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Asteroids are bigger versions of the meteoroids (流星) that race across the night sky. Most orbit the sun far from Earth and don't threaten us. But there
are also thousands of asteroids whose orbits put them on a collision course with Earth.
Buy $50 million worth of new telescopes right now. Then spend $10 million a year for the next 25 years to locate most of the space rocks. By the time we
spot a fatal one, the scientists say, we'll have a way to change its course.
Some scientists favor pushing asteroids off course with nuclear weapons. But the cost wouldn't be cheap.
Is it worth it? Two things experts consider when judging any risk are: 1) How likely the event is; and 2) How bad the consequences if the event occurs.
Experts think an asteroid big enough to destroy lots of life might strike Earth once every 500,000 years. Sounds pretty rare - but if one did fall, it would be the
end of the world. "If we don't take care of these big asteroids, they'll take care of us," says one scientist. "It's that simple."
The cure, though, might be worse than the disease. Do we really want fleets of nuclear weapons sitting around on Earth? "The world has less to fear from
doomsday (毁灭性的) rocks than from a great nuclear fleet set against them," said a New York Times article.
16. What does the passage say about asteroids and meteoroids?
A. They are heavenly bodies different in composition.
B. They are heavenly bodies similar in nature.
C. There are more asteroids than meteoroids.
D. Asteroids are more mysterious than meteoroids.
17. What do scientists say about the collision of an asteroid with Earth?
A. It is very unlikely but the danger exists.