文章大意:本篇是一篇说明文。主要介绍了美国国家航空和宇宙航行局(NASA)的行星防御专家实施的行星防御测试(planetary defense test):如果发现了危险的太空岩石,最安全解决措施其实很微妙,就是利用其与小型航天器与撞击,使它偏离轨道。
Nuclear bombs. That’s the go-to answer for incoming space objects like asteroids(小行星) and comets, as far as Hollywood is concerned. Movies like Deep Impact and Armageddon rely on nuclear weapons, delivered by stars like Bruce Willis, to save the world and deliver the drama.
But planetary defense experts say in reality, if astronomers spotted a dangerous incoming space rock, the safest and best answer might be something more subtle, like simply pushing it off course by crashing it with a small spacecraft.
That’s just what NASA did on Monday evening, when a spacecraft headed straight into an asteroid called Dimorphous, which is around 7 million miles away and poses no threat to Earth. It’s about 525 feet across and orbits another larger asteroid.
In images streamed as the impact neared, the egg-shaped asteroid grew in size from a little spot on screen to have its full rocky surface come quickly into focus before the signal went dead as the craft hit right on target.
Events happened exactly as engineers had planned, they said, with nothing going wrong. “As far as we can tell, our first planetary defense test was a success,” said Elena Adams, the mission systems engineer, who added that scientists looked on with “both terror and joy” as the spacecraft neared its final destination.
The impact was the peak of NASA’s Double Asteroid Redirection Test (DART) ,a 7-year and more than $300 million effort which launched a space vehicle in November of 2021 to perform humanity’s first ever test of planetary defense technology. It will be about two months, scientists said, before they will be able to determine if the impact was enough to drive the asteroid slightly off course, probably shortening its original orbit.
NASA plans to launch an asteroid-hunting space telescope named NEO Surveyor in 2026. “We’ve tacked lots of space rocks, especially the larger ones that could cause extinction-level events. Thankfully, none currently threaten Earth. But many asteroids the size of Dimorphous haven’t yet been discovered, and those could potentially take out a city if they came crashing down. ” explains Lindley Johnson, NASA’s Planetary Defense Officer.
12. How did scientists know the craft hit the asteroid successfully?
A.The signal from the craft was lost as it hit the target. |
B.They recorded the whole process with a telescope. |
C.The little spot on the screen suddenly disappeared. |
D.They monitored the craft with satellites in space. |
13. What is the purpose of launching the spacecraft?
A.To search for evidence of alien life. |
B.To end the asteroid’s threat to Earth. |
C.To save the world and deliver a drama. |
D.To test technology for defending Earth. |
14. What can be inferred about Dimorphous?
A.It is a dangerous incoming space rock. |
B.It is an egg-shaped asteroid around Earth. |
C.It may orbit the same asteroid after the hit. |
D.It is expected to blow up after the impact. |
15. Which statement will Lindley Johnson probably agree with?
A.Asteroids are equally destructive whatever the size. |
B.NEO Surveyor is aimed to track smaller asteroids. |
C.Larger asteroids will no longer threaten Earth. |
D.NASA is responsible for the safety of Earth. |