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22,000 |
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Rough number of known meteorite
discoveries on Earth. |
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120,000 |
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Weight (in pounds) of the largest
iron meteorite found on Earth. About 54,000 kg. |
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2,200 |
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Weight (in pounds) of the largest
rock meteorite found on Earth. About 1,000 kg. |
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1801 |
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Year Giuseppe Piazzi discovered
the first asteroid, Ceres. |
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4.6 |
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Earth years it takes the asteroid
Ceres to travel around the sun. |
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2880 |
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Year asteroid 1950 DA will
pass close to Earth - the greatest known impact
hazard. |
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Space
is a rocky place. The biggest space rocks are asteroids.
As they bang around out there in space, these rocks break
into smaller and smaller pieces that sometimes fall to Earth.
Most of them burn up in streaks of light. Some crash into our planet and leave behind meteorites. Every once and a while, a really big one makes a giant crater.
WHAT'S THE DIFFERENCE?Asteroids are made up of rock and iron like the four planets closest to our Sun. They are different from comets, which are mostly rock and ice. Comets have tails. Asteroids are more like planets and moons. Scientists often call asteroids minor planets.
Most asteroids orbit the Sun between Mars and Jupiter. This area is called the asteroid belt. There are millions of asteroids.
The biggest asteroid is Ceres. It is about 600 miles (960 km) around. It was the first asteroid discovered.
Smaller pieces of rock and iron that travel through space are called meteoroids. Meteoroids orbit our Sun just like asteroids and planets.
When a space rock enters a Earth's atmosphere, it becomes a meteor - or shooting star. The meteor heats up and makes the air around it glow. We see a streak of light. Most meteors burn up. Scientists think up to 10,000 tons of meteors fall on the Earth each day, but most are no bigger than a speck of dust.
A meteor makes it all the way to ground without burning up is called a meteorite. Meteorites range in size from tiny pebbles to boulders.
Some planets and moons don't have enough atmosphere to protect them against meteor and asteroid impacts. Earth's moon, Mercury and even Mars are covered with round impact craters from these collisions.
ASTEROID CHALLENGE
Find out why don't asteroids break out of the 'belt' and
crash into Earth and other planets. Start your research
here.
MISSIONS TO EXPLORE ASTEROIDS
Featured Mission: NEAR
On Feb. 12, 2000, flight controllers gently landed NASA's
NEAR spacecraft on asteroid Eros. It was the first controlled
landing on an asteroid.
More Missions to explore Asteroids:
Past
Missions
Future
Missions
Source:
NASA
