Kepler Finds 1,284 New Planets
By DENNIS OVERBYE

Planets keep falling out of the sky for the Kepler spacecraft. And as their number grows, so grows the age-old dream of ending human cosmic loneliness.

Astronomers operating NASA’s planet-finding spacecraft announced Tuesday that they had validated the planethood of 1,284 new candidates from Kepler’s voluminous catalog of potential exoplanets, the largest collection of new planets announced at one time. It brings the total of actual planets Kepler has discovered to more than 2,000.

All of them orbit stars in a patch of sky on the Cygnus-Lyra border, where Kepler, launched in 2009, spent four years staring at 150,000 stars looking for the characteristic dimming when planets crossed their faces, until its pointing system broke down and the team had to develop a new observing strategy. Since then, Kepler has identified some 4,700 possible planets, and more keep being found.

In the past, it took lengthy and arduous ground-based telescopic observations to winnow impostors like double stars and other pretenders from the planet list. But the numbers have grown too large, the cosmos too verdant, for this case-by-case analysis.

The new results rely on a statistical technique developed by Timothy Morton, an astronomer at Princeton University, to vet the potential candidates in bulk, by analyzing the shape of the dips they make in starlight and taking into account how common the various types of impostors are and assigning a reliability score to each one.

“Planet candidates can be thought of like bread crumbs,” said Dr. Morton in a NASA teleconference on Tuesday. “If you drop a few large crumbs on the floor, you can pick them up one by one. But if you spill a whole bag of tiny crumbs, you’re going to need a broom. This statistical analysis is our broom.”

So far, two dozen of the planets found and confirmed by Kepler occupy the so-called Goldilocks zones of their stars where liquid water and perhaps “Life as We Think We Know It” could exist.

Extrapolating these results to the entire galaxy, Natalie Batalha, Kepler mission scientist from the Ames Research Center, said there could be 10 billion roughly Earth-size planets in the galaxy within their stars’ habitable zones. The nearest habitable planet, she estimated, could be as close as 11 light-years. In the cosmic scheme of things, that is next door and reachable in our lifetimes with current or near-future technology. Last month, scientists announced a plan to try to send smartphone-like spacecraft to Alpha Centauri, which is 4.4 light-years away.

Kepler was conceived as a mission to determine how common Earth-size planets, possible habitable rocks, are in the universe. The Kepler team, Dr. Batalha said, is now approaching in the next year or two the closeout of that mission, one that has helped change humanity’s view of how friendly the cosmos might be to life, and has made exoplanets one of the most explosive fields in astronomy.

That quest will go on. Kepler will be passing the baton to future missions like NASA’s TESS, which will search for planets around nearby bright stars, starting in 2017.

系外行星 再發現9顆可能有水

美國太空總署（NASA）10日宣布，克卜勒太空望遠鏡在太陽系之外又發現1284顆行星，其中九顆可能有適合生物居住的水。

這是克卜勒2009年3月啟用以來，單次發現系外行星數量最多的一次，使得目前已確定的系外行星總數達到3264顆。科學家這次以新的分析技術，利用一套稱為Vespa的自動軟體系統，證實這批1284顆行星，它們是克卜勒在為期四年的初期任務中發現的，該任務已在2013年結束。

NASA天體物理學部門主管赫茲表示，太空總署對太陽系外研究的目的之一，就是回答地球是否是宇宙中唯一適合生物居住之地，而回答這個問題的第一步，就是偵測並了解其他星系行星的數量。他說：「我們現在知道，行星的數量可能比恆星多。」

1284顆系外行星中，將近550顆可能是類似地球的多岩石星球，其中九顆從其與恆星的距離來推測，氣溫大約是可能有水的範圍內，這使得目前已知可能適合生物居住的系外行星增加到21顆。

NASA華盛頓總部首席科學家史托方說：「這給了我們一線希望：在某個地方，圍繞類似我們太陽的某顆恆星，我們終將發現另一個地球。」

克卜勒任務科學家貝塔哈博士表示，計算結果顯示，銀河裡可能有數百億顆可居住的行星。她告訴英國廣播公司說：「如果你問下一個可居住行星在那裡，就在距離地球約11光年內，非常近。」

克卜勒太空望遠鏡自2009年3月發射升空以來，已審視15萬顆恆星，看是否有繞行的星體，特別是可以支持生命的星體。NASA在聲明中表示，在截至目前所發現的將近5000顆候選行星中，已有3200顆獲得證實，其中2325顆是克卜勒所發現。

原文參照：
http://www.nytimes.com/2016/05/11/science/kepler-planets-nasa.html

2016-05-11．聯合晚報．A6．國際焦點．編譯馮克芸