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月球在四十亿年前受到撞击并改变两极

2014-05-15    来源:dailymail    【      美国外教 在线口语培训

概要:据英国《每日邮报》5月12日报道,天文学家最新发现,月球并没有我们想象当中那么稳定,它曾在四十亿年前受到撞击并改变两极。

日本科研团队通过对日本月亮女神号以及美国航空航天局月球勘探者号两艘探测器在月球表面57个不同地质点的数据分析得出,月球曾经有磁场,并且磁场的两极曾经发生改变。

通过观察,研究人员在月球表面发现了许多磁力线,并且它们围绕月球的两极成聚合型分布。

然而与地球不同的是,月球上的磁场并不是以两极为顶点均匀分布,而是距极点发生了45度到60度的偏转。 并且,地球上的地磁南北极虽然正在发生偏移,但偏移的速度和程度均非常缓慢。然而月球表面的磁极偏转却是跳跃式的。

科学家表示,这些异常的反应都表明,月球曾经受到过剧烈撞击,促使其磁场两极发生过改变。另外,除了撞击的作用,太阳系内部的不稳定性以及重力失衡作用也是导致该现象的原因。

Is the moon lying on its SIDE? Giant impact might have knocked it off balance 4 billion years ago, claim experts

Japanese researchers have completed a study of the lunar magnetic field

Using data from two spacecraft they say the moon was once on its side

They postulate the existence of another set of poles different to today

A giant impact event could have caused the moon to rock as much as 60°

This is estimated to have happened about 4 billion years ago after it formed

Our moon might not be the stationary, boring place some thought it to be.

New research suggests our biggest natural satellite may have been rocked by an impact about four billion years ago that changed its orientation.

This suggests that the face we see now may not always have been the one pointing towards Earth.

The research, published in Nature Geoscience, was carried out by a team of Japanese researchers.

They used data from two lunar orbiters, Jaxa’s Kaguya and Nasa’s Lunar Prospector.

What they found is that, while it was already thought the moon likely formed when a Mars-sized object hit Earth, the moon may have been hit itself early in its life.

Now and then? On the left is how our moon looks today, while on the right is how it might have looked 4 billion years ago before being hit by in a giant impact event (exaggerated by 30 degrees) that rocked it onto its side

To come to the conclusion, the researchers studied 57 different sites on the moon from the two spacecraft.

Studying magnetic anomalies at each site, they calculated how the moon’s magnetic field would have looked in the past.

They found that many of their field lines clustered, as expected, around the moon’s poles.

Like Earth, the moon is thought to have an invisible ‘bar magnet’ running from pole to pole, so the magnetic field lines go in and out of the poles.

However, the researchers found a second clustering of magnetic fields about 45 to 60 degrees from the current poles.

On Earth, our magnetic poles are known to drift slightly – but on the moon it appears they jumped to their new location rather than drift gradually.

This suggests that an impact event made them move suddenly in a short amount of time.

The authors of the paper suggest this could have been to internal instabilities, gravitational imbalances in the solar system or a giant impact that literally knocked the moon on its side.

FINDING IT TOUGH TO COMPREHEND? HERE'S THE RESEARCH IN A NUTSHELL

The moon takes 27 days to circle Earth, during which time it completes one spin.

For comparison, it takes Earth 365 days to orbit the sun but just 24 hours to rotate.

In the moon's case it is 'tidally locked' to our planet, which means the same face always points towards us.

From the north to the south of the moon is an axis of rotation, just like on Earth, around which the moon rotates.

Very close to the north and south poles of the moon are the magnetic south and north poles, through which the moon's magnetic field lines run.

The evidence from the researchers suggests, though, that this axis of rotation was not always the same.

It appears that the magnetic fields once ran through poles up to 60 degrees away from where they are now.

This suggests the moon was once oriented in a different manner with respect to Earth, with its axis of rotation once in a different location entirely.

THE MOON - STATS AND FACTS

The Moon is Earth's only natural satellite, circling in a slightly elliptical orbit at 2,300 miles (3,700 kilometres) per hour.

At this speed, it takes about 27 days to completely circle Earth, which is 240,250 miles (384,400 kilometres) away.

Although it doesn't revolve around the sun, because of its size and composition, planetary scientists call the moon a 'terrestrial planet' - akin to Mercury, Venus, Earth and Mars.

Unlike the Earth, the Moon does not have a significant magnetic field, and it has no significant atmosphere.

This means its unprotected regolith (dust on the surface) is constantly being bombarded by the solar wind.

The sun continuously embeds chemical elements, such as hydrogen ions, into the lunar surface.

Thus, by studying the surface of the Moon, scientists can learn a lot about the Sun.



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