VOICE ONE:
This is Steve Ember.
VOICE TWO:
And this is Shirley Griffith with the VOA Special English programEXPLORATIONS. Today, we will tell about Near Earth Objects. Theseare objects made of rock or ice that travel in space. Their orbitsaround 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. Thecrater is named for Daniel Barringer, the first scientist to studyit. The Barringer Crater is more than forty-five meters across. Itis two-hundred-thirteen meters deep. It is in the shape of an almostperfect circle.
Scientists say the event that caused this hole took place aboutfifty-thousand years ago. In studying the crater, they foundevidence that an object from space traveling at more than sixty-fourthousand 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 thousandtons.
VOICE TWO:
The rock from space that created the Barringer Crater hit theEarth with the force of about twenty-million tons of explosives. Itcaused tons of rock and dirt to be thrown into the air.
Huge rocks fell back to earth for many kilometers around the hugehole. Some of these rocks are as large as houses. The force of theobject hitting the Earth killed all living things within one-hundredkilometers.
VOICE ONE:
The Barringer Crater is only one of about one-hundred-twentyknown examples of damage caused to the Earth by objects from space.The crater was the first one to be recognized as caused by somethingfrom space.
Workers who discovered pieces of the space rock that created thehuge hole identified it in the Nineteen-Twenties. Since theNineteen-Sixties, scientists have discovered more evidence toconfirm that a space object did cause the Barringer Crater. Theyfound evidence of massive pressure and extreme heat caused by anexplosion.
Scientists say it is hard to find evidence of damage caused byspace objects because as the years pass, wind, rain, ice, snow andother weather conditions change the land. Huge holes like theBarringer Crater are filled with rocks, dirt, plants or perhapswater. Many years later any evidence of damage is well hidden.
The Barringer Crater has not changed much from the time it wascreated. This is because the space rock hit the Earth in an area ofvery dry desert.
VOICE TWO:
The huge object that created the Barringer Crater caused a greatdeal of damage. Yet the damage was only in a local area. If anobject that size hit a modern city, it would cause massive damageand loss of life.
In July of Nineteen-Oh-Eight, a huge space rock exploded near thearea of Siberia called Tunguska. Russian scientists believe this wasthe largest object from space to hit the Earth in the pasttwo-thousand years.
A huge forest was destroyed, but no one was injured or killed inTunguska. Scientists never found a crater or pieces of the spacerock that caused the explosion. They believe it exploded as it gotvery near the ground. The explosion was so huge that devices inGermany which measure earthquakes recorded the event.
VOICE ONE:
Scientists now know that much larger space rocks have hit Earththan those involved in Tunguska or Barringer. Tests show that a hugespace object may have hit the area near the Gulf of Mexico aboutsixty-five million years ago. Scientists say the object was so largethat it caused millions of tons of dirt and dust to rise in theatmosphere.
The scientists believe the dirt and dust blocked sunlight fromreaching the ground for a very long time. Plants died from the lackof sunlight. Animals who ate these plants had no food and they diedalso. The lack of sunlight caused the planet to cool. Many areasbecame extremely cold. Millions of animals died because of the cold.
Many scientists say there is strong evidence to suggest that thisevent may have killed almost seventy percent of everything living onEarth. It probably killed all of the huge reptiles called dinosaursthat then ruled the Earth.
((MUSIC BRIDGE))
VOICE TWO:
Scientists say the Earth has been hit by objects from space manytimes in the past, and that it will be hit again in the future. Theyhave a saying about these kinds of events. They say the question isnot “will a space object ever hit the Earth again.” They say thequestion is “when will the Earth be hit.”
Scientists call objects in space that come near our planet, “NearEarth Objects.” They are mainly of two kinds…asteroids or comets.Asteroids are usually made of carbon or minerals. Comets are usuallymade of ice and rock.
VOICE ONE:
Scientists have identified about two-thousand Near Earth Objectsin orbit now. Of these, three-hundred-nine travel near Earth and areconsidered possible threats to our planet. They are calledPotentially Hazardous Asteroids…or P-H-As.
This does not mean all three-hundred-nine P-H-As will hit theEarth. It means only that it is possible they could. Space expertsin many countries closely observe these P-H-As.
VOICE TWO:
Earthquakes are measured by an international system known as theRichter scale. The Richter scale measures how strong an Earthquakeis when it happens. The higher the number on the Richter scale, thestronger the earthquake and the more damage it can cause.
Scientists who study Near Earth Objects and P-H-As have a similarmethod to measure the threat of asteroids and comets. It is calledthe Torino Scale. Richard Benzel of the Massachusetts Institute ofTechnology created the Torino Scale. He first explained the scale ata United Nations conference in Nineteen-Ninety-Five in Turin, Italy.
VOICE ONE:
The Torino Scale is a system of numbers from zero to ten. Anasteroid is given a Torino number after scientists learn its size,speed and how close to Earth it will pass in its orbit around theSun.
An asteroid that is rated zero on the Torino Scale is consideredto have almost no chance of ever hitting Earth.
An asteroid that is a number ten on the Torino Scale is a hugeobject which is going to hit Earth. It will cause massive damage andloss of life for most of our planet.
VOICE TWO:
Scientists say at the present time no space object they have seenhas a Torino Scale number greater than one. However they say thiscould easily change in the future.
There is one asteroid that could threaten Earth. It is calledAsteroid Two-Thousand-S-G-Two-hundred-Forty-Four.
This asteroid will not come near the Earth until Septembertwenty-first, Two-Thousand-Thirty. NASA experts say it has a Torinonumber of one now and should miss the Earth. They say they will knowmore about this asteroid in the future as they continue to study itsorbit. Scientists say the object is large enough to cause severelocal damage if it does hit the Earth.
NASA experts say their major concern is the asteroids and cometsthey do not know about. Learning to find and study the orbit of eachnew asteroid and comet is a difficult task. They say they mustimprove their ability to find space objects to provide the Earthwith a warning in time to take protective measures.
VOICE ONE:
Scientists have known about the threat from Near Earth Objectsfor many years. Teams of astronomers around the world are searchingthe sky for Near Earth Objects. These teams are involved in jointprojects with the United States Air Force, the Defense Department,NASA and several major universities. Recently they have begunstudying several methods that would protect Earth if it werethreatened by an object from space.
Scientists at the Los Alamos Laboratory in New Mexico and theLawrence Livermore Laboratory in California are studying ways todestroy Near Earth Objects that may threaten Earth. Methods mightinclude firing a nuclear device into space to destroy the object.
Some scientists say if they have the time and equipment, theycould 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 tochange its path. They say this could be done before the space rockbecomes a dangerous threat.
Scientists are quick to say there is no need for fear or alarm atthe present time. However they all agree that they must prepare forwhat could happen in the future.
((THEME))
VOICE TWO:
This Special English program was written and produced by PaulThompson. Our studio engineer was Keith Holmes. This is ShirleyGriffith.
VOICE ONE:
And this is Steve Ember. Join us again next week for anotherEXPLORATIONS program on the Voice of America.