion.

looking Both WaysWhat happened in Chelyabinsk is a

reminder of something that’s easy to forget: We live on a planet that is drifting through space, and we’re not alone. Drifting along with us are objects that may someday pose a threat.

But according to Murphy, there’s no reason to panic. Asteroids are just part of the universe. We can’t change that, but we have the technology to help us prepare for future impacts.

“We do lots of things to protect ourselves,” says Murphy. “Just like we look both ways for cars when we cross the street, we need to look both ways for asteroids.”

Fortunately, no one in Chelyabinsk was killed, and most of the injuries were minor. Many people in the area have a new hobby: hunting for meteorites. Even small fragments of the fireball can be worth thousands of dollars.

If you saw a meteorite, though, you probably wouldn’t think it was anything special. Most look an awful lot like boring old black rocks.

You’d probably walk right by it.

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Imagine you are a scientist who works for the B612 Foundation. Write a speech explaining why the Sentinel satellite could be helpful to people on Earth. Cite examples from the article. Send your speech to “Meteor Contest” by October 15, 2013. Ten winners will each receive a copy of Every Soul a Star by Wendy Mass. See page 2 for details.

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