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

EXPLORATIONS - Cassini-Huygens at Saturn
By Paul Thompson

Broadcast: Wednesday, July 14, 2004

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This is Faith Lapidus

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A false color image of Saturn's rings.
And this is Steve Ember with EXPLORATIONS in VOA Special English. Today we tell about NASA's Cassini-Huygens spacecraft that is now in orbit around Saturn. The spacecraft has already started sending back exciting information and photographs of Saturn's famous rings and its moon, Titan.

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A picture of Saturn from Cassini Huygens. 
The Cassini-Huygens spacecraft arrived at the planet Saturn on July first. It flew into orbit from below the famous rings that circle the planet. Carefully, Cassini crossed through a large space between two of the huge rings at speeds close to eighty-seven-thousand kilometers an hour. Cassini flew to within one-hundred-fifty-eight-thousand kilometers of Saturn's center. That is the closest Cassini will come to Saturn.

After passing through the rings, Cassini fired its rocket engines. This slowed the spacecraft, permitting it to be captured by Saturn's gravity. In this way, the Cassini spacecraft entered an orbit around Saturn. It had taken Cassini almost seven years to reach Saturn after traveling more than three-thousand-million kilometers through space.

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It did not take long for Cassini to start making discoveries. Cassini took photographs of Saturn's giant moon Titan in its first few days of orbit. These photographs provided details of Titan's surface that had never been seen before.

Dennis Matson is a scientist for the International Cassini-Huygens project. He says the photographs sent back by Cassini are difficult to understand.

He says the photographs do provide the first clear images of Titan's surface, but will require a great amount of study. Titan has a thick atmosphere that usually looks almost white in photographs taken with telescopes. However Cassini has special cameras that can see through the giant moon's atmosphere to study the surface.

Elizabeth Turtle is a scientist with the University of Arizona. She says Cassini's first photographs of Titan's surface have shown unusual features. Mizz Turtle says they do not know what some of these features mean. She says it will take a great deal of work to understand the surface of Titan.

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Cassini-Huygens carries a total of eighteen scientific instruments. It used several of these to photograph and make maps of the surface of Titan. It also used several instruments to study minerals and chemicals on the surface of the huge moon.

Kevin Baines is a science team member of the Cassini-Huygens project. He says Cassini provided evidence of pure water ice in some areas of the surface.

He said it also showed areas of non-ice materials such as hydrocarbons. Mister Baines said the evidence was much different from what scientists had expected. Mister Baines also said Cassini showed clouds of gas made of methane near the moon's south pole. He said the clouds showed good evidence that Titan has a very active atmosphere.

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The science team for Cassini says these first images of Titan are just the beginning. It is only the first information gathered in a four-year study of Saturn and its moons. In the future, the Cassini spacecraft will fly closer to Titan and be able to use radar to gather much better details of the moon's surface.

The study of Titan is one of the major goals of the Cassini-Huygens flight. Cassini's first trip near Titan was still more than three-hundred-thirty-nine thousand kilometers away. Future plans call for Cassini to make more than seventy orbits around Saturn. Forty-five of these will include passing close to Titan.

The closest flight will be only nine-hundred-fifty kilometers away from the giant moon. This very close flight will permit extremely detailed mapping of the surface.

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Scientists prepare the Huygens probe.
The Huygens part of the spacecraft will cut its link to Cassini on December twenty-fourth. It will then fly down through the atmosphere of Titan to the surface. As it passes into the atmosphere, it will deploy a large parachute. The Huygens instrument will send information back to Cassini. Cassini will then transmit the information back to Earth.

The Huygens instrument will land on the surface of Titan on January fourteenth, two-thousand-five. It will be the first scientific instrument to land on the surface of a moon of another planet.

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A real color image of Titan.
Saturn's moon, Titan, is very large. In fact, it is 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. It also has large amounts of nitrogen similar to Earth. And scientists believe it has large amounts of carbon material.

This is the same material needed to form life as we know it on Earth. However, scientists are quick to say this does not mean there is life on Titan.

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The exploration of Titan is exciting for many scientists. Scientists believe evidence found on Titan may help to answer the question of how life began on Earth. Most experts agree this question is hard to answer because not enough is known about the atmosphere when Earth was a young planet.

Scientists say they need to know what materials were present at the beginning of life on Earth. They say some of these answers may be present on Titan. The carbon material methane on Titan may have been easily found on Earth when it was young.

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Cassini carries more scientific instruments and can do more science work than any spacecraft ever sent to explore a planet. It carries twelve science instruments on the Cassini spacecraft and six more on the Huygens exploration device.

Cassini is six-point-seven meters high, four meters wide and weighs almost six-thousand kilograms. Electric power for the spacecraft is supplied by thirty-three kilograms of the nuclear fuel, plutonium.

The flight to Saturn represents the work of two-hundred-sixty scientists from the United States and seventeen European nations. The flight of the Cassini-Huygens spacecraft cost more than three-thousand-million dollars.

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The Cassini-Huygens spacecraft is expected to carry out many tasks. There is much to learn about Saturn. First, there are the seven huge rings that circle the planet. They are made of water ice, rock and dust.

Only minutes after it arrived in orbit, Cassini made sixty-one photographs of the beautiful rings. Cassini's radio sent the pictures to Earth. Radio signals travel at almost the speed of light. But even at that great speed, it took almost eighty-five minutes for the information to arrive on Earth. What scientists saw excited them.

They saw unusual designs and structures in the rings they had never seen before. Cassini's photographs provided evidence that the rings are not a solid mass of objects, but many individual lines that circle the planet. These thin lines are held together and kept in orbit by gravity. Scientists now believe there may be more than one-thousand different lines or rings that make up the seven great rings.

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The huge moon Titan is not alone in its orbit around Saturn. Saturn has thirty-one known moons. Thirteen of these moons were discovered after Cassini was launched on October fifteenth, nineteen-ninety-seven. Scientists want to learn more about how these moons affect the rings. New photographs already show that the gravity of the moons has a great effect on the rings. Scientists hope Cassini will provide more information about this in the future.

The Cassini spacecraft is named for astronomer Jean Dominique Cassini. He was born in Italy in the sixteen-hundreds. He later became a French citizen. He made important observations of Saturn and discovered four of its moons. The Huygens exploration device is named for Dutch astronomer Christiaan Huygens who also lived during the seventeenth century. He discovered the moon Titan.

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If you have a computer that can link to the Internet, you too can see the photographs of Saturn. You can see the moon Titan and the rings that make Saturn such a beautiful planet. Have your computer link with www.nasa.gov. Then follow the links to Cassini-Huygens.

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This program was written by Paul Thompson. It was produced by Mario Ritter. This is Steve Ember.

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And this is Faith Lapidus. Join us again next week for another EXPLORATIONS program in VOA Special English.