小行星为什么会撞击地球

Unless we spend money spotting and preventing asteroids(小行星) now, one might crash into Early and destroy life as we know it, say some scientists.
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 is 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 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(世界末日) rocks than from a great nuclear fleet set against it,” said a New York Times article.
9.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.
10.What do scientists say about the collision of an asteroid with Earth?
A.It is very unlikely but the danger exists.
B.Such a collision might occur once every 25 years.
C.Coilisions of smaller asteroids with Earth occur more often than expected.
D.lt’s still too early to say whether such a collision might occur.
11.What do people think of the suggestion of using nuclear weapons to alter the course of asteroids?
A.It sounds practical but it may not solve the problem.
B.It may create more problems than it might slove.
C.It is a waste of money because a collision of asteroids with Earth is very unlikely.
D.Further research should be done before it is proved applicable.
12.We can conclude from the passage that .
A.while pushing asteroids off course nuclear weapons would destroy the world
B.asteroids racing across the night sky are likely to hit Earth in the near future
C.the worry about asteroids can be left to future generations since it is unlike to happen in our lifetime.
D.workable solutions still have to be found to prevent a collision of asteroids with Earth

读下列材料回答问题。(13分)
材料一 国际小行星中心2008年8月24日发布的新小行星命名公报中,命名了一颗“北京奥运星”。据了解,“北京奥运星”沿着一个偏心率为0.19的椭圆轨道绕日运行,到太阳的平均距离为4.58亿千米,它在轨道上平均每天以147.6万千米的高速度奔腾前进,绕太阳一周需5.3年。
材料二

(1)图中所示包括 级天体系统,中心天体是 。(4分)
(2)”北京奥运星”位于小行星带,与此相邻的行星是② ,③ 。与两行星比较,”北京奥运星”具有 小、 小的特点。(8分)
(3)在图中标注行星的公转方向,”北京奥运星”绕日运行轨道的偏心率是0.19,说明八大行星与小行星绕日公转的方向具有 性,而且绕日公转轨道几乎在一个 上,说明其意义: 。(4分)
(4)①行星是太阳系中特殊的行星,其特殊性是 ,分析这种特殊性存在的基本条件 。(4分)