综合类：阅读理解Life Form Found
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.
Scientists have reportedly discovered clues showing primitive alien beings are"breathing" inTitans dense atmosphere filled with hydrogen.
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 some"bugs"5 consuming the hydrogen at the surface of the moon less than half the size of the Earth.
"We suggested hydrogen consumption because its the obvious gas for life to consume on Titan，similar to the way we consume oxygen on Earth，"says NASA scientist Chris McKay."If these signs do turn out to be a sign of life，it would be doubly exciting because it would represent a second form of life independent from water-based life on 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(minus 290 degrees Farenheit)，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.
Scientists had expected the Suns interactions with chemicals in the atmosphere to produce a coating of acetylene on Titans surface. But Cassini detected no acetylene on the surface.
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.
"Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed，"Allen said. "We have a lot of work to do to rule out8 possible non-biological explanations. It is more likely that a chemical process，without biology，can explain these results."
词汇：
Saturn /s?t?n/ n．土星 methane/mi:θein/ n．甲烷，沼气
Titan/tait?n/ n．土卫六 acetylene
setili:n/ n．乙炔
alien/eilj?n/ n．外星人；adj．外星球的；相异的
conservatism/k?ns?:v?tiz?m/ n．保守主义，守旧
注释：
1.hints of alien life：外星生命迹象。
2.the Saturns moon：指土卫六（Titan) 。土卫六又称泰坦星，是土星卫星中最大的一颗。
3.NASA：美国国家航空航天局的缩写，全称是： National Aeronautics and SpaceAdministration.
4.spacecraft Cassini：卡西尼号探测器，以出生于意大利的法国天文学家卡西尼的名字命名，其任务是环绕土星飞行，对土星及其大气、光环、卫星和磁场进行深人考察。1997 年10 月15日，重六吨的"卡西尼"号星际探测器被发射飞往土星的轨道。这是上世纪发射的最后一艘行星际探测的大飞船。"卡西尼"号用了将近七年时间，在2004 年7月1日飞达土星轨道。
5.bugs：微生物。非正式口语表达，所以使用了引号。
6.Kelvin：可翻译成"绝对温度"。Kelvin Scale ，绝对温标，开氏温标，是由Kelvin 勋爵于19世纪中叶发明的温度计量方法，其零度相当于摄氏一273. 15" C ，被认为是宇宙中最低温度。这种温度计量方法多为科学家使用。
7.principal investigator：研究项目负责人
8.rule out：排除……的可能性