Nasa has found what it calls 「strong evidence」 that life once existed on Mars after re-examining a meteorite.
A research team at Johnson Space Centre in Houston has been re-examining a meteorite that hit Antarctica 13,000 years ago, and found the most compelling evidence yet that the planet once harboured bacterial life.
The team says that microscopic crystals found in the rock are almost certainly fossilised bacteria that have many characteristics in common with bacteria found on Earth.
「The evidence supporting the possibility of past life on Mars has been slowly building up during the past decade,」 said David McKay, Nasa chief scientist for exploration and astrobiology.
「This evidence includes signs of past surface water including remains of rivers, lakes and possibly oceans and signs of current water near or at the surface.」
The debate centres on magnetite crystals found in the meteorite. A study carried out in 1996 suggested that they were biogenic - produced by living organisms.
Critics, however, suggested that the magnetite was formed by a chemical process called thermal decomposition.
The new paper uses more advanced instruments to refute the critics』 theory, arguing that ancient life remains the most plausible explanation.
「We believe that the biogenic hypothesis is stronger now than when we first proposed it 13 years ago,」 said Everett Gibson, a Nasa scientist.
(Read by Guanny Liu. Guanny Liu is a multimedia journalist at the China Daily Web site.)
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(Agencies)
近日，美國宇航局發現火星曾存在生物體的「有力證據」，這一結論是在該機構對一枚隕星進行重新檢測後得出的。
位於休斯敦詹森宇航中心的一個研究小組對1.3萬年前撞擊南極洲的一枚隕星進行了再次分析，發現了迄今為止可證明火星曾存在細菌生命體的最有說服力的證據。
研究小組稱，他們在巖石上發現的微小晶體幾乎可以斷定是石化細菌，這些細菌和地球上的細菌有很多共同特徵。
美國宇航局探測和天體生物學首席科學家戴維•麥凱說：「在過去十年間，火星可能曾存在生命體的證據逐漸增多。」
「這其中包括火星曾存在地表水的證據，如河流、湖泊、甚至可能大海殘留的痕跡；以及地表或地表附近存在水流的證據。」
有關火星存在生命體的爭論主要集中在這塊隕星中所發現的磁性晶體上。1996年開展的一項研究認為，這些晶體是有機生物體的生命遺蹟。
但批評人士認為，這枚隕星是在熱分解的化學過程中形成的。
為反駁批評人士的說法，新的研究報告使用更先進的儀器進行檢測，並稱遠古生命遺蹟是最合理的解釋。
美國宇航局科學家艾弗瑞特•吉布森說：「我們相信，現今有關火星存在生物體的假設比13年前剛提出時更有說服力了。」
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（中國日報網英語點津 Julie 編輯蔡姍姍）