Sterrekunde

Hoe het die ligter elemente in die middel van die sonnestelsel beland? Sonnestelselvorming

Hoe het die ligter elemente in die middel van die sonnestelsel beland? Sonnestelselvorming


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Die vorige generasie sterre is bekend as die oorsprong van al die swaarder elemente (tot yster?) In die sonnestelsel. 'N Groot deel van die sonnestelselmassa bestaan ​​dus eintlik uit koolstof, silikon, yster en dies meer. Maar in die middel, en net in die middel, is daar 'n ster met vermoedelik amper geen swaar elemente binne nie. Hoe kan dit wees? Is ek verkeerd oor die werklike massakonsentrasies of is daar regtig 'n wanbalans, d.w.s. is die elementverdeling regtig ligter in die middel van die sonnestelsel? Ek sou aanvaar dat die vorige generasie sterre net geëindig het in 'n min of meer eenvormige wolk van puin, waaruit die sonnestelsel gevorm het. Maar as dit so is, waarom is daar nie sterrestelsels waar die ster 'n heel ander samestelling het en 'n soort vuil, vuil samesmeltingsmasjien is nie (metafories, bedoel ek)?


Die sonnestelsel bevat min elemente wat swaarder is as Helium - minder as 2% per massa.

Dit word weerspieël in die chemiese oorvloed wat in die fotosfeer van die son gemeet word. dws die son bevat wel swaarder elemente.

U vraag is verkeerd; dit is nie dat die swaarder elemente nie in die middel gesink het nie, dit is dat die oorgrote meerderheid waterstof en helium wat op dieselfde plek was as die planete toe hulle gevorm het, nie as deel van die planete beland het nie. In werklikheid is dit selfs net gedeeltelik waar. Die massa planeetmateriaal in die sonnestelsel word ook oorheers deur die waterstof en helium in die gasreuse.

Die probleem is dus net die rede waarom die kleiner planete nie 'n soortgelyke samestelling het as die son nie. Die antwoord daarop is temperatuur en swaartekrag. 'N Klein, warm planeet het net nie die swaartekrag om vinnig bewegende waterstof- en heliumatome te behou nie, tensy dit vasgevang is in 'n verbinding (soos water!).

Dus is die klein planete naby die son uitgeput van ligte elemente.


Teen die einde van 'n sterre se lewensiklus verloor die ster die vermoë om waterstof ens te bly gebruik. Om homself aan te dryf, begin dit, (in 'n desperate poging om te lewe.) Swaarder elemente soos yster te skep. Nou kan yster beslis nie 'n ster onderhou nie.

As sodanig vernietig die yster die ster en merk dit dus die einde van sy lewensiklus.

Daar bestaan ​​waarskynlik klein hoeveelhede yster in sterre (vanuit die oogpunt van die heelal.) Maar dit is nie genoeg om die ster waarin dit is, werklik te beïnvloed nie.

Yster is natuurlik nie die enigste dinge wat sterre vorm wat die ster uiteindelik doodmaak nie, maar ek gebruik dit net as 'n voorbeeld hier.

Nietemin is sterre baie interessant, net soos enigiets anders in die ruimte.

P.S. Dit is net my basiese begrip van ruimte, en ek leer baie op hierdie webwerf.

Lekker dag / nag.


Hoe ons sonnestelsel in die verre toekoms sal eindig

Die aarde sal eendag vries sodra die son sterf, maar dit is net die begin. Beeldkrediet: Kevin. [+] Gill onder cc-by-2.0, via https://www.flickr.com/photos/kevinmgill/14326057397.

Dit het 13,8 miljard jaar kosmiese evolusie geneem om ons hierheen te bring. Geslagte sterre moes leef en sterf om die swaar elemente te skep, klein proto-sterrestelsels moes saamsmelt om die Melkweg te skep. Interstellêre gaswolke moes in duie stort en nuwe sterre vorm met rotsagtige planete rondom, komplekse anorganiese en organiese chemie wat nodig was om vas te vat op een van die nuutgevormde wêrelde het die biologiese evolusie - en natuurrampe - 'n baie besondere weg ondergaan, wat uiteindelik 'n paar honderdduisend jaar gelede op die ontstaan ​​van mense uitgeloop het. Die afgelope 12 000 jaar het ons landbou, wetenskap, nasies en die hele moderne beskawing ontwikkel soos ons dit vandag ken. Dit is 'n merkwaardige reis wat ons wêreld verander het en danksy die mensdom se ruimteprogram ook ons ​​sonnestelsel verander het.

Mense stuur al 50 jaar robotte en onbemaakte sondes om op wêrelde buite ons land te land. [+] nou. Die sonnestelsel was nog nooit dieselfde nie. Beelde-krediet: NASA en Roel van der Hoorn.

Maar die wêreld wat ons vandag geniet, maak nie saak wat ons doen nie, sal nie vir ewig op hierdie manier hou nie. 'N Aantal aardse gebeurtenisse gaan gebeur wat dinge in ons wêreld verander, en dit maak die aarde nouliks herkenbaar vir iemand wat vandag leef. Na ongeveer 60 000 jaar sal die son en sterre genoeg beweeg het om die huidige konstellasies deurmekaar te maak en heeltemal verskil van hoe ons dit vandag sien. Nog 100 000 jaar daarna kyk ons ​​waarskynlik na die volgende ystydperk, danksy faktore wat niks met menslike invloed te doen het nie. En voordat die volgende miljoen jaar verby is, sal die Yellowstone Supervulkaan waarskynlik waai en die landskap van die aarde vir altyd verander.

Maar dit is alles grondboontjies in vergelyking met wat die Heelal vir ons voorlê.

Anders as 'n simulasie van die samesmelting van die Melkweg en Andromeda-sterrestelsels. Beeld. [+] krediet: NASA, ESA, Z. Levay, R. van der Marel, T. Hallas en A. Mellinger.

Vanaf 'n bietjie minder as vier miljard jaar sal die Andromeda-sterrestelsel (en heel moontlik die kleiner driehoekstelsel) saamsmelt met ons eie Melkweg, wat 'n skouspelagtige verandering aan die struktuur van ons sterrestelsel en die naghemel in die algemeen sal veroorsaak. Ons beste simulasies dui tans aan dat die eerste botsing en die uitbarsting van stervorming (paneel 4 hierbo) in 3,8 miljard jaar plaasvind, en dat die samesmelting voltooi sal wees 8) na 5,5 miljard jaar. Gravitasie sal veroorsaak dat die hele plaaslike groep uiteindelik met ons saamsmelt en een reuse elliptiese sterrestelsel vorm: Milkdromeda, waarvan ons sonnestelsel steeds deel sal uitmaak. Op groter kosmiese skale sal al die ander sterrestelsels steeds van ons af versnel, en uiteindelik - na miskien 100 miljard jaar - heeltemal van ons siening af wegtrek.

Maar ons sonnestelsel sal deur alles ongeskonde bly, al lyk dit nie soos vandag nie. Die son sal steeds warmer word namate hy ouer word, ons oseane binne ongeveer 1-2 miljard jaar kook en die lewe op aarde soos ons dit ken, beëindig. Uiteindelik, ongeveer 5-7 miljard jaar later, sal ons kernbrandstof in die kern van die son opraak, wat sal veroorsaak dat ons ouerster 'n Rooi Reus word en Mercurius en Venus in die proses verswelg. As gevolg van die besonderhede van sterre-evolusie, sal die Aarde / Maan-stelsel waarskynlik na buite gedruk word en die vurige lot van ons innerlike bure gespaar word.

As die berekeninge korrek is, moet die aarde nie deur die son verswelg word as dit in 'n rooi kleur uitswel nie. [+] reus. Dit moet egter baie, baie warm word. Beeldkrediet: Wikimedia Commons-gebruiker Fsgregs.

Na die verbranding van sy oorblywende kernbrandstof - meestal die helium in sy kern - verdryf die son sy buitenste lae om 'n planetêre newel te vorm, en die kern van ons ster sal saamtrek om 'n wit dwerg te word. Dit is die uiteindelike lot van byna alle sterre in ons heelal. Maar die planete sal steeds hier wees, om ons koue, dowwe sterrestelsel wentel, en hierdie proses sal vandag ongeveer 9,5 miljard jaar voltooi.

Wanneer die son sy kernbrandstof heeltemal op is, sal dit sy buitenste lae in a afblaas. [+] planetêre newel, terwyl die middel in 'n warm, kompakte wit dwergster saamtrek. Beeldkrediet: Vicent Peris, José Luis Lamadrid, Jack Harvey, Steve Mazlin, Ana Guijarro.

Gedurende al hierdie tyd bly die aarde egter om die son wentel, terwyl die maan steeds swaartekrag daarop trek, en dit veroorsaak 'n wringkrag, wat u kry as u 'n eksterne krag op 'n draaiende voorwerp uitoefen. Dit laat die Maan verder van die Aarde af beweeg terwyl dit terselfdertyd die rotasie van die Aarde laat afneem! Die verlangsaming is amper onmerkbaar, want die rotasie van die aarde vertraag (en dus verleng die dag) met slegs 1,4 millisekondes per eeu, maar ons het tyd. Na ongeveer 50 biljoen jaar sal die wentelperiode van die maan meer as 47 dae wees (in vergelyking met die huidige 27,3 dae), en ons 24-uur-dag sal traag wees: dit sal 47 van vandag se dae neem om net te maak eendag op die Aardedag van 50 miljard jaar in die toekoms. Op hierdie punt sal die Maan en die Aarde getyvergrendel word, sodat die Aarde en Maan altyd in presies dieselfde posisie in mekaar se lug verskyn.

Terwyl die maan al gety vir die aarde is, bly ons planeet draai. Slegs wanneer die. [+] Die wringkrag van die maan vertraag die aarde om vir die maan te word, en druk die maan verder weg, sal ons regtig toegesluit wees. Beeldkrediet: Dang, dit is cool! via http://dangthatscool.wordpress.com/.

Terwyl stervorming sal voortduur, sal sterwende sterre hul brandstof aan die interstellêre ruimte gee en mislukte sterre sal inloop en saamsmelt, is die hoeveelheid materiaal vir die maak van sterre eindig. Selfs die langlewende sterre sal slegs ongeveer 100 triljoen jaar (10 ^ 14 jaar) duur, en na ongeveer 'n kwadriljoen (10 ^ 15) jaar sal stervorming heeltemal ophou. Slegs die af en toe botsing of samesmelting tussen mislukte sterre of sterreste sal ons sterrestelsel lig gee, aangesien die laaste sterreste afkoel en in die duisternis verdof. Uiteindelik sal wit dwergsterre swart word, aangesien hulle afkoel en hul energie uitstraal. Dit sal baie lank duur: miskien volgens my skatting 10 ^ 16 jaar (alhoewel u kilometerstand verskil), of ongeveer 'n miljoen keer die huidige ouderdom van die heelal. Die atome sal steeds daar wees, maar hulle sal net 'n paar grade bo absolute nul wees. Op hierdie stadium sal die hele naghemel werklik donker en swart wees, en glad nie sigbare lig nie, aangesien al die sterre in ons plaaslike groep uitgebrand het.

Ons Son kan die laaste kans wees om te inspireer, saam te smelt of met 'n ander uitgebrande ster te bots. [+] skyn. Beeldkrediet: Tod Strohmayer / CXC / NASA en Dana Berry / CXC.

U kan wonder hoe lank dit sal duur voordat ons swart dwerg, wat eens ons Son was, 'n ander een teëkom, wat dit moontlik saamsmelt en weer lewendig maak. Tussen ons, Andromeda en die res van die plaaslike groep, sal daar een triljoen sterre en sterre-oorblyfsels vlieg. In hierdie chaotiese stelsel kan 'n tipiese sterstelsel baie, baie lank duur sonder om met iets anders te bots, maar ons het allerhande tyd. Na ongeveer 10 ^ 21 jaar sal die nou swart dwerg in die middel van ons sonnestelsel lukraak met 'n ander swart dwerg bots, wat 'n tipe Ia Supernova-ontploffing teweegbring en die oorblyfsels van ons sonnestelsel effektief vernietig.

Ons son sal nie dadelik in 'n supernova sterf nie, maar as dit bots of met 'n ander saamsmelt. [+] swart dwerg in die verre toekoms, 'n Type Ia-supernova sal tog ons lot wees. Beeldkrediet: NASA, ESA, Zolt Levay (STScI).

Dit sal uiteindelik die lot van baie sterre in ons plaaslike groep wees, maar nie almal nie, en waarskynlik nie ons s'n nie! Daar is nog 'n mededingende proses wat doeltreffender is en dus meer waarskynlik met ons sal gebeur: swaartekraguitwerping van die plaaslike groep as gevolg van 'n proses genaamd gewelddadige ontspanning! As daar verskeie liggame in 'n swaartekrag-chaotiese baan is, sal 'n mens soms uitwerp, en die res nog strenger gebind word. Dit is wat met verloop van tyd in bolvormige trosse gebeur, en verklaar waarom hulle so kompak is en ook waarom daar soveel blou stralers - of ouer sterre wat saamgevoeg het - in die kern van hierdie antieke oorblyfsels is!

Die sterre in 'n bolvormige groep is stewig vasgebind in die middel en smelt gereeld saam, maar op die. [+] buitewyke, uitgestote sterre is algemeen danksy gewelddadige ontspanning. Beeldkrediet: M. Shara, R.A. Veiliger, M. Livio, WFPC2, HST, NASA.

Gravitasie-uitwerping is ongeveer 100 keer meer geneig as 'n ewekansige samesmelting, wat beteken dat ons ster en die oorblywende gebonde planete waarskynlik na ongeveer 10 ^ 19 jaar in die afgrond van die nou leë ruimte sal uitgestoot word. Maar selfs daarby, as die aarde om ons sterrestelsel wentel en met niks anders nie, sal dinge nie vir ewig duur nie. Elke baan - selfs gravitasiebane in die Algemene Relatiwiteit - sal mettertyd baie stadig verval. Dit kan buitengewoon lank duur, ongeveer 10 ^ 150 jaar, maar uiteindelik sal die wentelbane van die aarde (en al die planete, na genoeg tyd) verval en in die sentrale massa van ons sonnestelsel draai. Dit is ons lot as ons uitgegooi word.

Die gevolge van die beweging deur geboë ruimtetyd sal daartoe lei dat die baan van die aarde uiteindelik verval,. [+] draai in die son in. Beeldkrediet: American Physical Society.

Maar as ons in die reusagtige sterrestelsel bly waarin Milkdromeda ontwikkel, is dit nie ons lot om in die sentrale swart gat van ons sterrestelsel in te draai nie. Dit sal 10 ^ 200 jaar neem voordat dit gebeur, maar swart gate kan nie so lank leef nie! Danksy die gekombineerde eienskappe van algemene relatiwiteit en kwantumfisika, sal swart gate massa verloor en mettertyd verdamp deur middel van 'n proses bekend as Hawking-bestraling na die ontdekking daarvan: Stephen Hawking. Hierdie stralende verval sal selfs die mees supermassiewe swart gate in die heelal na ongeveer 10 ^ 100 jaar uithaal, en 'n swart gat in die sonmassa in 'n skrale 10 ^ 67 jaar.

Na ongeveer 10 ^ 100 jaar sal selfs die heelal se grootste supermassiewe swart gate dit doen. [+] verdamp heeltemal weens Hawking-straling. Beeldkrediet: NASA.

Nadat die swart gat verval het, sal slegs donker materie oorbly, wat beteken dat die aarde in swart dwerg sal draai wat tog eens ons son was. Die enigste ding wat dit kan vermy, is as 'n botsing of 'n noue gravitasie-interaksie die aarde uit ons sonbaan wentel, en ons sodoende bevry word om in die diepte van die leë ruimte vrygelaat te word. Dit maak nie saak hoeveel keer ons wêreld in vuur eindig nie, ons uiteindelike lot is om te vries in 'n koue, leë Heelal. Ook al hierdie dinge sal verbygaan.


Hoe is die sonnestelsel gevorm? 'N Beginnersgids

Die algemeen aanvaarde teorie oor die vorming van die sonnestelsel is die Nebulêre hipotese, wat verklaar dat dit gevorm is deur die swaartekrag ineenstorting van 'n massiewe reuse-wolk genaamd die Solar Nebula.

Die algemeen aanvaarde teorie oor die vorming van die sonnestelsel is die Nebulêre hipotese, wat verklaar dat dit gevorm is deur die swaartekrag ineenstorting van 'n massiewe reuse-wolk genaamd die Solar Nebula.

Vinnige feit!

Die massa van die son is 99,86% van die totale massa van die sonnestelsel. Nege-en-negentig persent van die oorblywende 0,14% massa word gevorm deur Jupiter, Saturnus, Uranus en Neptunus. As gevolg van sy groot massa, kan die son swaartekrag op die res van die liggame van die sonnestelsel uitoefen.

Die sonnestelsel is 'n versameling hemelliggame wat 'n ster bevat, met planete en ander voorwerpe wat om hom wentel. Ons sonnestelsel bestaan ​​uit die son wat om 8 planete wentel (insluitend ons eie aarde) en baie ander voorwerpe soos mane (wat om planete wentel), asteroïdes en meteore. Verskeie hemelliggame soos die Son, Maan, Mercurius, Venus, Mars, Jupiter en Saturnus is met die blote oog sigbaar, terwyl die res van die planete deur teleskope sigbaar is. Daar is ook verskillende helder asteroïdes, komete en meteore wat sigbaar is.

Wil u vir ons skryf? Wel, ons is op soek na goeie skrywers wat die woord wil versprei. Kontak ons ​​en ons gesels.

Die son is die belangrikste lid van die sonnestelsel omdat dit die meeste lig, hitte en ander energie voorsien wat lewensbelangrik is. Die agt bekende planete wentel om die son in effens ovaalbane, waarvan die eerste vier planete: Mercurius, Venus, Aarde en Mars rotsagtige planete is, terwyl die volgende vier: Jupiter, Saturnus, Uranus en Neptunus gasagtige planete is. Pluto was vroeër die negende planeet en aangesien dit baie klein is, het wetenskaplikes dit regoor die wêreld gesamentlik afgebring. Daarom word dit nou nie meer as 'n planeet beskou nie.

▶ Vorming van die sonnestelsel

Deur die radioaktiewe verval van radioaktiewe elemente in die meteoriete te ontleed, het sterrekundiges gesê dat die oorsprong van die sonnestelsel teruggevoer kan word tot 4,6 miljard jaar gelede. Dit was toe 'n swaartekrag ineenstort van 'n klein gedeelte van 'n reuse molekulêre wolk. Dit staan ​​bekend as Nebulêre hipotese wat in die 18de eeu vir die eerste keer deur Emanuel Swedenborg, Immanuel Kant en Pierre-Simon Laplace ontwikkel is, en 'n teorie is wat wêreldwyd aanvaar word. Hierdie teorie is egter uitgedaag en verfyn na die aanbreek van die ruimtetydperk en die ontdekking van ekstra sonplanete in onderskeidelik die 1950's en 1990's.

▶ Nebulêre teorie van vorming van sonnestelsels

Volgens hierdie Nebular-teorie is die sonnestelsel gevorm uit 'n massiewe, roterende wolk van stof en gas wat die Sonnewel.

Dit het so gebeur dat die Sonnevel onder sy eie swaartekrag begin ineenstort het. Verskeie wetenskaplikes meen dat die ineenstorting van hierdie reuse-gaswolk veroorsaak is deur 'n supernova (ontploffende ster) daar naby, wat tot die sametrekking van die newel gelei het. Namate die wolk ineengestort het, het die hitte toegeneem, wat die stofdeeltjies laat verdamp het en die wolk in die middel saamgedruk het.

Toe die newel instort, het 'n groot fragment hom daarvan geskei om die sonnestelsel te vorm. Die son het ontstaan ​​uit die grootste massaversameling in die middel van die newel. Die druk in die middel van die newel het hoog genoeg geword om kernreaksies te veroorsaak wat die son kon dryf. Namate die newel in grootte gekrimp het, het dit al hoe vinniger gedraai en in 'n skyf afgeplat. Daarom het die massa rondom die son saamgevoeg en 'n skyf rondom hom gevorm.

Verder het die deeltjies in die afgeplatte skyf met toenemende frekwensie teen mekaar gebots en saamgesmelt om sodoende asteroïedvormige voorwerpe te vorm, bekend as planetesimale. Sommige van hierdie planeetdiere het verder gebots en met mekaar gekombineer om die planete te vorm wat ons vandag ken. Die res van die planeetdiere het saam mane, meteore, komete en asteroïdes gevorm.

Namate sonuitbarstings plaasgevind het, is sonwinde geskep. Hierdie winde was so kragtig van aard dat hulle die meeste ligter elemente soos helium en waterstof uit die sonnestelsel weggevoer het. Hierdie winde was egter swakker in die buitenste streke, en dus het die buitenste planete 'n groot hoeveelheid waterstof en helium gelaat. Dit verklaar die gasagtige aard van die buitenste planete en die kontrasterende rotsagtige aard van die vier binneste planete.

Wetenskaplikes glo dat sterre steeds verander en nie konstant bly nie. Hulle glo dat die buitenste lae van die son in die volgende 5 miljard jaar sal uitbrei, wat die son groter en warmer sal maak. Die uitbreiding van die son sal veroorsaak dat dit 'n rooi vuurbal word wat al die planete insluit, insluitend die aarde. Wetenskaplikes glo dit ook na 'n tydperk van 100 miljoen jaar sal die son sy vermoë verloor om energie te maak en uiteindelik 'n klein planeet wees.

▶ Kuiper-gordel

Wil u vir ons skryf? Wel, ons is op soek na goeie skrywers wat die woord wil versprei. Kontak ons ​​en ons gesels.

Dit is 'n deel van die sonnestelsel wat buite die planete lê. Die Kuiper-gordel lyk baie soos die asteroïedegordel en is gevorm uit planetsimale. Die planetsimale is basies fragmente wat van die proto-planetêre skyf afkomstig is. Die Kuiper-gordel is baie groter en 20 keer so breed as die asteroïedegordel. Die grootte wissel van 30 tot 55 AU (1 AU = 92,956 × 10 ^ 6 myl). Die planeet, Pluto, is deel van die Kuiper-gordel.

▶ Interstellêre wolketeorie

Volgens die interstellêre teorie is ons sonnestelsel gevorm uit 'n interstellêre wolk. Die belangrike gebeurtenis in die vorming van sonnestelsel was die deurloop van son deur 'n interstellêre wolk. Hierdie gebeurtenis het daartoe gelei dat die son uit die wolk met gas en stof omhul het. Planete van die sonnestelsel het geleidelik uit hierdie omhulsel van gas en stof na vore gekom. Die teorie is voorgestel deur Otto Schmidt, 'n sterrekundige uit Rusland in 1944.

▶ Vasleggingsteorie

Die teorie is voorgestel deur Michael Mark Woolfson, 'n planetêre wetenskaplike en Britse fisikus, in 1964. Die sonnestelsel is gevorm deur gety-interaksies wat plaasgevind het tussen 'n protostar met lae digtheid en die son. Die son se swaartekrag het gehelp met die teken van materiaal van hierdie protestar met lae digtheid. Planete van ons sonnestelsel is gevorm uit die materiaal wat uit die protostêr getrek word. Volgens die vasleggingsteorie, verskil die ouderdom van die son van die planete van die sonnestelsel.

Die bogenoemde & # 8216 Nebulêre hipotese & # 8217 is die algemeenste aanvaarde teorie van die vorming van die sonnestelsel. Daar is egter nie ooreengekom as die uiteindelike teorie nie, weens die ontstaan ​​van verskillende teoretiese probleme wat dit moeilik maak om dit met nuwe waarnemings te versoen.


Hoe het die ligter elemente in die middel van die sonnestelsel beland? Sonnestelselvorming - Sterrekunde

HOOFSTUK 1: OORSPRONG VAN DIE PLANETTE & VANDAG DIE SOLSTELSEL

1. Figuur 1.3: Die sonnestelsel bestaan ​​uit die son, nege planete, 61 mane en 'n menigte asteroïdes, komete en meteoroïede.

2. Die wentelbane van die planete is ellipties om die son

3. Die planete draai in die algemeen in dieselfde rigting om die son en binne die vlak van die ekliptika, behalwe vir Pluto, wat teen 17 o na die ekliptika gekantel is.

4. Die meeste mane draai om die planete in dieselfde rigting as die planete om die son draai.

5. Meteoroïede, asteroïdes en komete volg ook om die son.

6. Die rotasies van planete, mane en ander liggame word geërf van die rotasie van die antieke gaswolk waaruit hulle gevorm het.

Die aardse (rotsagtige) planete

1. Naaste aan die son en bestaan ​​uit Mercurius, Venus, Aarde en Mars.

2. Is oor die algemeen klein, rotsagtige liggame wat baie ooreenkomste en verskille het.

3. Digthede groter as 3 gm / cm 3.

4. Benewens Fe en Ni, hoofsaaklik saamgestel uit silikate.

5. Vulkanisme is grotendeels basalties, 'n swart rots relatief ryk aan Mg, Si, O en Ca.

6. Verskille waargeneem tussen die rotsagtige planete weerspieël faktore soos grootte en afstand van die son eerder as samestelling. Dit vertel ons dat hierdie rotsagtige planete vroeg in die geskiedenis van die sonnestelsel min of meer uit soortgelyke materiaal gevorm het.

Die Joviese (gasagtige) planete

1. Kom voor buite die baan van Mars en bestaan ​​uit Jupiter, Saturnus, Uranus, Neptunus en Pluto.

2. Oor die algemeen groter as die aardse planete.

3. Digthede kleiner as 3 g / cm3.

4. Elkeen (behalwe Pluto) bestaan ​​uit 'n vaste kern (waarskynlik rotsagtig) omring deur 'n dik atmosfeer wat bestaan ​​uit metaan, ammoniak, waterstof, helium en ander gasse. Pluto ontbreek aan 'n dik atmosfeer en bestaan ​​eerder uit 'n soliede kern met 'n dik buitenste laag ys.

5. Die meeste Joviese planete het verskeie mane.

6. Die meeste Jovian-planete het indrukwekkende ringstelsels wat bestaan ​​uit stof- tot rotsagtige deeltjies van meestal ys.

Teorieë oor die ontstaan ​​van die sonnestelsel

1. Gedurende die laat 1700's het Buffon die planete voorgestel dat dit van die son gevorm het. Hy het voorgestel dat die aantrekkingskrag van komete wat verbygaan, warm, gasvormige materiaal uit die son getrek het. Hierdie materiaal het later afgekoel en gekondenseer om die planete te vorm. Volgens Buffon was die son dus baie ouer as die planete.

2. 'n Ander vroeë teorie het aangedring op kondensasie (stolling) van die planete vanuit 'n warm, gasagtige wolk, wat die sonnevel genoem word, eerder as om die planete van die son self af te lei.

3. In die vroeë 20ste eeu het wetenskaplikes die idee van kondensasie van planete direk vanaf 'n warm gaswolk verdiskonteer, maar eerder die hipotese dat die planete en ander sonnestelselliggame saamgevoeg is uit koue wolke van stof en gasse. Volgens hierdie model het die planete aanvanklik gevorm as koue sfere as gevolg van stadige ophoping van stof en gas.

4. Die koue oorsprong van planete is aanvanklik voorgestel in die planetesimale hipotese, wat vroeg in die twintigste eeu deur Chamberlin ('n geoloog) en Moulton ('n sterrekundige) ontwikkel is. Volgens hierdie model het die aantrekkingskrag van 'n ster wat verbygaan, vermoedelik sonvormige materiaal uit die son gehaal. Hierdie gasvormige materiale het die son omring en begin klein, soliede liggame kondenseer van die grootte van asteroïdes (tien tot honderde km in deursnee) genaamd planetesimals. Hierdie planeetdiere het uiteindelik saamgevoeg om die vroeë planete te vorm, wat dan verder gegroei het deur nog meer deeltjies te lok.

5. Figuur 1.6: Sodra die koue, groeiende planete voldoende groot geword het, het die aantrekkingskrag van die swaartekrag oorgeneem. Die planete het uiteindelik 'n massa behaal wat swaartekrag veroorsaak het, wat interne verwarming en versagting tot gevolg gehad het, gevolg deur die skeiding van die verskillende materiale in diskrete lae. Digter materiaal het in die binnekant van die planeet gesink, terwyl ligter materiaal na die oppervlak migreer of dryf.

1. Figuur 1.2: 'n Ander idee, wat die newelhipotese genoem word, is in die middel van die twintigste eeu deur sterrekundiges von Weizacher en Kuiper voorgehou. Die newe-hipotese vorm dat die son en die planete gelyktydig vorm. Volgens hierdie model het ons sonnestelsel ongeveer 5 of 6 miljard jaar gelede as 'n reuse, skyfvormige interstellêre wolk van gasse en stof begin.

2. Daar is in die vooruitsig gestel dat stadige rotasie van hierdie interstellêre wolk geleidelik veroorsaak dat baie van die massa naby die middel van die skyf gekonsentreer word. Hierdie sentrale massa het verder saamgepers deur swaartekrag-aantrekkingskrag totdat dit uiteindelik 'n paar miljoen grade bereik het, wat veroorsaak het dat termonukleêre reaksies begin het. Hierdie sentrale, termonukleêre massa het die vroeë son geword.

3. Figuur 1.2: Die embrioniese son is omring deur 'n omhulsel van gas en stof wat die sonnevel genoem word. Onstuimigheid in die newel het eers kondensasie van planeetdiere veroorsaak. Die koue planeetdiere, benewens stof en gasse, het dan vinnig gebots en saamgevoeg om 9 of 10 protoplanete met soortgelyke samestelling te vorm. Mane het moontlik op soortgelyke wyse rondom hul gasheerplanete gevorm of is moontlik later van elders gevang deur die aantrekkingskrag van die planeet. Die oorblywende planetesimale het baie elliptiese bane ontwikkel en is uiteindelik deur Jupiter se swaartekrag uit die binneste sonnestelsel geslinger om komete te word.

4. Figuur 1.6: Die koue, homogene aanwasmodel sê dat namate protoplanete gegroei het, het hul geleidelik sterker swaartekragvelde nog meer materiaal uit die stofwolk opgevat totdat hulle uiteindelik groot, samestellend homogene planetêre liggame geword het van selfs groter omvang as tans, maar van baie laer digtheid. Die groeiende gravitasievelde het uiteindelik veroorsaak dat die groot protoplanete saamtrek en digter geword het. Hierdie inkrimping het gelei tot differensiasie waar die meeste van die swaarder elemente na die middel van die protoplanete migreer terwyl ligter elemente na hul oppervlakke beweeg. Baie van die ligte gasse van H en Hy het verlore gegaan in die ruimte.

5. Die vier binneste, aardse planete was relatief klein en het swakker gravitasievelde in verhouding tot die buitenste, gasagtige planete. Die binneste aardse planete verloor dus baie meer van hul ligter elemente as hul groter eweknieë.

6. Die sonstraling, of sonwind, het die samestellings van die planete verder verander deur die oorblywende newegasse weg te waai na die buitenste deel van die sonnestelsel.

7. Onlangs is die warm heterogene aanwasmodel ondersoek. Volgens hierdie model het die interne sonering van die planete ontwikkel tydens, nie na akkretêre akkumulasie nie. Daar word vermoed dat aanwas met die sonnevel begin het op 'n tydstip toe die gasse nog baie warm was (& gt 1000 C). (A) Toe die newel begin afkoel, het primitiewe Fe en Ni eers opgehoop om die metaalkern van die planeet te vorm. (B) Silikate wat later rondom die vroeër gevormde kern opgegroei het namate die temperatuur steeds daal. (C) Ten slotte het die mantel gedifferensieer om die kors te vorm.

Figuur 1.5: Samevatting van die voorgestelde stadiums vir die vroeë evolusie van die Aarde.

Chemiese en termiese evolusie

1. Die vroeë aarde, ongeveer 4,5 miljard jaar gelede, het soveel as vyf keer soveel produksie van radioaktiewe hitte gehad as nou.

Na aanvaarding is die verhitting van die vroeë aarde veroorsaak deur:

(a) Aanvanklike verhitting as gevolg van gravitasiekrimping wat die temperatuur van die aarde se middelpunt met 1000 ° C kon verhoog het.

(b) Radioaktiewe hitteproduksie wat die temperatuur met nog 2 000 C verhoog het.

(c) Intense meteorietbombardement voor 4 miljard jaar gelede.

2. Figuur 1.6b: Vroeë verhitting van die aarde kan so intens gewees het dat dit die planeet vir 'n kort tydjie heeltemal smelt.

3. 'n Duidelike kern en mantel is geskep deur ongeveer 4,5 miljard jaar gelede toe die aarde se oppervlak bedek was deur 'n geweldige oseaan van gesmelte magma.

4. Selfs vandag nog dui voortdurende aktiwiteite vanaf vulkane en warmwaterbronne aan dat hitte steeds uit die binneland vrygestel word. Daar word beraam dat die binnekant vanweë die hitte-isolasie wat deur die aardkors en -mantel verskaf word, vandag net halfpad in sy verkoelingsgeskiedenis is, alhoewel baie van die radioaktiewe elemente lankal verval het.

1. Figuur 1.6b: Bewyse dui daarop dat die aardkors van die onderliggende mantel onderskei (skei) op ​​grond van die chemiese samestelling. Tydens manteldifferensiasie het relatief ligte elemente soos Si, O, Al, K, Na, Ca, C, N, H en He na die oppervlak gestyg om die kors, seewater en atmosfeer te vorm (Figuur 1.8).

2. Isotopiese datering dui aan dat kontinentale kors eers ongeveer 3,9 - 4,1 miljard jaar gelede stabiel geword het, amper 'n half miljard jaar na die vorming van die kern en mantel.

Oorsprong en evolusie van die atmosfeer en seewater

Verskeie hipoteses bestaan ​​om die oorsprong van die aarde se atmosfeer te verklaar. Hulle werk almal onder die aanname dat:

(a) Figuur 1.8: Aansienlike waterstof en helium het tydens die vroeë differensiasie van die aarde in die ruimte ontsnap (Figuur 1.6b). Die meeste van die oorblywende waterstof is in water opgesluit.

(b) Die vroeë atmosfeer het feitlik geen molekulêre O 2 gehad nie. Oorvloedige suurstof kom baie later as gevolg van stadige ophoping oor geologiese tyd.

(c) Die vroeë atmosfeer van die aarde het moontlik baie soos die van Jupiter van vandag gelyk en bevat gasse soortgelyk aan dié wat vandag in meteoriete voorkom. Hierdie vroeë gasse het hoofsaaklik bestaan ​​uit metaan, ammoniak en waterdamp.

Die uitgassende hipotese

1. Figuur 1.8: In 1951 het 'n geoloog met die naam W.W. Rubey was die teorie dat die meeste gasse in die vroeë atmosfeer van die aarde afkomstig is van die binneste van die planeet deur stollingsoordrag via vulkane en warmwaterbronne. Hierdie proses staan ​​bekend as uitgas.

2. Die spoorhoeveelheid van He en Ar wat in ons huidige atmosfeer aangetref word, verteenwoordig dogterprodukte van onderskeidelik U en K verval.

3. Deur aan te neem dat die atmosfeer gevorm word deur voortdurende ontgassing uit vulkane en warmwaterbronne, kan ons redelikerwys rekening hou met al die N, He, Ar en waterdamp wat vandag in die atmosfeer voorkom. Suurstof het 'n aparte oorsprong as 'n produk van fotosintese in die loop van 2-3 miljard jaar.

Fotochemiese dissosiasie hipotese

1. Die Photochemical Dissociation Hypotheses veronderstel 'n vroeë aardatmosfeer, baie soos dié wat vandag op die planeet Jupiter voorkom, wat oorheers word deur metaan, ammoniak en waterdamp.

2. According to this model, the early atmosphere of the earth was devoid of an ozone layer which today acts to filter out incoming ultraviolet radiation. Without an ozone layer in the early atmosphere, ultraviolet light was able to reach the earth’s surface and cause several reactions to take place within the primitive atmosphere.

Reactions of Ultraviolet Light with Primitive Earth Atmosphere:

(a) Dissociation of water vapor into hydrogen and oxygen with most hydrogen escaping into space: 2H 2 O + uv light = 2H 2 + O 2

(b) Newly formed molecular oxygen reacted with methane to form carbon dioxide and more water: CH 4 + 2O 2 = CO 2 +2H 2 O

(c) Oxygen also reacted with ammonia to form nitrogen and water: 4NH 3 + 3O 2 = 2N 2 + 6H 2 O

(d) After all the CH 4 and NH 3 were converted to CO 2 and N 2 , then excess O 2 could accumulate as more water vapor dissociated. Over time, our present atmosphere of N 2 , CO 2 and O 2 may have formed.

Oxygen from Photosynthesis

1. The early earth may have additionally contained a great deal of CO 2 in the primitive atmosphere.

2. The appearance of photosynthetic cyanobacteria about 3.5 billion years ago instigated the process of photosyntheses in which these early life forms extracted CO 2 from the atmosphere and released O 2 as a by-product. Over the course of hundreds of millions of years, O 2 slowly began to accumulate in the atmosphere.

1. The rate of seawater accumulation is directly tied to atmospheric production of water vapor following chemical differentiation of the earth. In other words, the outgassing hypothesis can also account for the accumulation of water on the earth’s surface.

2. The question remains, however, whether the atmosphere and oceans accumulated slowly at a more or less uniform rate or did they accumulate rapidly during the early stages of earth history?

3. Some suggest that intense early bombardment of the earth by icy comets may have contributed to the planet's supply of water and gasses, implying that the atmosphere and seawater formed early and rapidly.

4. On the other hand, if seawater accumulated slowly in a manner similar to the O 2 buildup by photosynthesis, then the earth's water supply may have been pretty well established by around 2.5 billion years ago.

1. The moon is a small, dense rocky object pock-marked by impact craters and numerous basalt flows.

2. Seismic measurements from seismometers placed on the moon by astronauts have determined that the moon is layered. The crust of the moon, where measured, is around 65 km thick. The moon is covered by a thin veneer of regolith (mixture of gray pulverized rock fragments and small dust particles) overlying a 2 km thick layer of shattered and broken rock. Below the broken-rock zone is about 23 km of basalt, followed by 40 km of feldspar-rich rock. The mantle composition is unknown but possibly similar to the Earth's mantle. The lithosphere is possibly as much as 1000 km thick and any asthenosphere would occur at deeper levels.

3. The Moon's surface includes light-colored mountainous areas called highlands , which are heavily cratered and primarily composed of plagioclase-rich rocks called anorthosite that formed early in the history of the moon (4.5 billion years ago).

4. The smooth, dark-colored lowland impact craters are called maria (singular mare ) which are nearly circular and filled with basaltic lava flows.

5. The moon probably formed 4.6 billion years ago. One theory states that the moon formed in its present orbit by accretion during condensation of the solar nebula. A second theory suggests that the moon was captured by the earth.

6. Figure 1.4 : The most widely accepted theory, however, is that the moon originated as a portion of the earth that was ejected during impact with a Mars-sized object about 4.5 billion years ago. The ejected material condensed to form the moon.

7. Intense meterorite impacts that occurred around 3.9 - 4.0 b.y. ago formed most of the craters seen on the moon today. Since that time, the Moon has remained a dead planet void of any tectonics or volcanism.

1. It's high density of 5.4 g/cm3 may be due to a large, metallic core about 3600 km in diameter.

2. Heavily pockmarked by ancient impact craters, many filled with basaltic flows.

3. Lacks an atmosphere and shows no evidence of tectonic activity (no evidence of moving lithospheric plates).

4. Mercury has a magnetic field about 1/100 as strong as that of the Earth. Planetary magnetic fields are typically formed by fluid motions in the core caused by rotation of the planet. Mercury's slow rotation (once every 59 days vs 24 hrs for earth) and lack of tectonic plate movements, however, pose problems with this interpretation.

1. Venus is about the same size and mass as Earth.

2. Thick atmosphere of CO 2 prevents direct visual observation of the planet’s surface and is largely responsible for surface temperatures of about 500 o due to the greenhouse effect.

3. Several spacecraft have landed on the surface and radioed back information from radar measurements of the surface topography. Spacecraft Magellan recently orbited Venus and has sent radar images back to earth.

4. Radar images show a surface consisting of broken rock fragments primarily basaltic in composition.

5. Vast volcanic plains and thousands of volcanoes shaped like broad domes, similar to those that occur today in Hawaii, dominate the surface. Several steeper-sided volcanoes indicate eruption of more Si-rich lava.

6. The topography also shows mountain ranges and rift valleys.

1. Mars is only 1/10 the size of earth and rotates once every 24.6 hours.

2. Mars has a thin atmosphere only 1/100 as dense as the Earth's and consists largely of CO 2 .

3. Mars has polar ice caps consisting mostly of CO 2 and small amounts of water ice. The ice caps grow and shrink with the seasons.

4. The composition of the Earth and Mars may be similar. Mars has a reddish-brown surface covered by loose stones and windblown sand. Two Viking spacecraft had landed on the martian surface during the 1970’s and analyzed the composition of the soils. Chemical analysis by the Viking spacecraft indicated clays and possibly gypsum, a mineral commonly precipitated from evaporating water.

5. The Viking spacecraft also monitored for earthquakes, but no earthquakes were recorded. The scarcity of earthquakes suggest that any former plate movements on Mars had now ceased.

6. Recently, the spacecraft Pathfinder landed on Mars and sent out its microrover, Sojourner, to study rocks on the surface. The rover found sedimentary and volcanic rocks much like what we have on earth.

7. Mars probably has a core that is completely solid since no magnetic field is apparent.

8. The SNC meteorites are considered martian in origin.

9. Recently, evidence of fossil bacteria were discovered in one of the martian meteorites, suggesting that simple life forms existed in the early martian crust.

10. The southern hemisphere is densly cratered and resembles the surfaces of the Moon and Mercury.

11. Craters are sparse in the northern hemisphere and large areas are relatively smooth, suggesting a younger surface. Huge shield volcanoes like Olympus Mons suggest extensive volcanism in the past. The youngest flows on Olympus Mons are probably less than 100 million years old. Long-lived sources of magma must still be present in the martian interior. Martian lithosphere also must be thick and strong in order to support the weight of Olympus Mons.

12. The martian surface also exhibits a system of huge canyons and branching valleys similar to those cut by intermittent desert streams on Earth. These features suggest that ice presently frozen beneath the surface may have melted during past warming episodes, creating torrential floods that carved these valleys.

13. Rain, lakes and streams may have existed early in martian history during a time of planetary differentiation and extensive volcanism. Mars eventually aquired a frozen regolith. Occasional melting of the frozen ground may have occurred during periods of magmatic activity or sudden changes in climate.

1. Jupiter is about twice the mass of the other planets combined.

2. Jupiter is unusual in that it gives off twice as much energy as it receives from the sun, suggesting that it is still undergoing gravitational contraction.

3. Jupiter has an atmosphere composed primarily of H 2 , He, NH 3 and CH 4 surrounding a rocky core.

4. Surface may be a giant ocean of liquid hydrogen.

5. Colored atmospheric bands produced by high-speed winds. Giant red spot (storm).

6. The moon closest to Jupiter is Io and is colored with shades of yellow and orange, suggesting that it is covered by sulfur and sulfurous compounds. Io is volcanically active. Volcanic products include basaltic lava as well as molten sulfur flows and sulfurous gases. Geyser-like volcanic plumes of SO 2 have been observed by the Voyager spacecraft. The heat energy which drives Io's volcanism may be caused by tidal stresses exerted by Jupiter's gravitational pull.

7. Europa, Ganymede and Callisto may have small metallic cores surrounded by thick mantles of ice and silicate minerals. Above the mantle are crusts of nearly pure ice in excess of 100 km thick. Europa is criss-crossed with fractures, suggesting that tidal stresses from Jupiter are manifested on the icy surface.

8. Ganymede (largest of Jupiter's moons) and Callisto have icy surfaces pitted by craters. Ganymede's surface contains dark areas covered by dust and impact debris, indicating ancient ice continents.

1. Saturn is known for its immense ring system.

2. The ring system is 10,000 km wide and a little over 100 m thick.

3. The Voyager spacecraft discovered that the major rings actually consist of hundreds of tiny ringlets.

4. Each ring is composed of dust- to boulder-sized particles consisting mostly of ice, some possibly stained with iron oxide. Color differences indicate slight compositional differences between the rings.

5. Saturn has an overall chemical composition similar to Jupiter.

6. Titan is the most distinctive among Saturn's moons. Titan is surrounded by an opaque, orange-colored atmosphere composed mostly of nitrogen with lesser amounts of ethane, acetylene, ethylene, and HCN. Titan may consist of 45% ice and 55% rocky matter. Surface temperature is estimated at around -180 o C, in which case Titan may consist of ice continents surrounded by an ocean of liquid ethane and methane.

2. Uranus has rings much like those encircling Jupiter.

3. Uranus has several moons, some with canyons while others are smooth.

1. Neptune is a bluish planet.

3. Neptune has visible white clouds of frozen methane.

4. Neptune has eight moons, six of which orbit in a direction opposite to the other two.

5. The largest of Neptune's moons is Tritan, which has a surface covered with solid nitrogen and methane.

1. Pluto is one-fifth the size of earth and 40 times farther from the sun.

2. Pluto is too small to be visible to the unaided eye.

3. It takes 248 years for Pluto to orbit the sun.

4. Pluto follows an elongated orbit, causing it at times to travel inside Neptune's orbit.

5. Pluto may possibly be a satellite of Neptune rather than a planet as originally thought.

6. Pluto is described as a dirty ice ball of frozen gases and rocky material.

7. Pluto has one moon, Charon, which is 1,300 km in diameter.

1. Asteroids are possibly fragments of broken planets.

2. Asteroids can reach 1,000 km in diameter, but most are only about 1 km or less across.

3. An extensive belt of asteroids occurs between the orbits of Mars and Jupiter.

4. Some asteroids have collided with the earth in the past.

1. Comets can be described as dirty snowballs of frozen gases in addition to rocky and metallic materials.

2. Some comets may contain organic material.

3. Comets develop a tail of dust and ionized gases when approaching the Sun due to the solar wind.

4. Millions of comets may orbit the Sun beyond Pluto.

5. Comets are thought to be relicts of the early Solar Nebula that were swept to the far reaches of the Solar System by the solar wind after formation of the planets.


Comments of the Week #2: From the Sun's death to the light elements

After all is said-and-done this week, and after all the new posts over at the main Starts With A Bang on Medium, you've had a chance to have your say here on our forum! And Kierkegaard would likely change his tune if everyone he came across left comments like yours.

From the end of the Sun's life to the light elements, let's take a look at your best comments this week!

From Ted Lawry concerning Ask Ethan #27: Will the Earth and Moon survive? -- "What about drag? The earth would be plowing through all that mass the sun is losing as solar wind?"

This is a reasonable thought as the Sun expands and gently blows off its outer layers, won't the Earth be plowing into that matter, the way a fast-moving car plows through rain?

In theory, there are two things we'll need to compare:

  1. The speed of the Earth as it moves in its orbit around the Sun.
  2. The speed of the matter being blown off from the Sun as it crosses Earth's orbit.

As it turns out, for the vast majority of the matter, it's not even close. On average, the Earth takes about 58 days to traverse the equivalent of the Earth-Sun distance, and on average, particles ejected from the Sun take about 3 days to reach the Earth. In other words, the Solar Wind travels more than ten times as fast as the Earth orbiting the Sun.

And so although the drag force exists, it's very small, and will likely help keep the Earth's orbit relatively circular as it spirals outwards, but won't play a significant role in causing the Earth's orbit to decay and inspiral. It's an important thing to consider, but quantitatively it won't be enough to cause the Sun to devour us.

From Robert H. Olley on Ask Ethan #27: Will the Earth and Moon survive? -- "You seem to be saying that red giant formation coincides with the onset of helium burning to carbon.
According to Jim Kaler of UIUC (one of America’s astronomy heavyweights) there’s a double process, first with hydrogen burning on a helium core and blowing up to an “ordinary” red giant. Then the helium core ignites, and the star contracts somewhat. This is followed by helium burning on a carbon-oxygen core, and the star becomes a bigger red giant.
See the following: http://stars.astro.illinois.edu/sow/star_intro.html#giantsfrom the short section “Giant stars” to “Bigger red giants and Miras”."

Stellar evolution has many stages, and I do my best to summarize what the important points are clearly and succinctly, and so does Jim Kaler, who's excellent at what he does and whom I respect tremendously. Die full details of the stages our Sun will go through are summarized in the diagram below, and I'll walk you through it and try to clear things up.

When the Sun runs out of hydrogen it its core, it expands into a subgiant and starts burning hydrogen in a shell around the core. It continues to expand and expand as its surface temperature cools, a process taking many hundreds of millions of years, eventually crossing the threshold to becoming a true giant star, and finally the helium in its core ignites. (That's the "helium flash.")

The star remains a giant star for some time, changing colors to yellow and then back to red as the innermost core runs out of helium fuel but helium burning continues in a shell, blowing off its outermost layers most rapidly during this time. (Although, to be fair, it's blowing off its outermost layers continuously during this entire process.) Stellar evolution is a huge, nuanced process that comprises an entire sub-field of astronomy and astrophysics research, and I think Jim does an excellent job, but I don't think anything I said contradicted that. At least, I hope not!

From PJ concerning Messier Monday: A Spiral Sliver headed our way: M98 -- "when you say M98 is headed toward us, do you mean that literally, or are we (our galaxy), in fact, overtaking M98 because its velocity is less than our Milky Way?"

Messier 98 is one of more than a thousand galaxies in the Virgo cluster, a dense galactic group located some 50-60,000 light years away. In the image above, it's visible on the right, with its relatively nearby neighbor, M99, on the left.

Gravitationally bound objects have what we call an gemiddeld velocity, where we can compute how quickly the cluster is moving relative to us. But each of them also has a peculiar velocity, where they can be moving either towards us or away from us on top of the average velocity. For the Virgo cluster, if we measure the recession speeds of each of the galaxies, they show up in the ellipse highlighted below.

On average, the Virgo Cluster is receding from us at right around 1,000 km/s, but galaxies within it can have peculiar velocities of up to 1,500 km/s, meaning that a few galaxies are (temporarily) moving towards us at up to a few hundred km/s (like M98), while some galaxies are moving weg from us at over 2,000 km/s (like M99)! They're all going to expand away from us as the Universe continues to age, although for the next few tens of millions of years, M98 (and M86, and a few other large Virgo galaxies) will continue to move towards us before turning around and plunging back towards the center-of-mass of the cluster.

It's literally heading towards us (and getting closer to us), but that's only temporary!

A lovely sentiment from John D. Whitehead after reading Why The World Needs Cosmos -- "I will be 50 this year, and the original Cosmos inspired me as a teen. My grandfather said “Read something and learn every day and you’ll be smarter than any ‘Professor’ and never be in need of a degree or ‘credentials’.” I was about to turn 8 when Apollo 17 ended all hopes of returning to the Moon in my lifetime, and I was short-sighted when it came to realizing that a life of exploration was still open to me. Thank you so much Ethan for rewarding all of us millions who still dream and are always searching the Universe with our questions every day. Your site is the first I go to every night at work, and you answer in a more satisfying depth than the usual spoon-fed pablum the ‘target audiences’ get on Nova and documentaries like ‘Cosmos’. I search out and explore every link, for the deeper nourishment, I have come to crave from a lifetime of learning. Thank you and Thanks to Carl and now Neil for pointing the way to the Cosmos in and around us, you have all made the Journey less lonely for me."

There were no comments on this post that really asked a question or warranted a response, but I felt I should say something about this one. The Universe is something that brings us all together, a story that we all share with one another and with everything else, living and inanimate, past, present and future, from the smallest atom to the largest black hole.

And our local group will stay with us for trillions upon trillions of years, while the rest of the matter in the Universe will disappear from our cosmic horizon. That's the truth of our reality. To quote Carl Sagan,

For small creatures such as we the vastness is bearable only through love.

Thanks for sharing in the journey we're all taking, and thanks for having me as a part of it.

From Sinisa Lazarek about The 3 Most Surprising Elements -- "I’ve read a while ago that Lithium abundance is significantly off in comparison with theory and observation.
Does this mechanism of spallation correct that or is Lithium data still a big problem. From the article it seems all is ok and fits the theory perfectly. Just wondering if Lithium problem was resolved in last couple of years?"

Sinisa is referring to these measurements, which are close for Lithium-7 to matching what the values ought to be from observations of the CMB, but which miss by a little bit. The predicted values are just a little high compared to what we observe.

There's also the Lithium-6 puzzle, where there's a little too much Lithium-6. The problem with these observations is that we are uncertain as to how much of the lithium we see is left over from the Big Bang, how much has been destroyed in stars, and how much has been produce from spallation: from cosmic rays causing the nuclear fission of heavier elements.

It's fair to say that this is an ongoing area of active research one person I follow quite closely and whom I respect is Karsten Jedamzik. The standard picture of Big Bang Nucleosynthesis is certainly not in jeopardy at this time, but it's worth keeping an eye on.

And finally, from Arun Kumar, also concerning The 3 Most Surprising Elements -- "Loved the article, but I do have a question. How does this explain the concentrations of Lithium that are mined, for the manufacture of batteries for example?"

You see, this is a good question! In the Solar System -- and in the Universe in general -- Lithium is somewhat rare.

But in the Earth's crust, there's actually a significant amount of Lithium, veel more than you'd expect from the above graph!

Image credit: Gordon B. Haxel, Sara Boore, and Susan Mayfield from USGS vectorized by Wikimedia Commons user michbich.

Why is lithium so much more common in our crust? Quite simply: because lighter elements buoyantly "float" atop the heavier ones! While the heaviest metals are concentrated in our planet's core, the lightest ones have preferentially risen to the crust. As it stands, die meeste of the lithium in our planet is located within the first few hundred km of the surface, which is crazy considering our planet is over 6,000 km to the core!

The segregation isn't perfect, but it's good enough to explain why there's a somewhat large amount of lithium in our crust, and why it's not rare to us at all!


How did the lighter elements end up in the center of the solar system? Solar System Formation - Astronomy

Is there any theory of the origin of Solar system which can explain these three things:

1) The chemical elements distribution between different planets (the Sun has very little of heavy elements, Venus and Earth lots of it, Jupiter and Saturn have little again)

This is explained by the Lewis Model. In the early Solar System, which was a cloud of gasses, the inner parts were warmer than the outer parts. In the inner region, only things like metal or rock could condense, so the inner planets (Mercury, Venus, Earth, and Mars) are composed chiefly of metal and rock. As you move out to the cooler outer regions, it gets cool enough for things like water ice, and then ammonia and methane ice to condense.

The reason why the outer layers of the gas giants (Jupiter, Saturn, Uranus, and Neptune) are composed of lighter elements is that these planets grew larger than the Earth, quickly. There are two reasons why. One is that, in the outer regions, it was cool enough for a larger range of materials to condense -- not only rock and metal, but also things that condense at cooler temperatures such as water ice and ammonia ice, so there was more "raw materials" for the planets to be made of. The other reason is that ice sticks together better than rocks and metals, so when the ice that had condensed in small pieces ran into other pieces of ice, it tended to make bigger pieces, rather than bounce off or fragment as pieces of rock do. The outer planets originated as big planets made of ice and rock. The were massive enough that their gravity allowed them to accummulate hydrogen and helium, which the inner planets did not have enough mass to hold on to, and grow to their current titanic proportions.

2) The upturned direction of Venus rotation around axis (in contrast with other planets)

An old idea about Venus' rotation (which is clockwise as viewed from the north as opposed to counter-clockwise like the other planets) is that gravitational influences of the Sun slowed it down until its rotational period equaled its orbital period. That situation is called a spin-orbit resonance. Mercury is in a slightly different type of spin-orbit resonance. However, that will not explain why Venus is rotating backward.

Another idea is that an impact with a large body gave Venus its strange spin state. This is not supported by any good physical evidence, and it is strange that Venus would end up rotating slowly backwards instead of tipped over at a random angle, like Uranus.

There is no widely-accepted explanation of Venus' rotation right now. Personally, I think that's good. It means that there is still a Great Mystery in the solar system waiting to be revealed, and reminds us astronomers not to get too full of ourselves.

3) The division of momentum (the Sun has less than 2% as I remember).

I don't think this is a problem according to the Cameron Model (which explains how the Solar System formed out of a spinning cloud of gas and dust.) There's no reason why we would expect the Sun to contain most of the angular momentum in the Solar System, especially since the planets are constantly stealing it through tidal interactions.

This page was last updated June 28, 2015.

Oor die skrywer

Dave Kornreich

Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.


The Origin of the Solar System

Here is a brief outline of the current theory of the events in the early history of the solar system:

  1. A cloud of interstellar gas and/or dust (the “solar nebula”) is disturbed and collapses under its own gravity. The disturbance could be, for example, the shock wave from a nearby supernova.
  2. As the cloud collapses, it heats up and compresses in the center. It heats enough for the dust to vaporize. The initial collapse is supposed to take less than 100,000 years.
  3. The center compresses enough to become a protostar and the rest of the gas orbits/flows around it. Most of that gas flows inward and adds to the mass of the forming star, but the gas is rotating. The centrifugal force from that prevents some of the gas from reaching the forming star. Instead, it forms an “accretion disk” around the star. The disk radiates away its energy and cools off.
  4. First brake point. Depending on the details, the gas orbiting star/protostar may be unstable and start to compress under its own gravity. That produces a double star. If it doesn’t …
  5. The gas cools off enough for the metal, rock and (far enough from the forming star) ice to condense out into tiny particles. (i.e. some of the gas turns back into dust). The metals condense almost as soon as the accretion disk forms (4.55-4.56 billion years ago according to isotope measurements of certain meteors) the rock condenses a bit later (between 4.4 and 4.55 billion years ago).
  6. The dust particles collide with each other and form into larger particles. This goes on until the particles get to the size of boulders or small asteroids.
  7. Run away growth. Once the larger of these particles get big enough to have a nontrivial gravity, their growth accelerates. Their gravity (even if it’s very small) gives them an edge over smaller particles it pulls in more, smaller particles, and very quickly, the large objects have accumulated all of the solid matter close to their own orbit. How big they get depends on their distance from the star and the density and composition of the protoplanetary nebula. In the solar system, the theories say that this is large asteroid to lunar size in the inner solar system, and one to fifteen times the Earth’s size in the outer solar system. There would have been a big jump in size somewhere between the current orbits of Mars and Jupiter: the energy from the Sun would have kept ice a vapor at closer distances, so the solid, accretable matter would become much more common beyond a critical distance from the Sun. The accretion of these “planetesimals” is believed to take a few hundred thousand to about twenty million years, with the outermost taking the longest to form.
  8. Two things and the second brake point. How big were those protoplanets and how quickly did they form? At about this time, about 1 million years after the nebula cooled, the star would generate a very strong solar wind, which would sweep away all of the gas left in the protoplanetary nebula. If a protoplanet was large enough, soon enough, its gravity would pull in the nebular gas, and it would become a gas giant. If not, it would remain a rocky or icy body.
  9. At this point, the solar system is composed only of solid, protoplanetary bodies and gas giants. The “planetesimals” would slowly collide with each other and become more massive.
  10. Eventually, after ten to a hundred million years, you end up with ten or so planets, in stable orbits, and that’s a solar system. These planets and their surfaces may be heavily modified by the last, big collision they experience (e.g. the largely metal composition of Mercury or the Moon).

Nota: this was the theory of planetary formation as it stood before the discovery of extrasolar planets. The discoveries don’t match what the theory predicted. That could be an observational bias (odd solar systems may be easier to detect from Earth) or problems with the theory (probably with subtle points, not the basic outline.)


3 antwoorde 3

Elements heavier than iron are produced mainly by neutron-capture inside stars, although there are other more minor contributors (cosmic ray spallation, radioactive decay). They are nie only produced in stars that explode as supernovae. This has now been established fact since the detection of short-lived Technetium in the atmospheres of red giant and AGB stars in the 1950s (e.g. Merrill 1952), and it is tiresome to have to continue correcting this egregious pop-sci claim more than 60 years later.

The r-process

Neutron capture can occur rapidly (the r-process) and this process occurs mostly inside and during supernova explosions (though other mechanisms such as merging neutron stars have been mooted). The free neutrons are created by electron capture in the final moments of core collapse. At the same time this can lead to the build up of neutron-rich nuclei and the decay products of these lead to many of the chemical elements heavier than iron once they are ejected into the interstellar medium during the supernova explosion. The r-process is almost exclusively responsible for elements heavier than lead and contributes to the abundances of many elements between iron and lead.

There is still ongoing debate about the site of the primary r-process. My judgement from a scan of recent literature is that whilst core-collapse supernovae proponents was in the majority, there is a growing case to be made that neutron star mergers may become more dominant, particularly for the r-process elements with $A>110$ (e.g. Berger et al. 2013 Tsujimoto & Shigeyama 2014). In fact some of the latest research I have found suggests that the pattern of r-process elemental abundances in the solar system could be entirely produced by neutron star mergers (e.g. Wanajo et al. 2004), though models of core-collapse supernovae that incorporate magneto-rotational instabilities or from rapidly-rotating "collapsar" models, ook claim to be able to reproduce the solar-system abundance pattern (Nishimura et al. 2017) and may be necessary to explain the enhanced r-process abundances found in some very old halo stars (see for example Brauer et al. 2020).

Significant new information on this debate comes from observations of kilonovae and in particular, the spectacular confirmation, in the form of GW170817, that kilonovae can be produced by the merger of two neutron stars. Observations of the presumably neutron-rich ejecta, have confirmed the opacity signature (rapid optical decay, longer IR decay and the appearance of very broad absorption features) that suggest the production of lanthanides and other heavy r-process elements (e.g. Pian et al. 2017 Chornock et al. 2017). Whether neutron star mergers are the dominant source of r-process elements awaits an accurate assessment of how frequently they occur and how much r-process material is produced in each event - both of which are uncertain by factors of a few at least.

A paper by Siegel (2019) reviews the merits of neutron star merger vs production of r-process elements in rare types of core collapse supernovae (aka "collapsars"). Their conclusion is that collapsars are responsible for the majority of the r-process elements in the Milky Way and that neutron star mergers, whilst probably common enough, do not explain the r-process enhancements seen in some very old halo stars and dwarf galaxies and the falling level of europium (an r-process element) to Iron with increased iron abundance - (i.e. the Eu behaves like "alpha" elements like oxygen and neon that are produced in supernovae).

The s-process

However, many of the chemical elements heavier than iron are also produced by slow neutron capture the so-called s-process. The free neutrons for these neutron-capture events come from alpha particle reactions with carbon 13 (inside asymptotic giant branch [AGB] stars with masses of 1-8 solar masses) or neon 22 in giant stars above 10 solar masses. After a neutron capture, a neutron in the new nucleus may then beta decay, thus creating a nucleus with a higher mass number and proton number. A chain of such events can produce a range of heavy nuclei, starting with iron-peak nuclei as seeds. Examples of elements produced mainly in this way include Sr, Y, Rb, Ba, Pb and many others. Proof that this mechanism is effective is seen in the massive overabundances of such elements that are seen in the photospheres of AGB stars. A clincher is the presence of Technetium in the photospheres of some AGB stars, which has a short half life and therefore must have been produced in situ.

According to Pignatari et al. (2010), models suggests that the s-process in high mass stars (that will become supernovae) dominates the s-process production of elements with $A<90$ , but for everything else up to and including Lead the s-process elements are mainly produced in modest sized AGB stars that never become supernovae. The processed material is simply expelled into the interstellar medium by mass loss during thermal pulsations during the AGB phase.

The overall picture

As a further addition, just to drive home the point that not all heavy elements are produced by supernovae, here is a plot from the epic review by Wallerstein et al. (1997), which shows the fraction of the heavy elements in the solar system that are produced in the r-process (i.e. an upper limit to what is produced in supernovae explosions). Note that this fraction is very small for some elements (where the s-process dominates), but that the r-process produces everything beyond lead.

A more up-to-date visualisation of what goes on (produced by Jennifer Johnson) and which attempts to identify the sites (as a percentage) for each chemical element is shown below. It should be stressed that the details are still subject to a lot of model-dependent uncertainty.


The early Earth, as with Mars, Mercury and Venus, was formed from elements that had gathered in a zone roughly between 55 million to 230 million kilometers (35 million to 140 million miles) from the sun. Although the Earth had some hydrogen and helium in its early atmosphere, its weak gravity lost these light gases soon after. The Earth was kept hot by the collisions with the many large meteorites that were still common in the solar system.

After several million years, the Earth separated into several layers. Iron, nickel and other heavy metals mostly settled to the core lighter elements remained in the mantle around the core. The lightest elements, such as oxygen and silicon, floated to the top and cooled, forming a solid crust. Because the Earth was not completely liquid, the layering process was uneven pockets of heavy elements remained in the crust.


How did the lighter elements end up in the center of the solar system? Solar System Formation - Astronomy

Is there any theory of the origin of Solar system which can explain these three things:

1) The chemical elements distribution between different planets (the Sun has very little of heavy elements, Venus and Earth lots of it, Jupiter and Saturn have little again)

This is explained by the Lewis Model. In the early Solar System, which was a cloud of gasses, the inner parts were warmer than the outer parts. In the inner region, only things like metal or rock could condense, so the inner planets (Mercury, Venus, Earth, and Mars) are composed chiefly of metal and rock. As you move out to the cooler outer regions, it gets cool enough for things like water ice, and then ammonia and methane ice to condense.

The reason why the outer layers of the gas giants (Jupiter, Saturn, Uranus, and Neptune) are composed of lighter elements is that these planets grew larger than the Earth, quickly. There are two reasons why. One is that, in the outer regions, it was cool enough for a larger range of materials to condense -- not only rock and metal, but also things that condense at cooler temperatures such as water ice and ammonia ice, so there was more "raw materials" for the planets to be made of. The other reason is that ice sticks together better than rocks and metals, so when the ice that had condensed in small pieces ran into other pieces of ice, it tended to make bigger pieces, rather than bounce off or fragment as pieces of rock do. The outer planets originated as big planets made of ice and rock. The were massive enough that their gravity allowed them to accummulate hydrogen and helium, which the inner planets did not have enough mass to hold on to, and grow to their current titanic proportions.

2) The upturned direction of Venus rotation around axis (in contrast with other planets)

An old idea about Venus' rotation (which is clockwise as viewed from the north as opposed to counter-clockwise like the other planets) is that gravitational influences of the Sun slowed it down until its rotational period equaled its orbital period. That situation is called a spin-orbit resonance. Mercury is in a slightly different type of spin-orbit resonance. However, that will not explain why Venus is rotating backward.

Another idea is that an impact with a large body gave Venus its strange spin state. This is not supported by any good physical evidence, and it is strange that Venus would end up rotating slowly backwards instead of tipped over at a random angle, like Uranus.

There is no widely-accepted explanation of Venus' rotation right now. Personally, I think that's good. It means that there is still a Great Mystery in the solar system waiting to be revealed, and reminds us astronomers not to get too full of ourselves.

3) The division of momentum (the Sun has less than 2% as I remember).

I don't think this is a problem according to the Cameron Model (which explains how the Solar System formed out of a spinning cloud of gas and dust.) There's no reason why we would expect the Sun to contain most of the angular momentum in the Solar System, especially since the planets are constantly stealing it through tidal interactions.

This page was last updated June 28, 2015.

Oor die skrywer

Dave Kornreich

Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.