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1、*第三＋八篇"LifeFormFound"onSaturn'sTitanScientistssaytheyhavediscoveredhintsofalienlife1ontheSaturn'smoon2.ThediscoveryofasortoflifewasannouncedafterresearchersattheUSspaceagency,NASA3,analyzeddatafromspacecraftCassini4,whichpointedto,theexistenceofmethane-basedformoflifeonSaturn'sb
2、iggestmoon.Scientistshavereportedlydiscoveredcluesshowingprimitivealienbeingsare"breathing"inTitan'sdenseatmospherefilledwithhydrogen.TheyarguethathydrogengetsabsorbedbeforehittingTitan'splanet-likesurfacecoveredwithmethanelakesandrivers.This,theysay,pointstotheexistenceofsome"b
3、ugs"5consumingthehydrogenatthesurfaceofthemoonlessthanhalfthesizeoftheEarth."Wesuggestedhydrogenconsumptionbecauseit'stheobviousgasforlifetoconsumeonTitan,similartothewayweconsumeoxygenonEarth,"saysNASAscientistChrisMcKay."Ifthesesignsdoturnouttobeasignoflife,itwouldbedoublyexci
4、tingbecauseitwouldrepresentasecondformoflifeindependentfromwater-basedlifeonEarth."Todate,scientistshavenotyetdetectedthisformoflifeanywhere,thoughthereareliquid-water-basedmicroorganismsonEarththatgrowwellonmethaneorproduceitasawasteproduct.OnTitan,wheretemperaturesarearound90K
5、elvin6(minus290degreesFarenheit),amethanebasedorganismwouldhavetouseasubstancethatisliquidasitsmediumforlivingprocesses,butnotwateritself.WaterisfrozensolidonTitan'ssurfaceandmuchtoocoldtosupportlifeasweknowit.ScientistshadexpectedtheSun'sinteractionswithchemicalsintheatmosphere
6、toproduceacoatingofacetyleneonTitan'ssurface.ButCassinidetectednoacetyleneonthesurface.TheabsenceofdetectableacetyleneontheTitan'ssurfacecanverywellhaveanon-biologicalexplanation,saidMarkAllen,aprincipalinvestigator7oftheNASATitanteam."Scientificconservatismsuggeststhatabiologic
7、alexplanationshouldbethelastchoiceafterallnon-biologicalexplanationsareaddressed,"Allensaid."Wehavealotofworktodotoruleout8possiblenon-biologicalexplanations.Itismorelikelythatachemicalprocess,withoutbiology,canexplaintheseresults."词汇：Saturn/'sætən/n．土星methane/'mi:θein/n．甲烷，沼气Ti
8、tan/'taitən/n．土卫六acetylene/ə'setili:n/n．乙炔alien
