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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.
近日，美国宇航局发现火星曾存在生物体的“有力证据“，这一结论是在该机构对一枚陨星进行重新检测后得出的。
位于休斯敦约翰逊宇航中心的一个研究小组对1.3万年前撞击南极洲的一枚陨星进行了再次分析，发现了迄今为止可证明火星曾存在细菌生命体的最有说服力的证据。
研究小组称，他们在岩石上发现的微小晶体几乎可以断定是石化细菌，这些细菌和地球上的细菌有很多共同特征。
美国宇航局探测和天体生物学首席科学家戴维•麦凯说：“在过去十年间，火星可能曾存在生命体的证据逐渐增多。”
“这其中包括火星曾存在地表水的证据，如河流、湖泊、甚至可能大海残留的痕迹;以及地表或地表附近存在水流的证据。”
有关火星存在生命体的争论主要集中在这块陨星中所发现的磁性晶体上。1996年开展的一项研究认为，这些晶体是有机生物体的生命遗迹。
但批评人士认为，这枚陨星是在热分解的化学过程中形成的。
为反驳批评人士的说法，新的研究报告使用更先进的仪器进行检测，并称远古生命遗迹是最合理的解释。
美国宇航局科学家艾弗瑞特•吉布森说：“我们相信，现今有关火星存在生物体的假设比13年前刚提出时更有说服力了。”
Vocabulary:
harbour：to house or contain(包含，藏有)
microscopic：so small as to be invisible or indistinct without the use of
the microscope(用显微镜可见的，精微的)
biogenic：produced by living organisms or biological processes(源于生物的)
thermal：of, pertaining to, or caused by heat or temperature(热的，热量的) |
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发表于 2016-7-10 17:43:07