VOA慢速英语 2008 0123b（在线收听）

VOICE ONE:

I'm Steve Ember.

VOICE TWO:

And I'm Shirley Griffith with EXPLORATIONS in VOA Special English.  This week, we hear some unusual sounds from space.  Scientists created them by taking radio wave observations and turning them into sound waves that we can hear.

But first we tell about the Venus Express spacecraft of the European Space Agency.  The spacecraft has made the most detailed maps yet of the atmosphere of the second planet from the sun.

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VOICE ONE: 
A picture by the Venus Express showing how the solar wind affects the atmosphere of Venus

Venus is a rocky world that is about the same size as Earth.  But its climate is anything but Earth-like.  It is a cloud-covered world where temperatures reach over four hundred degrees Celsius.  The atmosphere of Venus is so thick that the pressure at the surface is about one hundred times that of Earth. 

The European Space Agency's Venus Express space vehicle is exploring the planet's atmosphere in more detail than ever before.  The vehicle itself is small.  Venus Express is less than two meters wide and less than two meters long.  However, it carries seven scientific devices including ones that measure radio waves, magnetism and infrared radiation.

The goal is to better understand the complex atmosphere of Venus.  Space scientists say this is important for understanding more about the planet. 

Venus Express will help scientists find out why a planet so much like Earth in size and material could have such a different atmosphere.

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Some of the differences cannot be seen but are very important.  For example, unlike Earth, Venus does not have a strong magnetic field.  On Earth, the magnetic field protects the atmosphere from the powerful force of the solar wind, a flow of particles that moves out from the sun. 

Instead, a magnetic charge builds up around Venus.  But this magnetic field does not protect Venus completely from the force of the solar wind.  In fact, it causes the planet to slowly lose some of its atmosphere.

Venus Express has also suggested to scientists why Venus is so dry.  The planet loses mainly hydrogen and oxygen ions.  An ion is an atom that has lost or gained an electron.  That means Venus is slowly losing the elements that make up water by the action of the solar wind. Venus may have had more water and been more like Earth long ago. 

VOICE ONE:

There are other important differences between Earth and Venus.  The Earth has seasons but Venus does not.  Also, one day on Venus is two hundred forty-three Earth days. Venus's atmosphere is massive and made up mostly of carbon dioxide.  It also has clouds of sulfuric acid.

The winds in the atmosphere of Venus are severe.  They can move at one hundred meters a second.  Yet even these powerful winds high above Venus probably do not extend all the way down to the surface.  Powerful winds, especially at the south pole of Venus, cannot move the heavy atmosphere near the surface.

VOICE TWO:

David Grinspoon is a Venus Express scientist from the Denver Museum of Nature and Science in Colorado.  He says Venus suffered a climate disaster.  But we do not know how, why or when.  However, Mister Grinspoon says we do know what happened.  Venus lost much of its water.  Today, Venus is a very dry planet, unlike Earth, which has a large amount of water in its polar areas. 

For example, if you took all the water in the atmosphere of Venus and placed it on the surface of the planet it would cover the planet with only three centimeters of water. 

Venus Express has added a lot to what scientists know about our sister planet.  It has created a map of temperatures on Venus.  It has also discovered that there are electrical storms on the planet.  And it has suggested to scientists the process that robs Venus of some of its atmosphere.

Venus Express has enough fuel to last until two thousand thirteen.  In two thousand ten, it will be joined by a Japanese spacecraft, the Venus Climate Orbiter. Information from the new spacecraft will permit scientists to confirm the findings of Venus Express.

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VOICE ONE:

 
Jupiter
There is nothing wrong with your listening device.  These sounds were created from information gathered by Voyager One.  The spacecraft passed Jupiter in nineteen seventy-nine.  Its plasma wave instrument recorded the information used to create the sounds. 

The information, or data, was collected as the spacecraft came close to an area near Jupiter called the bow shock.  That is where particles flowing away from the sun move past Jupiter at extremely high speeds.

The sharp sounds you heard at the beginning are waves created by electrons coming from the bow shock and moving into the solar wind.  These sounds die out except for a slight low sound from one of the science instruments on the spacecraft.  There is also the sound of one of Voyager's engines.  Then things become quiet.  Suddenly the spacecraft enters the bow shock and is surrounded by the noise of this planetary "sonic boom." 

VOICE TWO:

Another spacecraft, Cassini, entered orbit around Saturn in two thousand four.  Before that the spacecraft traveled through Saturn's rings.  The spacecraft was struck by about one hundred thousand particles of dust in less than five minutes.  Its large round antenna protected the spacecraft. The event was measured by Cassini's radio and plasma wave instrument.  Here is what it sounds like:

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VOICE ONE:

The next sound you will hear is the sound of Saturn turning.  These were the first sounds of Saturn recorded by Cassini.  Scientists wanted to know: How long is a day on Saturn? Cassini gathered information showing that Saturn's day is ten hours, forty-five minutes and forty-five seconds long.  But that is about six minutes longer than information recorded by the spacecrafts Voyager One and Voyager two in nineteen eighty and nineteen eighty-one.  The difference remains a mystery.  Scientists continue to study Saturn to find out how the planet's turning motion creates radio emissions.

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Saturn is one of the few places in the solar system that is known to have lightning.  The Cassini spacecraft captured radio emissions they believed came from a large electrical storm on Saturn.  It took place on January twenty-third and twenty-fourth, two thousand six.  The radio emissions were turned into this sound recording. 

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VOICE ONE:

This next recording was put together in a laboratory.  It was taken from sounds collected by a recording device on the European Space Agency's Huygens probe.  The probe came down to the surface of Titan, Saturn's largest moon, in January, two thousand five.  Several sounds recorded at different times are combined.  They give a realistic recording of what a traveler on the Huygens probe would have heard during the ride down through Titan's atmosphere.

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VOICE TWO: 
A picture from the Cassini spacecraft showing Saturn's auroras 

We leave you with some unusual and mysterious sounds captured by the Cassini spacecraft.  They were made by Saturn's intense radio emissions.  The radio waves recorded by the spacecraft's radio and plasma instrument were turned into a sound recording.  These sounds are closely related to auroras near Saturn's north and south poles.  Auroras are areas of charged particles that give off light near the poles of some planets.  On Earth they are known as the northern and southern lights.

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VOICE ONE:

This program was written and produced by Mario Ritter.  I'm Steve Ember. 

VOICE TWO:

And I'm Shirley Griffith. You can find more space and technology news on our Web site, voaspecialenglish.com. Join us again next week for Explorations in VOA Special English.