綜合類：閱讀理解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."
詞匯：
Saturn /s?t?n/ n．土星 methane/mi:θein/ n．甲烷，沼氣
Titan/tait?n/ n．土衛六 acetylene
setili:n/ n．乙炔
alien/eilj?n/ n．外星人；adj．外星球的；相異的
conservatism/k?ns?:v?tiz?m/ n．保守主義，守舊
注釋：
1.hints of alien life：外星生命跡象。
2.the Saturns moon：指土衛六（Titan) 。土衛六又稱泰坦星，是土星衛星中最大的一顆。
3.NASA：美國國家航空航天局的縮寫，全稱是： National Aeronautics and SpaceAdministration.
4.spacecraft Cassini：卡西尼號探測器，以出生于意大利的法國天文學家卡西尼的名字命名，其任務是環繞土星飛行，對土星及其大氣、光環、衛星和磁場進行深人考察。1997 年10 月15日，重六噸的"卡西尼"號星際探測器被發射飛往土星的軌道。這是上世紀發射的最后一艘行星際探測的大飛船。"卡西尼"號用了將近七年時間，在2004 年7月1日飛達土星軌道。
5.bugs：微生物。非正式口語表達，所以使用了引號。
6.Kelvin：可翻譯成"絕對溫度"。Kelvin Scale ，絕對溫標，開氏溫標，是由Kelvin 勛爵于19世紀中葉發明的溫度計量方法，其零度相當于攝氏一273. 15" C ，被認為是宇宙中最低溫度。這種溫度計量方法多為科學家使用。
7.principal investigator：研究項目負責人
8.rule out：排除……的可能性