ITisalwayshardforasmallfishtoliveinabigpond.Pluto’srecentdeparture(离开)fromtheclassicalplanetfamilyclearlyprovesthatsizereallymatters.

AstronomersvotedonAugust24tocreatethefirstscientificdefinitionoftheword“planet”andPlutoobviouslydidn’tmakethecut.Itturnedouttobeonlya“dwarfplanet”(矮行星).

Afterweeksofheateddebateover2500astronomersfrom75countriesvotedonthedefinitionofa“planet”ataconferenceoftheInternationalAstronomicalUnion(IAU).Accordingtothedefinitionaplanetmusthaveaclearneighborhoodarounditsorbit(轨道).Plutohaswidelybeenconsideredaplanetsinceitsdiscoveryin1930.UnfortunatelyithasaspecialorbitwhichoverlapswithNeptune’s.ItisallbecausecomparedwithNeptunePlutoisverysmall.ItisattractedbyNeptune’sgravitywhenthetwoplanetsgetcloser.

AccordingtoIAU.a“dwarfplanet”shouldhaveanorbitaroundtheSun.Itwillnothaveaclearneighborhoodarounditsorbitandmustnotbeasatellite.Thenewclassificationmeansthatthesciencetextbookswillhavetobeupdated.Thesolarsystemisnowmadeupoftheeight“classicalplanets”togetherwithanumberofdwarfplanet.Theclassicalplanetsare:Mercury;VenusEarthMarsJupiterSaturnUranusandNeptune.ThedebateoverPlatesstatusstartedin1992.AfteranadvancedtelescopewassentintospaceastronomersstartedtofindabeltofobjectswhichliesbeyondNeptune.Thebeltcontainsnearly1000objectsincludingPluto.Astheycontinuedtheexplorationscientistsrecentlydiscoveredatleast41dwarfplanetsattheedgesofthesolarsystem.ThereareatleasttwoobjectsofasimilarsizetoPluto.

ItseemsthateveniftheIAUhadkeptPluto’sstatusasaplanettheclassicaltheoryofnineplanetsinthesolarsystemwouldhavehadtobechangedbuttheotherwayaround.MoredwarfplanetsofasimilarsizetoPlutowouldjointhefamilyofplanets.Scientistswillprobablyfindmanymoredwarfplanets.

1．AccordingtothepassagePlutois___________.

A．aplanetwhichhasaclearneighborhoodarounditsorbit

B．asatelliteofNeptunewhichwasdiscoveredin1930

C．isthesmallestplanetinthesolarsystem

D．aplanetwhichhasanorbitaroundthesun

2．These