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How can we search for life on exoplanets? Step one: examine the Earth as if it were an exoplanet. That’s the idea behind a recent look at earthshine.
我們怎樣尋找（太陽）系外行星上的生命？步驟一：把地球當做一個（太陽）系外行星進行研究。這是研究人員最近根據地球反照光想到的一個辦法。
Researchers aimed what’s officially called the Very Large Telescope, housed at the European Southern Observatory, at the moon. They measured earthshine: sunlight that reflects off the Earth, hits the moon and bounces back.
研究人員通過設在歐洲南方天文臺的超大望遠鏡觀測了地球照射在月球的反照光。他們對地球的反照光進行了測量：太陽光被地球反射到月球，然后又反射回來。
The scientists are looking for hints of life in the light—such as evidence of the gases associated with organic life. Such gas signatures are generally tough to find, because any planetary light is swamped by the light of its host star.
科學家們在反射光中尋找生命的跡象——例如，尋找同有機生命相關的氣體存在的證據。這種氣體一般很難找到，因為任何行星的光線往往淹沒在主星的光線中。
But in this effort, the research team also took into account polarized light. Because light reflected off a planet is polarized. But light from the star is not.
但通過這方面的努力，該研究小組還考慮到了偏振光的因素。因為行星的反照光往往會出現偏振，但恒星發出的光則不會如此。
The analysis of earthshine correctly revealed that the planet it came from has a partly cloudy atmosphere and is covered with oceans and some vegetation. The researchers could even ascertain changes in cloud cover and vegetation as the Earth turned. The research was published in the journal Nature.
對地球反照光的分析顯示：這個行星擁有一個云霧大氣層，還被海洋和一些植被所覆蓋。研究人員甚至可以確定地球轉動過程中的云層和植被所出現的變化。這項研究結果發表在《自然》雜志上。
Similar scrutiny of actual exoplanets may one day reveal the first good suspects for harboring life—via their light.
這種對系外行星反照光的類似分析也許有一天能夠找到其它暗藏生命的行星。
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