英语听力精选进阶版 7212（在线收听）

Background: 科学杂志《自然》上的一项新的研究报告认为地球可能曾经拥两个月亮，不过在天体碰撞后，比较小的一个消失了。科研人员认为，碰撞过程可能相当缓慢导致月球上出现了鲜为人见的凹凸不平的高地结构。

This new theory builds on the idea that around four billion years ago the Earth was struck by a Mars-like planet, but instead of the smash producing enough debris for one moon, this paper argues there was enough for two.

This small second moon become stuck in a gravitational tug of war between the Earth and its much larger sibling. After millions of years in this position the new moon was drawn into a collision at a speed of less than three kilometres per second.

The scientists say this slow paced crash may have caused a build up of material and the formation of highlands on the Moon's far side.

For decades scientists have been trying to understand why the visible near side of the Moon is covered in craters while the far side has mountain ranges higher than 3,000 metres.

The researchers hope that Nasa observational missions might prove this new theory within a year.

Glossary 词汇表

to be struck by 被撞击 

a smash 冲击 

debris 碎片；废墟 

a paper 学术文章报告 

to become stuck 被阻无法移动 

a gravitational tug of war 天体碰撞 

a sibling 姊妹（类似天体） 

slow paced 慢速 

the far side 远处 

crater 火山口

Questions:

1. When was the Earth hit by a planet the size of Mars? 

Around four billion years ago.

2. What was the consequence of the collision of the second moon? 

The formation of hills on an area of the Moon rarely seen.

3. What was it about the Moon that scientists could not understand before? 

The reason why the near side of the Moon is covered in craters while the far side has mountain ranges.

4. True or false? The small second moon lasted millions of years. 

True. Between its formation and its disappearance after a collision the second moon lasted millions of years.