天文學家發現和地球相同質量行星

05-30

New Planet in Neighborhood, Astronomically Speaking

By DENNIS OVERBYE October 18, 2012

天文學家發現和地球相同質量行星

DENNIS OVERBYE 報道 2012年10月18日

Bringing the search for another Earth about as close as it will ever get, a team of European astronomers was scheduled to announce on Wednesday that it had found a planet the same mass as Earth』s in Alpha Centauri, a triple star system that is the Sun』s closest neighbor, only 4.4 light-years away.

周三，一組歐洲天文學家宣布，在半人馬座阿爾法星系(Alpha Centauri)中發現了一顆和地球有著相同質量的行星。半人馬座阿爾法星系是一個離太陽系最近的三合星系統，距我們僅4.4光年。這一發現也許是科學家尋找「第二個地球」的努力所得到的最接近的結果。

The planet is the lightest one ever found orbiting another star and — in the words of its discoverer, Xavier Dumusque, a graduate student at the Geneva Observatory — 「it will surely be the closest one ever.」

這是迄今發現的、圍繞著另一個恆星運轉的、質量最小的行星，用其發現者、日內瓦天文台(Geneva Observatory)的研究生格扎維埃·杜穆斯克(Xavier Dumusque)的話來說，「它肯定是目前發現的最近的一個。」

It is presumably a rocky ball like our own, but it is not habitable. It circles Alpha Centauri B, a reddish orb about half as luminous as the Sun, every three days at a distance of only about four million miles, resulting in hellish surface temperatures of 1,200 degrees.

該行星很可能像地球一樣，是個岩石球體，但是不適宜人類居住。它繞著呈微紅色、亮度為太陽一半的半人馬座阿爾法星B運轉，每三天一圈，其軌道離阿爾法星B的距離為600萬公里，這導致它的表面溫度極高、達1200攝氏度。

L. Calcada/European Southern Observatory, via Associated Press

歐洲宇航員在地球附近發現一顆新的星球，但是表面溫度非常高，不適宜人類居住。

So this is not 「Earth 2.0.」 Yet.

所以它還不能算是「地球2.0」。

Astronomers said the discovery raised the possibility that there were habitable Earthlike planets right next door and that methods and instruments were now precise enough to detect them.

天文學家說，此發現增加了在近鄰星系內存在可居住的、類地球行星的可能性，而且現有方法和工具已具有足夠的精確度來探測此類行星。

「Very small planets are not rare,」 said Mr. Dumusque, who is the lead author of a paper being published on Wednesday in Nature. 「When you find one small planet, you find others.」 He and his colleagues discussed the results on Tuesday in a news conference hosted by the European Southern Observatory in Garching, Germany.

杜穆斯克是周三發表在《自然》(Nature)雜誌上的有關論文的第一作者，他說，「小型行星不罕見。你發現了一個，就會發現另外的。」周二，杜穆斯克和同事們在位於德國加興(Garching)的歐洲南方天文台(European Southern Observatory)召開的新聞發布會上討論了這些結果。

Astronomers were electrified by the news of the planet, but also cautioned that it needed confirmation by other astronomers, not an easy task.

發現該行星的消息令天文學家異常興奮，但是他們也謹慎地表示，仍需要得到其他天文學家的確認，而這並非易事。

Debra Fischer, a Yale astronomer who has been searching for planets in that same system for years, said: 「The discovery that our nearest neighbor has rocky planets is the story of the decade. I』d bet $100 that there are other planets that are there as well.」

來自耶魯大學(Yale University)的天文學家黛布拉·費希爾(Debra Fischer)多年來也一直在同一星系內尋找行星，她說：「離我們最近的星系內存在著岩石行星，這個發現是十年來最大的新聞。我賭100美元，那裡還有其他的行星。」

The discovery also underscored the allure of Alpha Centauri as a target of space and scientific exploration.

該發現還增強了半人馬座阿爾法星系作為一個太空和科學考察目標的吸引力。

「This is close enough you can almost spit there,」 said Geoffrey Marcy, an exoplanet astronomer at the University of California, Berkeley.

「那兒離我們如此之近，你幾乎可以吐口痰過去，」來自加州大學伯克利分校(University of California, Berkeley)研究太陽系外行星的天文學家傑弗里·馬西(Geoffrey Marcy)這樣說。

Sara Seager, an astronomer at the Massachusetts Institute of Technology, said in an e-mail, 「I feel like we should drop everything and send a probe there to study the new planet and others that are likely in the system.」

麻省理工學院(Massachusetts Institute of Technology)的薩拉·西格(Sara Seager)在一封郵件中說，「我恨不得放下手中所有的事情，發一個航天探測器到那裡，來研究這個新行星和那個星系可能存在的其他行星。」

There are three stars in that system. Alpha Centauri A, which is slightly larger and brighter than the Sun, and Alpha Centauri B, slightly smaller, are close companions, circling each other and passing as close as nine billion miles every 80 years. They in turn are being circled at a much greater distance, some one trillion miles, by a dwarf star that is known as Proxima Centauri because it is slightly closer to the Earth, due to that trillion miles, than the other two.

那個星系裡有三顆恆星。其中半人馬座阿爾法星A，體積比太陽稍大、亮度也更高，半人馬座阿爾法星B，比太陽稍小些；它們是伴星，圍繞彼此運轉，每80年會在一個最近距離約14億公里的位置相匯。而一個名為比鄰星(Proxima Centauri)的矮星，在距這兩顆恆星約2萬億公里的軌道上繞著它們運轉。之所以叫比鄰星是因為，這個矮星離地球最近，比阿爾法星AB近約2萬億公里。

The so-called habitable zone of Alpha Centauri B, where temperatures would be moderate enough for water and creatures like us, is about 65 million miles from the star, where a year would take 200 days or so, about the same as the orbit of Venus in our own system.

半人馬座阿爾法星B所謂的宜居帶，也就是氣溫適中、可以有液態水、適合我們這樣的生物生存的區域，距該恆星約1億公里遠。如果這裡有顆行星，其一年約有200天左右，與太陽系裡金星的軌道周期大致相同。

Mr. Dumusque and his colleagues found the planet by the so-called wobble method, using a specially built spectrograph called HARPS on a 140-inch diameter telescope at the European Southern Observatory in La Silla, Chile, to track the host star as it is tugged to and fro by the planet』s gravity. After four years and 450 observations, they found that in the case of Alpha Centauri B, that tug imparts a velocity of about 20 inches a second, a leisurely walking speed.

杜穆斯克和他的同事用所謂的「多普勒方法」發現了這顆行星。他們用名為高精度徑向速度行星搜索器(HARPS)的特殊光譜儀，來探測恆星受其行星引力影響而產生的微小速度變化。HARPS光譜儀安裝在位於智利拉西拉(La Silla)歐洲南方天文台的一台直徑為3.6米的望遠鏡上。他們在四年的時間裡進行了450次觀測，發現半人馬座阿爾法星B受行星引力影響而產生的速度擺動約為每秒0.5米，相當於緩慢的步行速度。

That is the smallest wobble the Swiss team has ever observed.

這是該瑞士團隊觀測到的最小的速度擺動。

A planet only four times as massive as the Earth would produce the same amount of wobble if it was out in the habitable zone and would thus be detectable by their instrument, Mr. Dumusque said. But it would take a long time. 「If you want to find a planet at 200 days,」 he said referring to the orbital period, 「you need 8 to 10 years.」

杜穆斯克說，一顆質量僅為地球四倍的行星，如果它位於半人馬座阿爾法星B的宜居帶，它的引力將使恆星產生同樣大小的速度擺動，因此會被他們的儀器探測到。但這需要更長的時間。他說，「發現一顆周期為200天的行星需要八到十年的時間」，200天是位於半人馬座阿爾法星B宜居帶行星的軌道周期。

Dr. Marcy said this was the kind of discovery that could reignite interest in other experiments like the Terrestrial Planet Finder, a space observatory for studying exoplanets that was once at the top of NASA』s wish list but is now languishing.

馬西博士說，這樣的新發現將重新激起人們對其他試驗的興趣，比如類地行星搜索者(Terrestrial Planet Finder)，這個探索系外行星的太空望遠鏡計劃曾排在美國國家航空航天局(NASA)的希望一覽表的首位，但後來被打入冷宮。

Two years ago, Dr. Marcy startled his colleagues at an M.I.T. symposium with a bitter criticism of NASA, the National Academy of Sciences and the planetary community itself for failing to define and sell advanced exoplanet missions. He went on to call for an international project to launch a scientific probe to Alpha Centauri.

兩年前，馬西博士在麻省理工學院的一次研論會上嚴厲批評了NASA、美國國家科學院(National Academy of Sciences)以及行星學術界本身，指責他們在確立和推動先進系外行星太空項目上的失敗，很讓同事們震驚。她接下來呼籲開展一個國際項目，向半人馬座阿爾法星系發射科學探測器。

It could take hundreds of years, but such a mission, Dr. Marcy said, could jolt NASA out of its doldrums.

馬西說，這可能需要幾百年的時間，但這樣的太空項目也許能激勵NASA改變其萎靡不振的狀態。

The new planet, Dr. Marcy said, 「fits right into that rant.」 He went on, 「What a great scientific educational mission to have a probe out there, making its way decade after decade.」

馬西說，新行星的發現「映證了那次慷慨陳詞」。她繼續說道，「一個遙遠的探測器，十幾年、幾十年地在太空向目的地飛行，那將是一個具有多麼偉大的科學和教育意義的項目」。

翻譯：谷菁璐、任芯序