環(huán)球英語20160504 The Rosetta Comet Mission
Welcome to Spotlight. I’m Liz Waid.
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And I’m Christy VanArragon. Spotlight uses a special English method of broadcasting. It is easier for people to understand, no matter where in the world they live.
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Imagine that it is night. You look up into the dark sky. You see millions of stars. But then you see something strange. You see a bright point of light with a long end or tail behind it. It is a comet.
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This space object is made of frozen gases, rock and dust. It orbits the sun in a long path. It orbits the sun again and again. The orbit of some comets lasts tens of years. But the orbit of other comets lasts thousands of years. The comet gets hotter every time it gets close to the sun. The dust and gas flow out behind it for millions of kilometres. This is why a comet looks like a bright point of light with a long tail behind it.
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25 years ago space scientists started to plan a special project involving a comet. They wanted to learn more about the atmosphere of a comet and more about its centre or nucleus. So they decided to land a spaceship on a passing comet. They called this project ‘Rosetta’. Today’s Spotlight programme is on project Rosetta.
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Long ago people were frightened by comets. They did not know when comets would arrive in the sky. And they believed comets were a sign that something bad would happen. Ancient astronomers from China observed stars, planets and comets. They kept clear records of where and when comets appeared. People in other places also recorded when comets appeared. For example, there is a cloth tapestry that shows an old battle in the United Kingdom. The tapestry also shows a comet in the sky. This battle was fought in the United Kingdom in 1066.
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Old records like these helped scientists discover when particular comets would arrive in the sky. In 1705 Edmund Halley discovered when a particular comet would return. This comet became known as Halley’s comet. It was the same comet that had appeared in 1066. Halley’s comet returns every 76 years. It most recently returned in 1986.
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During that year, many people wanted to study Halley’s comet. Russia, France and Japan sent spaceships or probes to investigate the comet. They could only pass by the comet and collect information about its atmosphere. A probe from Europe called Giotto flew to about 600 kilometres from the comet. Giotto was almost destroyed by the fierce dust of the comet. But it survived. It saw the nucleus of the comet. And then it sent images of the comet back to earth. Gerhard Schwehm of the European Space Agency said,
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‘It was a once-in-a-life-time event. It had a big effect on the general public. It may sound simple to say this, but the picture was the best thing. The minute you saw it, it was amazing. Giotto excited the space science community in Europe. We had demonstrated that we could successfully lead demanding missions. And people started thinking about what else we could do.’
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After that success the European Space Agency decided to land a probe on a passing comet. The Rosetta spaceship lifted off planet Earth in 2004. Its purpose was to catch a comet called Comet 67P. This comet orbits the sun every 6 1/2 years and travels between the orbits of Jupiter and Earth. The scientists worked hard to establish the exact path of comet. They had to make sure that Rosetta and the comet would meet. This was not easy. The comet travels at 55,000 km/h. And it is only about four kilometres wide.
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Rosetta travelled for ten years. It went round the sun five times facing great extremes of hot and cold. At last on August 6th, 2014 Rosetta caught the comet. The spaceship went into a powered orbit around the comet. At times Rosetta was only ten kilometres above the comet. And Rosetta took pictures and made maps of the surface of the comet.
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Then on the 12th of November 2014 Rosetta launched a small landing vehicle called Philae. Philae flew down toward the surface of the comet.
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Seven hours later Philae landed! But back on earth the scientists waited for news. The comet was 500 million kilometres away from earth. So the signal took about 30 minutes to reach earth.
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At last Stephan Ulamec of the European Space Agency excitedly announced,
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‘We are sitting on the surface. Philae is talking to us. We are on the comet.’
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The scientists at the European Space Agency cheered loudly. They knew the first landing on a comet was a historic achievement. At the control centre Professor Monica Grady jumped up and down joyfully. She told BBC News:
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‘I can’t believe it. It’s wonderful. We have landed. We have waited so long for this’
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But Philae had settled on its side by a rock. It was in shadow and would not get much sunlight. Philae needed sunlight for power. Without sunlight it only had a few hours of power. But it collected and tested some pieces of the comet. And it sent lots of information back to the scientists on Earth. Matt Taylor of the European Space Agency said:
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‘The science is only just beginning. The science teams are already buried with information.’
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The scientists also continued to receive information from Rosetta. As Rosetta orbited the comet it found water, methane and hydrogen and other rarer gases in the comet’s thin atmosphere. Rosetta also discovered important information about water. Many scientists believed that most water on earth came from comets. But Rosetta showed that water on the comet was different from water on planet Earth. So now the scientists think their theory could be wrong.
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As the comet nears the sun it will become hotter. Dust and gas will flow out behind it. Rosetta will go through this dust and gas tail. And Rosetta will send more information back to earth. The scientists hope this will help them learn how comets formed.
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Then the comet will travel back into deep space. And its tail will slowly disappear. Rosetta will continue to orbit the comet for several months. It will continue to send back information about the comet’s journey. Who knows what it may send back? Scientists are excited to know!
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The writer of this programme was Katy Blake. The producer was Luke Haley. The voices you heard were from the United States and the United Kingdom. All quotes were adapted for this programme and voiced by Spotlight. You can listen to this programme again, and read it, on the internet at www.radioenglish.net. This programme is called, ‘The Rosetta Comet Mission’.
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We hope you can join us again for the next Spotlight programme. Goodbye.
