Life Form Found on Saturns Titan
Scientists say they have discovered hints of alien life1 on the Saturns moon2. The discovery of a sort of life was announced after researchers at the US space agency,NASA3,analyzed data from spacecraft Cassini4,which pointed to,the existence of methane-based form of life on Saturns biggest moon.
They argue that hydrogen gets absorbed before hitting Titans planet-like surface covered with methane lakes and rivers. This,they say,points to the existence of somebugs5 consuming the hydrogen at the surface of the moon less than half the size of the Earth.
To date,scientists have not yet detected this form of life anywhere,though there are liquid-water-based microorganisms on Earth that grow well on methane or produce it as a waste product. On Titan, where temperatures are around 90 Kelvin6,a methanebased organism would have to use a substance that is liquid as its medium for living processes, but not water itself. Water is frozen solid on Titans surface and much too cold to support life as we know it.
The absence of detectable acetylene on the Titans surface can very well have a non-biological explanation,said Mark Allen,a principal investigator7 of the NASA Titan team.
词汇：
methane n.甲烷，沼气
acetylene n.乙炔
conservatism n.保守主义,守旧
1.hints of alien life：外星生命迹象。
3.NASA：美国国家航空航天局的缩写，全称是： National Aeronautics and Space Administration。
5.bugs：微生物。非正式口语表达，所以使用了引号。
7.principal investigator：研究项目负责人
练习：
A They have found a new moon orbiting Saturn.
C They have found methane-based life on Titan.
2. What do scientists say about Titan?
B There is acetylene there.
D Rivers and lakes there contain life formls.
A Water-based life.
C Liquid-water-based microorganisms.
4. What can be inferred from what Allen said?
B Scientists all agree that there is life on Titan.
D Scientists all agree that a non-biological chemical reaction is a possible explanation.
A Earthlike Living Beings Found on Titan.
C Titan,a New Satellite Found.
答案与题解：
2.A根据第二段Scientists have reportedly discovered clues showing primitive alien beings are breathing in Titans dense atmosphere filled with hydrogen.，说明土卫六有生命迹象。因此A是答案。
4.A科学家至今对土卫六是否存在生物有不同的观点和解释。Allen 说要做出土卫六上有生
5.D该短文的主题是，科学家在土卫六上发现了一种与地球生物不同的生命形式的迹象，即以甲烷为生命基础呼吸氢气的生物，但科学家还未能最后验证这一发现。第四段中的一个句子能够揭示该短文的主题：If these signs do turn out to be a sign of life, it would bedoubly exciting because it would represent a second form of life independent from water-based life on Earth.