Home away from home The existence of the most Earthlike planet yet has just beenconfirmed Dec 10th 2011 | from the print edition ONE of the more memorable slogans to come out of the climate-changetalks in Durban over the past few days is: there is no planet B. But whatif there were? Over the past couple of decades astronomers have loggedthousands of so-called exoplanetsworlds which orbit stars other than the sun. On December 5th thescientists in charge of Kepler, a space telescope designed to look for suchplanets, confirmed their instruments discovery of itsfirst Earthlike world. It is dubbed, rather unromantically, Kepler 22b. The existence of this planet, which circles a star 600 light-yearsaway, in the constellation of Lyra, had previously been suspected. Kepler,which belongs to NASA, Americas space agency, works by observing dips in a stars brightnessas a planet passes in front of it. It flags likely looking reductions as candidateplanets, of which Kepler 22b was one. But three passes are needed to confirma planets existence, and Kepler 22b has now passed this test. Crucially, itorbits well within its stars Goldilocks zone: neither too close nor too far away for liquid water to exist on its surface. It joins two other Earthlike planetsGliese 581d and HD85512 bdiscovered by another instrument within the past few years. Intruth, the term Earthlike is a stretch. Kepler 22b has a radius 2.4 times that of Earth, andif it is made from roughly the same stuff its surface gravity will also beabout 2.4 times as strong. But NASAs astronomers remainunsure whether it is predominantly gaseous, liquid or solid. Nevertheless, Kepler 22b is the most promising exoplanet yet found.Unlike the others, which skirt the edges of their stars Goldilockszones, Kepler 22b orbits comfortably within its own. NASAsresearchers reckon its surface temperature is about 22C, comparedwith 15C on Earth. Its parent star is similar to thesun, again unlike those of the other two candidates, both of which orbitcooler, dimmer stars. Indeed Gliese 581ds parent is a reddwarfthe tiniest stellar species. That means its Goldilocks zone is soclose to it that the planet may be tidally locked, as the moon is to the Earth.If that were the case, one side of Gliese 581d would be permanently lit while the other experienced unending darkness. These three potentially habitable exoplanets may soon be joined bymany more. In the two and a half years since its launch, Kepler has spotted2,326 candidate planets. About 650 others have been discovered by otherinstruments. That plethora allows astronomers to start drawing conclusionsabout how common various sorts of planets are. Of Keplers haul, 9%seem to be of a similar size to Earth ; a further 29% are Super Earthsplanetssubstantially larger than Earth that are nevertheless rocky. Forty-eight ofKeplers unconfirmed candidates look as if they orbit within their stars habitablezones; of those, ten seem to be Earth-sized. The ultimate goal, of course, is to let astronomers make a plausibleestimate of the total number of planets in the galaxy, of the number that couldconceivably support life, and of the fraction of those that could sustain human colonists. If only a few of Keplers possibleEarthlike planets turn out to be real, that third number is likely to be in themillions. Such knowledge will mark an historic transition, says Chris Lintott,an astronomer at Oxford University who is giving the Kepler team a hand withthe data analysis, since the uncertainties around the question of whether lifeexists elsewhere will cease to be astronomical and become purely biological . Based on the preliminary data,it looks as if there are numerous suitable planets. The science of exobiologymay soon cease to be an oxymoron.
英蕊乐园游历记全集:Story 01 你好
学前英语口语学习教程汇总
英蕊乐园游历记全集:Story 08 我喜欢橘子
英蕊乐园游历记全集:Story 03 我爱我的家
跟小小孩说英文:Eat it up 吃干净
跟小小孩说英文:Buying clothes 买衣服
跟小小孩说英文:Dining 吃饭
英蕊乐园游历记全集:Story 07 那是一个苹果
英蕊乐园游历记全集:Story 05 这是什么
跟小小孩说英文:Eating too much 吃太多肚子痛
学前英语口语学习教程:第六单元
跟小小孩说英文 :Feeding the baby 喂宝宝
跟小小孩说英文:Dining on Dragon Boat Festival 端午节吃饭
跟小小孩说英文:Putting on a raincoat 穿雨衣
英蕊乐园游历记全集:Story 06 我想要牛奶
跟小小孩说英文:Having cotton candy 吃棉花糖
跟小小孩说英文:Going out on a rainy day 下雨天出门
跟小小孩说英文:What to wear? 穿什么衣服
学前英语口语学习教程:第七单元
学前英语口语学习教程:第一单元
学前英语口语学习教程:第八单元
跟小小孩说英文:Concentrate on Eating 专心吃饭
跟小小孩说英文:In the supermarket 在超市(一)
英蕊乐园游历记全集:Story 02 你叫什么名字
跟小小孩说英文:Shopping in the Market 逛市场
跟小小孩说英文:Dining courtesy 吃饭礼节
跟小小孩说英文:Snacks 点心
跟小小孩说英文:In the supermarket 在超市(三)
跟小小孩说英文:At the dining table饭桌上
跟小小孩说英文:In the fast food restaurant 在快餐店
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