2006年VOA标准英语-Solar System Could Gain New Planets Under Defin

By David McAlary
Was
16 August 2006
 

Artist's rendition of solar system  
  
There may soon be three new planets in our solar system.  The expansion would be the result of a proposed new definition of what a planet is.  The change is controversial, but if adopted by astronomy's governing body, it could eventually mean there will be many more than 12 planets.

-------

Distant Pluto¹, the last official planet to be discovered, may keep its rank. For years, astronomers³ have wanted to demote it from planetary status because it was not quite like the eight classical planets closer to the sun. Its tilted⁴ orbit and its icy composition set it apart from the rocky planets such as Earth and the gas giants Saturn⁵ and Jupiter.

But a new definition of planets proposed at the International Astronomical⁶ Union meeting in Prague would retain Pluto's standing⁷ and add three more bodies.

Pluto and its satellite Charon   
  
They are Pluto's companion Charon, the asteroid⁸ Ceres, and a more distant body discovered last year that is not yet named, but known temporarily as UB 313.

"This is a revolution in our understanding of the solar system," explained Massachusetts Institute of Technology scientist Richard Binzel, a member of the astronomical union's planet definition committee.  He says it took two years of tough deliberations to reach the new definition.

The revision is necessary, says Binzel, because of improved observations that make better distinctions within our solar system. This includes the 1992 discovery that there are icy bodies in the region beyond Pluto called the Kuiper Belt.

"We now know that out beyond Neptune⁹ and, in fact, out beyond Pluto, is a zone of bodies, literally¹⁰ thousands of bodies, that are basically a third region of our solar system. In that region, we know that there are many Pluto-like objects remaining to be discovered," Binzel said.

The long accepted view of a planet has been anything that orbits a star and is not itself a star.  This broad meaning included asteroids¹¹ and many other smaller objects as minor¹² planets.

The new definition is much more exclusive.  Binzel and his colleagues eliminated the minor planet category and included only those bodies orbiting stars that have enough gravity to pull themselves into a sphere.  They do not include moons of planets.

"After we made that definition, we stopped and looked back and said, 'Okay, where is Pluto?'  Pluto falls well above the boundary. It's a spherical¹³ object and, by gosh, Pluto makes the list," Binzel says.

Charon also makes the list because it is not a moon of Pluto as once thought.  But in recognition that Pluto, Charon, UB 313 and other similar bodies are different in composition and angle of orbit, the new planet definition calls them plutons.

The change is controversial. Astronomer² Scott Sheppard of the Carnegie Institution in Washington argues that plutons should not be considered planets because, unlike the eight major ones, their orbits are not independent.  Instead, they are attuned¹⁴ to that of Neptune.  Furthermore, he says their gravitational fields do not dominate their local environment.

"Pluto and UB 313 and the rest of the thousands of Kuiper Belt objects beyond Neptune, since they formed and evolved in a very similar manner, should be grouped together.  So I would personally consider Pluto and the rest of the Kuiper Belt objects not really planets, but the third domain¹⁵ of the solar system or something like that," Sheppard says.

The astronomer who discovered UB 313 last year, Michael Brown of the California Institute of Technology, takes a middle view.  He maintains that size should be considered.

"Pluto has been called a planet for so long that I think we are never going to not call Pluto a planet," Brown said. "If Pluto is going to be called a planet, then anything larger than Pluto is a planet.  Things that are smaller I think we just call them typical members of the Kuiper Belt and they do not join this very special class of things that are planets."

His view would maintain his discovery as a planet because it is bigger than Pluto.

The new planet definition must now be approved by a majority of the nearly 2,500 astronomers attending the Prague meeting from 75 nations.  But Scott Sheppard is not sure that would settle the issue.

"I think no matter what the International Astronomical Union decides, it will still be a debate for years to come," Sheppard said.

1 Pluto   

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 astronomer   

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。

3 astronomers   

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》

4 tilted   

v. 倾斜的

参考例句：

• Suddenly the boat tilted to one side. 小船突然倾向一侧。
• She tilted her chin at him defiantly. 她向他翘起下巴表示挑衅。

5 Saturn   

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。

6 astronomical   

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。

7 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

8 asteroid   

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。

9 Neptune   

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。

10 literally   

adv.照字面意义，逐字地；确实

参考例句：

• He translated the passage literally.他逐字逐句地翻译这段文字。
• Sometimes she would not sit down till she was literally faint.有时候，她不走到真正要昏厥了，决不肯坐下来。

11 asteroids   

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。

12 minor   

adj.较小(少)的，较次要的；n.辅修学科；vi.辅修

参考例句：

• The young actor was given a minor part in the new play.年轻的男演员在这出新戏里被分派担任一个小角色。
• I gave him a minor share of my wealth.我把小部分财产给了他。

13 spherical   

adj.球形的；球面的

参考例句：

• The Earth is a nearly spherical planet.地球是一个近似球体的行星。
• Many engineers shy away from spherical projection methods.许多工程师对球面投影法有畏难情绪。

14 attuned   

v.使协调( attune的过去式和过去分词 )；调音

参考例句：

• She wasn't yet attuned to her baby's needs. 她还没有熟悉她宝宝的需要。
• Women attuned to sensitive men found Vincent Lord attractive. 偏爱敏感男子的女人，觉得文森特·洛德具有魅力。 来自辞典例句

15 domain   

n.(活动等)领域，范围；领地，势力范围

参考例句：

• This information should be in the public domain.这一消息应该为公众所知。
• This question comes into the domain of philosophy.这一问题属于哲学范畴。