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1、*第三＋八篇"LifeFormFound"onSaturn'sTitanScientistssaytheyhavediscoveredhintsofalienlife1ontheSaturn'smoon2.ThediscoveryofasortoflifewasannouncedafterresearchersattheUSspaceagency,NASA3,analyzeddatafromspacecraftCassini4,whichpointedto,theexistenceofmethane-basedf
2、ormoflifeonSaturn'sbiggestmoon.Scientistshavereportedlydiscoveredcluesshowingprimitivealienbeingsare"breathing"inTitan'sdenseatmospherefilledwithhydrogen.TheyarguethathydrogengetsabsorbedbeforehittingTitan'splanet-likesurfacecoveredwithmethanelakesandrivers.T
3、his,theysay,pointstotheexistenceofsome"bugs"5consumingthehydrogenatthesurfaceofthemoonlessthanhalfthesizeoftheEarth."Wesuggestedhydrogenconsumptionbecauseit'stheobviousgasforlifetoconsumeonTitan,similartothewayweconsumeoxygenonEarth,"saysNASAscientistChrisMcK
4、ay."Ifthesesignsdoturnouttobeasignoflife,itwouldbedoublyexcitingbecauseitwouldrepresentasecondformoflifeindependentfromwater-basedlifeonEarth."Todate,scientistshavenotyetdetectedthisformoflifeanywhere,thoughthereareliquid-water-basedmicroorganismsonEarththatg
5、rowwellonmethaneorproduceitasawasteproduct.OnTitan,wheretemperaturesarearound90Kelvin6(minus290degreesFarenheit),amethanebasedorganismwouldhavetouseasubstancethatisliquidasitsmediumforlivingprocesses,butnotwateritself.WaterisfrozensolidonTitan'ssurfaceandmuch
6、toocoldtosupportlifeasweknowit.ScientistshadexpectedtheSun'sinteractionswithchemicalsintheatmospheretoproduceacoatingofacetyleneonTitan'ssurface.ButCassinidetectednoacetyleneonthesurface.TheabsenceofdetectableacetyleneontheTitan'ssurfacecanverywellhaveanon-bi
7、ologicalexplanation,saidMarkAllen,aprincipalinvestigator7oftheNASATitanteam."Scientificconservatismsuggeststhatabiologicalexplanationshouldbethelastchoiceafterallnon-biologicalexplanationsareaddressed,"Allensaid."Wehavealotofworktodotoruleout8possiblenon-biol
8、ogicalexplanations.Itismorelikelythatachemicalprocess,withoutbiology,canexplaintheseresults."词汇：Saturn/'sætən/n．土星methane/'mi:θein/n．甲烷，沼气Titan/'taitən/n．土卫六acetylene/ə'setili:n/n．乙炔alien
