英语听力：自然百科 地球力场 Earth's Force Field—5
时间：2014-05-26 07:04:05
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（单词翻译）
If we could flip1 a switch and just turn off the Earth's magnetic field, it will take about 15,000 years to disappear, based on the rate of decay of the field that we've seen over the last 150 years. It's currently decaying at a rate that would see and disappear in 1500 years.
Earth's magnetic field is decaying fast. Discovering the consequences for our planet, is a top priority. Earth's magnetic field is fading. But what would happen if it disappeared completely? The answer lies on another planet in the solar system.
In 1996, NASA launched the Mars Global Surveyor, its mission to unlock the red planet's secrets.
Of all the planets in the solar system, Mars is the most similar to Earth. Both planets are made from the same materials. They each have / hard crusts,
dense2 cores and
relatively3 similar
atmospheric4 chemistry. Scientists believe that as on Earth water flowed on Mars' surface, but that was billions of years ago. Today, the planet is a frozen desert. To find out why, the orbiting Mars Global Surveyor collects data from the red planet. Professor Ben
Vice5 uses this data to reconstruct its past.
Unlike the Earth, Mars' today does not have a global magnetic field generated in its core. But if you will walk around the ancient southern highlands of Mars, you'll be walking in many places and fields as strong as the Earth. But it is very complicated, almost like spaghetti, pointing, you know, in different directions, not pointing in North at all.
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