宜居行星不斷髮現 卻依舊神祕難測

It’s a big universe, but it’s full of small planets.

這是一個很大的宇宙，但卻充滿了小型的行星。

A group of astronomers led by Guillermo Torres of the Harvard-Smithsonian Center for Astrophysics announced on Tuesday that they had found eight new planets orbiting their stars at distances compatible with liquid water, bringing the total number of potentially habitable “Goldilocks planets” to a few dozen, depending on how the habitable zone is defined.

週二，以哈佛-史密森尼天體物理中心(Harvard-Smithsonian Center for Astrophysics)的吉耶爾莫·托裏斯(Guillermo Torres)爲首的一組天文學者宣佈，他們新發現有八顆行星在容許液態水存在的距離圍繞它們的恆星運行。這樣一來，可能適宜居住的“適居帶(Goldilocks)行星”的總數就上升到了數十顆。當然，這還取決於如何定義適居帶。

NASA’s Kepler spacecraft, now in its fifth year of seeking out the shadows of planets circling other stars, has spotted hundreds, and more and more of these other worlds look a lot like Earth — rocky balls only slightly larger than our own home, that with the right doses of starlight and water could turn out to be veritable gardens of microbial Eden.

美國國家航空航天局(NASA)的開普勒(Kepler)太空望遠鏡目前已進入搜尋圍繞其他恆星旋轉的行星的陰影的第五年。它已經發現了數百個，以及越來越多與地球十分相似的世界——只比我們的家園地球體積稍大的石球，只要有適量的光和水，就可能會成爲名副其實的微生物伊甸園。

As the ranks of these planets grow, astronomers are beginning to plan the next step in the quest to end cosmic loneliness, gauging which hold the greatest promise for life and what tools will be needed to learn about them.

隨着此類行星的數量不斷增加，天文學者開始計劃相關探索的下一步，測算哪顆行星存在生命的可能性最大，以及瞭解它們需要什麼工具，從而終結我們在宇宙中的孤獨感。

On Monday another group of astronomers said they had managed to weigh precisely a set of small planets and found that their densities and compositions almost exactly matched those of Earth. Both groups announced their findings at a meeting of the American Astronomical Society in Seattle.

週一，另一組天文學者表示，他們已經成功精確計算出了一系列小行星的重量，發現它們的密度和構成幾乎與地球完全一致。這兩組天文學者都在西雅圖的美國天文學會 (American Astronomical Society)的會議上公佈了自己的研究結果。

Alluding to the popularity of food shows and cooking apps, Courtney Dressing, also of the Harvard-Smithsonian Center for Astrophysics, said at a news conference, “I’m going to give you the recipe for a rocky planet.”

同樣來自哈佛-史密森尼天體物理中心的考特妮·德雷辛(Courtney Dressing)在新聞發佈會上借用美食節目和烹飪軟件的話說，“我現在要告訴你該如何製作巖態行星。”

She began, “Take one cup of magnesium....”

她說，“用一杯鎂……”

Reviewing the history of exoplanets, Debra Fischer, a Yale astronomer, recalled that the first planet found orbiting another sunlike star, a Jupiter-like giant, was discovered 20 years ago. Before that, she recalled, astronomers worried that “maybe the Star Trek picture of the universe was not right, and there is no life anywhere else.”

耶魯大學(Yale)天文學者德布拉·費希爾(Debra Fischer)在回顧系外行星曆史時說，第一次發現圍繞類似太陽的恆星運行的行星是在20年前。這顆行星很像木星，體積巨大。她回憶道，在那之前，天文學者擔心“或許《星際迷航》(Star Trek)中的宇宙景象是不正確的，其他地方根本沒有生命”。

She termed the progress in the last two decades “incredibly moving.”

她表示，過去20年的進步“十分驚人”。

So far, Kepler has discovered 4,175 potential planets, and 1,004 of them have been confirmed as real, according to Michele Johnson, a spokeswoman at NASA’s Ames Research Center, which operates Kepler.

負責運行開普勒的NASA艾姆斯研究中心(NASA Ames Research Center)的女發言人米歇爾·約翰遜(Michele Johnson)稱，迄今，開普勒已經發現了4175顆疑似行星，其中有1004顆已經得到證實。

Most of them, however, including the new ones announced Tuesday, are hundreds of light-years away, too far for detailed study. We will probably never know any more about these particular planets than we do now, including whether anybody can or does live on them.

不過，它們中的大多數，其中包括週二宣佈的新發現的行星都距離地球數百光年，因爲太遠，而不適合進行詳細研究。我們對於這些特殊行星的瞭解，或許永遠無法比現在更多，其中包括人們是否能夠，以及是否有人在這些行星上生存。

“We can count as many as we like,” said Sara Seager, a planet theorist at the Massachusetts Institute of Technology who was not involved in the new work, “but until we can observe the atmospheres and assess their greenhouse gas power, we don’t really know what the surface temperatures are like.”

“我們可以想數出多少就數出多少，”麻省理工學院（Massachusetts Institute of Technology，簡稱MIT）的行星理論家薩拉·西格(Sara Seager)說，“但在能夠觀察它們的大氣，評定它們的溫室氣體含量之前，我們無法真正瞭解它們的地表溫度。”她並沒有參與這項新研究。

Still, she added, “it’s heartening to have such a growing list.”

不過，她補充道，“這樣的行星越來越多，也很令人鼓舞。”

Finding Goldilocks planets closer to home will be the job of TESS, the Transiting Exoplanet Survey Satellite, scheduled to be launched in 2017. But if we want to know what the weather is like on these worlds, whether there is water or even life there, more powerful instruments will be needed.

尋找離地球較近的適居帶行星將是凌日系外行星勘測人造衛星（Transiting Exoplanet Survey Satellite，簡稱TESS）的任務。這種衛星將於2017年發射。但是，如果我們想知道這些行星上的天氣狀況、上面是否有水乃至生命，還需要更強大的工具。

Dr. Seager is heading a NASA study investigating the concept of a starshade, which would float in front of a space telescope and block light from a star so that its much fainter planets would be visible, the way a driver flips down a shade to block the glare of the sun.

西格正在負責一項研究遮星板(starshade)概念的NASA研究。這種遮星板將漂浮在太空望遠鏡前方，遮擋恆星發出的光，這樣就能看見它比較暗淡的行星了，就像司機拉下遮陽板擋住刺眼的陽光那樣。

Another group, led by Karl Stapelfeldt of NASA’s Goddard Space Flight Center, is studying the alternative method known as a coronagraph, in which the occulting disk is inside the telescope.

由NASA戈達德航天中心(Goddard Spaceflight Center)的卡爾·斯塔佩爾費爾德特(Karl Stapelfeldt)所帶領的另一個小組正在研究被稱作日冕儀(coronagraph)另一種辦法。根據這種辦法，擋板會被放在望遠鏡裏面。

Both studies are expected to be completed in the next couple of months, and could affect plans to repurpose a former spy telescope, a clone of sorts of the Hubble, that was bequeathed to NASA three years ago by the National Reconnaissance Office. Astronomers hope to launch it in the early 2020s to study dark energy, under the unwieldy name of Wfirst/ are planning for now to include a coronagraph to search for exoplanets, according to Paul Schechter of M.I.T., chairman of a design team. Depending on the probe’s orbit, said Dr. Seager, it could be also be made “starshade ready.”

兩項研究都有望在未來幾個月內完成，它們可能影響到改變原來的間諜望遠鏡的使用目的的計劃。這種望遠鏡是對哈勃(Hubble)望遠鏡的一種複製，三年前由國家偵察局(National Reconnaissance Office)贈送給NASA。天文學者希望能在本世紀20年代初將其發射升空，用來研究暗能量。它有個複雜的名字，叫做寬視場紅外巡天望遠鏡/天體物理學專用資產(Wfirst/Afta)。某設計團隊的主席、來自MIT的保羅·謝克特(Paul Schechter)表示，他們目前正計劃在上面安裝一臺日冕儀，用來搜索系外行星。西格說，根據這個探測器的軌道，還可以對它進行調整，使之“能夠使用遮星板”。

NASA’s James Webb Space Telescope, due for a 2018 launch, will have a coronagraph capable of seeing Jupiter-size planets, but it is too late to adapt it to a star shade.

NASA的詹姆斯·韋伯太空望遠鏡(James Webb Space Telescope)將於2018年發射，它上面也將安裝一臺能看到木星大小的行星的日冕儀，但現在已經來不及對它進行調整，使它能使用遮星板。

Meanwhile, Dr. Seager and Julianne Dalcanton of the University of Washington are writing a separate report for AURA, a consortium of universities that runs observatories. The goal is have a pool of dozens of “exoEarths” to study in order to have any chance of seeing signs of life or understanding terrestrial planets, Dr. Seager said. Amassing them will require a space telescope 10 or 12 meters in diameter (the Webb will be 6.5, and the largest currently on Earth is 10).

同時，西格和華盛頓大學(University of Washington)的朱莉安娜·達爾坎頓(Julianne Dalcanton)正分別在爲AURA撰寫一篇報告。AURA是一個負責天文臺運營的大學聯盟。西格說，他們是想對數十個“系外地球”(exoEarth)進行研究，看看是否有機會發現生命跡象或瞭解類地行星。要想積累這麼多的行星，需要一臺直徑爲10或12米的太空望遠鏡（韋伯太空望遠鏡的直徑將爲6.5米；目前，地球上直徑最大的是10米）。

All of this will be grist for the mill at the end of the decade when a panel of the National Academy of Sciences produces its decadal and very influential wish list for astronomy in the 2020s.

到這一個10年臨近結束、國家科學院(National Academy of Sciences)的工作小組爲天文學擬定極有影響力的20年代十年規劃時，這一切都將非常有用。