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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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It’s February 15, 2013. the people of Chelyabinsk, russia, start the day as usual. they eat breakfast. they go to work and school. But the 1.1 million people of this city are in for a strange day. this morning, a space rock is falling from the sky. the rock is 55 feet across. It’s headed straight for Chelyabinsk. And no one knows it’s coming.

the rock has been circling close to Earth for thousands of years. this morning, it enters our atmosphere—the layer of gases that surrounds Earth.

the rock zooms toward Earth’s surface. It grows so hot that it starts to crumble. 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. It won’t be long before 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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rock burns up in Earth’s atmosphere. Our solar system has millions of rocks. They include asteroids (large space rocks), comets (part rock and part ice), and meteoroids (smaller space rocks). Very large and bright meteors, like the one in Chelyabinsk, are called fireballs. Pieces of space rocks that land on Earth are called meteorites.

Long ago, people believed that falling rocks really came from Earth. They thought strong winds swept the rocks into the sky. Then, in 1794, German scientist Ernst Chladni suggested that such rocks came from outer space. No one took him seriously. Later, in 1803, thousands of meteorites fell on the French town of L’Aigle. A scientist named Jean-Baptiste Biot studied them. Biot’s findings convinced people that rocks can and do fall from space.

Now we know that space rocks are

People are puzzled as they see a fireball streak across the sky. It disappears in a flash of light brighter than the sun. A 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 tense minutes pass. And then—BOOM! SMASH!shock waves shake the city. Loud bangs

echo. Walls collapse. People are knocked to the ground. Windows break. Pieces of glass fly into homes, schools, and offices. In an instant, 1,200 people are hurt.

They are lucky. It could have been worse.

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

a shooting star? Pretty, right? But don’t be fooled. A shooting star is not a star. It’s a meteor, the stream of light produced when a

Above and top right: Many people took pictures of the Chelyabinsk fireball with their cell phones and cameras. Their photos have greatly aided scientists. Bottom right: A large hole where a meteorite crashed into a frozen lake.

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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. They mostly stay in the asteroid belt between Mars and Jupiter. But sometimes they bounce against each other and stray close to us. Each day, about 100 tons of debris flies toward Earth. Most of it burns up in the atmosphere and does no harm.

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

Could that happen again?

Another Close CallThe last time a space rock caused as much

damage as the one in Chelyabinsk did was more than 100 years ago. By chance, it was

also in Russia.It was June 30, 1908. A farmer named

S.B. Semenov was sitting on a porch in Siberia, an area in eastern Russia. Suddenly the sky lit up. A shock wave knocked him to the ground. He felt fierce heat. “It almost burned the shirt off me,” he wrote later.

Semenov was more than 40 miles away from the center of what is now called the Tunguska event. Tunguska is a remote area of Siberia. The explosion had the force of nearly 200 atomic bombs. It felled 80 million trees in an area more than twice the size of New York City.

Because Tunguska is so remote, it took decades for scientists to figure out what happened. There were many theories. Was it 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. The Tunguska meteor was simply larger and closer to the ground. These events are very rare. Few of today’s scientists ever thought they would live to see one. Huge asteroid events,

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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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like the one that likely doomed the dinosaurs, are even more rare. They happen only once every 100 million years or so. Now a group of experts is working to make sure such an event never happens again.

Spaceship EarthThe B612 Foundation was started by

former astronauts. It aims to protect Earth from asteroids. NASA, America’s space research agency, has found most of the largest asteroids. But it has other important projects (like exploring Mars). It can’t spend all its time and money on asteroids. So B612 is building a satellite called Sentinel. Sentinel will orbit the sun. It will hunt for asteroids.

“Right now, we’re on Spaceship Earth, and we’re flying through the universe without any windows,” says Diane Murphy. Murphy works for B612. “We’re creating windows for

Spaceship Earth.”But what if we saw a large

asteroid coming toward us? Is there anything we could do? The experts at B612 say yes. We could turn the rock away from Earth by crashing an unpiloted spacecraft into it. If we couldn’t do that, we might at least have time to move people out of an area before a crash.

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 drifting along with us are objects that could do us harm.

But Murphy says there’s no reason to panic. Asteroids are out there. We can’t change that. But we can 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.”

Luckily, no one in Chelyabinsk was killed. Most of the injuries were minor. Many people there have a new hobby: hunting for meteorites. Even small pieces 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 like plain 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.

WRITE TO WIN!

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A researcher holds up a

meteorite from Chelyabinsk.

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