By Matt McGrath, BBC News

媒體英語(yǔ)會(huì)帶大家一起學(xué)習(xí) BBC 撰稿人在報(bào)道世界大事時(shí)常用到的單詞和短語(yǔ)。

Background: 科學(xué)雜志《自然》上的一項(xiàng)新的研究報(bào)告認(rèn)為地球可能曾經(jīng)擁兩個(gè)月亮，不過(guò)在天體碰撞后，比較小的一個(gè)消失了。科研人員認(rèn)為，碰撞過(guò)程可能相當(dāng)緩慢導(dǎo)致月球上出現(xiàn)了鮮為人見(jiàn)的凹凸不平的高地結(jié)構(gòu)。

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.