彗星可能是普遍的系外行星
文章来源:未知 文章作者:enread 发布时间:2013-01-09 06:40 字体: [ ]  进入论坛
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Comets trailing wispy1(纤细的) tails across the night sky are a beautiful byproduct of our solar system's formation, icy leftovers2 from 4.6 billion years ago when the planets coalesced4 from rocky rubble5. The discovery by astronomers7 at the University of California, Berkeley, and Clarion8 University in Pennsylvania of six likely comets around distant stars suggests that comets -- dubbed9 "exocomets" -- are just as common in other stellar systems with planets.
 
Though only one of the 10 stars now thought to harbor comets is known to harbor planets, the fact that all these stars have massive surrounding disks of gas and dust ‑ a signature of exoplanets -- makes it highly likely they all do, said Barry Welsh, a research astronomer6 at UC Berkeley's Space Sciences Laboratory.
 
"This is sort of the missing link in current planetary formation studies," Welsh said. "We see dust disks -- presumably the primordial10(原始的) planet-forming material -- around a whole load of stars, and we see planets, but we don't see much of the stuff in between: the asteroid-like planetesimals and the comets. Now, I think we have nailed it. These exocomets are more common and easier to detect than people previously11 thought."
 
Welsh will present the findings on Monday, Jan. 7, during a meeting of the American Astronomical12 Society in Long Beach, Calif. Three of the new exocomets were reported in the Oct. 2012 issue of the journal Publications of the Astronomical Society of the Pacific by Welsh and colleague Sharon L. Montgomery of the Department of Physics at Clarion University.
 
Welsh also will participate in a media briefing on Tuesday, Jan. 8, at 2:30 p.m. PST in Room 204 on Level 2 of the Long Beach Convention Center.
 
Welsh summarized the current theory of planet formation as "interstellar dust under the influence of gravity becomes blobs, and the blobs grow into rocks, the rocks coalesce3(合并,结合) and become bigger things -- planetesimals and comets -- and finally, you get planets."
 
Many stars are known to be surrounded by disks of gas and dust, and one of the closest, beta-Pictoris (β-Pic), was reported to have comets in 1987. In 2009, astronomers found a large planet around β-Pic about 10 times larger than Jupiter. Three other stars -- one discovered by Welsh in 1998 -- were subsequently found to have comets.
 
"But then, people just lost interest. They decided13 that exocomets were a done deal, and everybody switched to the more exciting thing, exoplanets," Welsh said. "But I came back to it last year and thought, 'Four exocomets is not all that many compared to the couple of thousand exoplanets known -- perhaps I can improve on that.'"
 
Detecting comets may sound difficult -- after all, the snowballs are typically only 5-20 kilometers (3-13 miles) in diameter. But Welsh said that once comets are knocked out of their parking orbit in the outer reaches of a stellar system and fall toward a star, they heat up and evaporate. The evaporating comet, which is what we see with comets such as Halley and next year's highly anticipated Comet ISON, creates a brief, telltale absorption line in the spectrum14 of a star.
 
The six new exocomet systems were discovered during three five-night-long observing runs between May 2010 and November 2012 using the 2.1-meter telescope of the McDonald Observatory15 in Texas. The telescope's high resolution spectrograph revealed weak absorption features that were found to vary from night to night, an outcome that Welsh and Montgomery attributed to large clouds of gas emanating16 from the nuclei17 of comets as they neared their central stars.


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1 wispy wispy     
adj.模糊的;纤细的
参考例句:
  • Grey wispy hair straggled down to her shoulders.稀疏的灰白头发披散在她肩头。
  • The half moon is hidden behind some wispy clouds.半轮月亮躲在淡淡的云彩之后。
2 leftovers AprzGJ     
n.剩余物,残留物,剩菜
参考例句:
  • He can do miracles with a few kitchen leftovers.他能用厨房里几样剩饭做出一顿美餐。
  • She made supper from leftovers she had thrown together.她用吃剩的食物拼凑成一顿晚饭。
3 coalesce oWhyj     
v.联合,结合,合并
参考例句:
  • And these rings of gas would then eventually coalesce and form the planets.这些气体环最后终于凝结形成行星。
  • They will probably collide again and again until they coalesce.他们可能会一次又一次地发生碰撞,直到他们合并。
4 coalesced f8059c4b4d1477d57bcd822ab233e0c1     
v.联合,合并( coalesce的过去式和过去分词 )
参考例句:
  • The puddles had coalesced into a small stream. 地面上水洼子里的水汇流成了一条小溪。
  • The views of party leaders coalesced to form a coherent policy. 党的领导人的各种观点已统一为一致的政策。 来自辞典例句
5 rubble 8XjxP     
n.(一堆)碎石,瓦砾
参考例句:
  • After the earthquake,it took months to clean up the rubble.地震后,花了数月才清理完瓦砾。
  • After the war many cities were full of rubble.战后许多城市到处可见颓垣残壁。
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 clarion 3VxyJ     
n.尖音小号声;尖音小号
参考例句:
  • Clarion calls to liberation had been mocked when we stood by.当我们袖手旁观的时候,自由解放的号角声遭到了嘲弄。
  • To all the people present,his speech is a clarion call.对所有在场的人而言,他的演讲都是动人的号召。
9 dubbed dubbed     
v.给…起绰号( dub的过去式和过去分词 );把…称为;配音;复制
参考例句:
  • Mathematics was once dubbed the handmaiden of the sciences. 数学曾一度被视为各门科学的基础。
  • Is the movie dubbed or does it have subtitles? 这部电影是配音的还是打字幕的? 来自《简明英汉词典》
10 primordial 11PzK     
adj.原始的;最初的
参考例句:
  • It is the primordial force that propels us forward.它是推动我们前进的原始动力。
  • The Neanderthal Man is one of our primordial ancestors.的尼安德特人是我们的原始祖先之一.
11 previously bkzzzC     
adv.以前,先前(地)
参考例句:
  • The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  • Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
12 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。
13 decided lvqzZd     
adj.决定了的,坚决的;明显的,明确的
参考例句:
  • This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
  • There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。
14 spectrum Trhy6     
n.谱,光谱,频谱;范围,幅度,系列
参考例句:
  • This is a kind of atomic spectrum.这是一种原子光谱。
  • We have known much of the constitution of the solar spectrum.关于太阳光谱的构成,我们已了解不少。
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 emanating be70e0c91e48568de32973cab34020e6     
v.从…处传出,传出( emanate的现在分词 );产生,表现,显示
参考例句:
  • Even so, there is a slight odour of potpourri emanating from Longfellow. 纵然如此,也还是可以闻到来自朗费罗的一种轻微的杂烩的味道。 来自辞典例句
  • Many surface waters, particularly those emanating from swampy areas, are often colored to the extent. 许多地表水,特别是由沼泽地区流出的地表水常常染上一定程度的颜色。 来自辞典例句
17 nuclei tHCxF     
n.核
参考例句:
  • To free electrons, something has to make them whirl fast enough to break away from their nuclei. 为了释放电子,必须使电子高速旋转而足以摆脱原子核的束缚。
  • Energy is released by the fission of atomic nuclei. 能量是由原子核分裂释放出来的。
TAG标签: solar planets comets
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