天文学家发现新型态行星
文章来源:未知 文章作者:enread 发布时间:2011-05-19 02:48 字体: [ ]  进入论坛
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University of Notre Dame1 astronomer2 David Bennett is co-author of a new paper describing the discovery of a new class of planets — dark, isolated3 Jupiter-mass bodies floating alone in space, far from any host star. Bennett and the team of astronomers4 involved in the discovery believe that the planets were most likely ejected from developing planetary systems. The study is described in a paper appearing in the May 19th issue of the journal Nature.

The discovery stems from an analysis of observations of the central bulge5 of the Milky6 Way galaxy7 taken in 2006 and 2007 by a joint8 Japan-New Zealand survey. This analysis provides evidence of what appear to be 10 free-floating planets roughly the mass of Jupiter. Bennett explains the likely origin of these isolated planets, "Our results suggest that planetary systems often become unstable9, with planets being kicked out from their places of birth by close encounters with other planets".

This discovery not only confirms that free-floating planets exist in space, but also indicates that they are quite common. Free-floating planets are very hard to detect, so the fact that the survey found up to 10 implies that there are many more that are not detected. The team of scientists that made the discovery estimates that there are about twice as many free-floating Jupiter-mass planets as stars. This implies that free-floating planets are likely to be least as common as planets, like ours, that orbit stars.

"Our survey is like a population census10(普查) — we sampled a portion of the galaxy and, based on these data, can estimate overall numbers in the galaxy," Bennett said. "The survey is not sensitive to planets less massive than Jupiter and Saturn11, but theories suggest that lower-mass planets like Earth should be ejected from their stars more often and are thus more common that free-floating Jupiters." Some scientists have even suggested that free-floating Earth-mass planets could be warm enough to host life, due to the greenhouse effect of a large amount of Hydrogen in their atmospheres. NASA's planned WFIRST mission will use the microlensing method to reveal how many free-floating Earth-mass planets inhabit the Milky Way galaxy.

The survey that revealed the planets is called the Microlensing Observations in Astrophysics (MOA). A 1.8-meter (5.9-foot) telescope at Mt. John University Observatory12 in New Zealand is used to regularly scan the stars at the center of the Milky Way galaxy for what are referred to as "gravitational microlensing events."

Bennett is a pioneer in the gravitational microlensing method, which takes advantage of the fact that light is bent13 as the rays pass close to a massive object, like a star. The gravity from the mass of the foreground planet warps14 surrounding space and acts like a giant magnifying glass. As predicted by Albert Einstein and later confirmed, this phenomena15 causes an apparent brightening of the light from a background "source" star. The effect is seen only if the astronomer's telescope lies in almost perfect alignment16(校准,队列) with the source star and the lens star. The primary challenge of the microlensing method is the precise alignments17 needed for the planetary microlensing signals are quite rare and brief, lasting18 less than two days.

Astronomers are also able to detect planets orbiting stars if the light from the background star is warped19 by both the planet and its host star.

Bennett and the team of scientists found about 10 short microlensing events, indicating planets of roughly Jupiter's mass. The team said that it can't rule out the possibility that some of the planets may be in very distant orbits about stars, but previous observations by other groups suggests that Jupiter-mass planets in such distant orbits are rare. Future observations by the Hubble Space Telescope should detect many of these host stars, if they exist.

"If free-floating planets formed like stars, then we would have expected to see only one or two of them in our survey instead of 10," Bennett said.



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1 dame dvGzR0     
n.女士
参考例句:
  • The dame tell of her experience as a wife and mother.这位年长妇女讲了她作妻子和母亲的经验。
  • If you stick around,you'll have to marry that dame.如果再逗留多一会,你就要跟那个夫人结婚。
2 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。
3 isolated bqmzTd     
adj.与世隔绝的
参考例句:
  • His bad behaviour was just an isolated incident. 他的不良行为只是个别事件。
  • Patients with the disease should be isolated. 这种病的患者应予以隔离。
4 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》
5 bulge Ns3ze     
n.突出,膨胀,激增;vt.突出,膨胀
参考例句:
  • The apple made a bulge in his pocket.苹果把他口袋塞得鼓了起来。
  • What's that awkward bulge in your pocket?你口袋里那块鼓鼓囊囊的东西是什么?
6 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。
7 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。
8 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。
9 unstable Ijgwa     
adj.不稳定的,易变的
参考例句:
  • This bookcase is too unstable to hold so many books.这书橱很不结实,装不了这么多书。
  • The patient's condition was unstable.那患者的病情不稳定。
10 census arnz5     
n.(官方的)人口调查,人口普查
参考例句:
  • A census of population is taken every ten years.人口普查每10年进行一次。
  • The census is taken one time every four years in our country.我国每四年一次人口普查。
11 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。
12 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。
13 bent QQ8yD     
n.爱好,癖好;adj.弯的;决心的,一心的
参考例句:
  • He was fully bent upon the project.他一心扑在这项计划上。
  • We bent over backward to help them.我们尽了最大努力帮助他们。
14 warps 0971e679caf9e581c1c1f5312249a54c     
n.弯曲( warp的名词复数 );歪斜;经线;经纱v.弄弯,变歪( warp的第三人称单数 );使(行为等)不合情理,使乖戾,
参考例句:
  • This wood warps easily in damp conditions. 这种木料受潮容易变形。 来自《简明英汉词典》
  • Matt Lauer: Renewable biofuels. Park Ranger Rick Marshall Close. Time warps. 马特·劳尔:“可再生生物燃料。”瑞克:“不说了,时间都扭曲了。” 来自互联网
15 phenomena 8N9xp     
n.现象
参考例句:
  • Ade couldn't relate the phenomena with any theory he knew.艾德无法用他所知道的任何理论来解释这种现象。
  • The object of these experiments was to find the connection,if any,between the two phenomena.这些实验的目的就是探索这两种现象之间的联系,如果存在着任何联系的话。
16 alignment LK8yZ     
n.队列;结盟,联合
参考例句:
  • The church should have no political alignment.教会不应与政治结盟。
  • Britain formed a close alignment with Egypt in the last century.英国在上个世纪与埃及结成了紧密的联盟。
17 alignments c6eb4749b4b3c5cb9bbdf54b3852ad84     
排成直线( alignment的名词复数 ); (国家、团体间的)结盟
参考例句:
  • Along some active faults we can see clear alignments of microearthquakes. 微震清晰地沿着某些活动断层排列着。
  • The technique requires critical and difficult optical alignments. 这种技术要求严格,并且光学调整困难。
18 lasting IpCz02     
adj.永久的,永恒的;vbl.持续,维持
参考例句:
  • The lasting war debased the value of the dollar.持久的战争使美元贬值。
  • We hope for a lasting settlement of all these troubles.我们希望这些纠纷能获得永久的解决。
19 warped f1a38e3bf30c41ab80f0dce53b0da015     
adj.反常的;乖戾的;(变)弯曲的;变形的v.弄弯,变歪( warp的过去式和过去分词 );使(行为等)不合情理,使乖戾,
参考例句:
  • a warped sense of humour 畸形的幽默感
  • The board has warped. 木板翘了。 来自《现代汉英综合大词典》
TAG标签: space star planets
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