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1、*第三＋八篇"LifeFormFound"onSaturn'sTitanScientistssaytheyhavediscoveredhintsofalienlife1ontheSaturn'smoon2.ThediscoveryofasortoflifewasannouncedafterresearchersattheUSspaceagency,NASA3,analyzeddatafromspacecraftCassini4,whichpointedto,theexistenceofmethane-basedformoflifeonSaturn'sbiggestmoon.Sc
2、ientistshavereportedlydiscoveredcluesshowingprimitivealienbeingsare"breathing"inTitan'sdenseatmospherefilledwithhydrogen.TheyarguethathydrogengetsabsorbedbeforehittingTitan'splanet-likesurfacecoveredwithmethanelakesandrivers.This,theysay,pointstotheexistenceofsome"bugs"5consumingthehydrogena
3、tthesurfaceofthemoonlessthanhalfthesizeoftheEarth."Wesuggestedhydrogenconsumptionbecauseit'stheobviousgasforlifetoconsumeonTitan,similartothewayweconsumeoxygenonEarth,"saysNASAscientistChrisMcKay."Ifthesesignsdoturnouttobeasignoflife,itwouldbedoublyexcitingbecauseitwouldrepresentasecondformo
4、flifeindependentfromwater-basedlifeonEarth."Todate,scientistshavenotyetdetectedthisformoflifeanywhere,thoughthereareliquid-water-basedmicroorganismsonEarththatgrowwellonmethaneorproduceitasawasteproduct.OnTitan,wheretemperaturesarearound90Kelvin6(minus290degreesFarenheit),amethanebasedorgani
5、smwouldhavetouseasubstancethatisliquidasitsmediumforlivingprocesses,butnotwateritself.WaterisfrozensolidonTitan'ssurfaceandmuchtoocoldtosupportlifeasweknowit.ScientistshadexpectedtheSun'sinteractionswithchemicalsintheatmospheretoproduceacoatingofacetyleneonTitan'ssurface.ButCassinidetectedno
6、acetyleneonthesurface.TheabsenceofdetectableacetyleneontheTitan'ssurfacecanverywellhaveanon-biologicalexplanation,saidMarkAllen,aprincipalinvestigator7oftheNASATitanteam."Scientificconservatismsuggeststhatabiologicalexplanationshouldbethelastchoiceafterallnon-biologicalexplanationsareaddress
7、ed,"Allensaid."Wehavealotofworktodotoruleout8possiblenon-biologicalexplanations.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
