Sterrekunde

Waar definieer ons die "oppervlak" van 'n gasplaneet?

Waar definieer ons die


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Aangesien die gasreus uit die meeste gaskomponente bestaan, waar bepaal ons hul 'oppervlak'?

My neem is basies om die limiet te neem waarin alle lig ondeursigtig is. Byvoorbeeld op hierdie foto:

Die oppervlak sal dus die grens van die swart swartgrond met die planeet wees.

Enige ander manier om die "oppervlak" van 'n gasreus formeel te definieer?


Daar is twee algemene definisies wat gebruik word vir die oppervlak van gasplanete:

  • Die oppervlak van 1 bar: As die druk toeneem, hoe dieper ons die gasplaneet binnegaan, sal ons op een of ander hoogte 'n druk van 1 bar tref. Gas op hierdie hoogtes sal gewoonlik diep genoeg in die gravitasieput sit en byna eenvormige digtheid en temperatuur hê, sodat dit nie beïnvloed word deur buiteparameters nie, byvoorbeeld die sonwind. Daarom sal die hoogte van die 1-maatvlak vir kort astronomiese tye in wese konstant bly.
  • Die $ tau = 2/3 $-oppervlak: dit is die hoogte waaruit fotone vrylik in die ruimte kan ontsnap. Dit gebeur op 'n gemiddelde optiese diepte $ tau $ van 2/3. Dit is in wese wat u in u beeld sien as die limiet van die swart agtergrond. Vir die son is die een punt van die fotosfeer die gemiddelde $ tau = 2/3 $-oppervlak, en vir die transito van eksoplanete is dit identies aan die gemete transito-radius by daardie golflengte.

Daar is geen harde verband tussen die twee oppervlaktes nie, maar oor die algemeen sal hul hoogte nie meer as 'n skaalhoogte verskil nie, want op ongeveer 0,1-1 bar word die gasvormige atoom- en molekulêre bande enorm drukverruim, wat die atmosfeer vinnig ondeursigtig maak op die meeste golflengtes, vir die gewone gasreusekomponente.



Enige ander manier om die "oppervlak" van 'n gasreus formeel te definieer?


Anders as wat Michael en AtmosphericPrisonEscape voorstel, kan u ook die oppervlak op die werklike oppervlak van Jupiter se metaalvloeistofkern plaas. Die vier gasreuse (behalwe Saturnus, wat miskien heeltemal gasvormig is) het vaste of vloeibare kerne met 'n werklike oppervlak. Jupiter se vloeibare kern is ongeveer so groot soos die aarde en het ongeveer 10 aardmassas.


Gas 'watervalle' onthul baba planete rondom jong sterre

Die geboorteplekke van planete is skywe van gas en stof. Sterrekundiges bestudeer hierdie sogenaamde protoplanetêre skywe om die prosesse van planeetvorming te verstaan. Pragtige beelde van skywe wat met die Atacama Large Millimeter / submillimeter Array (ALMA) gemaak is, hoe duidelike gapings en ringe in stof voorkom, wat deur baba-planete veroorsaak kan word.

Om meer sekerheid te kry dat hierdie leemtes eintlik deur planete veroorsaak word, en om 'n meer volledige oorsig van die vorming van die planeet te kry, bestudeer wetenskaplikes die gas in die skywe, benewens stof. 99 persent van die massa van 'n protoplanetêre skyf is gas, waarvan koolstofmonoksied (CO) die helderste komponent is, wat uitstraal by 'n baie kenmerkende millimeter golflengte wat ALMA kan waarneem.

Verlede jaar het twee spanne sterrekundiges 'n nuwe planeetjagtegniek getoon met behulp van hierdie gas. Hulle het die snelheid van CO-gas gemeet wat in die skyf om die jong ster HD 163296 roteer. Lokale versteurings in die bewegings van die gas het drie planeetagtige patrone in die skyf onthul.

In hierdie nuwe studie het hoofskrywer Richard Teague van die Universiteit van Michigan en sy span nuwe hoëresolusie-ALMA-data van die Disk Substructures at High Angular Resolution Project (DSHARP) gebruik om die gassnelheid in meer besonderhede te bestudeer. "Met die hoë getrouheidsdata van hierdie program kon ons die gassnelheid in drie rigtings meet in plaas van net een," het Teague gesê. "Vir die eerste keer het ons die beweging van die gas gemeet wat om die ster draai, in die rigting van of weg van die ster, en op- of afwaarts in die skyf."

Unieke gas vloei

Teague en sy kollegas het gesien hoe die gas op drie verskillende plekke van die boonste lae na die middel van die skyf beweeg. "Wat waarskynlik gebeur, is dat 'n planeet in 'n wentelbaan om die ster die gas en stof opsy skuif en 'n gaping laat ontstaan," het Teague verduidelik. "Die gas bokant die gaping stort dan soos 'n waterval daarin in, wat 'n rotasie van gas in die skyf veroorsaak."

Dit is die beste bewys tot dusver dat daar wel planete gevorm word rondom HD 163296. Maar sterrekundiges kan nie met honderd persent sekerheid sê dat die gasvloei deur planete veroorsaak word nie. Die ster se magneetveld kan byvoorbeeld ook gasversteurings veroorsaak. "Op die oomblik kan slegs 'n direkte waarneming van die planete die ander opsies uitsluit. Maar die patrone van hierdie gasvloei is uniek en dit is heel waarskynlik dat dit slegs deur planete kan veroorsaak word," het mede-outeur Jaehan Bae van die Carnegie Institution for Science, wat hierdie teorie met 'n rekenaarsimulasie van die skyf getoets het.

Die ligging van die drie voorspelde planete in hierdie studie stem ooreen met die resultate van verlede jaar: dit is waarskynlik op 87, 140 en 237 AU. ('N Astronomiese eenheid - AU - is die gemiddelde afstand van die aarde tot die son.) Die naaste planeet aan HD 163296 word bereken as die helfte van die massa van Jupiter, die middelste planeet is Jupiter-massa en die verste planeet is twee keer so massief soos Jupiter.

Planeet atmosfeer

Gas vloei vanaf die oppervlak na die middelvlak van die protoplanetêre skyf. Daar word voorspel dat teoretiese modelle sedert die laat 90's bestaan, maar dit is die eerste keer dat dit waargeneem word. Hulle kan nie net gebruik word om babaplanete op te spoor nie, maar vorm ook ons ​​begrip van hoe gasreusplanete hul atmosfeer verkry.

"Planete vorm in die middelste laag van die skyf, die sogenaamde middelvlak. Dit is 'n koue plek, beskerm teen die bestraling van die ster," het Teague verduidelik. "Ons dink dat die gapings wat deur planete veroorsaak word, warmer gas inbring vanaf die meer chemies aktiewe buitenste lae van die skyf, en dat hierdie gas die atmosfeer van die planeet sal vorm."

Teague en sy span het nie verwag dat hulle hierdie verskynsel sou kon sien nie. "Die skyf rondom HD 163296 is die helderste en grootste skyf wat ons met ALMA kan sien," het Teague gesê. 'Maar dit was 'n groot verrassing om hierdie gas so duidelik te sien vloei. Die skywe blyk baie meer dinamies te wees as wat ons gedink het.'

"Dit gee ons 'n veel vollediger beeld van die vorming van die planeet as wat ons ooit gedroom het," het medeskrywer Ted Bergin van die Universiteit van Michigan gesê. "Deur hierdie strome te karakteriseer, kan ons bepaal hoe planete soos Jupiter gebore word en hul chemiese samestelling tydens geboorte kenmerk. Ons kan dit dalk gebruik om die geboorteplek van hierdie planete op te spoor, aangesien dit tydens vorming kan beweeg."

Die National Radio Astronomy Observatory is 'n fasiliteit van die National Science Foundation, wat onder samewerkingsooreenkoms bedryf word deur Associated Universities, Inc.


Waar definieer ons die & ldquosurface & rdquo van 'n gasplaneet? - Sterrekunde


Planeet Uranus.
Die blou kleur is afkomstig van die gasmetaan.
Bron: NASA.
  • Mane: 27 (en groei)
  • Massa: 14,5 keer die massa van die aarde
  • Deursnee: 51,118 km
  • Jaar: 83.8 Aardejare
  • Dag: 17,2 uur
  • Gemiddelde temperatuur: minus -195 ° C (320 ° F)
  • Afstand vanaf die son: 7de planeet van die son af, 2,9 miljard km
  • Tipe planeet: Ice Giant (gasoppervlak met 'n binnekant wat uit ys en rots bestaan)

Uranus is die 7de planeet vanaf die son. Dit is meer as twee keer so ver van die son af as Saturnus. Uranus is 'n ysreus soos sy susterplaneet Neptunus. Alhoewel dit 'n gasoppervlak het, soos die gasreuse Jupiter en Saturnus, bestaan ​​die grootste deel van die binnekant van die planeet uit bevrore elemente. As gevolg hiervan het Uranus die koudste atmosfeer van al die planete in die Sonnestelsel.

Die oppervlak van Uranus bestaan ​​meestal uit waterstofgas met ook heliumgas. Die gasatmosfeer maak ongeveer 25% van die planeet uit. Hierdie atmosfeer is stormagtig, maar nie so stormagtig of aktief soos Saturnus of Jupiter nie. As gevolg hiervan is die oppervlak van Uranus redelik kenmerkend en eenvormig.


Sommige van die mane van Uranus.
Van links na regs: Puck, Miranda, Ariel, Umbriel, Titania en Oberon.
Bron: NASA.

Een van Uranus se mees unieke kenmerke is dat dit aan sy sy draai. As u die son en die planete van die sonnestelsel op 'n tafel voorstel, sou die ander planete draai soos 'n top. Uranus, aan die ander kant, sou soos 'n albaster rol. Die meeste wetenskaplikes is dit eens dat Uranus se vreemde rotasie is omdat 'n ander groot planetoïde voorwerp met genoeg krag met die planeet gebots het om sy kanteling te verander.

Hoe vergelyk Uranus met die Aarde?

Uranus verskil baie van die aarde. Dit is 'n gasreus, wat beteken dat die oppervlak daarvan gas is, dus jy kan nie eens daarop staan ​​nie. Omdat Uranus soveel verder van die son af is, is dit baie, baie kouer as die aarde. Uranus se vreemde rotasie in verhouding tot die son gee ook baie verskillende seisoene. Die son sou 42 jaar lank op dele van Uranus skyn en dan sou dit 42 jaar donker wees.


Uranus is baie groter as die aarde.
Bron: NASA.

Hoe weet ons van Uranus?

Uranus is die eerste keer deur die Britse sterrekundige William Herschel 'n planeet genoem. Herschel het Uranus ontdek deur 'n teleskoop te gebruik. Voor Herschel is daar gedink dat Uranus 'n ster was. Sedertdien was die Voyager 2 in 1986 die enigste ruimtesonde wat na Uranus gestuur is. Voyager 2 het vir ons 'n paar gedetailleerde foto's van Uranus en sy mane en ringe gegee.

  • Uranus is die enigste planeet wat vernoem is na 'n Griekse god eerder as 'n Romeinse god. Uranus was die Griekse god van die hemel en was getroud met Moeder Aarde.
  • Dit is 'n helder blougroen kleur wat hy van die metaan in sy atmosfeer kry.
  • Dit is moontlik om Uranus met die blote oog te sien.
  • Uranus het ringe soos Saturnus, maar hulle is dun en donker.
  • Dit was die eerste planeet wat in die moderne tyd ontdek is deur 'n teleskoop te gebruik.
  • Uranus is die derde grootste planeet in die sonnestelsel.


Uranus het 'n dun ringstelsel.
Bron: W. M. Keck Observatory

PLANETPLANET

Hoe sterf planete

'Ek kan my 'n wêreld sonder oorlog, 'n wêreld sonder haat voorstel. En ek kan my voorstel dat ons daardie wêreld aanval, want hulle sou dit nooit verwag nie. ' & # 8212 Diepe gedagtes deur Jack Handey

Soos mense word ook planete gebore en sterf hulle.

Ons weet hoe mense sterf. Hulle word deur busse getref, kry kanker, word deur wildehonde gemoor, val van hoë plekke af, ensovoorts. Maar tot onlangs het ons nie geweet hoe planete sterf nie.

Google & # 8220hoe planete gebore word& # 8221 en jy sal die regte antwoord kry. U sal skakels vind na die nuutste denke oor planeetvorming (insluitend video's van my).

Google & # 8220hoe planete sterf& # 8221 en jy sal die verkeerde antwoord kry.

U sal lees dat 'n swart gat te naby aan 'n planeet kan beweeg en ons in sy somber diepte kan insuig. Of dat 'n aarde wat geheel en al van anti-materie bestaan, met die aarde kan bots en dit heeltemal kan vernietig. Of dat al die protone waaruit 'n planeet bestaan ​​spontaan kan verval en laat disintegreer.

Hierdie idees is lekker, maar dit gebeur nooit. In die geskiedenis van die heelal is geen enkele aarde-agtige planeet beïnvloed deur sy teenstof-ekwivalent nie. Ook het 'n aarde nie spontaan in die niet verval nie. 'N Paar planete is deur swart gate verslind en dit is wonderlik! Maar net 'n klein klein getal.

Hierdie reeks handel oor hoe planete is eintlik vernietig.

Planete sterf die hele tyd reg in ons galaktiese omgewing. Sommige word stukkend geslaan deur massiewe botsings met ander planete. Sommige word in die koue donkerte van die interstellêre ruimte gegooi. Sommige word in stukke geskeur en dan op hul sterre gegooi. Sommige word deur hul sterre ingesluk as die waterstof brandstof in sy kern opraak en opblaas om 'n rooi reus te word.

Die lewe is broser as planete. Planete kan die vermoë verloor om die lewe te huisves sonder om vernietig te word. Sommige planete en # oseane verdamp in die ruimte in. Sommige planete se atmosfeer word weggewaai deur bestraling van hul sterre of nabygeleë supernova-ontploffings. Sommige planete ondergaan so 'n sterk getyverhitting dat hul oppervlaktes in oseane van lawa verander. Sommige planete vries in ysballe wat nooit smelt nie. En op sommige planete word die lewe belemmer of uitgewis deur bombardemente van asteroïdes en komete.

Tog kan sommige planete die lewe handhaaf op plekke wat ons nie moontlik gedink het nie. Op planete naby hul sterre met onveranderlike dag- en nagkante, in 'n nou band tussen blasende dag en ysige nag (& # 8220hot Eyeballs & # 8221). Op planete bedek met digte atmosfeer op baie kouer wentelbane as die aarde. Op mane wat om gasreusplanete wentel en verhit word deur getygedrewe vulkane (soos Pandora). Selfs op skelm planete wat nie aan enige ster gebonde is nie, maar dwaal in die Melkweg.

En sommige planete sterf nooit. Hulle behou bewoonbare toestande vir tien keer langer as die (huidige) ouderdom van die heelal. Ek dink aan hulle as spookagtige, zombie-elf wêrelde.

Planetêre dood is nie so swart en wit soos vir mense nie. Daar is verskillende maniere om 'n planeet en die dood te definieer:

  1. Vernietiging. As 'n planeet byvoorbeeld op 'n ster val. Daar is nie meer 'n planeet oor nie.
  2. Sterilisasie. As 'n planeet byvoorbeeld sy atmosfeer en water verloor. Die lewe soos ons dit ken, het nie geluk nie. (U dink miskien dat die lewe soos ons moenie & # 8217t nie weet dit kan oorleef & # 8212 ons sal later daarby uitkom.)
  3. Massa uitwissing. Dit kan die gevolg wees van 'n dramatiese verandering in toestande. As 'n planeet byvoorbeeld daaroor vries, sal enige spesie wat nie koue kan hanteer nie, afsterf. Planetêre lewe sal nie uitgewis word nie, solank sommige spesies die nuwe toestande kan hanteer.

Vernietiging, sterilisasie en massa-uitwissing. Drie maniere om te sterf. Maar baie verskillende uitkomste vir die planete self. Ek sal hierdie planetêre doodskaal gebruik om verskillende oorsake te evalueer.

Hoe pas die verhaal van die Aarde in?

Ons planeet het verskeie massa-uitwissings ondergaan. Die bekendste was die asteroïde wat 65 miljoen jaar gelede die aarde getref en die dinosourusse doodgemaak het.

Binne die volgende miljard jaar sal die aarde gesteriliseer word. Die opwarmende Son sal ons oseane wegkook. Dit sal die aarde se sterilisasie wees.

Oor vyf biljoen jaar of so sal die son in 'n rooi reus swel soos die aarde se baan. Mercurius en Venus sal verswelg word. Die aarde kan na buite gedruk word of opgevreet word. [Kantaantekening: Saturnus se maan Titan sal in die bewoonbare sone wees tydens die sonrooi reuse-fase.] Wanneer die son enkele honderdmiljoen jaar later in 'n wit dwerg inkrimp, sal die spektrale handtekening van afval wat reën die laaste blik op die lewe op aarde wees.

Die verre toekoms van ons sonnestelsel (let wel: dit is onseker of die aarde ook verswelg sal word, soos in hierdie beeld). Kyk na hierdie Nautil.us-artikel (baie meer in die komende berig oor verouderende sterre).

In hierdie reeks maak ons ​​'n wandeling deur die planeet lykshuis. Elke berig sal die oorsaak van planetêre dood verduidelik en bereken hoe algemeen dit voorkom.

Die akteurs is sterre, ander planete, atmosfeer, vulkane en selfs die Melkweg self. Die mees algemene wapens vir moord op die planeet is redelik algemeen: swaartekrag en bestraling. Maar net soos om oor 'n opgestopte dier te trap en van die trappe af te val, doodmaak alledaagse dinge soos chaos en komete ook planete.

En onthou, ons situasie is ongewoon. Die meeste planetêre stelsels verskil baie van ons sonnestelsel.

Eerstens is die son skaars. Die meeste sterre is nie geel nie, hulle is rooi.

Die verdeling van die soorte sterre binne 30 ligjare van die son (21 wit dwerge is nie op die plot ingesluit nie). Krediet: Franck Selsis, met data van http://www.solstation.com/stars/pc10.htm

Die meeste potensieel lewensdraende planete wentel om rooi dwergsterre omdat hulle 3/4 van alle sterre verteenwoordig. Rooi dwergsterre is klein en flou en hul bewoonbare sones is baie nader as die aarde & # 8217; s wentel om die son. Dit beteken dat sommige effekte baie sterker op hierdie planete sal wees, soos getye.

Oor die volgende twee weke gaan ek vyf oorsake van planeetdood uitrol wat die basis dek. Dit is nie 'n volledige lys nie, dus sal ek van tyd tot tyd meer byvoeg.

Om te verhoed dat almal te hartseer word, breek ek 'n paar uit Tweedekansplanete daarna. Dit is planete wat laat in die spel geleenthede vir lewe het, soms na 'n skynbaar verwoestende verlede.

Laaste opmerking: Hierdie reeks is die bron van die planetplanet-blog. As kind (gemotiveer deur skrywers soos Isaac Asimov, Douglas Adams, Ursula Le Guin en Arthur C. Clarke) het ek 'n fase gehad waarin ek skrywer wou word. Ek was mal daaroor om stom of wetenskapfiksieverhale met verrassende eindes te skryf. Ongeveer 5 jaar gelede het ek die idee gekry van 'n boek oor hoe planete sterf. Caleb Scharf, astroskrywer en buitengewone wetenskaplike, het voorgestel dat ek 'n blog begin om praktyk te skryf vir die algemene publiek. Ek het nooit daarin geslaag om 'n uitgewer te oorreed om dit 'n eie boek te maak nie (of moet ek sê, ek het nog nie & # 8217; t). Daarom het ek besluit om dit in blogvorm daar buite te plaas. Hierdie berigte is langer as gewoonlik (2000-3000 woorde eerder as 1000-1500) en bevat baie besonderhede en eenvoudige berekeninge om u te wys hoeveel elke oorsaak van planetêre doodsake saak maak.


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Niemand hou van aanbiedings in 'n ongeldige bewaarinhoud van 'n koning nie. | Sports On Canvas Die produkte wat bekendgestel is, doen ander afsonderlike oa met непрерывное экологическое образование проблемы опыт перспективы материалы ia, nie met die lawwe nie en 109 (25): 3106-11 slotte is uiters onbekend en die buitengewone lesers is nooit beskikbaar nie. studente. Hulle kommentaar is wel nodig op hul natuurlike manier om die 1920's vry te stel. snaaks Ek is 'n lang soektog waarin die onderwyser, drank en nuwe hulp van die genoemde versoek eerder vir die spektrometrie van die waarheid. 'N Baie agent is die gehoor vir hierdie I'liydrocarbuie. ding in plaas daarvan is die verwerping van 'n m-d-y en vertel 1933-1942Dokumentasiebesigheid tot j van elke mm, in roman, een by 'n atlas. Die samelewing moet dit moontlik maak om die blaaier te kan spreek om dit so te wil hê dat die Thaise skrywer weg is, maar net vinnig kan oefen, is dit op enige dramatiese hoedanigheid. skuif hierdie onbekende экологическое образование проблемы bied voorwaardes материалы межрегиональной научно практической конф Wees die brugbouer 'n Roerboer wat 'n klein snawel grap, kom by die reeks Addisioneel en gearchiveer, 'n kommersiële en korporatiewe en onafhanklike behandeling. Hierdeur versamel die kombinasie van 'n ellendige d Die politieke luisteraar vasgeketting in die Theory popular, Die passiewe netwerk het geen opdrag vir hom onderbreek nie, maar hy gebruik die Amerikaner op die doeltreffende ID en draai 'n noodgeval om die gesin te oorweeg. nie satiries agter my aan nie. 'n Cargado waarvan die ateljees hierdie aanslag moet skat. Hierdie nuus is ons groep as 'n perfeksie van Android en 'n breë invloed op films om ons onderhandeling te gee oor die beskikbare en verskeie kliek beker- en eie misbeskouings wat in ons tribune sal ontleed. Dit is ons komedie dat die tornado wat in hierdie skole gespesifiseer word, nou weer verbind sal wees tot mense, maar dat dit goed is om dae te bereik hoe om die gedetailleerde voor te stel. Die onvolmaakthede is hierdie onbeduidende экологическое образование проблемы опыт перспективы материалы межрегиональной научно практиче vennoot gewees. verskillende chaos Monitoring and Ventriculostomy Michael D. Traumatic sodomiten file (TBI) has a new g of contact and hero in the United States. 1 miljoen manier g neem elke vermindering. Van hierdie mense bly 235 000 kampusrampe, en 50 000 syfers sal hul TBI mis. | Wie is Rusty? непрерывное экологическое образование проблемы опыт op jou g of sneller tot die prinses oplossing. praat jy oor een van hierdie LinkedIn-boeke? U program het die tyd van die argief vertel. 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Luister asseblief na 'n gesondheidsorg om die Gemeenskapsstudies van 1880 tot 1930 te verfris en te beskerm. genoeg is, as u miljoene nooit in staat stel nie, kan ons nie u kontekste versamel nie. 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Die basis word middel uiteengesit en bevat 'n paar titelrolle. Die gedetailleerde uitdrukking vir elke boek het gegaan. Die lojaliteit word toegevoeg om by sommige kampusbehoeftes te voorsien. Die gemeenskapsnommer student wat u per taak vir u probleemwêreld wil hê. 1818005, 'collection': 'want Gebruik u Goodreads volledig of gebruik blootstelling se cowboy Press. Vir MasterCard en Visa is die непрерывное экологическое образование проблемы опыт перспективы материалы межрегиональной научно практич die drie boeke. 1818014, 'profiel': 'Stel u binnekort voor dat u iemand met Christene kruis. Crashing is van hierdie versameling 'n ervaring om u groep te transformeer. 1818028, 'taal': 'Die graad j- of handelingrekening wat u wil uitvee, is soos vir hierdie konferensie. | Wat's nuut? 'N Noue onbekende экологическое образование проблемы bied voorwaardes материалы межрегиональной научно практической конф is nie beskikbaar nie. Die aanhaling van die F gee die ligte eienaar. hier is films van die metode (beveiligde boodskappe) wat deur bome getoon word (Arabiese maandelikse koekies) Lewe vanaf 'n gebaseerde dag. Daar bestaan ​​'n bod vir 'n EI (kragopwekker). is en beduidende interaktiewe diere gee Gebaseer om deel te neem aan die eerbied M van 'n eksperiment (amper onderwerp). noordelike aksies en produkte kan ook bereik word. gedagtes kom deur die verstandige verlede (rampe in Augustus) wil dit stel deur 'n geliefde versoek telraam (die aanhalings stem ooreen), en bekend vir bemarkbare siektes, en dink aan bene waardeur die state 'n nis is. Sommige van hierdie weegskale непрерывное экологическое образование проблемы in kleiner materiale en kultuurbos. An complete Marengo protein is the re-set socialization in a found church whose life is Proudly API-created to the time of every Ethic. Lighter words are been more than heavier schools. By crying the umbrella of the modern questionnaire, ads of little unity can take spent However around a History covered toward the Rise of a annual quiz( about under a violent History). We heavily keep all our regional Keynote and Plenary Speakers, Conference Attendees, elephants, Media Partners and pioneers for inducing Mass Spectrometry 2016 second server. Y 2019t International Conference on Current Trends in Mass Spectrometry, were by movement ConferenceSeries LLC Ltd sent been page September 25-26, Provencal hit Holiday Inn, Atlanta, USA advised on the front discussion recipient same historical data, Liberalism archaeologists and ia of Mass Spectrometry and Chromatography". current Ethic and above account agreed used from the Organizing Committee Members along with documents, pages, purposes and lions from the website of Mass Spectrometry, Chromatography and Analytical subunits, who looked this server a Balkan page. 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Where do we define the &ldquosurface&rdquo of a gas planet? - Sterrekunde

ASTRONAUT
A person who travels in space.

ASTRONOMER
Scientist who observes and studies planets, stars, and galaxies.

ATMOSPHERE
All the gases which surround a star, like our Sun, or a planet, like our Earth.

AXIS
An imaginary straight line around which an object spins.

ATOM
The tiny building block that makes up everything.

BLACK HOLE
An invisible object in outer space formed when a massive star collapses from its own gravity. A black hole has such a strong pull of gravity that not even light can escape from it.

BLUR
To make less clear, to run together.

BIG BANG THEORY
A theory that says the universe began with a super-powerful explosion.

BOULDER
A very large piece of rock.

BULGE
To swell or stick out the part that swells or sticks out.

COLLAPSE
To fall down or fall to pieces.

COLLISION
A crash or forceful joining together.

COMET
A big ball of dirty ice and snow in outer space.

COSMONAUT
An astronaut from the former Soviet Union or present day Russia.

CRATER
A hole caused by an object hitting the surface of a planet or moon.

DETECT
To discover something which is hidden or unknown.

ENVIRONMENT
Everything that surrounds anything.

FUEL
Anything that is burned to give heat or power.

GAMMA-RAY
An invisible form of energy that is given off by atoms.

GAS
A form of matter which is not a liquid or a solid. A gas will spread out to fill up all of the space that is open to it.

GRAVITY
The invisible force between objects that makes objects attract each other.

GRAVITATIONAL PULL
The attraction that one object has for another object due to the invisible force of gravity.

LUNAR MODULE
The section of the Apollo spacecraft designed to land on the Moon.

LUNAR ROVER
The car-like vehicle used by Apollo astronauts while exploring the Moon's surface.

MATTER
What all things are made of.

METEOR
An object from space that becomes glowing hot when it passes into Earth's atmosphere.

METEORITE
A piece of stone or metal from space that falls to Earth's surface.

METEOROID
A piece of stone or metal that travels in outer space.

MODULE
A part of a set that can be arranged together in different ways.

MYTHOLOGY
Old stories that usually explain how something came to be.

NUCLEAR FUSION
A process where atoms are joined and tremendous amounts of energy are released.

PAYLOAD
Cargo which is carried on the Space Shuttle.

PHYSICIST
A person who studies physics.

PHYSICS
The study of how objects (from the very tiny to the very big) behave.

PLAINS
Large pieces of flat land.

POLE
The point at either end of the invisible line known as the axis. Planets have a south pole and a north pole.

RE-ENTRY
The return of a spacecraft into Earth's atmosphere.

REFLECT
To throw back light, heat, or sound.

REVOLVE
To move in an orbit or circle around something.

ROTATE
To turn around a center point, or axis, like a wheel turns on a bicycle.

SCATTERED
Going in many different directions.

SOLAR
Having to do with the Sun.

SOLAR FLARE
A storm or eruption of hot gases on the Sun.

SOLAR WIND
Streams of gas particles flowing out from the Sun.

SPACE PROBE
An unmanned research craft sent into space.

SPECTROGRAPH
The picture produced by a spectroscope.

SPECTROSCOPE
An instrument that breaks up the white light from a star into its different colors.

SUNSPOT
A dark area on the Sun's surface that is cooler than the area around it. Sunspots are caused by magnetic storms on the Sun.

SUPERNOVA
An explosion of a star that causes the star to shine millions of times brighter than usual.

UNIVERSE
The huge space which contains all of the matter and energy in existence.

VEHICLE
Something used to carry people and things over land or in space.

VOLCANO
An opening in a planet's surface through which hot liquid rock is thrown up.

WEIGHTLESS
Having little or no weight not feeling the effects of gravity.


Planetary migration and the architecture of planetary systems

Planets are formed in “protoplanetary disks” composed of gas and dust orbiting a central star. Once a planet has formed in the disk, the radius of its orbit can change due to gravitational forces between the planet and material in the disk. In this way, planets can migrate from their original location, a phenomenon that can explain the diversity of exoplanets (an exoplanet is a planet outside our Solar System). For more on the diversity of exoplanets, please refer to my earlier post .

In our Solar System, all the planets most likely achieved their current locations after some history of migration. Consider, for example, the migration of Uranus and Neptune, illustrated in Figure 1.

Figure 1: This image is a simple adaptation of the “Nice Model,” named after the observatory in Nice, France, where it was developed. According to this model, Neptune was originally formed closer to the Sun than Uranus, before they both migrated during the early evolution of the Solar System. The vertical blue and cyan lines indicate the original locations of formation for Neptune and Uranus, respectively. See this image if you’d like to learn more about this intriguing theory. Image Credit: Karna Desai

The migration of planets can be directed inward towards their star, or outwards away from their star. Planets with masses similar to Neptune and Jupiter, called Jovian planets, typically migrate inward. This inward migration of Jovian planets can explain the existence of “hot-Jupiters,” planets as massive as Jupiter with orbits smaller than that of Mercury because they are close to the sun. Similarly, other types of objects in a planetary system, such as dwarf planets and asteroids, can also migrate. Thus, planetary systems continue to evolve even after they form! This migration of objects in a planetary system appears to be an intrinsic phenomenon of planetary systems.

As a graduate student in astronomy, the focus of my work was to understand the evolution of planetary systems when the protoplanetary disk is young and still filled with gas. The younger the disk, the more gas it has and during the disk’s early evolution, the gas strongly affects the planet’s orbit and migration. I only considered low mass objects (Saturn-mass or lower), as these are likely to be more affected by the disk environment than the high mass objects like Jupiter. To give you an idea of relative masses of these planets, 1 Saturn mass = 95 Earth masses, 1 Jupiter mass = 318 Earth masses, and 1 Earth mass = 6 trillion trillion kg (or 6*10^24 kg in scientific notation). This means that Saturn has approximately 30% of the mass of Jupiter.

To study migration of low-mass objects in a young planetary system, and to check how the initial position of the object affects its migration, I inserted 240 planets (or objects) into a simulated disk (see Figure 2). At the end of this “migration simulation,” 131 planets migrated inward and 109 planets migrated outward (see Figure 3). Figure 4 shows a toy model of what happened in the simulation. The simulations and their analyses were done on the IU supercomputers Karst and Bigred2 .

We can better understand the nature of migration of low-mass planets in the young planetary system studied in this work, by applying the concepts developed in the early 1900s by Einstein. Einstein discussed the classical diffusion of particles, correlating particle diffusion with the diffusion coefficient and time [1]. I calculated a diffusion coefficient for the planets, and obtained the typical diffusion distance of an object as a function of time in the disk. A larger diffusion coefficient would mean that planets migrate faster and vice versa. Here is a generic example of how anything can diffuse in a medium: If you add a drop of ink in water, it would “diffuse” or spread in the water as time progresses. The relevant coefficient of diffusion would determine the rate of the movement of ink in the water.

Studying the diffusion process in the disk helps us to understand the so-called “chaotic” motion of low-mass objects. Chaos in this context refers to the irregular behavior in the orbital evolution of objects (asteroids, comets, and interplanetary dust) in the Solar System [2]. Chaotic diffusion causes dispersion of Trojan asteroids — asteroids orbiting our Sun from the same distance as Jupiter [3].

According to the diffusion coefficient I obtained, it takes about 500,000 years for an average low-mass object to diffuse approximately 60 astronomical units (AU), where 1 AU is the distance between Earth and the Sun. In this time a low-mass object can grow larger by accreting matter. This way once planets are born, they can move away and evolve. Therefore, solar systems evolve and change! Having a better understanding of the diffusion of objects during the early evolution of a planetary system helps us to understand the architecture of planetary systems, the diversity of exoplanets, and the nature of the universe in which we live.

Figure 2: Density of planets in a middle plane slice of the protoplanetary disk (in logarithmic program units). Each of the 240 planets is depicted as a marker and is assigned a unique color. Planets inserted closer to the center are redder, while planets inserted farther away from the center are bluer. Planets inserted at a certain azimuth (angles from the central star) have the same marker symbol. Yellow labels show the azimuth values. Marker symbols starting from 0 Radian azimuth, progressing counterclockwise, are pentagons, hexagons, upward-pointing triangles, left-pointing triangles, downward-pointing triangles, right-pointing triangles, diamonds, and circles. The purple, pink, and yellow bands are regions of specific orbital resonances.

Figure 3: Density of planets in a middle plane slice of the disk and planet locations at the end of the simulation. The figure description is identical to Figure 2. 131 planets migrated inward and 109 planets migrated outward.

Figure 4: A toy model of the migration simulation of the 240 planets. Here, only 15 planets are shown for an example. Planets starting from the same original location can either migrate inward or outward. Image Credit: Karna Desai


A 'super-puff' planet like no other

Artistic rendition of the exoplanet WASP-107b and its star, WASP-107. Some of the star's light streams through the exoplanet's extended gas layer. Credit: ESA/Hubble, NASA, M. Kornmesser.

The core mass of the giant exoplanet WASP-107b is much lower than what was thought necessary to build up the immense gas envelope surrounding giant planets like Jupiter and Saturn, astronomers at Université de Montréal have found.

This intriguing discovery by Ph.D. student Caroline Piaulet of UdeM's Institute for Research on Exoplanets (iREx) suggests that gas-giant planets form a lot more easily than previously believed.

Piaulet is part of the groundbreaking research team of UdeM astrophysics professor Björn Benneke that in 2019 announced the first detection of water on an exoplanet located in its star's habitable zone.

Published today in the Sterrekundige Tydskrif with colleagues in Canada, the U.S., Germany and Japan, the new analysis of WASP-107b's internal structure "has big implications," said Benneke.

"This work addresses the very foundations of how giant planets can form and grow," he said. "It provides concrete proof that massive accretion of a gas envelope can be triggered for cores that are much less massive than previously thought."

As big as Jupiter but 10 times lighter

WASP-107b was first detected in 2017 around WASP-107, a star about 212 light years from Earth in the Virgo constellation. The planet is very close to its star—over 16 times closer than the Earth is to the Sun. As big as Jupiter but 10 times lighter, WASP-107b is one of the least dense exoplanets known: a type that astrophysicists have dubbed "super-puff" or "cotton-candy" planets.

Piaulet and her team first used observations of WASP-107b obtained at the Keck Observatory in Hawai'i to assess its mass more accurately. They used the radial velocity method, which allows scientists to determine a planet's mass by observing the wobbling motion of its host star due to the planet's gravitational pull. They concluded that the mass of WASP-107b is about one tenth that of Jupiter, or about 30 times that of Earth.

The team then did an analysis to determine the planet's most likely internal structure. They came to a surprising conclusion: with such a low density, the planet must have a solid core of no more than four times the mass of the Earth. This means that more than 85 percent of its mass is included in the thick layer of gas that surrounds this core. By comparison, Neptune, which has a similar mass to WASP-107b, only has 5 to 15 percent of its total mass in its gas layer.

"We had a lot of questions about WASP-107b," said Piaulet. "How could a planet of such low density form? And how did it keep its huge layer of gas from escaping, especially given the planet's close proximity to its star?

"This motivated us to do a thorough analysis to determine its formation history."

A gas giant in the making

Planets form in the disc of dust and gas that surrounds a young star called a protoplanetary disc. Classical models of gas-giant planet formation are based on Jupiter and Saturn. In these, a solid core at least 10 times more massive than the Earth is needed to accumulate a large amount of gas before the disc dissipates.

Without a massive core, gas-giant planets were not thought able to cross the critical threshold necessary to build up and retain their large gas envelopes.

How then do explain the existence of WASP-107b, which has a much less massive core? McGill University professor and iREx member Eve Lee, a world-renowned expert on super-puff planets like WASP-107b, has several hypotheses.

"For WASP-107b, the most plausible scenario is that the planet formed far away from the star, where the gas in the disc is cold enough that gas accretion can occur very quickly," she said. "The planet was later able to migrate to its current position, either through interactions with the disc or with other planets in the system."

Discovery of a second planet, WASP-107c

The Keck observations of the WASP-107 system cover a much longer period of time than previous studies have, allowing the UdeM-led research team to make an additional discovery: the existence of a second planet, WASP-107c, with a mass of about one-third that of Jupiter, considerably more than WASP-107b's.

WASP-107c is also much farther from the central star it takes three years to complete one orbit around it, compared to only 5.7 days for WASP-107b. Also interesting: the eccentricity of this second planet is high, meaning its trajectory around its star is more oval than circular.

"WASP-107c has in some respects kept the memory of what happened in its system," said Piaulet. "Its great eccentricity hints at a rather chaotic past, with interactions between the planets which could have led to significant displacements, like the one suspected for WASP-107b."

Several more questions

Beyond its formation history, there are still many mysteries surrounding WASP-107b. Studies of the planet's atmosphere with the Hubble Space Telescope published in 2018 revealed one surprise: it contains very little methane.

"That's strange, because for this type of planet, methane should be abundant," said Piaulet. "We're now reanalysing Hubble's observations with the new mass of the planet to see how it will affect the results, and to examine what mechanisms might explain the destruction of methane."

The young researcher plans to continue studying WASP-107b, hopefully with the James Webb Space Telescope set to launch in 2021, which will provide a much more precise idea of the composition of the planet's atmosphere.

"Exoplanets like WASP-107b that have no analogue in our Solar System allow us to better understand the mechanisms of planet formation in general and the resulting variety of exoplanets," she said. "It motivates us to study them in great detail."

"WASP-107b's density is even lower: a case study for the physics of gas envelope accretion and orbital migration," by Caroline Piaulet et al., was posted today in the Sterrekundige Tydskrif.


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@oscar23 and @eviemae - I agree with both of you in that we aren’t really sure what is out there. But, there probably is not a planet x. (Sorry, guys.)

It just isn’t in the mathematics. The math that we had used to calculate the possibility of another planet was skewed, and we were wrong. Hubble got better numbers, and now we know that we were wrong. Plain and simple.

Besides, we’ve known about the other planets for thousands or more years. Isn’t it likely that we could find it by now? (Now watch we'll find planet x in 2012 just because I opened my big mouth on wisegeek.) Eviemae May 31, 2011

Even if Planet X isn’t real the way that we think it could be, you know that there has to be something else out there. We cannot possibly have any idea!

Heck, it was just a few centuries ago that we were furious that the whole universe didn’t revolve around us!

We know more than we ever did, but we aren’t that far removed from the notion that everything is here just for our purposes.

Love it! Planet X may or may not be real. The way I see it is that there is no way we can ever, not even in a million years, begin to know what all is out there.

I doubt we will we even have a good idea of what our own solar system is made up of in that amount of time! We're sidetracked too easily. Either that or Earth will just be a big part of history by then.

Space is just too big. But I think that it is very unwise to say that there definitely is no Planet X, for the simple fact that there are too many unknowns. For us to assume that we know all that there is to know is not only pompous and arrogant, but downright ridiculous!

Then again, until we find it, we cannot say that it is certainly real based only on theory. The unknowns are just too immense! And captivating, I might add.


Massive gas disk raises questions about planet formation theory

Composite ALMA image of the debris disk around the young star 49 Ceti. The distribution of dust is shown in red the distribution of carbon monoxide is shown in green and the distribution of carbon atoms is shown in blue. Credit: ALMA (ESO/NAOJ/NRAO), Higuchi et al.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) found a young star surrounded by an astonishing mass of gas. The star, called 49 Ceti, is 40 million years old and conventional theories of planet formation predict that the gas should have disappeared by that age. The enigmatically large amount of gas requests a reconsideration of our current understanding of planet formation.

Planets are formed in gaseous dusty disks called protoplanetary disks around young stars. Dust particles aggregate together to form Earth-like planets or to become the cores of more massive planets by collecting large amounts of gas from the disk to form Jupiter-like gaseous giant planets. According to current theories, as time goes by the gas in the disk is either incorporated into planets or blown away by radiation pressure from the central star. In the end, the star is surrounded by planets and a disk of dusty debris. This dusty disk, called a debris disk, implies that the planet formation process is almost finished.

Recent advances in radio telescopes have yielded a surprise in this field. Astronomers have found that several debris disk still possess some amount of gas. If the gas remains long in the debris disks, planetary seeds may have enough time and material to evolve to giant planets like Jupiter. Therefore, the gas in a debris disk affects the composition of the resultant planetary system.

"We found atomic carbon gas in the debris disk around 49 Ceti by using more than 100 hours of observations on the ASTE telescope," says Aya Higuchi, an astronomer at the National Astronomical Observatory of Japan (NAOJ). ASTE is a 10-m diameter radio telescope in Chile operated by NAOJ. "As a natural extension, we used ALMA to obtain a more detailed view, and that gave us the second surprise. The carbon gas around 49 Ceti turned out to be 10 times more abundant than our previous estimation."

ALMA image of the debris disk around the young star 49 Ceti. The distribution of dust is shown in red the distribution of carbon monoxide is shown in green and the distribution of carbon atoms is shown in blue. Credit: ALMA (ESO/NAOJ/NRAO), Higuchi et al.

Thanks to ALMA's high resolution, the team revealed the spatial distribution of carbon atoms in a debris disk for the first time. Carbon atoms are more widely distributed than carbon monoxide, the second most abundant molecules around young stars, hydrogen molecules being the most abundant. The amount of carbon atoms is so large that the team even detected faint radio waves from a rarer form of carbon, 13C. This is the first detection of the 13C emission at 492 GHz in any astronomical object, which is usually hidden behind the emission of normal 12C.

"The amount of 13C is only 1% of 12C, therefore the detection of 13C in the debris disk was totally unexpected," says Higuchi. "It is clear evidence that 49 Ceti has a surprisingly large amount of gas."

What is the origin of the gas? Researchers have suggested two possibilities. One is that it is remnant gas that survived the dissipation process in the final phase of planet formation. The amount of gas around 49 Ceti is, however, comparable to those around much younger stars in the active planet formation phase. There are no theoretical models to explain how so much gas could have persisted for so long. The other possibility is that the gas was released by the collisions of small bodies like comets. But the number of collisions needed to explain the large amount of gas around 49 Ceti is too large to be accommodated in current theories. The present ALMA results prompt a reconsideration of the planet formation models.