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Long-termiionsandstabilityofparyorbitsinourSorsystem
Abstract
Wepresenttheresusofverylong-termnumericaliionsofparyorbitalmotionsover109-yrtime-spansincludingallnineps.Aquispeofournumericaldatashowsthattheparymotion,atleastinoursimpledynamicalmodel,seemstobequitestableevehisverylongtime-span.Acloserlookatthelowest-frequencyosciionsusingalow-passfiershowsusthepotentiallydiffusivecharacterofterrestrialparymotion,especiallythatofMercury.ThebehaviouroftheetriercuryinouriionsisqualitativelysimirtotheresusfromJacquesLaskar''''''''ssecurperturbationthe.emax~0.35yr.However,therearenoapparentsecreasesofetricityorinationinanyorbitalelementsoftheps,whichmayberevealedbystillloermnumericaliions.Wehavealsoperformedacoupleoftrialiionsincludingmotionsoftheouterfivepsoverthedurationof±5×1010yr.Theresuindicatesthatthethreemajorresoheune–Plutosystemhavebeenmaintainedoverthe1011-yrtime-span.
1Introdu
1.1Definitionoftheproblem
ThequestionofthestabilityofourSorsystemhasbeeedoverseveralhundredyears,siheeraofon.Theproblemhasattractedmanyfamousmathematisovertheyearsandhaspyedatralroleinthedevelopmentofnon-lineardynamidchaostheory.However,wedohaveadefihequestionofwhetherourSorsystemisstableornot.Thisispartlyaresuofthefactthatthedefinitionoftheterm‘stability’isvaguewhenitisusediiontotheproblemofparymotionintheSorsystem.Actuallyitisogiveaclear,rigorousandphysicallymeaningfuldefinitionofthestabilityofourSorsystem.
Amongmanydefinitionsofstability,herettheHilldefinitionGdman1993:actuallythisisnotadefinitionofstability,butofinstability.Wedefineasystemasbeingunstablewhenacloseenteroccurssomewhereiem,startingfromacertaininitialfigurationChambers,Wetherill&Boss1996Ito&Tanikawa1999.AsystemisdefinedasexperiengacloseenterwhentwobodiesapproaeahinahergerHillradius.Otherwisethesystemisdefinedasbeingstable.HenceforwardwestatethatourparysystemisdynamicallystableifnocloseenterhappensduringtheageofourSorsystem,about±5Gyr.Ially,thisdefinitionmayberepcedbyoneinwhioccurrenceofanyorbitalcrossiweeherofapairofpakespce.ThisisbecauseweknowfromexperiehatanorbitalcrossingisverylikelytoleadtoacloseenteriaryandprotoparysystemsYoshinaga,Kokubo&Makino1999.Ofcoursethisstatementotbesimplyappliedtosystemswithstableorbitalresonancessuchastheune–Plutosystem.
内容未完,下一页继续阅读 </p><p style="font-size:16px">1.2Previousstudiesandaimsofthisresearch
Inadditiontothevaguenessoftheceptofstability,thepsinourSorsystemshowacharactertypicalofdynamicalchaosSussman&Wisdom1988,1992.ThecauseofthischaoticbehaviourisnowpartlyuoodasbeiofresonanceoverppingMurray&Holman1999Lecar,Franklin&Holman2001.However,itwouldrequireiingoveranensembleofparysystemsincludingallninepsforaperiodcseveral10Gyrtothhlyuandthelong-termevolutionofparyorbits,sinceicalsystemsarecharacterizedbytheirstrongdependeninitialditions.
Fromthatpointofview,manyofthepreviouslong-termnumericaliionsincludedonlytheouterfivepsSussman&Wisdom1988Kinoshita&Nakai1996.Thisisbecausetheorbitalperiodsoftheouterpsaresomuchlohanthoseoftheinnerfourphatitismucheasiertofollowthesystemfiveniionperiod.Atpresent,thelonumericaliionspublishedinjournalsarethoseofDun&Lissauer1998.Ahoughtheirmaintargetwastheeffectofpost-main-sequenasslossoabilityofparyorbits,theyperformedmanyiionscupto~1011yroftheorbitalmotionsofthefourjovias.TheinitialorbitalelementsandmassesofpsarethesameasthoseofourSorsysteminDun&Lissauer''''''''spaper,buttheydecreasethemassoftheSungraduallyintheirnumericalexperiments.Thisisbecausetheysidertheeffectofpost-main-sequenasslossinthepaper.sequently,theyfoundthatthecrossingtime-scaleofparyorbits,whibbeatypidicatoroftheinstabilitytime-scale,isquitesensitivetotherateofmassdecreaseoftheSuhemassoftheSunisclosetoitspresentvalue,thejoviasremainstableover1010yr,orperhapslonger.Dun&LissaueralsoperformedfoursimirexperimentsontheorbitalmotionofsevesVenustoune,whichcoveraspanof~109yr.Theirexperimentsonthesevesarepreheitseemsthattheterrestrialpsalsoremainstableduringtheiionperiod,maintainingalmurosciions.
Oherhand,inhisaccuratesemi-analyticalsecurperturbationtheoryLaskar1988,Laskarfindsthatrgeandirregurvariationsappeariricitiesandinationsoftheterrestrialps,especiallyofMercuryandMarsonatime-scaleofseveral109yrLaskar1996.TheresusofLaskar''''''''ssecurperturbationtheoryshouldbefirmedandiigatedbyfullynumericaliions.
Inthispaperwepresentpreliminaryresusofsixlong-termnumericaliionsonallnineparyorbits,caspanofseveral109yr,andoftwootheriionscaspanof±5×1010yr.Thetotalepsedtimeforalliionsismorethan5yr,usingseveraldedicatedPdworkstations.Ohefualclusions-termiionsisthatSorsystemparymotioobestableintermsoftheHillstabilitymentionedabove,atleastoveratime-spanof±4Gyr.Actually,inournumericaliioemwasfarmorestablethanwhatisdefiheHillstabilitycriterion:notonlydidnocloseenterhappenduringtheiionperiod,butalsoalheparyorbitalelementshavebeenfinedinanarrionbothintimeandfrequenain,thoughparymotioochastic.Sihepurposeofthispaperistoexhibitandoverviewtheresus-termnumericaliions,weshowtypicalexamplefiguresasevideheveryloabilityofSorsystemparymotion.Forreaderswhohavemorespecifiddeeperisinournumericalresus,reparedawebpageaccess,whereweshowraworbitalelements,theirlow-passfieredresus,variationofDeunayelementsandangurmomentumdeficit,asofoursimpletime–frequenalysisonallofouriions.
Iion2webrieflyexpinourdynamicalmodel,numericalmethodandinitialditionsusedinouriions.Se3isdevotedtoadescriptionofthequickresusofthenumericaliions.VeryloabilityofSorsystemparymotionisapparentbothiarypositionsandorbitalelements.Aroughestimationofnumericalerrorsisalsogiveiooadiscussionoftheloermvariationofparyorbitsusingalow-passfierandincludesadiscussionofangurmomentumdeficit.Iion5,wepreseofnumericaliionsfortheouterfivephatspans±5×1010yr.Iion6wealsodiscusstheloabilityoftheparymotionanditspossiblecause.
2Descriptionofthenumericaliions
本部分涉及比较复杂的积分计算,作者君就不贴上来了,贴上来了起点也不一定能成功显示。
2.3Numericalmethod
Weutilizeased-orderWisdom–HolmansymplecticmapasourmainiiohodWisdom&Holman1991Kinoshita,Yoshida&Nakai1991ecialstart-upproceduretoreducethetruncationerrorofanglevariables,‘warmstart’Saha&Tremaine1992,1994.
Thestepsizeforthenumericaliionsis8dthroughoutalliionsoftheninepsN±1,2,3,whichisabout1/11oftheorbitalperiodoftheinnermostpMercury.Asforthedeterminationofstepsize,wepartlyfollowthepreviousnumericaliionofallninepsinSussman&Wisdom1988,7.2dandSaha&Tremaine1994,225/32d.Werouhedecimalpartofthetheirstepsizesto8tomakethestepsizeamuipleof2ioreducetheaccumutionofround-offerroriationprocesses.Iiontothis,Wisdom&Holman1991performednumericaliionsoftheouterfiveparyorbitsusingthesymplecticmapsizeof400d,1/10.83oftheorbitalperiodofJupiter.Theirresuseemstobeaccurateenough,whichpartlyjustifiesourmethodofdeterminiepsize.However,siheetricityofJupiter~0.05ismuchsmallerthanthatofMercury~0.2,weneedsomecarewhenweparetheseiionssimplyintermsofstepsizes.
内容未完,下一页继续阅读 </p><p style="font-size:16px">IegrationoftheouterfivepsF±,wefixedthestepsizeat400d.
tGauss''''''''fandgfunsinthesymplecticmaptogetherwiththethird-orderHalleymethodDanby1992asasolverforKeplerequations.ThenumberofmaximumiteratioinHalley''''''''smethodis15,buttheyneverreachedthemaximuminanyofouriions.
Theintervalofthedataoutputis200000d~547yrforthecalcutionsofallninepsN±1,2,3,andabout8000000d~21903yrfortheiionoftheouterfivepsF±.
Ahoughnooutputfieringwasdohenumericaliionswereinprocess,liedalow-passfiertotheraworbitaldataafterletedalhecalcutions.SeeSe4.1formoredetail.
2.4Errorestimation
2.4.1Retiveerrorsintotalenergyandangurmomentum
Aceofthebasicpropertiesofsymplectitegrators,whichservethephysicallyservativequantitieswelotalorbitalenergyandangurmomentum,-termnumericaliioohavebeenperformedwithverysmallerrors.Theaveragedretiveerrorsoftotalenergy~10?9andoftotangurmomentum~10?11haveremainednearlystantthroughouttheiionperiodFig.1.Thespecialstartupprocedure,warmstart,wouldhavereducedtheaveragedretiveerrorintotalenergybyaboutoneorderofmagnitudeormore.
RetivenumericalerrorofthetotangurmomentumδA/A0aalenergyδE/E0inournumericaliionsN±1,2,3,whereδEandδAaretheabsolutegeofthetotalenergyandtotangurmomentum,respectively,andE0andA0aretheirinitialvalues.ThehorizontalunitisGyr.
hatdiffereingsystems,differentmathematicallibraries,anddifferenthardwarearchitecturesresuindifferentnumericalerrors,throughthevariationsinround-offerrorhandlingandnumericalgorithms.IntheupperpanelofFig.1,wereizethissituationintheseumericalerrurmomentum,whichshouldberigorouslypreserveduptomae-εprecision.
2.4.2Erroriarylongitudes
SihesymplecticmapspreservetotalenergyandtotangurmomentumofN-bodydynamicalsystemsilywell,thedegreeoftheirpreservationmaynotbeagoodmeasureoftheaccuraericaliions,especiallyasameasureofthepositionalerrorofps,i.e.theerroriarylongitudes.Toestimatethenumericalerrorintheparylongitudes,weperformedthefollowingprocedures.Weparedtheresuofourmainlong-termiionswithsometestiions,whichspanmuchshorterperiodsbutwithmuchhigheraccuracythanthemainiions.Forthispurpose,weperformedamuchmoreaccurateiionsizeof0.125d1/64ofthemainiionsspanning3×105yr,startingwiththesameinitialditionsasintheN?1iion.Wesiderthatthistestiionprovidesusseudo-true’solutionofparyorbitalevolutio,weparethetestiionwiththemainiion,N?1.Fortheperiodof3×105yr,weseeadifferenmeananomaliesoftheEarthbetweewoiionsof~0.52°inthecaseoftheN?1iion.Thisdifferenbbeextrapotedtothevalue~8700°,about25rotatiohafter5Gyr,siheerroroflongitudesincreaseslinearlywithtimeinthesymplecticmap.Simirly,thelongitudeerrorofPlutobeestimatedas~12°.ThisvalueforPlutoismuchbetterthantheresuinKinoshita&Nakai1996wherethedifferenceisestimatedas~60°.
内容未完,下一页继续阅读 </p><p style="font-size:16px">3Numericalresus–I.Gtherawdata
Inthissewebrieflyreviewtheloabilityofparyorbitalmotihsomesnapshotsofrawnumericaldata.Theorbitalmotionofpsindicatesloabilityinallofournumericaliions:noorbitalcrossingsnorcloseentersbetairofpookpce.
3.1Generaldescriptionofthestabilityofparyorbits
First,webrieflylookatthegeneralcharacteroftheloabilityofparyorbits.Ouriherefocusesparticurlyontheinnerfourterrestrialpsforwhichtheorbitaime-scalesaremuchshorterthanthoseoftheouterfiveps.AsweseeclearlyfromthepnarorbitalfigurationsshowninFigs2and3,orbitalpositionsoftheterrestrialpsdifferlittlebetweeiandfinalpartofeaumericaliion,whichspansseveralGyr.Thesolidliingthepresentorbitsofthepsliealmostwithintheswarmofdotseveninthefinalpartofiionsbandd.Thisindicatesthatthroughouttheeegrationperiodthealmurvariationsofparyorbitalmotionremainnearlythesameastheyareatpresent.
Verticalviewofthefourinnerparyorbitsfromthez-axisdireattheinitiandfinalpartsoftheiionsN±1.Theaxesunitsareau.Thexy-pneissettotheinvariantpneofSorsystemtotangurmomentum.aTheinitialpartofN+1t=0to0.0547×109yr.bThefinalpartofN+1t=4.9339×108to4.9886×109yr.cTheinitialpartofN?1t=0to?0.0547×109yr.dThefinalpartofN?1t=?3.9180×109to?3.9727×109yr.Iotalof23684pointsareplottedwithanintervalofabout2190yrover5.47×107yr.SolidlinesineaeldehepresentorbitsofthefourterrestrialpstakenfromDE245.