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  3. A new look at an asteroid orbiting the sun shows it could possibly smash into the Earth with tremendous force. But experts say

A new look at an asteroid orbiting the sun shows it could possibly smash into the Earth with tremendous force. But experts say

admin2012-10-23  57
问题    A new look at an asteroid orbiting the sun shows it could possibly smash into the Earth with tremendous force.  But experts say the potential impact is still 872 years away, time enough for the speeding space rock to alter its course.
   Named 1950DA, the asteroid--1 kilometer wide--is the most threatening to the Earth of all of the known large asteroids, but the odds are only adout one in 300 that it would impact the planet, researchers said. "One in 300 is pretty long odds," said Jon D. Giorgini, a scientist in Califonia. "I’m not personally going to worry about it. It is so far in the future that lots of things could change."
   There are approximately 1,000 asteroids bigger than a kilometer that can pass near the Earth in their orbit of the sun. About 580 have been found and their orbits plotted. Of these, only 1950DA represents a possible threat. Scientists continue an effort to identify all the other large asteroids that pass near the Earth, and it is their great hope that they don’t find any that are greater threats. If 1950DA did hit the Earth, said Giorgini, it would have planet-wide effects, setting off fires, changing the weather and perhaps creating immense tidal waves.  But it would not be a planet killer like the asteroid thought to have snuffed out the dinosaure some 65 millions years ago.
   Asteroid 1950DA was first discovered in 1950, but then not noted in astronomy logs again for decades. It was rediscovered in the year 2000 and in March 2001 whizzed within about 77 million miles of Earth, giving astronomers an opportunity to gather visual and radar readings. From that, the astronomers projected the orbital path 1950DA would take on its next 15 near passes of the Earth--over a period covering nearly nine centuries.  For the 15th near pass, on March 16,2880, the analysis showed it was mathematically possible, though unlikely, that the asteroid could hit the Earth.
   He said the highest probability is that the asteroid in 2880 will miss the Earth by about 290, 000 kilometers--a distance closer than the 370, 000-kilometer orbit of the Moon around the Earth.  
Talking about asteroids, the author tells us that ______.
选项 A、nothing can alter the course of an asteroid in its orbit of the sun
B、only about one in 300 asteroids near the sun would hit the Earth
C、scientist have managed to identify all the asteroids orbiting the sun
D、there is no immediate threat to the Earth from an asteroid
答案D
解析 从第1段“but experts say the potential impact is still 872 years away, time enough for the speeding space rock to alter its course”可判断，短时间内小行星对地球不会有威胁。
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