星团中的凌日行星首次被发现
文章来源:未知 文章作者:enread 发布时间:2013-06-27 06:19 字体: [ ]  进入论坛
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All stars begin their lives in groups. Most stars, including our Sun, are born in small, benign1(良性的,亲切的) groups that quickly fall apart. Others form in huge, dense2 swarms3 that survive for billions of years as stellar clusters. Within such rich and dense clusters, stars jostle for room with thousands of neighbors while strong radiation and harsh stellar winds scour4 interstellar space, stripping planet-forming materials from nearby stars. It would thus seem an unlikely place to find alien worlds. Yet 3,000 light-years from Earth, in the star cluster NGC 6811, astronomers5 have found two planets smaller than Neptune6 orbiting Sun-like stars. The discovery, published in the journal Nature, shows that planets can develop even in crowded clusters jam-packed with stars.
 
"Old clusters represent a stellar environment much different than the birthplace of the Sun and other planet-hosting field stars," says lead author Soren Meibom of the Harvard-Smithsonian Center for Astrophysics (CfA). "And we thought maybe planets couldn't easily form and survive in the stressful environments of dense clusters, in part because for a long time we couldn't find them."
 
The two new alien worlds appeared in data from NASA's Kepler spacecraft. Kepler hunts for planets that transit7, or cross in front of, their host stars. During a transit, the star dims by an amount that depends on the size of the planet, allowing the size to be determined8. Kepler-66b and Kepler-67b are both less than three times the size of Earth, or about three-fourths the size of Neptune (mini-Neptunes).
 
Of the more than 850 known planets beyond our solar system, only four -- all similar to or greater than Jupiter in mass -- were found in clusters. Kepler-66b and -67b are the smallest planets to be found in a star cluster, and the first cluster planets seen to transit their host stars, which enables the measurement of their sizes.
 
Meibom and his colleagues have measured the age of NGC 6811 to be one billion years. Kepler-66b and Kepler-67b therefore join a small group of planets with precisely9 determined ages, distances, and sizes.
 
Considering the number of stars observed by Kepler in NGC 6811, the detection of two such planets implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars (stars not within a cluster or association) in the Milky10 Way galaxy11.
 
"These planets are cosmic extremophiles," says Meibom. "Finding them shows that small planets can form and survive for at least a billion years, even in a chaotic12 and hostile environment."
 
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint13 collaboration14 between the Smithsonian Astrophysical Observatory15 and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.


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1 benign 2t2zw     
adj.善良的,慈祥的;良性的,无危险的
参考例句:
  • The benign weather brought North America a bumper crop.温和的气候给北美带来大丰收。
  • Martha is a benign old lady.玛莎是个仁慈的老妇人。
2 dense aONzX     
a.密集的,稠密的,浓密的;密度大的
参考例句:
  • The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
  • The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。
3 swarms 73349eba464af74f8ce6c65b07a6114c     
蜂群,一大群( swarm的名词复数 )
参考例句:
  • They came to town in swarms. 他们蜂拥来到城里。
  • On June the first there were swarms of children playing in the park. 6月1日那一天,这个公园里有一群群的孩子玩耍。
4 scour oDvzj     
v.搜索;擦,洗,腹泻,冲刷
参考例句:
  • Mother made me scour the family silver.母亲让我擦洗家里的银器。
  • We scoured the telephone directory for clues.我们仔细查阅电话簿以寻找线索。
5 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》
6 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。
7 transit MglzVT     
n.经过,运输;vt.穿越,旋转;vi.越过
参考例句:
  • His luggage was lost in transit.他的行李在运送中丢失。
  • The canal can transit a total of 50 ships daily.这条运河每天能通过50条船。
8 determined duszmP     
adj.坚定的;有决心的
参考例句:
  • I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
  • He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。
9 precisely zlWzUb     
adv.恰好,正好,精确地,细致地
参考例句:
  • It's precisely that sort of slick sales-talk that I mistrust.我不相信的正是那种油腔滑调的推销宣传。
  • The man adjusted very precisely.那个人调得很准。
10 milky JD0xg     
adj.牛奶的,多奶的;乳白色的
参考例句:
  • Alexander always has milky coffee at lunchtime.亚历山大总是在午餐时喝掺奶的咖啡。
  • I like a hot milky drink at bedtime.我喜欢睡前喝杯热奶饮料。
11 galaxy OhoxB     
n.星系;银河系;一群(杰出或著名的人物)
参考例句:
  • The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
  • The company has a galaxy of talent.该公司拥有一批优秀的人才。
12 chaotic rUTyD     
adj.混沌的,一片混乱的,一团糟的
参考例句:
  • Things have been getting chaotic in the office recently.最近办公室的情况越来越乱了。
  • The traffic in the city was chaotic.这城市的交通糟透了。
13 joint m3lx4     
adj.联合的,共同的;n.关节,接合处;v.连接,贴合
参考例句:
  • I had a bad fall,which put my shoulder out of joint.我重重地摔了一跤,肩膀脫臼了。
  • We wrote a letter in joint names.我们联名写了封信。
14 collaboration bW7yD     
n.合作,协作;勾结
参考例句:
  • The two companies are working in close collaboration each other.这两家公司密切合作。
  • He was shot for collaboration with the enemy.他因通敌而被枪毙了。
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。
TAG标签: planet space stars
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