第76章 对火星轨道变化问题的最后解释 (第2/12页)

xperiengacloseenterwhentwobodiesapproaeahinahelargerhillradius.otherwisethesystemisdefinedasbeingstable.henceforwardwestatethatourplaarysystemisdynamicallystableifnocloseenterhappensduringtheageofoursolarsystem，about±5gyr.ially，thisdefinitionmaybereplacedbyoneinwhioccurrenceofanyorbitalcrossiweeherofapairofplaakesplace.thisisbecauseweknowfromexperieanorbitalcrossingisverylikelytoleadtoacloseenterinplaaryandprotoplaarysystems(yoshinaga，kokubomakino1999).ofcoursethisstatementotbesimplyappliedtosystemswithstableorbitalresonancessuchastheune–plutosystem.

    1.2previousstudiesandaimsofthisresearch

    inadditiontothevaguenessoftheceptofstability，theplasinoursolarsystemshowacharactertypicalofdynamicalchaos(sussmanwisdom1988，1992).thecauseofthischaoticbehaviourisnowpartlyuoodasbeiofresonanceoverlapping(murraylecar，franklinholman2001).however，itwouldrequireiingoveranensembleofplaarysystemsincludingallnineplasforaperiodcseveral10gyrthlyuandthelong-termevolutionofplaaryorbits，sincechaotiamicalsystemsarecharacterizedbytheirstrongdependeninitialditions.

    fromthatpointofview，manyofthepreviouslong-termnumeritegrationsincludedonlytheouterfiveplas(sussmankinoshitanakai1996).thisisbecausetheorbitalperiodsoftheouterplasaresomugerthanthoseoftheinnerfourplahatitismucheasiertofollowthesystemfiveionperiod.atpresent，thelonumeritegrationspublishedinjournalsarethoseofdunlissauer(1998).althoughtheirmaintargetwastheeffectofpost-main-sequenasslossoabilityofplaaryorbits，theyperformedmanyiionscupto～1011yroftheorbitalmotionsofthefourjovianplaheinitialorbitalelementsandmassesofplasarethesameasthoseofoursolarsystemindunlissauer'spaper，buttheydecreasethemassofthesungraduallyintheirnumericalexperiments.thisisbecausetheysidertheeffectofpost-main-sequenasslossinthepaper.sequently，theyfoundthatthecrossingtime-scaleofplaaryorbits，whibeatypidicatoroftheinstabilitytime-scale，isquitesensitivetotherateofmassdecreaseofthesuhemassofthesunisclosetoitsp