VOA常速英语2015--科学家研究地球磁场（在线收听）

科学家研究地球磁场

WASHINGTON— Most of us hardly ever think about the Earth's magnetic field. We might be aware that it helps guide birds as they migrate and ensures that our compasses point north, but not realize that it is one of the crucial components that make life on Earth possible. Yet, the processes in the Earth’s core that create the magnetic field are poorly understood.

At a lab of University of Maryland, scientists are trying to replicate the conditions that reign 3,000 kilometers below our feet.

Deep inside our planet, a 3,400 kilometer-wide sphere of molten iron and nickel, with a smaller solid iron ball at its center, creates the electric currents responsible for Earth’s magnetic field.

在地球的深处是直径3400米的熔铁和镍构成的球体，其核心处是个较小的固体铁球，它们产生了导致地球磁场的电流。

The most immediate benefit is its role in navigation.

它最直接的作用就是在导航方面。

But there’s more, says University of Maryland physics professor Daniel Lathrop.

但马里兰州立大学物理教授丹尼尔·莱思罗普说地磁场还有其他作用。

“It’s an important part of what makes the Earth a habitable planet because it shields us from a lot of the worst radiation from the sun,” he said.

“地磁场能保护人类免受来自太阳的严重辐射，因此使得地球适宜生存。”

Evidence shows that the Earth’s magnetic field is not stationary. It wanders around and sometimes even ventures [expands?] far away.

有证据表明地球的磁场并不是静止的，会徘徊不定，有时甚至会游离到远处。

“We do know the Earth’s magnetic field has reversed north-south hundreds of times in Earth’s history," said Lathrop. "Of course, the spin of the Earth stays the same, but where the magnetic pole is - moves and has actually reversed.”

“我们知道在地球的历史上，地磁场曾经南北颠倒过数百次，当然，地球的转动仍保持不变，但磁极会运动，而且相互颠倒。”

In their laboratory, funded by the National Science Foundation, Lathrop and his team are trying to find out how and why that happens.

在国家科学基金会的资助下，莱思罗普及其团队在实验室里努力研究这一切是如何发生的，以及为何会这样。

Spinning a ball of molten iron being somewhat impractical, researchers built a suitable substitute: a 3-meter wide spinning steel ball filled with 12.5 tons of sodium, a soft metal that melts at just under 100 degrees Celsius.

转动融化的铁球有点不现实，于是研究者们就建造了一个适当的替代品：一个直径三米、充满12.5吨钠的旋转的钢球，钠这种软金属能在100摄氏度以下融化。

A 1-meter-wide inner non-magnetic steel sphere substitutes for the solid core. Both can be rotated independently.

一个直径1米的内部非磁性钢球替代了固体内核，两个球体都能独立旋转。

Spinning them slowly has not created the so-called dynamo effect, thought to be responsible for creating magnetic fields.

旋转这两个球体并不能制造所谓的发电机效应，这种效应被认为能制造磁场。

“We only see them when we impose small magnetic fields from the outside. But imposing small magnetic fields from outside we get a factor of 10 larger magnetic fields induced by the flow. We get large gain without the so-called dynamo. Now we’re aiming to go full speed,” said Lathrop.

“只有从外界施加小磁场时才能看到这种效应，但从外部施加小磁场，就可以得到电磁产生的10倍大的磁场，无需所谓的发电机效应就能得到这种效果，现在我们希望能加速进展。”

Will these experiments prepare us for the possible reversal of the Earth’s magnetic field? Lathrop says it is difficult to predict changes that happen over thousands of years.

这些试验能让我们应对地磁场可能的逆转吗？莱思罗普说很难预测未来几千年内会发生什么改变。

“One second of operation of the experiment models 5,000 years of evolution of the magnetic field. So the goal is to take data from the experiment to do mock predictions and then you can improve the predictions,” he said.

“实验中一秒钟的操作能模拟磁场5000年的演变，所以我们的目标是从实验中得出数据来进行模拟预测，这样就能改善预测结果。”

Lathrop notes that the intensity of our planet’s magnetic field has dropped about 10 percent in the last 170 years, so the reversal process may have already started.

莱思罗普指出，在过去170年里地磁场的强度下降了大约10%，所以逆转过程可能才刚刚开始。

Fortunately for us, the change is too slow to affect our regular lives.

对我们来说，幸运的是，这一改变太缓慢，还不足以影响我们的日常生活。