The Kepler mission, for example, has confirmed and announced seven new alien worlds to date.

例如，开普勒任务至今已经证实并宣布了7个新的外星世界。

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The Kepler mission has the opposite problem: it can measure a planet's size, by how much starlight it blocks, but not the mass.

而开普勒行动则存在截然相反的问题：它能通过一个行星的遮光情况测出它的体积，却不能得出其质量。

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But, he estimated that pinpointing any Earth-like planets is still a few years off-near the end of the Kepler mission as it stands.

但是，他估计定位这样一个行星还需要几年时间——知道开普勒计划的末期。

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But the Kepler mission's chief scientist, William Borucki,says eighty percent of the possible planets will probably be confirmed in the coming months and years.

VOA: special.2011.02.09

That's what we'll be seeing as the years go on with the Kepler mission, because it was designed to find many Earths.

BBC: Kepler telescope: Earth-sized planets 'number 17bn'

William Borucki, the driving force behind and principal investigator on the Kepler mission, said he was "delighted" by the fresh batch of results.

BBC: Kepler telescope: Earth-sized planets 'number 17bn'

Dr Boss estimates that Nasa's Kepler mission, due for launch in March, should begin finding some of these Earth-like planets within the next few years.

BBC: Galaxy has 'billions of Earths'