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SCIENCE IN THE NEWS - Criticism Weighs Heavy on New Solar System With Pluto1 as a 'Dwarf2 Planet'By Mario Ritter and produced by Brianna Blake

Broadcast: Tuesday, September 05, 2006

VOICE ONE:

This is SCIENCE IN THE NEWS in VOA Special English. I'm Bob Doughty3.

VOICE TWO:

And I'm Faith Lapidus. This week -- the debate over what is a planet.

(MUSIC)

VOICE ONE:


Photo provided by New Mexico State University shows Al Tombaugh, whose father discovered Pluto, at a protest for Pluto at the school on September 1

People might think they know a planet when they see one. But even the people who study planets get into arguments. Those disputes have only intensified4, now that the International Astronomical5 Union has voted to define a planet for the first time.

The vote in Prague on August twenty-fourth leaves our solar system with eight planets instead of nine -- take Pluto off the list. But astronomy has gained a new kind of object: the dwarf planet.

Astronomers7 say new discoveries made the need for a scientific definition of a planet increasingly urgent. New bodies with orbits more distant from the Sun than Neptune8 and Pluto are being discovered all the time.

But one object changed a balance of ideas that held together for more than seventy years.

VOICE TWO:

In January of last year, a team of astronomers in the United States discovered a large object farther away than Pluto. Scientists have discovered other very distant objects in our solar system.


Artist's image of UB313 -- nicknamed Xena -- looking back toward the Sun

But the team -- Mike Brown, Chad Trujillo and David Rabinowitz -- later found that the object was bigger than Pluto. It does not have an official name yet; for now it is known as Xena [ZEE-nuh].

Xena presented a problem: If Pluto was big enough to be considered a planet, then what did that make Xena?

VOICE ONE:

Some astronomers have never considered Pluto a planet. They see it as just one of many objects in the Kuiper [KY-per] Belt. The Kuiper Belt is an area where comets and other small icy bodies come from.

But whatever people said about Pluto, one thing was clear: the existing model of the solar system was no longer working.

VOICE TWO:

Planet comes from a Greek word meaning wanderer. Planets are wanderers in a sky filled with stars that appear fixed9 in their positions.

No one knows when humans first recognized the movement of planets. But people used to think of the Moon and the Sun as planets because they appeared to orbit Earth.

By the fifteenth century, Nicolas Copernicus changed the model of thinking about the solar system. The Polish astronomer6 established that Earth was, in fact, one of the planets orbiting the Sun.

Later, the German astronomer Johannes Kepler believed there was an importance to the number of planets. He suggested that their distances from the sun were related to the forces that create musical notes.

There were six known planets -- Mercury, Venus, Earth, Mars, Jupiter and Saturn10.

VOICE ONE:

Then, in seventeen eighty-one, astronomer William Herschel discovered a seventh planet. Herschel was a native of Germany but had moved to Britain.

The planet was Uranus11 [YER-uh-nuhs]. This huge world, like Jupiter and Saturn, is mostly gas. It is also extremely cold, with Celsius12 temperatures of two hundred degrees below zero at its cloud tops.

For his discovery, Herschel was named the Astronomer Royal of Britain. He and his sister, Caroline, continued to make important astronomical discoveries.

The discovery of Uranus showed that the solar system was not unchanging, as many people believed at that time. But this was only the beginning of a new period of discovery.

VOICE TWO:

On January first, eighteen-oh-one, Giuseppi Piazzi discovered an object between the orbits of Mars and Jupiter. At first, the Italian astronomer thought it was a comet, an icy, dusty ball with a long gas tail. But he soon came to think it might be a planet.

What Piazzi found was Ceres -- the first recorded asteroid13, and the largest one known. Asteroid means star-like. Asteroids14 are mostly rock or metal, or a combination.

The astronomers who met in Prague agreed that objects like asteroids will now be described collectively as small solar-system bodies. The orbits of these bodies can bring them very close to the sun. Sometimes they cross paths with Earth's orbit.

Piazzi's discovery of an asteroid changed the model of the solar system again. And there were more changes to come.

VOICE ONE:

Scientists suspected that the orbit of Uranus was being influenced by the gravity of another planet-sized object. Progress in mathematics led Urbain Jean Joseph Leverrier to discover the orbit of this body.

In eighteen forty-six, the French astronomer wrote Johan Gottfried Galle at the Berlin Observatory15. He told Galle where to point his telescope to find the new planet. In about half an hour, Galle found Neptune.

VOICE TWO:

With Neptune, the discovery of the so-called classical planets came to a close. These planets move around the sun in nearly circular orbits. They include the rocky worlds of Mercury, Venus, Earth and Mars. They also include the huge gas planets Jupiter, Saturn, Uranus and Neptune.

But the American astronomer Percival Lowell was not satisfied. He believed there was evidence of yet another planet -- Planet X. From his observatory near Flagstaff, Arizona, he searched and searched beyond the orbit of Neptune.

Lowell died in nineteen sixteen, but the observatory continued his work. Success came in February of nineteen thirty when Clyde Tombaugh [TOM-baw] discovered the planet that would be called Pluto.

VOICE ONE:


Pluto, left, and its moon Charon as seen through NASA's Hubble Space Telescope

Astronomers still know little about Pluto because of its great distance. It takes Pluto close to two hundred fifty years to circle the sun. Pluto is only a point of light even to the largest telescopes.

Percival Lowell had expected Planet X to be massive. But for many years Pluto was believed to be a little smaller than Earth. Then, in nineteen seventy-eight, American astronomers discovered that Pluto had a moon. The discovery led scientists to further shrink their estimates of the size of Pluto. Suddenly this planet was smaller than our own Moon.

In January of this year, the American space agency NASA launched the first spacecraft to study Pluto. The robotic ship, called New Horizons, will not arrive until two thousand fifteen.

(MUSIC)

VOICE TWO:

Earlier this year, the International Astronomical Union created a committee to propose a definition of a planet. The first proposal would have given us twelve planets.

There would have been eight classical planets. And there would be a new group called plutons, or Pluto-like planets. Among them would have been Charon -- Pluto's moon. Charon does not exactly orbit Pluto. They both orbit a common center of gravity between them.

Xena and Ceres would have also been called plutons.

But after heated debate that proposal was rejected. Instead, the astronomers voted to have eight planets and a group called dwarf planets.

For now, the dwarf planets are Pluto, Xena and Ceres. But other objects are expected to join the list before long.

VOICE ONE:

The International Astronomical Union was established in nineteen nineteen. The group holds a general assembly meeting every three years.

Two thousand five hundred of its nine thousand members attended the meeting last month in the Czech capital. Two weeks of discussions took place. But the vote was left to a reported four hundred twenty-four astronomers who stayed to the end.

The definition they agreed to sets three requirements for a planet. It must orbit the sun. It must have enough mass so that its own gravity makes it nearly round. And it must have cleared the neighborhood around its orbit.

Astronomers who supported this definition say they do not consider the area around Pluto's orbit cleared. They say Pluto has not gathered up enough nearby material and they note that its orbit crosses Neptune's orbit.

Yet some people say that by this reasoning, the continued presence of Pluto could mean that Neptune should no longer be called a planet.

VOICE TWO:

Many astronomers criticize the definition, which considers planets and dwarf planets as two separate classes of objects. Astronomy historian Owen Gingerich led the committee that proposed the idea for twelve planets. The Harvard University professor says it does not make sense to say that a dwarf planet is not a planet.

And other issues remain, like what to call huge objects that orbit stars other than the Sun.

Yet science is a process of continual discovery and change. For now, it means we have to remember that our solar system -- officially, at least -- has only eight planets. But to future generations, today's thinking might seem like the ideas of the first people who looked up and saw stars wandering in the sky.


Pluto loses planetary status, leaving eight

(MUSIC)

VOICE ONE:

SCIENCE IN THE NEWS was written by Mario Ritter and produced by Brianna Blake. I'm Bob Doughty.

VOICE TWO:

And I'm Faith Lapidus. You can download transcripts16 and audio files of our programs at www.unsv.com. And listen again next week for more news about science in Special English on the Voice of America.



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1 Pluto wu0yF     
n.冥王星
参考例句:
  • Pluto is the furthest planet from the sun.冥王星是离太阳最远的行星。
  • Pluto has an elliptic orbit.冥王星的轨道是椭圆形的。
2 dwarf EkjzH     
n.矮子,侏儒,矮小的动植物;vt.使…矮小
参考例句:
  • The dwarf's long arms were not proportional to his height.那侏儒的长臂与他的身高不成比例。
  • The dwarf shrugged his shoulders and shook his head. 矮子耸耸肩膀,摇摇头。
3 doughty Jk5zg     
adj.勇猛的,坚强的
参考例句:
  • Most of successful men have the characteristics of contumacy and doughty.绝大多数成功人士都有共同的特质:脾气倔强,性格刚强。
  • The doughty old man battled his illness with fierce determination.坚强的老人用巨大毅力与疾病作斗争。
4 intensified 4b3b31dab91d010ec3f02bff8b189d1a     
v.(使)增强, (使)加剧( intensify的过去式和过去分词 )
参考例句:
  • Violence intensified during the night. 在夜间暴力活动加剧了。
  • The drought has intensified. 旱情加剧了。 来自《简明英汉词典》
5 astronomical keTyO     
adj.天文学的,(数字)极大的
参考例句:
  • He was an expert on ancient Chinese astronomical literature.他是研究中国古代天文学文献的专家。
  • Houses in the village are selling for astronomical prices.乡村的房价正在飙升。
6 astronomer DOEyh     
n.天文学家
参考例句:
  • A new star attracted the notice of the astronomer.新发现的一颗星引起了那位天文学家的注意。
  • He is reputed to have been a good astronomer.他以一个优秀的天文学者闻名于世。
7 astronomers 569155f16962e086bd7de77deceefcbd     
n.天文学者,天文学家( astronomer的名词复数 )
参考例句:
  • Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
  • Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪,为什么只有土星有光环。 来自《简明英汉词典》
8 Neptune LNezw     
n.海王星
参考例句:
  • Neptune is the furthest planet from the sun.海王星是离太阳最远的行星。
  • Neptune turned out to be a dynamic,stormy world.海王星原来是个有生气、多风暴的世界。
9 fixed JsKzzj     
adj.固定的,不变的,准备好的;(计算机)固定的
参考例句:
  • Have you two fixed on a date for the wedding yet?你们俩选定婚期了吗?
  • Once the aim is fixed,we should not change it arbitrarily.目标一旦确定,我们就不应该随意改变。
10 Saturn tsZy1     
n.农神,土星
参考例句:
  • Astronomers used to ask why only Saturn has rings.天文学家们过去一直感到奇怪,为什么只有土星有光环。
  • These comparisons suggested that Saturn is made of lighter materials.这些比较告诉我们,土星由较轻的物质构成。
11 Uranus 3pZyA     
n.天王星
参考例句:
  • Uranus is unusual because it is tilted.天王星非常特殊,因为它是倾斜的。
  • Uranus represents sudden change and rebellion.天王星代表突然性的改变和反叛。
12 Celsius AXRzl     
adj.摄氏温度计的,摄氏的
参考例句:
  • The temperature tonight will fall to seven degrees Celsius.今晚气温将下降到七摄氏度。
  • The maximum temperature in July may be 36 degrees Celsius.七月份最高温度可能达到36摄氏度。
13 asteroid uo1yD     
n.小行星;海盘车(动物)
参考例句:
  • Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
  • It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小,但这样的危险还是存在的。
14 asteroids d02ebba086eb60b6155b94e12649ff84     
n.小行星( asteroid的名词复数 );海盘车,海星
参考例句:
  • Asteroids,also known as "minor planets",are numerous in the outer space. 小行星,亦称为“小型行星”,在外太空中不计其数。
  • Most stars probably have their quota of planets, meteorids, comets, and asteroids. 多数恒星也许还拥有若干行星、流星、彗星和小行星。
15 observatory hRgzP     
n.天文台,气象台,瞭望台,观测台
参考例句:
  • Guy's house was close to the observatory.盖伊的房子离天文台很近。
  • Officials from Greenwich Observatory have the clock checked twice a day.格林威治天文台的职员们每天对大钟检查两次。
16 transcripts 525c0b10bb61e5ddfdd47d7faa92db26     
n.抄本( transcript的名词复数 );转写本;文字本;副本
参考例句:
  • Like mRNA, both tRNA and rRNA are transcripts of chromosomal DNA. tRNA及rRNA同mRNA一样,都是染色体DNA的转录产物。 来自辞典例句
  • You can't take the transfer students'exam without your transcripts. 没有成绩证明书,你就不能参加转学考试。 来自辞典例句

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