第76章 对火星轨道变化问题的最后解释 (第7/12页)

asignifitextent.thisispartlybecausetheorbitaltime-scaleoftheplaheshortestofalltheplas，whichleadstoamorerapidorbitalevolutionthanotherplaheinnermostplamaybeoinstability.thisresultappearstobeinsomeagreementwithlaskar's(1994，1996)expectationsthatlargeandirregularvariationsappearintheetricitiesandinationsofmercuryonatime-scaleofseveral109yr.however，theeffectofthepossibleinstabilityoftheorbitofmercurymaynotfatallyaffecttheglobalstabilityofthewholeplaarysystemowingtothesmallmassofmercury.wewillmentiohelong-termorbitalevolutionofmercurylateriion4usinglow-passfilteredorbitalelements.

    theorbitalmotionoftheouterfiveplasseemsrigorouslystableandquiteregularoverthistime-span(seealsose5).

    3.2time–frequencymaps

    althoughtheplaarymotionexhibitsveryloabilitydefiheenceofcloseenterevents，thechaotiatureofplaarydynamigetheoscillatoryperiodandamplitudeofplaaryorbitalmotiongraduallyoversugtime-spans.evensuchslightfluctuationsoforbitalvariationinthefrequenain，particularlyinthecaseofearth，potentiallyhaveasignifiteffeitssurfaceclimatesystemthroughsolarinsolationvariation(cf.berger1988).

    togiveanoverviewofthelong-termgeinperiodicityinplaaryorbitalmotion，weperformedmanyfastfouriertransformations(ffts)aloimeaxis，andsuperposedtheresultingperiodgramstodrawtwo-dimensionaltime–frequencymaps.thespecificapproachtodrawiime–frequencymapsinthispaperisverysimple–muchsimplerthanthewaveletanalysisorlaskar's(1990，1993)frequenalysis.

    dividethelow-passfilteredorbitaldataintomanyfragmentsofthesamelenh.thelenhofeachdatasegmentshouldbeamultipleof2ioapplythefft.

    eachfragmentofthedatahasalargeoverlappingpart:forexample，whehdatabeginsfromt=tiandendsatt=ti t，thedatasegmentrangesfromti δt≤ti δt t，whereδt?t.wetihisdivisionuntilwereachacertainnumbernbywhi treachesthetotaliionlenh.

    lyanffttoeachofthedatafragments，andobtainnfrequencydiagrams.

    ineachfrequencydiagramobtainedabove，thestrenhofperiodicitybereplacedbyagrey-scale(orcolou