EXPLORATIONS - Cassini-Huygens at Titan（在线收听）

EXPLORATIONS - Cassini-Huygens at Titan
By Paul Thompson

Broadcast: Wednesday, February 02, 2005

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VOICE ONE:

I'm Faith Lapidus.

VOICE TWO:

And I'm Steve Ember with EXPLORATIONS in VOA Special English. On January fourteenth, a human-made object landed on the surface of Saturn's largest moon, Titan. For one hour and twelve minutes it sent back exciting information and photographs.

 
The surface of Titan. (Picture - ESA)
Our program today is about the landing device named Huygens and the Cassini spacecraft that carried it through our solar system to land on that distant moon.

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VOICE ONE:

On October fifteenth, nineteen ninety-seven, a huge rocket was launched from the Kennedy Space Center in the state of Florida. The rocket carried a spacecraft named Cassini. The Cassini spacecraft carried a deployment vehicle named Huygens. The launch of these two spacecraft was the beginning of a seven-year flight to the planet Saturn. The flight was the joint effort of America's space agency, NASA; the European Space Agency, and the Italian Space Agency.

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On July first of last year, the Cassini-Huygens spacecraft arrived at Saturn after traveling almost four thousand million kilometers. Scientists said they were able to guide it into a near-perfect orbit around Saturn. Cassini flew into orbit from below the famous rings that circle the planet.

Cassini immediately began sending back photographs and information about Saturn and its huge moon, Titan.

 
Titan is the only known moon to have an atmosphere. (Picture - NASA)
The study of Titan is one of the major goals of the Cassini-Huygens flight. Titan is very large -- even larger than the planets Mercury and Pluto. Scientists are very interested in Titan because it is the only known moon in our solar system to have an atmosphere. Plans call for Cassini to make more than seventy orbits around Saturn. Forty-five of these will include passing close to Titan.

The photographs and information about the huge moon sent by Cassini only added to the excitement about the Huygens landing device.

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VOICE ONE:

On December twenty-fifth, Cassini released the Huygens lander. Cassini quickly moved away from Huygens to lessen the chance of an accident between the two vehicles. After twenty days of circling the huge moon, Huygens started to move into Titan's thick atmosphere. Huygens entered Titan's atmosphere moving at eighteen thousand kilometers an hour. It had to immediately slow its great speed to keep from burning up.

Huygens slowed down by using three different parachutes. After its main parachute opened in the upper atmosphere, the vehicle slowed to a little more than fifty meters per second. This is about as fast as an automobile moves on a highway.

As it moved lower into the atmosphere, Huygens slowed to about five meters per second. This permitted it to safely prepare to land on the surface.

Martin Tomasko is the member of the team that guided the flight of the Huygens lander. He said the flight down to the surface of Titan was not as smooth as the team thought it would be.

Mister Tomasko said the lander moved from side to side while hanging from the parachute. He said it often moved as much as twenty degrees from side to side.

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The scientific instruments on Huygens began measuring about one hundred sixty kilometers from the surface of Titan. This permitted the instruments to gather information about the atmosphere. The instruments included sound recording equipment.

Huygens began sending back information and photographs to Cassini four minutes into its flight to the surface of Titan. Cassini immediately began to transmit this information back to Earth using its more powerful radio equipment. NASA's Deep Space Communications Network received the information and photographs. Then NASA transmitted them to the European Space Operation Center in Darmstadt, Germany.

VOICE ONE:

Slowly and safely, the three hundred seventeen kilogram vehicle moved down through the atmosphere of Titan. It quickly transmitted information about a rich mix of nitrogen and methane in the upper atmosphere.

Huygens' instruments showed that the amounts of the gas methane increased as the lander moved closer to the surface of Titan.

While scientific instruments were investigating the atmosphere, cameras were ready to begin taking photographs from high above the surface. The cameras were able to begin their work thirty kilometers above the surface of Titan. Thick clouds above thirty kilometers did not permit photography.

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Titans surface from a height of about sixteen kilometers. (Picture - ESA)
The first photographs looked much like those taken here on Earth from an aircraft high in the sky. Part of one photograph shows a land area next to what might be a large area of liquid, similar to a lake. Some areas of the surface looked like islands.

There were photographs of areas of water ice. Some areas showed rivers created by liquid methane. Other photographs of the surface area seemed to show mountains and huge rocks. Still others showed deep lines in the surface that seem to have been cut by fast- moving liquid.

The scientific instruments on Huygens showed the temperature of the atmosphere of Titan is extremely cold. The instruments recorded a temperature of minus one hundred eighty degrees Celsius.

VOICE ONE:

When Huygens was seven hundred meters above the surface, a special landing lamp was turned on. The lamp was used to light the surface of Titan to aid Huygens' cameras and see where the vehicle was going to land. The lamp was designed to last for about fifteen minutes.

It continued to light the immediate area for more than one hour after Huygens landed on the surface. Scientists believe the Huygens lander hit an area of Titan's surface that may be mud or wet sand. The lander's recording equipment transmitted a sound similar to a large object hitting a wet surface.

Instruments on Huygens showed the surface landing area is mostly a mix of dirty water ice, hydrocarbon ice, sand and clay. This mix of water and chemicals makes the ground a dark color. The instruments on Huygens began to quickly send back large amounts of information about the surface. This information included air temperature, air pressure and wind speed. It also sent information about chemicals on the surface of Titan and in the air. Experts say Huygens sent back enough information and photographs to keep researchers very busy for several years.

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After it landed, Huygens immediately began transmitting photographs from the surface of Titan. The photographs are orange in color. Scientists say the surface of Titan is orange because of its huge distance from the sun. The large amounts of methane gas in the atmosphere also add to the orange color.

These photographs show an area of rocks of many sizes. The rocks can be seen for as far as the camera can see. Experts say many of the rocks look as if they have been shaped by fast-moving liquid.

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VOICE ONE:

The Huygens lander stopped transmitting information after one hour and twelve minutes. The fierce atmosphere of Titan and extremely low temperatures halted the vehicle's ability to gather information. Yet it lasted longer than scientists had planned.

Scientists will use the information gathered by the Huygens lander to learn a great deal about this unusual moon. One of the main reasons for sending Huygens to the surface is that Titan has a rich nitrogen atmosphere. It is also rich in methane gas. And its surface may have many of the same kinds of chemicals that existed on Earth millions of years ago. Titan may help scientists learn more about the very beginnings of our planet.

David Southwood is the Director of the European Space Agency's scientific program. Mister Southwood says Titan is a very interesting world. And scientists now have good information about this far away moon.

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If you have a computer that can link with the Internet communications system, you too can see the orange photographs taken on the surface of Titan. NASA's Jet Propulsion Laboratory in Pasadena, California has many links to both Huygens and Cassini. J-P-L can be found at www.jpl.nasa.gov. That address again is www.jpl.nasa.gov.

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VOICE ONE:

This program was written by Paul Thompson. It was produced by Mario Ritter. I'm Faith Lapidus.

VOICE TWO:

And I'm Steve Ember. Join us again next week for another EXPLORATIONS in VOA Special English.