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EXPLORATIONS - Near Earth Objects

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VOICE ONE:

This is Steve Ember.

VOICE TWO:

And this is Shirley Griffith with the VOA Special English program EXPLORATIONS. Today, we will tell about Near Earth Objects. These are objects made of rock or ice that travel in space. Their orbits around the sun often bring them near Earth.

((THEME))

VOICE ONE:

In the southwestern American state of Arizona there is a huge, round hole in the ground. This kind of hole is called a crater. The crater is named for Daniel Barringer, the first scientist to study it. The Barringer Crater is more than forty-five meters across. It is two-hundred-thirteen meters deep. It is in the shape of an almost perfect circle.

Scientists say the event that caused this hole took place about fifty-thousand years ago. In studying the crater, they found evidence that an object from space traveling at more than sixty-four thousand kilometers an hour crashed into the ground.

Scientists say the object was made of the metals iron and nickel. It was about forty-five meters across and weighed several thousand tons.

VOICE TWO:

The rock from space that created the Barringer Crater hit the Earth with the force of about twenty-million tons of explosives. It caused tons of rock and dirt to be thrown into the air.

Huge rocks fell back to earth for many kilometers around the huge hole. Some of these rocks are as large as houses. The force of the object hitting the Earth killed all living things within one-hundred kilometers.

VOICE ONE:

The Barringer Crater is only one of about one-hundred-twenty known examples of damage caused to the Earth by objects from space. The crater was the first one to be recognized as caused by something from space.

Workers who discovered pieces of the space rock that created the huge hole identified it in the Nineteen-Twenties. Since the Nineteen-Sixties, scientists have discovered more evidence to confirm that a space object did cause the Barringer Crater. They found evidence of massive pressure and extreme heat caused by an explosion.

Scientists say it is hard to find evidence of damage caused by space objects because as the years pass, wind, rain, ice, snow and other weather conditions change the land. Huge holes like the Barringer Crater are filled with rocks, dirt, plants or perhaps water. Many years later any evidence of damage is well hidden.

The Barringer Crater has not changed much from the time it was created. This is because the space rock hit the Earth in an area of very dry desert.

VOICE TWO:

The huge object that created the Barringer Crater caused a great deal of damage. Yet the damage was only in a local area. If an object that size hit a modern city, it would cause massive damage and loss of life.

In July of Nineteen-Oh-Eight, a huge space rock exploded near the area of Siberia called Tunguska. Russian scientists believe this was the largest object from space to hit the Earth in the past two-thousand years.

A huge forest was destroyed, but no one was injured or killed in Tunguska. Scientists never found a crater or pieces of the space rock that caused the explosion. They believe it exploded as it got very near the ground. The explosion was so huge that devices in Germany which measure earthquakes recorded the event.

VOICE ONE:

Scientists now know that much larger space rocks have hit Earth than those involved in Tunguska or Barringer. Tests show that a huge space object may have hit the area near the Gulf of Mexico about sixty-five million years ago. Scientists say the object was so large that it caused millions of tons of dirt and dust to rise in the atmosphere.

The scientists believe the dirt and dust blocked sunlight from reaching the ground for a very long time. Plants died from the lack of sunlight. Animals who ate these plants had no food and they died also. The lack of sunlight caused the planet to cool. Many areas became extremely cold. Millions of animals died because of the cold.

Many scientists say there is strong evidence to suggest that this event may have killed almost seventy percent of everything living on Earth. It probably killed all of the huge reptiles called dinosaurs that then ruled the Earth.

((MUSIC BRIDGE))

VOICE TWO:

Scientists say the Earth has been hit by objects from space many times in the past, and that it will be hit again in the future. They have a saying about these kinds of events. They say the question is not "will a space object ever hit the Earth again." They say the question is "when will the Earth be hit."

Scientists call objects in space that come near our planet, "Near Earth Objects." They are mainly of two kinds…asteroids or comets. Asteroids are usually made of carbon or minerals. Comets are usually made of ice and rock.

VOICE ONE:

Scientists have identified about two-thousand Near Earth Objects in orbit now. Of these, three-hundred-nine travel near Earth and are considered possible threats to our planet. They are called Potentially Hazardous Asteroids…or P-H-As.

This does not mean all three-hundred-nine P-H-As will hit the Earth. It means only that it is possible they could. Space experts in many countries closely observe these P-H-As.

VOICE TWO:

Earthquakes are measured by an international system known as the Richter scale. The Richter scale measures how strong an Earthquake is when it happens. The higher the number on the Richter scale, the stronger the earthquake and the more damage it can cause.

Scientists who study Near Earth Objects and P-H-As have a similar method to measure the threat of asteroids and comets. It is called the Torino Scale. Richard Benzel of the Massachusetts Institute of Technology created the Torino Scale. He first explained the scale at a United Nations conference in Nineteen-Ninety-Five in Turin, Italy.

VOICE ONE:

The Torino Scale is a system of numbers from zero to ten. An asteroid is given a Torino number after scientists learn its size, speed and how close to Earth it will pass in its orbit around the Sun.

An asteroid that is rated zero on the Torino Scale is considered to have almost no chance of ever hitting Earth.

An asteroid that is a number ten on the Torino Scale is a huge object which is going to hit Earth. It will cause massive damage and loss of life for most of our planet.

VOICE TWO:

Scientists say at the present time no space object they have seen has a Torino Scale number greater than one. However they say this could easily change in the future.

There is one asteroid that could threaten Earth. It is called Asteroid Two-Thousand-S-G-Two-hundred-Forty-Four.

This asteroid will not come near the Earth until September twenty-first, Two-Thousand-Thirty. NASA experts say it has a Torino number of one now and should miss the Earth. They say they will know more about this asteroid in the future as they continue to study its orbit. Scientists say the object is large enough to cause severe local damage if it does hit the Earth.

NASA experts say their major concern is the asteroids and comets they do not know about. Learning to find and study the orbit of each new asteroid and comet is a difficult task. They say they must improve their ability to find space objects to provide the Earth with a warning in time to take protective measures.

VOICE ONE:

Scientists have known about the threat from Near Earth Objects for many years. Teams of astronomers around the world are searching the sky for Near Earth Objects. These teams are involved in joint projects with the United States Air Force, the Defense Department, NASA and several major universities. Recently they have begun studying several methods that would protect Earth if it were threatened by an object from space.

Scientists at the Los Alamos Laboratory in New Mexico and the Lawrence Livermore Laboratory in California are studying ways to destroy Near Earth Objects that may threaten Earth. Methods might include firing a nuclear device into space to destroy the object.

Some scientists say if they have the time and equipment, they could use non-nuclear explosives to move an object out of its path. They might be able to place a small rocket motor on an asteroid to change its path. They say this could be done before the space rock becomes a dangerous threat.

Scientists are quick to say there is no need for fear or alarm at the present time. However they all agree that they must prepare for what could happen in the future.

((THEME))

VOICE TWO:

This Special English program was written and produced by Paul Thompson. Our studio engineer was Keith Holmes. This is Shirley Griffith.

VOICE ONE:

And this is Steve Ember. Join us again next week for another EXPLORATIONS program on the Voice of America.

网友的学习评论(1条):
作者:舞客
it is a little difficult ,i can't understand very clear.may be i should listen more.
作者:chensheng
me too.there are so many professional words.
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