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Gety-slot van aarde en maan

Gety-slot van aarde en maan


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Aangesien die maan getyd op die aarde toegesluit is, beteken dit dat ons van die aarde af net een kant van die maan kan sien.

Kan ons al die kante van die aarde vanaf die maan sien?


Die Aarde en die Maan doen interaksie, maar omdat hulle verskillende groottes en massas het, is die effek op elkeen anders.

Die maan draai een keer in sy baan om die aarde, wat veroorsaak dat dit voortdurend dieselfde gesig vertoon. Dit was die uitwerking van die aarde op die maan as gevolg van swaartekrag deur gety.

Dit is redelik stabiel, die maan sal dieselfde gesig na die aarde bly wys, alhoewel die getykragte dit al hoe verder laat wentel.

Ons sien eintlik meer as 50% van die maan. Die baan van die maan laat sy aspek knik omdat die baan effens ellipties en skemerig is omdat dit nie direk oor die ewenaar wentel nie. Met verloop van tyd sien ons eintlik amper 60 persent van die maanoppervlak ('n effek wat librasie genoem word).

Die effek van die maan op die aarde was om die daaglikse rotasie tot 24 uur te vertraag. In die verlede was die maan baie nader aan die aarde, en die dag was baie korter. Namate die tyd verbygaan en die maan in 'n wyer baan beweeg, sal die lengte van die aarde se dag toeneem (sien bv. Hierdie Scientific American post).

Ek het gelees dat die maan tot op 'n sekere punt sou terugtrek en dan weer die aarde sou begin nader, maar helaas sal die son voor dan in 'n rooi reus opswel en die aarde en die maan insluk.


Ja. Die getyvergrendeling van die maan ten opsigte van die aarde beteken dat die maan een keer draai en dat dit op presies dieselfde tyd as wat dit nodig is om die aarde wentel, draai. Om altyd dieselfde kant van die aarde te sien, moet u dit wentel op dieselfde tyd as wat die aarde om sy as moet draai, dit wil sê binne 24 uur. Die maanbaan om die aarde duur ongeveer 27 dae, dus vanaf die maan sien jy die aarde onder jou draai en mettertyd sien jy alle kante daarvan.

Die wenteltydperk word bepaal deur die afstand vanaf die aarde; voorwerpe verder van die aarde af sal dit stadiger wentel, voorwerpe vinniger nader. Om altyd dieselfde kant van die aarde te sien, moet 'n voorwerp op 'n bepaalde plek wees, a geostasionêre baan, wat in die ekwatoriale vlak is. Dit is op 42000 km van die middelpunt van die aarde af, of ongeveer 36000 km bo die oppervlak.
Televisie- en ander kommunikasiesatelliete is in 'n geostasionêre baan, en hierdie baan is so druk dat satelliete net 'n paar tien kilometer van hul bure af sit. Almal wil hê dat haar satelliet op die regte lengte is om Noord-Amerika of Europa te bedien.

Volgens Kepler se 3de wet is daar 'n vaste verband tussen die baanperiode in die kwadraat en die afstand in kubus. Die maan se tydperk in vierkante dae is byvoorbeeld ongeveer 750. As u die maan se afstand in blokkies deel deur die afstand van die geostationêre baan, dan kry u dieselfde getal.


Wanneer 'n maan aansienlike massa het, soos die aarde se maan, word iets genoem getykrag voorkom. Getyekrag verwys na die ongelyke swaartekrag tussen twee voorwerpe. Dit is ook waar hoogwater en laagwater word gebore, afhangende van watter oseaan op 'n gegewe tyd die naaste aan die maan is. In die loop van die geskiedenis het die sterk swaartekrag van die Maan deur die Aarde die rotasie van die Maan verskuif, wat uiteindelik die ooreenstemmende wentelpatrone tot gevolg gehad het. Hierdie eenvormige rotasie is presies wat bedoel word as daar gesê word dat die maan is gety gesluit na die aarde.

In eenvoudige terme, as gevolg van jare se verskuiwing veroorsaak deur ongebalanseerde swaartekrag, wanneer die Aarde draai, kopieer die Maan sy presiese draai, wat dit onmoontlik maak om ooit die ander kant van die maan te sien, tensy dit vanaf 'n ruimtetuig is.


Inhoud

Mane [wysig | wysig bron]

Die meeste mane is getyvergrendeld, word getyvergrendel met hul primêre, omdat hulle baie nou wentel en die getykrag die afnemende afstand vergroot. Pluto en Charon is 'n spesiale voorbeeld van 'n getyslot waar Charon 'n groot maan is in vergelyking met sy primêre baan en 'n relatief noue baan het. Pluto se ander mane is chaoties gety weens die effek van Charon. Rotasie en wentelperiodes van die Aarde se maan is getyd met mekaar, dus maak nie saak wanneer die maan vanaf die aarde waargeneem word nie, dieselfde halfrond van die maan word altyd gesien. & # 160 Wanneer die aarde vanaf die maan waargeneem word, kan die aarde nie ' Dit lyk asof dit dwarsoor die lug gesien word, maar dit bly op dieselfde plek en draai op sy eie as.

Asteroïedmane se getyvergrendeling is tans grotendeels onbekend.

Planete [wysig | wysig bron]

Mercurius het 'n wentelbaan van 3: 2, wat drie keer draai vir elke twee omwentelings rondom die son, wat dieselfde posisionering by daardie waarnemingspunte tot gevolg het. Mercurius was vroeg in die rotasietoestand van 3: 2, ongeveer 10-20 miljoen jaar. Venus en Aarde het 'n uiters noue wentelbaan, onbekend as 'n getyvergrendeling tot gevolg het.
Exoplanet Proxima Centauri b wentel om sy ouerster is getyd gesluit, wat beide 'n gesinkroniseerde rotasie en 'n 3: 2-draai-wentel-ooreenkoms soos Mercurius uitdruk.

Sterre [wysig | wysig bron]

Daar word gevind dat nabye sterre gety gesluit is voordat dit in 1 ster gevorm word. Tau Boötis, 'n ongewone voorbeeld, 'n ster kan deur die planeet Tau Boötis b gety word. Aangesien sterre gasvormige liggame is wat met verskillende snelhede op verskillende breedtegrade draai, gebeur die getyslot deur die magnetiese veld van Tau Boötis.


Maanresessie

  • Lewer 'n netto versnelling vorentoe van die Maan
  • Skuif die maan 'n bietjie groter wentelbaan

Die Lunar Resession-koers is meetbaar met behulp van Laser Ranging-eksperimente wat retroreflektorarrays gebruik wat deur die Apollo-missies op die Maan gelaat is (Apollo 11, 14 en 15), en twee Sowjetlanders (Lunakhod 1 en 2). Teleskope op aarde weerkaats laserstrale van die reflektorstelsels en meet die afstand tot die maan tot millimeter akkuraat.


Planetêre impak

3.3 Biosfeer Evolusie

Bewyse uit die Aarde-Maan-stelsel dui daarop dat die kratersnelheid in werklikheid gestabiliseer het tot iets wat met 3,0 Ga 'n konstante waarde nader. Alhoewel daar nie meer groot gevolge vir komvorming was nie, was daar nog steeds af en toe impakte wat gelei het tot kraters in die grootte van 'n paar honderd kilometer. Die landelike rekord bevat oorblyfsels van die Sudbury, Kanada en Vredefort, Suid-Afrika, met strukture met oorspronklike kraterdiameters van onderskeidelik ~ 250 km en ~ 300 km en ouderdomme van ~ 2 Ga. Dit is onwaarskynlik dat gebeure van hierdie grootte het aansienlike langtermynveranderings in die vaste geosfeer veroorsaak, maar dit het waarskynlik die biosfeer van die aarde beïnvloed. Benewens hierdie werklike prekambriese impakkraters, is daar relatief onlangs in Australië en Suid-Afrika 'n aantal afwykende bolletjiesbeddings met ouderdomme van ~ 2.0 tot 3.5 Ga ontdek. Geochemiese en fisiese bewyse (geskokte kwarts) dui tans op die oorsprong van sommige van hierdie beddings, maar die oorspronklike kraters is onbekend. As een van hierdie bolvormige beddens in Australië tydelik gekorreleer word met een in Suid-Afrika, sou die ruimtelike omvang daarvan meer as 32 000 km 2 wees.

Op die oomblik is die enigste geval van 'n direkte fisiese en chemiese verband tussen 'n groot impakgebeurtenis en veranderinge in die biostratigrafiese rekord aan die "Kryt-tersiêre grens", wat ongeveer 65 miljoen jaar gelede (Ma) plaasgevind het. Die wêreldwye fisiese bewys vir impak sluit in: skok geproduseerde, mikroskopiese plat vervormingseienskappe in kwarts en ander minerale, die voorkoms van stishoviet ('n hoëdruk polimorf van kwarts) en impak diamante hoë temperatuur minerale wat vermoedelik dampkondensate is en verskillende, gewoonlik veranderde, impaksmeltende bolletjies. Die chemiese bewyse bestaan ​​hoofsaaklik uit 'n geochemiese anomalie, wat dui op 'n mengsel van meteorietmateriaal. In ongestoorde Noord-Amerikaanse dele, wat in moerasse en poele op land neergelê is, bestaan ​​die grens uit twee eenhede: 'n onderste een, gekoppel aan ballistiese uitwerping, en 'n boonste een, gekoppel aan atmosferiese verspreiding in die impak vuurbal en die daaropvolgende neerslag oor 'n tydperk. Hierdie vuurballaag kom wêreldwyd voor, maar die uitwerphorison is slegs in Noord-Amerika bekend.

Die Kryt-tersiêre grens is 'n massa-uitwissing in die biostratigrafiese verslag van die Aarde. Oorspronklik is gedink dat stof in die atmosfeer van die impak gelei het tot wêreldwye verdonkering, die staking van fotosintese en verkoeling. Ander moontlike moordmeganismes is voorgestel. Roet is byvoorbeeld ook in grensafsettings geïdentifiseer en die oorsprong daarvan word toegeskryf aan wêreldwyd verspreide veldbrande. Roet in die atmosfeer het die effekte wat deur wêreldwye stofwolke veroorsaak, versterk of selfs oorweldig. Onlangs word toenemende klem gelê op die begrip van die uitwerking van verdampte en gesmelte uitwerpsels op die atmosfeer. Modelle van die warmtestraling wat geproduseer word deur die ballistiese toetrede van uitwerpings wat gekondenseer word uit die damp en die smeltpluim van die impak, dui op die voorkoms van 'n warmtestralingspuls op die aarde se oppervlak. Die oorlewingspatroon van landdiere 65 Ma gelede stem ooreen met die konsep dat hierdie intense termiese pols die eerste wêreldwye slag vir die biosfeer was.

Alhoewel die rekord in die kryt-tersiêre grensafsettings ooreenstem met die voorkoms van 'n groot impak, is dit duidelik dat baie van die besonderhede van die potensiële moordmeganisme (s) en die gepaardgaande massa-uitwissing nie volledig bekend is nie. Die 'moordenaarkrater' is geïdentifiseer as die struktuur van 180 km in deursnee, bekend as Chicxulub, begrawe onder ~ 1 km sedimente op die Yucatan-skiereiland, Mexiko. Variasies in die konsentrasie en grootte van geskokte kwartskorrels en die dikte van die grensafsettings, veral die uitwerplaag, dui op 'n bronkrater in Sentraal-Amerika. Geskokte minerale is gevind in afsettings binne en buite die struktuur, sowel as impaksmeltgesteentes, met 'n isotopiese ouderdom van 65 Ma.

Chicxulub hou moontlik die leidraad vir moontlike uitsterwingsmeganismes. Die teikengesteentes sluit beddings van anhidriet (CaSO) in4), en modelberekeninge vir die Chicxulub-impak dui aan dat die SO2 vrygestel sou tussen 30 miljard en 300 miljard ton swaelsuur die atmosfeer in gestuur het, afhangende van die presiese impakstoestande. Studies het getoon dat die verlaging van die temperatuur na groot vulkaniese uitbarstings hoofsaaklik te wyte is aan swaelsuuraërosols. Modelle, wat beide die boonste en onderste skatting gebruik van die massa swaelsuur wat deur die Chicxulub-impak geskep word, lei tot 'n berekende daling in die globale temperatuur van 'n paar grade Celsius. Die swaelsuur sou uiteindelik na die aarde terugkeer as suurreën, wat die versuring van die bo-oseaan sou veroorsaak en moontlik tot mariene uitwissings sou lei. Daarbenewens sal impakverhitting van stikstof en suurstof in die atmosfeer NO veroorsaakX gasse wat die osoonlaag beïnvloed, en dus die hoeveelheid ultravioletstraling wat die aarde se oppervlak bereik. Soos die swaeldraende aërosols, sal hierdie gasse met water in die atmosfeer reageer om salpetersuur te vorm, wat addisionele suurreën tot gevolg sal hê.

Die frekwensie van Chicxulub-grootte gebeure op Aarde is in die orde van elke 100 ∼ Ma. Kleiner, maar steeds beduidende, impak kom op korter tydskale voor en kan die landelike klimaat en biosfeer in verskillende mate beïnvloed. Sommige modelberekeninge dui daarop dat stof wat deur die vorming van impakkraters tot so klein as 20 km in die atmosfeer ingespuit word, wêreldwye ligvermindering en temperatuuronderbrekings kan veroorsaak. Sulke gevolge kom op die aarde voor met 'n frekwensie van ongeveer twee of drie elke miljoen jaar, maar sal waarskynlik nie die biosfeer ernstig beïnvloed nie. Die mees brose komponent van die huidige omgewing is egter die menslike beskawing, wat baie afhanklik is van 'n georganiseerde en tegnologies ingewikkelde infrastruktuur vir sy voortbestaan. Alhoewel ons selde in miljoene jare aan beskawing dink, bestaan ​​daar min twyfel dat as die beskawing lank genoeg duur, dit ernstig kan ly of selfs deur 'n impakgebeurtenis vernietig kan word.

Impak kan op historiese tydskale voorkom. Die Tunguska-gebeurtenis in Rusland in 1908 was byvoorbeeld die gevolg van die atmosferiese ontploffing van 'n relatief klein liggaam op 'n hoogte van ~ 10 km. Die energie wat vrygestel word, gebaseer op die vereiste om die waargenome seismiese versteurings te produseer, is geskat as gelykstaande aan die ontploffing van ~ 10 megatons TNT. Alhoewel die lugontploffing tot 'n verwoesting van ongeveer 2000 km 2 van die Siberiese woud gelei het, het daar geen menselewens verloor nie. Gebeurtenisse soos Tunguska vind plaas op tydskale van duisend jaar. Gelukkig is 70% van die aarde en die oseaan en is die grootste deel van die land nie dig bevolk nie.


Moon se "gety lock" rotasieteorie - Wat is verkeerd daarmee?

Die doel vir my om hierdie bedreiging te skep, is om 'n rasionele verklaring te vind, nie noodwendig 'n wetenskaplike nie, waarom die rotasie van die maan op sy wentelbaan om die aarde is.

"Gety lock" is problematies omdat wetenskaplikes nie hier op aarde 'n ordentlike verklaring het waarom elke dag twee getye is nie, een aan die kant van die maan en een aan die ander kant. Dit is in stryd met ons begrip van swaartekrag. (Waarom neem oseane nie 'n eierwit vorm aan nie, met die aarde die dooier?) Ons sien die getye al duisende jare waar, maar ons kan die helfte daarvan nie verklaar nie. Om te beweer dat ons "weet" dat die maan se rotasie veroorsaak word deur "gety lock" - waar ons geen getye kan waarneem nie, en nog minder "getykragte", is pure skynheiligheid, nie wetenskap nie.
en.wikipedia.org.

Die selfaangestelde taak van die wetenskap is om verskynsels waar te neem en met 'n teorie te verklaar. Maar elke teorie is slegs geldig totdat EEN weerspreking gevind is. Mense moet besef dat die wetenskap slegs teorieë bied, NIE kennis nie. Dit is aan almal om self te besluit watter verklaring of teorie voldoende is en watter nie.

en.wikipedia.org.
"wringkrag word gedefinieer as die kruisproduk van die hefboom-armafstand en -krag, wat geneig is om te draai."
Om my meningsverskil te verklaar, gaan ek eers na 'n maan wat solied is en 'n swaartepunt het wat weg is van sy rotasie-as. As u probeer draai, sal die swaartekrag dit vertraag, want die "wringkrag" aan die een kant sal groter wees as aan die ander kant. Wanneer die swaartepunt aan die ander kant kom, sal die wringkrag egter dieselfde hoeveelheid krag toepas om dit weer te versnel.

en.wikipedia.org.
AS 'n maan 'n perfekte sfeer is, maar oseane of ander vloeistowwe het, dan sal die aarde se swaartekrag die vloeistowwe nader trek en sodoende bult of uitdruk (vandaar die naam 'getykrag'). Die langwerpige vorm van gesmelte metaal in die kern van 'n maan sou dit in wese asimmetries maak, wat veroorsaak dat die wringkrag nie in balans is nie en sodoende die rotasie vertraag. In teenstelling met die voorbeeld hierbo met die vaste maan, sal die swaartepunt NIE na die ander kant toe hang nie (versnel dit dus nie weer nie).

Hierdie effek van die wringkrag is egter nie van toepassing op water nie. As gevolg van die lae "viskositeit" (weerstand teen vloei: heuning teenoor water), vloei water maklik en so vinnig as wat swaartekrag dit beveel. Daarom sal die langwerpige vorm altyd direk na die aarde wys. Aangesien die swaartepunt NIE van die simmetrie-as verwyder word nie, geld die wringkrag ewe veel vir beide, die naderende kant as die kant wat wegdraai.

en.wikipedia.org.
Aan die ander kant veroorsaak bewegende vloeistowwe wrywing. Met wrywing genereer getykrag hitte, wat 'n verlies aan energie is, wat die traagheid (neiging om die spoed te handhaaf) van die rotasie verminder.

Kom ons kyk na ons werklike maan. Dit het 'n kern wat tot 'n sekere mate gesmelt is. As gevolg van die klein grootte (relatief tot sy hele liggaam), lyk die hoë viskositeit en die hoë druk wat enige beduidende beweging voorkom, die uitpuil of enige ander beweging minimaal. Die omvang van die uitputting moet bereken word as 'n funksie van hierdie faktore voordat u eers kan kyk na die wringkrag wat dit sal veroorsaak.

Gevolgtrekking: Om vas te stel hoeveel miljoene of miljarde jare dit sal neem voordat so 'n bult 'n maan of planeet "gety lock" laat word, is 'n monsteragtige berekening nodig, met baie faktore wat weinig meer is as vae ramings. Dit kan skaars iets beweer word met die huidige insigte en tegnologiese vermoëns om te meet. Ek sou dit beskou as ons 'beste beskikbare' wetenskaplike teorie, 'n aanneemlike aanname, nie kennis nie.

Waar dink jy is ek korrek of verkeerd? Ek hoop om kritiek en / of regstellings op my verduidelikings en gevolgtrekkings te kry. Ek hoef nie te vertel dat ek 'hardnekkig' is nie, of enige ander verkeerde karakterisering omdat ek weier om 'n teorie te aanvaar net omdat dit die teorie is wat deur hoofwetenskaplikes as 'kennis' beskou word nie - en tog lyk dit my te weerspreek of te min rasionele, logiese redenasie.


'N Diep duik in die gety-slot

Noem rooi dwerg bewoonbare sones en getyvergrendeling kom altyd voor. As 'n planeet naby genoeg is aan 'n dowwe rooi ster om temperatuur geskik vir die lewe te handhaaf, sou dit nie een gesig gedurig daarna gedraai hou nie? Maar gety lock, soos Ashley Baldwin in die onderstaande opstel verduidelik, is meer kompleks as wat ons soms besef. En hoewel daar maniere is om gematigde klimaatmodelle vir sulke planete te vervaardig, is getyvergrendeling self 'n faktor in nie net M-dwerge nie, maar ook K- en selfs G-klas sterre soos die Son. Draai 'n paar begintoestande om en die Aarde self sou moontlik in die gety-slot gewees het. Die onvermoeide Dr. Baldwin hou die nuutste eksoplanetnavorsing fyn dop, en balanseer sy astronomiese studiebeurs op een of ander manier met 'n loopbaan as konsultantpsigiater by die 5 Boroughs Partnership NHS Trust (Warrington, UK). Lees verder om baie te leer oor die huidige denke oor 'n onderwerp wat van kritieke belang is vir die vraag na rooi dwergbewoonbaarheid.

deur Ashley Baldwin

& # 8220Tydelike vergrendeling & # 8221, & # 8220 gevange rotasie & # 8221 of & # 8220spin-baanvergrendeling & # 8221 ens kom voor in die mees erkende gedaante wanneer 'n astronomiese liggaam (of dit nou 'n maan, planeet of selfs 'n ster is) altyd dieselfde gesig vertoon na die voorwerp wat dit wentel. In hierdie geval kan na die baan van die & # 8220satellite & # 8221 liggaam verwys word as & # 8220synchronous & # 8221, waardeur die getyvergrendelde liggaam so lank neem om om sy eie as te draai as om sy maat te wentel. Dit vind plaas as gevolg van die primêre liggaam se swaartekrag wat die wentelende liggaam in 'n langwerpige & # 8220prolate & # 8221-vorm buig. Dit word dan weer blootgestel aan wisselende gravitasie-interaksie met die sentrale liggaam.

Figuur 1: Gety spanning en gety sluit

Terwyl die & # 8220orbiter & # 8221 draai, val sy nou langwerpige as buite die lyn met die sentrale massa, wat dit gevolglik steur as dit oor sy baan draai. Dit word dus onderhewig aan swaartekrag-geïnduseerde wringkragte wat kan werk as 'n rem & # 8212 deur middel van energie-uitruil en dissipasie, laasgenoemde deur wrywing-geïnduseerde hitteverlies in die versteurde wentelende liggaam. Aangesien M-dwergbewoonbare sones nader aan hul sentrale ster is en hul swaartekrag-invloed dus groter is, is dit maklik om te sien hoe hierdie verspreide hitte aansienlik kan bydra tot 'n eksoplanet se algehele energievloei en dit kan selfs die potensiaal vir die bewoonbaarheid daarvan beïnvloed & # 8211 om dit in 'n wegholkweekhuis-scenario te gee. (Kopparapu 2013).

Oor miljoene jare (of meer) kan hierdie proses lei tot & # 8220orbitale sinchronisasie & # 8221. Dit ontstaan ​​wanneer die wentelende liggaam 'n toestand bereik waar daar geen netto rotasie-uitruil meer is gedurende die loop van 'n voltooide baan nie (Barnes 2010). Om 'n getyvergrendelingstoestand te verlaat, sou slegs moontlik wees met die toevoeging van energie aan die stelsel. Dit kan voorkom as 'n ander massiewe voorwerp (soos 'n planeet of 'n ster in byvoorbeeld 'n binêre stelsel) die ewewig breek. As die massas van die twee liggame (byvoorbeeld Pluto & # 038 Charon) soortgelyk is, kan hulle getyds vir mekaar vasgesluit word.

Nie alle getyvergrendeling behels sinkronisasie nie. & # 8220Super-sinchronisasie & # 8221 vind plaas wanneer 'n wentelende liggaam getyd aan sy ouerliggaam toegesluit word, maar teen 'n vaste, maar vinniger tempo draai. 'N Aktuele voorbeeld hiervan is die voormalige & # 8220geosynchronous oordragbaan & # 8221 (GTO). Ons sien dit heeltyd op lanseerder-spesifikasies: & # 8220Betaal aan GTO & # 8221. Hierdie baan is buite die geosinchrone baan, waar baie satelliete hul bedryfslewe begin, maar dit moontlik maak om veranderings van die hellings voor die orbitale invoer moontlik te maak en minder dryfmiddel ekonomies te bestee voor die finale invoeging. Alternatiewelik kan sulke wentelbane gebruik word as stortterreine vir nie-funksionerende satelliete of verwante puin, sogenaamde & # 8220geo-kerkhofgordels & # 8221 (Luu 1998). Simulasies dui daarop dat baie eksoplanete in variante van sulke wentelsoorte kan bestaan.

Gravitasie-interaksie met 'n sentrale ster lei tot progressiewe vertraagde rotasie van 'n kleiner planetêre liggaam soos Mercurius via energie-uitruil en hitte-afvoer. Dit is te wyte aan subtiele, maar belangrike getykragvariasies oor die wentelende liggaam (onthou dat die swaartekrag omgekeerd eweredig is aan die vierkant van die afstand tussen twee liggame en # 8212, dus bestaan ​​die swaartekraggradiënte oor soliede liggame, wat lei tot bultings) . As die aanvanklike planeetbaan egter aansienlik eksentries is, wissel hierdie effek aansienlik oor die wenteltydperk (veral by periapsis & # 8212 as die punt van die sterkste gravitasie-interaksie) en kan dit eerder 'n draai-wentel resonansie tot gevolg hê. In die geval van Mercury is dit 3: 2 (drie rotasies per twee wentelbane), maar ander verhoudings kan van 2: 1 tot 5: 2 voorkom (Mahoney 2013). Dit is die moeite werd om daarop te let dat hierdie effek die meeste uitgespreek word vir nader-in-planete waar die swaartekrag-effekte die grootste is, dus moet die effek selfs meer relevant wees vir die dig verpakte eksoplanetêre argitekture (bv. TRAPPIST-1) wat blykbaar algemeen voorkom.

In uiterste gevalle waar die wentelbaan & # 8217; s wentelbaan byna sirkelvormig is EN 'n minimale of nul aksiale kanteling & # 8212 het, soos met die maan & # 8212, dan is dieselfde halfrond (met librasie moontlik) na die primêre massa.

Dit gesê, vir die eenvoud gaan ons nou aanneem dat 'n kleiner massaliggaam (eksoplaneet) om 'n baie massiewer liggaam (ster) wentel & # 8212 dit is die fokus van hierdie oorsig, met 'n onvermydelike knik na bewoonbaarheid.

As gevolg van bondigheid en ook met betrekking tot die eksoplanet-onderwerp van onlangse poste, sal ons ons beperk tot die spesifieke geval van aardse eksoplanete en hul wentelbane rondom kleiner hoofreekssterre.

Die tyd tot getyvergrendeling kan selfs deur die aangepaste vergelyking beskryf word:

Tslot ≈ wa 6 (0,4 m*R 2) / (3 Gmbl 2 kR 5) (Goldreich, Goldreich & # 038 Soter 1966) (Peale 1977) (Gladman 1996) (Greenberg 2009)

Waar Tslot is & # 8220 tyd tot getyvergrendeling & # 8221, w en k is konstantes wat eenvoudig geïgnoreer kan word, m* is massa van die ster, mbl is massa van die planeet, R is die radius van die eksoplanet en & # 8220G & # 8221 is Newton se belangrike gravitasiekonstante.

Tslot word aansienlik verleng deur & # 8220a & # 8221 & # 8212 toenemende planetêre semi-hoofas (tot die sesde mag!). Getyvergrendelingstyd word ook met 0,4 X m verhoog* in hierdie vergelyking. Dit is egter belangrik om die konteks te onthou en hoe massief 'n ster, inderdaad ENIGE ster, baie keer selfs 'n M-dwergster is, selfs groter, groter as 'n planeet. 'N Ster speel dus die hoofrol in die getyvergrendeling van sy gepaardgaande planete.

Die gravitasiekonstante G verseker dat toenemende sterremassa T aansienlik sal afneemslot. Alhoewel dit gelyk is, is dit 'n belangrike faktor in die vermindering van tyd tot getyvergrendeling.

Figuur 2: Sterremassa & # 038 tipe teenoor die semi-hoofas oranje / rooi grafiek met 'n toevoeging van Tsinkroniseer vir 0,1,1 en 10 gigayear keer vir 'n Aarde massa planeet. (Penz 2005)

Die konsep van sinchronisasie is relatief nuut en dateer uit Stephen Dole & # 8217 s seminal Bewoonbare planete vir die mens aan die begin van die ruimtetydperk in die vroeë 1960's. Die konsep was op hierdie stadium suiwer teoreties, met ietwat arbitrêre parameters, maar dit het geïmpliseer dat getyvergrendeling 'n groot belemmering sou wees vir die mensvriendelike & # 8220bewoonbare & # 8221 exoplanete wat Dole in gedagte gehad het vir sy boek. Dit was hier waar getyvergrendelde wentelbane en planete in M-dwergstelsels die eerste keer gekoppel is, op 'n negatiewe manier wat tot op hede nog bestaan ​​(voordat ons selfs koronale massa-uitwerpings, EUV en sterfakkels ens. Bereik!) Atmosferiese ineenstorting weens om te vries aan die kant van die planeet wat van die ster af wys, is nie die minste van hierdie probleme nie.

Eers in 1993 het Kasting et al gesofistikeerde 1-D klimaatmodellering gebruik as deel van die beskrywing van bewoonbare planete. Bewoonbare planete het nou eintlik planete beteken met toestande wat vloeibare water op hul oppervlaktes kon onderhou. Dit is nogal 'n laer maat as wat Dole dertig jaar tevore gestel het, maar baie meer toepaslik en vandag nog 'n pilaar van die eksoplanetwetenskap. Belangriker nog, Kasting se span het ook gravitasie-interaksie tussen ster en planeet gesimuleer.

Hulle het dit gedoen deur die & # 8220Equilibrium Tide & # 8221 model (ET) te gebruik. Verfynde variante hiervan het nou die stapelvoedsel geword van alle daaropvolgende verwante studies, aangesien dit ook & # 8220 ontwikkel het & # 8221. Die model veronderstel in wese dat die swaartekrag van die gety-raiser (ster) 'n langwerpige vorm in die versteurde liggaam (eksoplanet) lewer en dat die lang as daarvan effens verkeerd uitlyn is ten opsigte van 'n denkbeeldige lyn wat die twee massasentrums verbind.

Die wanaanpassing is van kardinale belang en is te wyte aan die ontbindingsprosesse binne die & # 8220 gedeformeerde & # 8221 eksoplanet, wat lei tot evolusie van die wentelbaan en draai-oomblikke. Hieruit kan verskillende vergelykings geskep word wat die baan- en rotasie-evolusiegeskiedenis van eksoplanete met verloop van tyd in kaart bring (sien hierbo). ET is oorspronklik afgelei van die Aarde / Maan-stelsel deur Darwin in 1880 voor verfyning deur Pearle in 1977. Iterasies wissel op subtiele maar beduidende maniere en word gebruik as basis vir toenemend gesofistikeerde simulasies namate die rekenaarkrag toeneem. Barnes 2017 het 'n gedetailleerde oorsig van sinchronisasie en ET-modellering gedoen (sien hieronder).

Kasting et al het sinchronisasie getoon van vermeende eksoplanete wat in die bewoonbare sones van M-dwerge wentel, sterre met 'n massa van tot 0,42 Mson, binne 4,5 miljard jaar. Hulle het die nou bekende term & # 8220gety locking radius & # 8221 bekendgestel. Alhoewel dit 'n groot stap vorentoe was, het dit die ongelukkige gevolg gehad om voort te gaan met die verspreiding van 'n pessimistiese siening van bewoonbare eksoplanete wat om sulke sterre wentel. Wat belangrik is, is dat sterelmassa steeds as die belangrikste oorsaak van sinchronisasie beskou word. Die onderstaande grafiek (van Yang et al 2014), hoewel dit gebaseer is op gesofistikeerde modellering, hou hierdie tipe denke steeds vas. Hier word verskillende bewoonbare sone-modelreekse op 'n grafiek van relatiewe ster-insolasie (en sterre tipe) teenoor semi-hoofas-voorbeelde van bekende eksoplanete aangebring, wat 'n realistiese perspektief toevoeg. U sal ook daarop let dat vir 'n 0,42 Mson ster, met 'n temperatuur van ongeveer 3500 K, is die 1-D innerlike bewoonbare reeks baie naby aan die waarde wat toegeskryf word aan die onlangs ontdekte TOI 700d & # 8212 middel-80 persent.

Figuur 3: Temperatuur van ster teenoor sterre-vloeidiagram met gekleurde sterklasse op mekaar geplaas en grys & # 8220 gety-sluitradius & # 8221-lyn.

Die gevolge van ander faktore & # 8212, soos die begin van wentel-eksentrisiteit (reeds hierbo met Mercurius aangetref), rotasietempo op die basis, die teenwoordigheid van metgeselle (Greenberg, Corriea 2013) termiese getye voortspruitend uit atmosferes (Leconte et al 2015) en sterre en planetêre interieurs (Driscoll & # 038 Barnes 2015), wentelbaan (Barnes 2017) & # 8212 is nie oorweeg nie. Soos gesien kan word, is dit eers die afgelope vyf jaar dat hierdie dinge by simulasies gevoeg is. Inderdaad, die resultate van hierdie studies verander die hele gety-sluitparadigma baie, veral met betrekking tot bewoonbare sones, wat ondanks verfyning (Kopparapu 2013, Selsis 2007) net effens verander het, 'n groot kompliment vir die werk van Kasting & # 8217; s in 1993.

Altesame bewoonbare sone-planete van M-, K- en G-sterre het almal die potensiaal om getysluit te word. Nie net M-dwerge nie, maar hul potensiaal bly steeds die grootste en veral vir 0,1 mson sterre soos TRAPPIST-1. Selfs die Aarde, as sy beginrotasie langer as net drie dae was, sou volgens Barnes 2017 dalk sinchronies geword het.

Ter wille van die beknoptheid het hierdie oorsig hoofsaaklik gefokus op sterremassa as 'n belangrike dryfveer in eksoplanetêre sinchronisasie. Soos hierbo gesien word, kom ander prosesse in aanmerking as die kennis op hierdie gebied vorder. Dit word ook al hoe moeiliker om dit uit te dryf van drywers van eksoplanetêre bewoonbaarheid. Daarom moet ons meer in detail kyk na sommige van die faktore hierbo genoem.

Die planeet Venus is op baie maniere ongewoon, maar veral een val op: sy retrograde en stadige rotasiesnelheid wat langer is as sy wentelperiode. Hoekom? Wat maak Venus anders? Een faktor is dat dit 'n rotsagtige planeet is met 'n aansienlike atmosfeer (92 bar op sy oppervlak). Ons weet almal van die berugte weghol-kweekhuiseffek wat dit bewerkstellig, wat Venus die warmste planeet in die sonnestelsel maak, alhoewel dit verder van die son af is as Mercurius (draai- / wentelende resonansie). Het hierdie atmosfeer egter enige ander effekte?

Op die aarde lei die dag- / nagsiklus tot variasies in hitteverspreiding in die atmosfeer. Dit is bekend dat die warmste tyd op die aarde nie plaasvind wanneer die son op sy hoogtepunt is nie en dus die naaste aan die aarde is, maar 'n paar uur later. Dit is as gevolg van termiese traagheid. Daar is 'n vertraging tussen sonverwarming en termiese reaksie, wat lei tot massaherverdeling. Aangesien die atmosfeer en die aarde se oppervlak oor die algemeen goed verbind word deur wrywing, kan dit lei tot onbeduidende termiese wringkragte.

Hierdie wringkrag is soortgelyk aan die wringkragte wat voortspruit uit die ongelyke swaartekraginteraksie met die aarde hierbo beskryf, alhoewel nie so kragtig nie. Op die Aarde met sy uitgebreide baan van 1 AE is hulle grotendeels onbelangrik, maar vir 0,3 AE nader aan Venus word hulle betekenisvol. Afhangend van hul rigting, kan hulle die rotasie vertraag of die snelheid van die planeet versnel, maar dit help om die sinchronisasie te weerstaan. Met verloop van tyd het wringkragte wat in Venus ontstaan, die rotasie daarvan vertraag, soveel so dat dit teruggekeer het na die retrograde patroon wat ons vandag sien.

Dus as dit waar is met Venus, hoe gaan dit met eksoplanete? Kan hierdie atmosferiese wringkrag weerstaan ​​of sinkronisering en getyvergrendeling in kwesbare gebiede rondom 'n ster weerstaan? Dit is breedvoerig deur Leconte et al 2015 gemodelleer en die antwoord was 'n dawerende ja, veral vir kleiner, minder helder sterre met nabygeleë bewoonbare sones, en nie net vir eksoplanete met 90 bar-atmosfeer nie. Selfs 1 bar Aardagtige atmosfeer kan help om sinkronisasie vir die bewoonbare sones in sterre van 0,5 M te weerstaanaarde & # 8211 0,7 Maarde.

Ten bar atmospheres were simulated and shown to resist synchronisation even for habitable zone planets orbiting 0.3 Maarde stars (mid-M dwarfs). These are the high bar “maximum greenhouse” CO2 atmospheres that are postulated to occur in the outer regions of stellar habitable zones. But there are limits. Venus’ 92 bar atmosphere is ironically so thick that most of the incident sunlight that isn’t reflected back into space is either absorbed or scattered before it can reach the planetary surface and exert the driving effect of thermal torques (Leconte et al 2015).

Figuur 4: Red arrow synchronous rotation / blue arrow asynchronous rotation graph (Leconte 2015).

Orbital synchronisation and exoplanet habitability remains a contentious theoretical field that is subject to continual debate and constant change. Modern Global Climate Modelling (GCM) has become a sophisticated sub-science. Using an earlier iteration of GCM, Yang et al showed in 2013 that synchronised M-dwarf habitable zone planets would form thick cloud banks above their sub-stellar point. This would then reflect much of the incident stellar flux, thus reducing the energy reaching the surface. In turn, this would reduce the overall energy reaching the planet and so reduce global temperatures. The net effect in theory is to extend the stellar habitable zone inwards. However, the same author collaborated with Wolf and Kopparapu in 2016 to apply an updated 3-D model to the same problem. This showed that a sub-stellar cloud bank could not form, or would form and then move, a result effectively rebutting the 2013 findings and moving the habitable zone back to its original pre 2013 starting point. Expect more of this !

So, all things considered, just how easy is it for an exoplanet to become tidally locked and just how easy can habitable zone planets become tidally locked ? Barnes 2017 attempted to address just this question for exoplanets in circular orbits. He applied two well recognised refined variants (CPL left, CTL right in the graphic below) of the ET to two model populations of exoplanets orbiting differing stellar masses, and ran thousands of giga-year simulations for each (think of the computing power and time!) One population had a starting orbital period of 8 hours and an orbital tilt of 60°. The other had a starting period of ten days and a tilt of 0°. This produced the four outcomes illustrated below. The superimposed grey shading represents the latest habitable zones (Kopparapu 2013) iteration, with the dark grey representing the “conservative” and the light the “optimistic”.

Figuur 5: “Four in one” black and white stellar mass vs semi-major axis / superimposed greyscale habzone graphs.

These results are indicative and significantly different from the status quo, which is that tidal locking is only something that applies to exoplanets orbiting in close to M dwarf and smaller K dwarf stars. For one thing, even this older paradigm implies that at least some “Goldilocks” stars are not quite as homely as expected (more Kasting than Dole). The Barnes work hints at potential overlap of the habitable zone for potentially a large fraction of K-class and even many G-class stars, driven by factors beyond simple stellar mass. Clearly planets with a slow initial rotation rate and low orbital tilt are at greater risk, as may prove the case. Opposed to this are non-synchronising factors such as, inter alia, higher baseline orbital eccentricities and the close proximity of other orbiting bodies (moons, planets …thinking TRAPPIST-1 and binary stars/brown dwarfs, as with the recently described Gliese 229Ac system).

What this also shows is the inextricable link between orbital features and planet habitability. No more so demonstrated than by Kepler, and likely even more so with its greater number of short orbital period planets, with any potential habitable zone planetary candidates lying within just tenths or less of an AU from their parent star. This is very much in the “red arrow” synchronous zone in the Leconte graphic above.

There are now over 4000 known exoplanets. The current focus is on their “characterisation” and this is largely about atmospheres and biosignatures. However, it is obvious that we need to know far more about their evolving and historical orbital properties. This is a part of a process of determining habitable planets/zones, which are about so much more than stellar mass.

Most of the exoplanets discovered already by Kepler et al orbit close in to their stars, including those few in the potential tidal lock habitable zone. Ongoing Doppler photometry and TESS will identify thousands more such exoplanets, many of which will be even closer to their latest star given TESS’ shorter 27 day observation runs. TOI 700d and Gliese 229Ac are just for starters. Hopefully the search for habitability will expand to encompass the unavoidable connexion with planetary orbital features.

Know the star to know the planet, but know the orbit to know them both.

Figuur 6: Stellar effects/planetary properties/planetary systems (Meadows and Barnes 2018)

Barnes,R. Formation and evolution of exoplanets. John Wiley & Sons, p248, 2010

Barnes, R. Tidal locking of habitable exoplanets. Celestial mechanics and dynamical astronomy Vol 129, Issue 4, pp 509-536, Dec 2017

Darwin, G H. On the secular changes in the elements of the orbit of a satellite revolving about a tidally distorted planet. Royal Society of London Philosophical Transactions, Series I, 171:713-891 1880.

Dole, S H. Habitable Planets for Man. 1964

Goldreich, P. Final spin rates of planets and satellites. Sterrekundige Tydskrif, 71, 1966

Goldreich, P., Soter, A., Q in the solar system. Ikarus 5, 375-389, 1966

Gladman, B et al. Synchronous locking of tidally evolving satellites. Ikarus 133 (1) 166-192, 1996

Greenberg, R. Frequency dependence of tidal Q, Die Astrofisiese Tydskrif, 698, L42-45, 2009

Kasting, J. F. Habitable zones around main sequence stars. Ikarus,101 d 108-128 Jan 1993

Kopparapu, R K et al. Habitable zones around main sequence stars: New Estimates. Die Astrofisiese Tydskrif, 765131, March 2013

Kopparapu R K, Wolf E, Yang et al. The inner edge of the habitable zone for synchronously rotating planets around low-mass stars using general circulation models. Die Astrofisiese Tydskrif Volume 819, Number 1, March 2016

Luu, K. Effects of perturbations on space debris in super-synchronous storage orbits. Air Force Research Laboratory Technical Reports, 1998

Mahoney,T J. Mercury. Springer Science & Business Media, 2013

Meadows V S, Barnes R K. Factors affecting exoplanet habitability. In Handbook of Exoplanets P57, 2018

Peale, S J. Rotation histories of natural satellites. Burns, J A, Editor, IAU Colloquium 28 Planetary Satellites, p 87-111, 1977

Penz,T et al. Constraints for the evolution of habitable planets: Implications for the search of life in the Universe: Evolution of Habitable planets, 2005

Yang, J et al. Stabilising cloud feedback dramatically expands the habitable zone of tidally locked planets. Die astrofisiese joernaalbriewe: 771:L45, July 2013

Yang, J et al. Strong dependence of the inner edge of the habitable zone on planetary rotation rate. Die astrofisiese joernaalbriewe: 787:1, April 2014

Kommentaar op hierdie inskrywing is gesluit.

Hi Ashley, very interesting article. One question from the extract below though:

“It is known that the hottest time of day on Earth does not occur when the Sun is at its zenith and thus nearest to the Earth, but rather several hours later.”

Agreed that 3 pm, plus or minus, is warmer due to thermal inertia, just as mid January in the northern hemisphere is colder than December 21st. What I don’t understand is the “and thus nearest to Earth” comment. The Sun is always directly overhead over some point of Earth and thus at zenith all the time somewhere. Solar zenith is not related to our distance from the Sun. Our orbit around the sun is elliptical. We are closest in January and farthest in July. Maybe I missed something.

I was using “zenith” here in its broadest generic sense as a point directly above a specific location rather than in a formal celestial sphere sense.

It would be interesting to know what effect the creation of the Moon had on the rotation of the Earth. Would the Earth be tidally locked if not for the creation of the Moon?

Known examples plenty: Venus is not tidally locked. (but the situation is maybe even worse than being tidally locked.) the best analogy is probably the situation of Mars though: a 24 hour day but with much bigger swings in seasons and greater instability variations of its axis over long periods of time.

Very good explanation of tidal locking and synchronization.

Are you intending to do a follow up to look into the issue of tidal lock (and synchronization) on habitability? Is it a “life killer”, or does it offer a “temperate” zone on the terminator? Does it offer some shielding from high energy flare radiation?

If you read the many excellent reviews of this subject by Meadows and Rory Barnes in particular, referenced above ( they are all great reads ) the general consensus is that synchronous rotation is not a habitability killer. This is the view of much ( but not all of course) of the astro/geophysics community.

With enough atmosphere and/or ocean, heat can be distributed around the putative tidally locked planet enough to atmospheric collapse via freeze out on the “dark side” (although as you can see from the Leconte graph atmospheres help resist synchronicity ) .

The thing that troubles the scientific community far , far more is the extended pre-main sequence luminosity of all but the largest M dwarfs. Something Barnes has demonstrated in his sophisticated simulations too.

That’s why JWST finding CO2 in TRAPPIST-! d,e and/or f via transit spectroscopy is so vital ( and difficult – involving a sizeable chunk of the time et aside for exoplanet science) as that will show that secondary atmospheres can develop and persist around even active late M dwarfs of which TRAPPIST-1 is a representative example.

Hi Ashley,
Nice review, thanks.
Regarding the effects of the elevated stellar luminosity during the long pre-main sequence for M dwarfs, Kenyon and Bromley wrote a paper a few years ago pointing out that planet formation can occur well outside the habitable zone up to a billion years after the formation of an M dwarf. In about

5 percent of their simulations, the planet ends up in the habitable zone so this may be one way to have planets in the HZ that still have an atmosphere.

Thanks David . I am familiar with this work and it is indeed very much my hope although not everyone agrees with this scenario. But it’s important to take away from both this – and the content of my article – that most if not all of what is known is based purely on simulation . Until we have hard atmospheric characterisation data from JWST, the ELTs and hopefully WFIRST this will remain the case. Certainly in terms of habitability potential. Not too long to wait though .

Interesting paper, but I have never heard the idea of “thermal torques” before this article. I doubt any effects of a large atmosphere could slow down the rotation or speed of the axial spin of a planet if I have understood this idea presented here correctly. The reasons for Venus slow rotation are some interaction with Earth’s gravitational field and the Sun’s which slowed down Venus rotation since Venus might never have had much axial spin from the start.

Earth got it’s fast rotation or axial spin from a collision with a large body called Theia which gave the Earth the needed kinetic energy and angular momentum as theorized in the large impact hypothesis which is why a Moon is needed for an exoplanet to have a fast axial spin.

Consequently, the Earth will not be tidally locked with the Moon for tens of billions of years if these survive the red giant phase.

I assumed what Ashley meant was either an atmospheric version of the friction from ocean tides, or the effect of the bulge in the atmosphere due to heating having a similar effect to the gravitational bulge as outlined in the post.

Although ocean tide friction was not mentioned, it would be useful to have some orders of magnitude size effects for the various mechanisms that slow rotation.

From the link above it looks like the Earth has added about 3 hours to the length of day since the “Cambrian explosion”. Unlikely as it seems, the day would be 25 hours longer after 4 billion years, i.e. longer than our current day length, suggesting that this rate of rotation deceleration must be increasing over time.

There’s nothing new about the concept of atmospherically induced torques or “tides” . The theory originally dates back to Gold & Soter’s work in the late sixties . It continued unabated till culmination and definitive description with Leconte’s sophisticated computer modelling and simulations of 2015 – cited and referenced here. They are both very real and very potent as is clearly shown in the enclosed graph and related citation .

Levonte’s work is recognised and confirmed in Barnes’ far reaching “tidal locking” paper of 2017. This then goes on to explore the evolution of tidal locking in a wide range of planets of varying mass in varying orbits around the different mass stars – up to an including Earth mass at 1 AU from of a Sun analogue.

Regardless of the Earth’s rotation time before and after the putative (and still debated ) high angle impact of “Theia”, Barnes’ extensive simulation runs show that a moonless Earth mass planet in a 1 AU orbit about a sun mass star could become tidally locked within 4.5 billion years. Unless it’s baseline rotation rate was less than three days.

Pedantic comment, but important. PEMDAS! In the equation, if everything to the right of the solidus is meant be the denominator, as I suspect, then they MUST be enclosed in parentheses or the answer will be wrong by (Gmp^2 kR^5)^2.

No, this is not pedantry. Notation is all important. For example, try to interpret this sentence in the context of that ambiguous equation:

“The gravitational constant G ensures that increasing stellar mass will substantially decrease Tlock.”

It would also be helpful to add explanatory information to a few of the charts (which must be in the original source) since they are otherwise a mystery.

I’m in agreement about the importance of notation here. I’ve inserted the needed parentheses, as per djlactin.

Analyses such as these may help by guidance on where to look and what to look for. That could reset the Fermi paradox.

Ja. As has been pointed out there are a lot of m dwarfs and one thing that has been shown is that these stars seem to possess planets in abundance. If any of these can be shown to harbour habitable planets then the game is well and truly afoot.

Magnetic fields, torque, magma oceans, and the music of the spheres, every time the Earth and Venus come close together she has the same face looking at the earth. A very good read is the book called “A Little Book of Coincidence” by John Martineau all about the graceful music of the solar system’s planets. This pattern is already being seen in the tightly packed planets around red dwarfs. One idea that may also influence these planets are the strong magnetic field of the red dwarfs and the other planets that come so close by each other. Many of these planets are earth to super earth size and have large oceans or large magma oceans beneath their surface, as in the large thick atmosphere of Venus would have large effects on rotation.

The other side of the coin is the possibility of elongated planets as the molten planet forms in the early age of the miniature solar systems. The chaotic nature that developed in these larger planets under the stress of close neighbors and a much closer star would make for variety of Io type planets with higher order aberrations in shape then anything in our solar system.

But what may be most intriguing are planets further out that have solidified enough that their surface is stable but would have a oval shape with oceans on the sun facing pole and glaciers on the twilight world of the opposite pole. In between would be low radiation lands with volcanoes and life migrating back and forth as the tides oscillate the planet. A nice day dream but maybe it will not be too long till we see the beauty of the chaos and its enchanting music.

Thank you Ashley for some very good food for my imagination!

Very good explanation of tidal locking and synchronization, with Pluto-Charon as outstanding examples of total lock.
Larry Niven & I took Pluto-Charon as a guide to our concluding novel in our Bowl of Heaven series. Our last megastructure is a gigantic tubular lifezone between Earth-scale worlds with Pluto-Charon locking. That expands beyond our Bowl ideas and yields an immense system with transport along the axis that deploys using pressure elevators to run the biosphere. The novel is Glorious, out in June. The first two Bowl novels are out in mass market paperback, over a thousand pages!

As ever I look forward to reading it .

I’m glad too if this all underpins just how important tidal locking is in planetary astronomy . Barnes’ findings alone have huge implications .

JWST allowing I’m hoping that with a bit of CO2 on TRAPPIST-1 e and you’ll get even more and exotic fictional opportunity with it in terms of life in M dwarf systems !

Even the Earth, had its starting rotation been greater than just three days, according to Barnes 2017, might have become synchronous.

If that means a 72 hour day, I thought the Earth was rotating faster than a 24 hour day after the Moon was formed and has since slowed down. Can you explain this?

Nearer to five hours according to simulations.

The 72 hour period for an Earth mass planet around a sun mass star is simply one of many hypothetical permutations Barnes ran through his (literally) thousands of sophisticated simulations over ‘giga years’. Counterintuitively showing that under arbitrary circumstances even terrestrial mass planets can become tidally locked as far out as the hab zone of early G stars.

All this based around two refined variants (see ‘ four in one ‘ graph and accompanying text) of the established and robust ‘equilibrium tide’ model that was in turn derived from the same maths that created the very simplified demonstration equation cited above .

Venus had oceans earlier but they were evaporated into space and a lot of water was lost from atmospheric stripping based on the DH2O ratio being higher in Venus atmosphere than Earth’s, a two to one ratio. Maybe the weight of the atmosphere or it’s torque slowed down Venus and gave it a retrograde rotation.

There does not have to be synchronization to have tidal locking, e.g., Mercury.

Alex Tolley, The reason why the Earth’s rotation is being slowed down by the tidal forces of the Earth and the angular momentum of the Earth’s axial spin or rotation is being transferred to the Moon’s orbital momentum so the Moon is slowly moving further away from the Earth a few centimeters per year. In the distant future we won’t have total eclipses anymore. At the same time the Earth is gaining time in it’s daily revolution which slowing down a small amount like one and one half miliseconds per century. Kopal 1979, The Realm of Terrestrial Planets.

This indicates that the Earth had to be spinning faster in the past. There is geological evidence: Scallops make one line on their shells every day which is visible under the microscope. They are the deposits of calcium carbonate made every day on their shells everyday so we know the Devonian year had to be 400 days long instead of 365 as today the scallops have 400 lines on their shells. Also the tides were larger and came further into the land shown by fossil evidence, so that indicates the Moon had to be closer to the Earth and the gravitational tidal forces were greater. Lyle, 2016, The Abyss of Time. Library book so I don’t have the page number.

Kopal’s Book, says in the Cambrian there were 500 days a year with only 21 hours a day. Devonian: 380 days a year with a 21.6 hour day. Carboniferrous 290, and 22.6 hour day, Upper Crataceous, 23.67 hour day etc. Library book.

This is the point I was trying to make. Using your example of a 21 hour day in teh Cambrian (0.55 bya), that is a decrease of 3 hours. Now extrapolate back to 4 bya and the decrease is now 21.8 hours. So the day length was just 2.2 hours. If the Moon was formed 4.5 bya (a tad early), the day length would be MINUS 30 minutes. I seriously doubt that Earth had such a rapid rotation rate even after a collision with the body that formed the Moon. While the effect of the Moon receding is due to momentum transfer, the key point is that it is due to the tidal friction. But when the moon was much closer, those tides would have been much larger and the frictions concomitantly higher as well, implying an even faster slowing down of the Earth’s rotation in the past than today. Something must have been different in teh past so that these extremely short daylengths cannot have been correct even using the more recent daylength calculations, and assuredly even faster [!] when the Moon was closer and the tides higher.

Does this make sense, or am I missing something?

A lot , indeed most of its angular momentum was probably lost through tidal interactions with the moon – which is moving further away taking energy with it as it goes . The rotation immediately after the Moon formation impact 4.5 billion years ago is currently modelled at just five and half hours . ( before that, who knows ? – but hazarding a guess – and looking at the non synchronised planets in the solar system whose angular momentum must have arisen from the same accretion disk – somewhere between 8 and 20 hours ) It then reduced over the next 4 billion years , simulated at about 21 hours by the pre/ Cambrian 600 million years ago .

The deceleration since then has increased at a greater rate – apparently due to extended periods of severe glaciation. ( without going into detail here – but it’s all available on line )

I should have read your comment first. So the relatively recent glaciations are the cause of a more recent faster slowdown in rotation compared to the earlier Earth eras? [My initial calculations used the 2.3 ms/day per century rotation slowdown from the NASA link which I assumed to be current during our interglacial period.]

Try “Analysis of Precambrian resonance-stabilised day length” Bartlett C and Stevenson D, Geophysical research letters, July 2016

Yet another mooted “Snowball Earth” heavyweight glaciation

So, the difference the moon-formation-impact made for the Earth rotation was anywhere between roughly 3 and 15 hours. Is there a way to narrow this down this a bit more?
And does the above equation indeed imply that a larger planet decelerates more rapidly (Tlock is divided by mp^2)? That puzzles me, since I would expect a heavier planet to retain more momentum.

Further with regard to the impact of the moon on Earth’s rotation rate, and after checking some more literature (e.g. Williams, G.E., 2000. “Geological constraints on the Precambrian history of Earth’s rotation and the Moon’s orbit” Bartlett, B.C., Stevenson, D.J., 2016. “Analysis of a Precambrian resonance-stabilized day length”), I wonder which of the effects of the moon has been strongest:

1) Angular momentum transfer, slowing down Earth’s rotation.
2) Atmospheric tidal resonance (as described in this post), stabilizing Earth’s rotation.
3) The moon-creating impact, speeding up Earth’s rotation.

Anyway, I understand now that this is a complex issue, which can work out both for better or for worse on a planet’s rotation.

What about libration? The Moon wobbles a bit in it’s orbit, so that we can see about 60% of it’s surface from Earth.

Is libration likely to be significant in tidally locked exoplanets, especially in those around M-dwarfs? If so,what effect would that have on climate?

Libration , like relativity is function of perspective . Like relativity it also demonstrates underlying theory

Libration is an observational phenomenon arising from oscillations in the gravitational evolution of the Earth/Moon orbital system . As seen from the Earth .

It is the product of three separate features. The first two are evolutionary facts of the tidal locking process and the last a quirk of observational viewpoint.

Firstly: ‘libration by longitude ‘ – the fact that despite orbital synchronisation the Moon’s orbit is not perfectly circular and retains a low eccentricity . So the moon leads or lags in its orbit of the Earth over time . This allows observers from the Earth to see ‘around the edges ‘ of Earth facing hemisphere over the course of an orbit.

Secondly : ‘ libration by latitude ‘ – despite synchronisation the moon retains a small but significant 6.7* tilt with respect to the Earth / Moon orbital plane . This again leads to observers being able to ‘see around the edges’ as above .

Finally the gravitational interaction that leads to synchronisation arises from the centre of mass of the combined system . This occurs on an imaginary ‘straight line’ connecting the centres of mass of the Earth and Moon. So any observer at the edge of the Earth as its rotates can again quite literally see around the edge of the hemisphere as opposed to that seen by a hypothetical observer situated at a point on the straight line ( on the Earth’s surface )

Each individually small but added up these three facets allow 59% of the Moon to be viewed in total.

As time progresses and left to itself tidal locking should reduce the orbital tilt of the smaller body in a ‘two body’ system to zero. Then (and much slower ) it’s orbital eccentricity to zero too. The Earth/ Moon is not a true two body system though ( are any ?) . Nor is the Earth a particularly massive body in the astrophysical terms . As such it is subject to constant additional gravitational perturbation from other solar system bodies not least the much more massive Sun and Jupiter. It is these interactions that drive the oscillations that translate into libration.

So I would guess that ‘pure’ synchronisation never occurs though libration itself though arising from gravitational interaction and orbital dynamics is ‘in the eye of the beholder’ .

In terms of exoplanets it serves to offer a diluted snapshot and insight into the consequences of tidal locking , synchronisation and their evolution .

If there are indeed exomoons out there – and circling tidal locked planets, the gravitational effects of their much closer star will be far more pronounced than that of the Sun on the Earth/Moon system . So libration would likely be even more pronounced.

Thanks for the detailed explanation. So from the perspective of an observer on an exoplanet, would the sun appear to rock back and forth over the course of an orbit? This could be a significant factor on the climate of the terminator.

Excellent post explaining tidal locking very well.
“Know the star to know the planet, but know the orbit to know them both” I used the first part myself a lot as a slogan, but you taught me the relevance of the 2nd part!
BTW, I think there is a slight error in the text: “stars of 0.5 Mearth – 0.7 Mearth”, I think that should be Msol instead.

I am a bit late in this discussion, due to being busy at work and at home, but this topic, related to stellar type and habitability is one of my favorite. I am familiar with the seminal work of Barnes et al. “The Barnes work hints at potential overlap of the habitable zone for potentially a large fraction of K-class and even many G-class stars, driven by factors beyond simple stellar mass. Clearly planets with a slow initial rotation rate…”. Darn, that’s a very sobering thought! I used to think that high initial rotation was the logical result of the disc accretion into planets. But if a moon-creating impact is necessary for it as well, then high rotation, not tidally locked planets might be much rarer.

With due respect, I have one minor disagreement:”increasing stellar mass is a major factor in reducing time to tidal locking”. Well, since the correlation is linear and solar type stars vary only a little in mass (about from 0.7 tot 1.1 Msol), I think that is a relatively modest factor, in comparison with the overwhelming impact of orbital distance (AU), as Fig. 2 also shows clearly.

Please see my comment (Ronald January 20, 2020, 8:52) under the recent post:https://www.centauri-dreams.org/2020/01/13/orange-dwarfs-goldilocks-stars-for-life/What I have tried to do myself is to show the combined importance of the concept of CHZ ánd that of T-lock, by plotting both T-lock and T-CHZ (= residence time in the continuous HZ) for an earthlike planet against stellar Teff (and all other factors, such as initial rotation rate and eccentricity equal). Ok, maybe it would have been better to use stellar luminosity instead of Teff, but Teff is a rather good proxy, because it correlates to the 4th power with luminosity. I have the T-CHZ from table 2 in the cites paper “About Exobiology: The Case for Dwarf K stars” by Cuntz and Guinan. And I based T-lock upon their baseline in chapter 4: that T-lock for a planet in de CHZ of a star with Teff of 4800 K (about K3) is 4.5 gy, and working from there, given the fact that T-lock correlates with the 6th (!) power of orbital distance.

What we see is that T-CHZ and T-lock are correlated with Teff (and hence stellar luminosity) in sort of opposite ways:The result is a large ‘X’ shaped graph, in which T-lock is going from low to high with increasing Teff, and T-CHZ going from high to low with increasing Teff.

Since both tidal locking and leaving the CHZ are detrimental to higher (= complex multi-celled) life, I consider both as absolutely limiting factors. So a planet would have to be underneath both lines in the graph, in order to be habitable for higher life. Hence, only the bottom section of the 4 sections of the X is habitable (for higher life).

In this graph the optimal stellar Teff would be where T-lock and T-CHZ are the same: the intersection of the 2 lines which is also the highest point of the bottom section. Here both T’s are at their combined maximum. I think that optimum lies somewhere around 5200 K, or about K0, where T-lock and T-CHZ are both around 20 gy.

Ok, the exact numbers may have to be amended, but I hope the principle idea is clear. Again, I did not consider different initital rotation rates, eccentricity, axial tilt, moons etc., just assuming an earth analogue.(I could sent the graph to Paul for your review and critique).


Will the earth and sun ever be tidally locked?

twice the tidal effect on the Earth as the Sun does hasn't had enough time to tidally lock the Earth it.

twice the tidal effect on the Earth as the Sun does hasn't had enough time to tidally lock the Earth it.

twice the tidal effect as the sun, so it would seem unlikely until the moon's orbit moves far enough away from earth that the sun has a greater effect or that the period of lunar orbit equals one earth year.

You can estimate the time it would take for one body to tidal lock to another by the formula:

Tidal locking takes time to occur.

The factors include the initial rotation speed of the body, its distance from the other body, Its moment of Inertia, the Mass and radius of the body it is orbiting, plus a couple of coupling factors.

I mentioned the Moon because its tidal effect on the Earth is larger than the Sun's, so if not enough time has passed for the Moon to slow the Earth's rotation to match its orbit, then definitely not enough time has passed for the Sun the tidally lock the Earth to it.

Ummm. Die maan is tidally locked.

The above equation is a good one though.

Not to sound rude, but: so? The earth-moon and earth-sun systems are independent (barring the rotational effects the moon has on the earth). There's no sense in comparing the two.

Besides, the question is whether the Earth will become tidally locked to the Sun. In this case, the earth is the satellite and the sun is the primary. In the earth-moon, the earth is the primary and the moon is the satellite. The OP asked whether or not the earth will be tidally locked to the Sun, not the other way around.

You can estimate the time it would take for one body to tidal lock to another by the formula:

Tidal locking takes time to occur.

The factors include the initial rotation speed of the body, its distance from the other body, Its moment of Inertia, the Mass and radius of the body it is orbiting, plus a couple of coupling factors.

I mentioned the Moon because its tidal effect on the Earth is larger than the Sun's, so if not enough time has passed for the Moon to slow the Earth's rotation to match its orbit, then definitely not enough time has passed for the Sun the tidally lock the Earth to it.

I mentioned the Moon because its tidal effect on the Earth is larger than the Sun's, so if not enough time has passed for the Moon to slow the Earth's rotation to match its orbit, then definitely not enough time has passed for the Sun the tidally lock the Earth to it.

Tidal force is proportional to the mass exerting the force and inversely proportional to its distance. The moon is 1/27210884 the mass of the Sun, but it is 400 times closer. So the Sun's tidal force on the Earth is 27210884/400^3 = 0.4252 times that of the Moon.

It is This tidal force acting on the Earth which would cause it to lock with either the Earth or Moon. Since the Moon exerts the greater tidal force on the Earth, It would be the first to tidally lock the Earth to it.

Actually, if you look at the formula I gave for the time for tidal locking to occur, you will note that it increases by the distance between the bodies (a) to the power of 6, and decreases by the mass of the acting body by only the square of the mass.

So 400^6/27210884^2 = 5.53, meaning that it would take

5.5 times longer for the Sun to lock the Earth to it than it would for the Moon to lock the Earth.


What is the Wicked High Tides program?

SciStarter, Northeastern University, NISE Network, Arizona State University and Museum of Science, Boston are working together on a National Oceanic and Atmospheric Administration-funded project to educate and engage the public in climate hazard resilience planning. This includes engaging participants with citizen science, deliberative forums and civic action.

The projects connect the general public to various climatic hazards by allowing them to participate in climate resilience planning in their communities and introduces citizen science projects related to each hazard. Engaging participants in citizen science activities allows community members to understand, learn and contribute meaningful data to projects centered around climate resilience.

In the summer of 2019, MOS studied the impact of extreme heat and the urban heat island effect through citizen science. Nicknamed “ Wicked Hot Boston ,” the pilot year recruited members of the general public to participate in the ISeeChange project and urban heat mapping and then asked them to share their experiences and potential solutions . The program’s success inspired other, similar programs focused on environmental hazards, such as Climate-Conscious Durham with the Museum of Life + Science in Durham, North Carolina.

In the second year of the project, the MOS team focused on the extreme hazard of sea-level rise with the catchy nickname “Wicked High Tides.” In 2020 and 2021, the project involves the citizen science projects MyCoast and ISeeChange .

MyCoast invites participants to document tides, storm damage, beach cleanups and more via their app, and ISeeChange asks citizen scientists to investigate how weather and climate change impact their lives and community by sharing photos and stories about multiple hazards, including sea-level rise. In addition, the project involved a webinar and two deliberative forums one in person and one online .

Discover both ongoing projects on SciStarter’s Museum of Science, Boston microsite .

What is Citizen Science?

Citizen science is public engagement in real scientific research, most often by collecting data or analyzing data for ongoing research projects. SciStarter connects a community of over 100,000 citizen scientists with thousands of different projects spanning astronomy, health, biodiversity and everything in between.

Via the portals on SciStarter.org/NOAA , SciStarter works with the museums and science centers, as well as the project leaders for featured projects, to walk patrons through the process of engaging in an ongoing environmentally-focused citizen science project to better understand a particular climate hazard. The goal is to introduce them to a forum or another event for further engagement.

Wicked High Tides Forum

All citizen scientists who participated in ISeeChange and MyCoast via the Museum of Science, Boston’s SciStarter microsite were invited to participate in a climate hazard resilience forum on sea-level rise. The first forum was held in person on March 3, 2020, and the second forum was held online due to Covid-19 on November 10, 2020.

Forum programs engage participants in deliberative, inclusive conversations about issues that lie at the intersection of science and society. These programs allow Museum visitors, scientists and policymakers to share their perspectives and learn from one another.

This project uses the climate hazard resilience forums , and the goal of the forums is to explore potential vulnerabilities to city infrastructures, social networks and ecosystems from sea level rise, extreme precipitation, drought and extreme heat, then discuss potential strategies for addressing these threats. Participants learn and discuss stakeholder values, consider the trade-offs of various resilience strategies, make a final resilience plan, and then view an interactive StoryMap that visualizes how their plan will affect the city and the people who live there.

Snehal Pandey, a student from the Berklee College of Music, attended the in-person event and said it would change the conversations that she had with friends. Her classmate, Nathhania Pasila, a freshman pianist from Jakarta, echoed the sentiment. She said the event opened her eyes, because she didn’t realize that there were multiple ways and equally valid choices about how to manage water. From her perspective as a musician, Pasila thought she could use her platform as a way to “treat the planet better.”

Once the tables were done discussing the resilience strategies they would implement in the anonymized Town of Kingtown, they turned their attention to the front of the room where Julie Wormser , the Deputy Director of Mystic River Watershed Association gave a presentation on how sea level rise affects the Boston area and what resilience strategies have been, or are going to be, employed in Boston to mitigate sea level rise. Finally, the participants were able to talk to eight local community groups who work daily on sea level rise issues about how to be part of the solution.

Reverend Vernon K Walker, a participant in the project and collaborator with the Museum of Science, Boston forum team in both the extreme heat and the sea level rise projects, is an organizer of Communities Responding to Extreme Weather . He attended the in-person forum event. Walker’s organization fosters resilience hubs, places where people can take refuge from climate impacts, and provides other services related to resilience — for example, cooling centers in the summertime, emergency preparedness kits for flooding. “We’re a statewide organization, and we know that there is going to be more in-land flooding,” said Walker. “Projects like this prove the point that this is going to get worse with climate change. It’s critical that this information is captured.”

What Comes Next?

This work is still ongoing. Over 20 sites across the United States have been accepted to receive a stipend to implement the NOAA-funded Citizen Science, Civics, and Resilient Communities (CSCRC) project between March and September 2021. This program model will increase resilience to extreme weather and environmental hazards through citizen-created data, local knowledge and community values.

And thanks to NOAA Grant NA15SEC0080005, more than just museums and science centers are using the free forum materials . Brittney Beck, Assistant Professor of Education at California State University, Bakersfield, used the forum materials with a group of educators, who were exploring new resources for their students. “As I facilitated each phase, I noticed their conversations became increasingly nuanced,” she said. “The teachers transitioned from talking about sea-level rise in abstraction to engaging in an intense, interdisciplinary debate regarding how to address it.”

After the Forum facilitated by Beck, one teacher reflected, “I knew about the potential of sea-level rise, but I never had an emotional reaction to it until now. I want to empower students to do something about climate change.”

The 20+ museum and science center sites will participate in citizen science projects and climate hazard resilience forums over the next year. If you are close to any of these host institutions, we encourage you to participate in citizen science and attend a “Climate Hazard Resilience” Forum near you. And no matter where you are in the world, you can study environmental impacts with citizen science and take part in one of the open, online forums. Stay up to date on all the projects at SciStarter.org/NOAA .

Take part: RSVP for the first open, online forum on June 23 about Sea-Level Rise.


Problems for uniformitarianism posed by tidal lock

Tidal locking is as likely to happen to the primary as to the moon. Indeed, Pluto and Charon are mutually locked. But tidal lock has its most profound implications for the Earth-Moon system. Though the presence of tidal locking might appear to militate in favor of a great age for the solar system, the dynamics of tidal lock suggest youth, not age.

As earth's rotation decreases, the moon must recede from the earth, or else angular momentum is not conserved (see above). Therefore, the rate of deceleration of Earth's rotation must itself decelerate over time. For that reason alone, the Earth-Moon system cannot be more than 1.2 billion years old, because at such a time the Earth would have been rotating dangerously fast, and the Moon would have been touching the Earth.


Kyk die video: Zomer en Winter Dag en Nacht: Hoe seizoenen ontstaan, en hoe aarde, zon, maan en satellieten draaien (Desember 2022).