Astronomija

Kaj bi se zgodilo, če bi Soncu podobna zvezda zaužila planet, podoben Jupitru?

Kaj bi se zgodilo, če bi Soncu podobna zvezda zaužila planet, podoben Jupitru?


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Veliko odkritih eksoplanetnih sistemov verjetno vsebuje več kot enega plinskega velikana z razdaljo, ki je daleč bližje zvezdi kot v našem sončnem sistemu.

Znano je, da lahko v evoluciji sončnega sistema gravitacijski učinki med predmeti povzročijo, da se nekateri med njimi selijo navzven, drugi pa navznoter.

Ali so že kdaj preučevali, kaj se zgodi, ko se plinski velikan približa svoji zvezdi dovolj blizu, da ji začne izgubljati maso? Ali bi lahko planet v tem primeru popolnoma končal v zvezdi?

Za namene tega vprašanja izberemo zvezdo G-tipa sončne mase in plinskega velikana, kot je Jupiter, saj imamo o teh predmetih toliko znanja iz prve roke.

Jupiter ima veliko vodika, kar bi pomenilo dodatek več nukleosintetičnega goriva.

Bi bilo to dovolj, da bi Sonce v tem primeru postalo rdeči velikan?


Ne bo veliko vplivalo. Sonce ima maso, ki je 1000-krat večja od Jupitra. Dodajanje Jupitra soncu bo spremenilo maso iz 1,989 $ times10 ^ {30} $ do 1,991 $ krat10 ^ {30} $kg

Če soncu dodate več mase, bo sončno življenje nekoliko zmanjšalo. Večja masa bo povzročila stiskanje in segrevanje jedra, kar bo povečalo hitrost jedrske fuzije. Sonce bo gorivo porabilo hitreje. Večje zvezde živijo krajši čas.

Toda razmeroma majhen dodatek mase se ne bi veliko spremenil.


Obstajajo scenariji, ko bi bili učinki povečanja planeta na soncu podobno zvezdo resnično zelo pomembni, vsaj kratkoročno. Medtem ko bi bila količina mase, ki jo zvezda prirašča, majhna motnja, količina priraščene energije in / ali kotni moment morda ne bo.

1. scenarij: Scenarij, ko vroč Jupiter samo pade v zvezdo iz oddaljenega polmera, bi zagotovo imel drastične kratkoročne učinke. Toda kratkoročno tukaj pomeni v primerjavi z življenjem zvezde.

Kinetična energija recimo Jupitra, ki pada na površino zvezde od daleč (več kot nekaj sončnih polmerov), bi bila pravilna $ GM _ { odot} M_ mathrm {Jup} / R _ { odot} sim 4 krat 10 ^ {38} $ džuli.

Za primerjavo, sončna svetilnost je 3,83 $ krat 10 ^ {26} mathrm {J / s} $.

Dodatek te toliko energije (če se ji dovoli segrevanje) bi potencialno vplivajo na svetilnost Sonca v časovnih okvirih deset tisoč let. Natančni učinki bodo odvisni od tega, kje se odlaga energija. V primerjavi z vezavno energijo zvezde je dodatna energija zanemarljiva, toda če se energija razprši v konvekcijskem območju, bi kinetična energija delovala in dvignila konvekcijski ovoj. Z drugimi besedami, zvezda bi se povečala tako v svetilnosti kot v polmeru. Če so bili učinki le omejeni na konvektivno ovojnico, potem je ta približno enaka 0,02 milijona USD _ { odot} $ in tako bi ga lahko "dvignili" $ sim 4 krat 10 ^ {38} R _ { odot} ^ 2 / GM _ { odot} M _ { rm conv} sim 0,05 R _ { odot} $.

Torej, v tem scenariju bi se zvezda tako razširila in postala bolj svetleča. Ustrezni časovni okvir je časovni razpon Kelvin-Helmholtz konvektivne ovojnice, ki je v redu $ GM _ { odot} M _ { rm conv} / R _ { odot} L _ { odot} sim $malo $10^5$ letih.

Če bi planet nekako preživel in se prebil do središča zvezde, bi se v konvekcijskem območju odložilo veliko manj energije in učinki bi se zmanjšali.

V daljših časovnih okvirih bi se zvezda spet spustila v glavno zaporedje, s polmerom in svetilnostjo le malo večja, kot je bila prej, sorazmerno z majhnim (0,1%) povečanjem mase.

Vse to predpostavlja, da lahko planet ob padcu ostane nedotaknjen. V tem scenariju neposrednega padca zagotovo ne bi "izhlapilo", bi pa se naglo zdrobil, preden bi lahko izginil pod površjem? Omejitev Rocheja je pravilna $ R _ { odot} ( rho _ { odot} / rho _ { rm Jup}) ^ {1/3} $. Toda povprečne gostote zvezde in (plinskega velikana) planeta so skoraj enake. Zato se zdi verjetno, da bi bil planet zagon tidalno raztrgati, toda ko v tem trenutku potuje proti zvezdi z nekaj sto km / s, razpada plimovanja ni bilo mogoče doseči, preden je izginila pod površjem.

Moj zaključek je torej, da spuščanje Jupitra v Soncu podobno zvezdo v tem scenariju bi bilo, kot bi padli globinski naboj, z zaostankom reda $10^{5}$ let preden so se pokazali popolni učinki.

2. scenarij: Vroč Jupiter prispe na mejo Rocheja (tik nad zvezdno površino), ko je izgubil velik kotni zagon. V tem primeru lahko pride do učinkov na človeški časovni okvir.

V tem primeru se bo zgodilo, da bo planet zaradi plime in oseke (hitro) razdrobil in morda pustil veliko jedro. V polmeru orbite $ 2 R _ { odot} $, bo obdobje kroženja približno 8 ur, hitrost kroženja približno $ 300 mathrm {km / s} $ in orbitalni kotni moment okoli $ 10 ^ {42} mathrm {kg m ^ 2 s ^ {- 1}} $. Ob predpostavki popolnega uničenja bo večji del materiala tvoril priraščevalni disk okoli zvezde, saj mora izgubiti nekaj svojega kotnega zagona, preden se lahko priraste.

Koliko zvezdine svetlobe je blokirano, ni jasno. Odvisno je predvsem od tega, kako je material razdeljen na disku, zlasti višina lestvice diska. To pa je odvisno od ravnovesja ogrevalnih in hladilnih mehanizmov in s tem od temperature diska.

Nekakšna minimalna ocena bi lahko bila domneva, da je disk ravninski in enakomerno razporejen med sončno površino in $ 2R _ { odot} $ in da se približa temperaturi sončne fotosfere pri $ sim 5000 mathrm K $. V tem primeru je območje diska $ 3 pi R _ { odot} ^ 2 $, z "površinsko gostoto" $ sigma sim M _ { rm Jup} / 3 pi R _ { odot} ^ 2 $.

V hidrostatičnem ravnotežju bo višina lestvice $ sim kT / g m_ mathrm H $, kje $ g $ je gravitacijsko polje in $ m_ mathrm H $ masa vodikovega atoma. Teža (ravnine) bo $ g sim 4 pi G sigma $. Dajanje noter $ T sim 5000 mathrm K $, dobimo višino lestvice $ sim 0,1 R _ { odot} $.

Kako dolgo bi ostal diskretni disk, nisem prepričan, kako izračunati. Odvisno od predvidene viskoznosti in temperaturne strukture ter od tega, koliko mase se izgubi z izhlapevanjem / vetrovi. Naraščeni material bo oddajal velik del svoje gravitacijske potencialne energije, zato bodo energijski učinki veliko manj resni kot scenarij 1. Vendar bo zvezda narasla $ sim 10 ^ {42} mathrm {kg m ^ 2 s ^ {- 1}} $ kotnega momenta, ki je primerljiv s trenutnim kotnim momentom Sonca.

Prirast eksoplaneta na ta način je torej dovolj za povečanje kotnega momenta zvezde, kot je Sonce, za znatno velikost. Dolgoročno bo to drastično vplivalo na magnetno aktivnost soncu podobne zvezde - povečalo jo bo za nekajkrat do reda velikosti.


Zakaj bi lahko bil Jupiter zadnje dekle sončnega sistema - dokler ga zvezda ne izžene

Približno čez 5,4 milijarde let se bo zgodila vesoljska groza. Sonce bo padlo v ognjeno smrt, pihalo bo v rdečega orjaka, ki bo zlahka požrl Merkur, Venero, Zemljo in morda Mars, nato pa izgubil polovico mase. Brez gravitacije Sonca, ki bi jih zadržala v orbiti, bodo zunanji planeti na koncu postali prevarantski. Neptun? Ne poznam je.

Jupiter bo verjetno zadnje dekle v vsem tem. Ker je plinski velikan tako masiven, ima največjo gravitacijsko vez z našo zvezdo in bo še nekaj časa, tudi ko ta zvezda umira. Težava je v tem, da se bo masa Sonca še naprej zmanjševala, ko bo v naslednjih 7 milijard letih prehajala iz faze rdečega orjaka v fazo belega škrata. Ko se Sonce zmanjšuje, Jupiter ne bo več tako gravitacijsko vezan nanj, zaradi česar bo dovzeten za srečanja z minevimi zvezdami vsakih 20 milijonov let. Bodisi bodo ti mimoidoči potisnili nestabilnega Jupitra iz njegove orbite, dokler ne dobi namiga - ali pa ga bo en velikanski brcnil ven.

Več prostora

"Za odstranitev Jupitra iz primeža Sonca ni potrebna zelo masivna zvezda," je povedal Jon Zink, študent astronomije na UCLA, ki je pred kratkim objavil študijo Astronomski vestnik, je povedal SYFY WIRE. »S simulacijo smo ugotovili, da je za razdružitev Jupitra potrebnih približno 4000 zvezdnih mušic, vendar je večina teh zelo oddaljenih in ima le majhen vpliv na sistem. Samo dolgo moramo čakati, da se eden od njih približa dovolj blizu, da odvrže planet. "

Ko bo Sonce zašlo za vedno, Zink verjame, da bo najverjetnejša usoda tistih planetov, ki jih ne bo zajela velika krogla rdečega orjaškega ognja, sama krožila okoli središča galaksije v polmeru približno 53.000 svetlobnih let , podobno kot pri njihovih sončnih orbitah. Ti planeti, ki neodvisno krožijo, bodo razvijali vedno večje in večje orbite, ko jih sonce izgubi gravitacijsko zadrževanje, in sčasoma preidejo na drugo stran galaksije. Vendar obstajajo bolj čudni in manj verjetni scenariji. Lahko bi obstajala zvezda z dovolj gravitacije, da bi ujela enega od zunanjih planetov, če se prikrade na ta planet s pravo razdaljo in hitrostjo.

Drug alternativni scenarij si predstavlja zvezdo, ki vdira, ki bi lahko uporabila ogromno energije, da bi enega od teh planetov zagnala iz Rimske ceste, kdo ve kje.

Če pogledamo v daljno prihodnost, so potrebne simulacije N-telesa, ki simulirajo interakcije v nenehno spreminjajočih se sistemih. S tovrstnimi simulacijami lahko napovemo, kaj se bo zgodilo z vsemi, od najmanjših delcev do največjih planetov, kot je Jupiter, za katerega je bilo dokazano, da je izgubil gravitacijsko silo med njim in soncem za faktor 6. Jupiter in Saturn bosta izgubila njihova orbitalna resonanca, kar pomeni, da bodo njihove orbite postale nestabilne, saj ne bodo več izvajale stabilnih gravitacijskih sil drug na drugega. To se bo zgodilo zaradi nezmožnosti Sonca, da se jih drži. Ko bo Sonce še naprej izgubljalo oprijem na Jupiter, bo planet postal ranljiv za zunanje sile.

Če bi Jupiter ali drug planet tako nasilno vrgli iz galaksije, bi morala biti njegova hitrost do 50-krat večja, kot je pokazala Zinkova simulacija, a kaj takega, kar se zgodi, ni nemogoče. Simulacije N-telesa nam morda še vedno ne povedo vsega. Vesolje je dinamično, vedno se spreminja in razkriva nepričakovane stvari, ki jih trenutno nihče ne napoveduje.

"Obstaja več neznank, ki bi lahko vplivale na naše rezultate," je dejal Zink. "Model izgube mase, ki se uporablja tukaj, predpostavlja popolno razumevanje osnovnih fizikalnih procesov, ki jih bo Sonce izvajalo v življenju. Če bodo odkriti novi mehanizmi, se bo ta model spremenil skupaj s pričakovanim prihodnjim razvojem. "

Binarne zvezde niso bile vključene, ker bi otežile delo, toda Jupiter bi lahko na koncu postal žrtev binarnega zvezdnega sistema. Kljub temu bo morala zvezda (ali zvezde), ki bodo Jupiter najverjetneje odvrgle v medzvezdni prostor, biti dovolj velika, da se bo lahko zadovoljila s takim behemotom, vendar tudi na pravem mestu ob pravem času in s pravo hitrostjo. Zvezde sončne mase ali manj do bodo vplivale na impozantni planet, ker je toliko manjših zvezd raztresenih po galaksiji. Zink verjame, da je najverjetneje, da bo ena ognjena krogla, ki izpolnjuje vse ustrezne pogoje, Jupitra pregnala z Rimske ceste.

"Medtem ko zvezdna masa vpliva na obseg interakcije, je pomembnejši parameter razdalja najbližjega pristopa," je dejal. "Medtem ko tukaj igrata vlogo tako količina kot moč interakcije, smo ugotovili, da bo eno samo bližnje srečanje glavni vzrok za osvoboditev Jupitra, kar pomeni, da bo verjetno prišlo do bližnjega srečanja in izmet planeta, preden bodo majhne oddaljene interakcije sposobne popolnoma kopičijo. "

Letos bi bil morda zemeljski požar smeti, toda drugi planeti bodo nekoč imeli svojo distopično dobo. Jupiter, pripravi se.


Metoda lova na planete uspe: Jupiter podoben planet, ki kroži okoli ene najmanjših zvezd

Dolgo predlagano orodje za lovljenje planetov je ustvarilo svoj prvi ulov - Jupiterju podoben planet, ki kroži okoli ene najmanjših znanih zvezd.

Tehniko, imenovano astrometrija, smo prvič poskusili iskati planete zunaj našega sončnega sistema, imenovane eksoplaneti. Vključuje merjenje natančnih gibov zvezde na nebu, ko neviden planet vleče zvezdo naprej in nazaj. Toda metoda zahteva zelo natančne meritve v daljšem časovnem obdobju in do zdaj ni uspela razkriti nobenega eksoplaneta.

Skupina dveh astronomov iz NASA-jevega Laboratorija za reaktivni pogon v Pasadeni v Kaliforniji zadnjih 12 let na teleskop v Observatoriju Palomar blizu San Diega montira instrument za astrometrijo. Po natančnih, občasnih opazovanjih 30 zvezd je ekipa identificirala nov eksoplanet okoli enega od njih - prvega, ki so ga odkrili okoli zvezde z uporabo astrometrije.

"Ta metoda je optimalna za iskanje konfiguracij sončnega sistema, kot je naša, ki bi lahko vsebovale druge Zemlje," je povedal astronom Steven Pravdo iz JPL, vodilni avtor študije o rezultatih, ki bodo objavljeni v Astrofizični časopis. "Jupiterju podoben planet smo našli na približno istem relativnem mestu kot naš Jupiter, le okoli veliko manjše zvezde. Možno je, da ima ta zvezda tudi notranje kamnite planete. In ker je več kot sedem od desetih zvezd majhnih, kot je ta, to bi lahko pomenilo, da so planeti bolj pogosti, kot smo mislili. "

Ugotovitev potrjuje, da je lahko astrometrija močna tehnika lova na planete tako za zemeljske kot vesoljske teleskope. Na primer, podobno tehniko bi uporabil SIM Lite, NASA-in koncept za vesoljsko misijo, ki jo trenutno raziskujejo.

Novonastali eksoplanet, imenovan VB 10b, je v ozvezdju Aquila oddaljen približno 20 svetlobnih let. Je plinski velikan, katerega masa je šestkrat večja od Jupitrove in je dovolj oddaljena od svoje zvezde, da jo lahko označimo za "hladnega Jupitra", podobno naši. V resnici bi mu lastna notranja toplota dala Zemljo podobno temperaturo.

Planetova zvezda, imenovana VB 10, je majhna. To je tisto, kar je znano kot M-škrat in je le dvanajsta masa našega sonca, komaj dovolj velika, da v svojem jedru stopi atome in zasije z zvezdami. VB 10 je bila leta najmanjša znana zvezda - zdaj ima nov naslov: najmanjša zvezda, za katero je znano, da gosti planet. Čeprav je zvezda bolj masivna od novoodkritega planeta, bi imela oba telesa podoben obseg.

Ker je zvezda tako majhna, bi bil njen planetarni sistem naša miniaturna, pomanjšana različica. Na primer, VB 10b, čeprav velja za hladen Jupiter, se nahaja približno tako daleč od svoje zvezde, kot je Merkur od sonca. Vsi kamniti planeti velikosti Zemlje, ki bi se lahko znašli v soseščini, bi ležali še bližje.

"Nekateri drugi eksoplaneti okoli večjih zvezd M-pritlikav so prav tako podobni našemu Jupitru, zaradi česar so zvezde plodna tla za prihodnja iskanja Zemlje," je povedal Stuart Shaklan, soavtor Pravda in znanstvenik za instrumente SIM Lite pri JPL. "Astrometrija je najprimernejša za iskanje hladnih Jupitrov okoli vseh vrst zvezd in s tem za iskanje več planetarnih sistemov, urejenih kot naš dom."

V zadnjih 12 letih sta Pravdo in Shaklan dva do šestkrat na leto z instrumentom Stellar Planet Survey pritrdila Palomarjev petmetrski teleskop Hale za iskanje planetov. Instrument, ki ima 16-milijona slikovnih pik napolnjeno napravo ali CCD, lahko zazna zelo majhne spremembe v položaju zvezd. Na primer, planet VB 10b povzroči, da se njegova zvezda premakne majhen delček stopinje. Zaznavanje tega nihanja je enakovredno merjenju širine človeškega las s približno treh kilometrov oddaljenosti.

Druge široko uporabljene zemeljske tehnike lova na planete vključujejo radialno hitrost in način prehoda. Tako kot astrometrija tudi radialna hitrost zazna gibanje zvezde, vendar meri Dopplerjeve premike v zvezdni svetlobi, ki jih povzroča gibanje proti nam in stran. Tranzitni način išče padce svetlosti zvezde, ko planeti, ki krožijo okoli, prečkajo in blokirajo svetlobo. Nasina vesoljska misija Kepler, ki je začela iskati planete 12. maja, bo s tranzitno metodo iskala zemeljske svetove okoli zvezd, podobnih soncu.

"To je vznemirljivo odkritje, ker kaže, da lahko planete najdemo okoli izjemno lahkih zvezd," je dejal Wesley Traub, glavni znanstvenik za Nasin program za raziskovanje eksplanetov pri JPL. "To je namig, da narava rada oblikuje planete, tudi okoli zvezd, ki se zelo razlikujejo od sonca."


* REDKI DOGODEK * Astronomska zima se nocoj začne z Veliko konjunkcijo Jupitra in Saturna & # 8211, zakaj ne bo videti kot božična zvezda?

Dva največja planeta sončnega sistema, Jupiter in Saturn, sta nocoj zelo blizu. Pravzaprav sta bila nazadnje tako blizu, pred skoraj 400 leti! In njun naslednji zelo tesni par se bo zgodil čez približno 60 let. Toda nocoj bo to Velika konjukcija dveh planetov, ki se ne bosta približala ali zasijala kot ena sama božična zvezda, ki ste jo morda prebrali.

Še ena spektakularna nebesna predstava se bo zgodila nocoj, 21. decembra. Prvi dan astronomske zime 2020/21 (solsticij). Minilo je skoraj 400 let od Velike konjukcije velikanov v našem sistemu, planetov Jupiter in Saturn. To se je zgodilo podnevi in ​​blizu Sonca, zato ga je bilo težko najti na nebu.

Torej najbližji podoben nočni dogodek tesne povezave obeh velikanov je pred skoraj 800 leti. Nazadnje je večina svetovne populacije & rsquos imela ugoden pogled na ta dva velikana, 5. marca leta 1226. Takrat sta bila še bolj skupaj (le 2 ločni minuti narazen) v primerjavi s tem, kar bomo videli nocoj (0,1 stopinje narazen ).

Jupiter in Saturn največji luni. Vir: Univerza Rice

Leta 1226 se je poravnava Saturna in Jupitra zgodila ponoči, tako bo tudi leta 2020, tako da bodo številni po vsem svetu lahko priča temu spektakularnemu dogodku. Naslednje super tesno povezovanje Jupitra in Saturna bo 15. marca 2080.

Toda Jupiter že več mesecev & lsquochasing & rsquo obročasti planet Saturn in se zdaj pripravlja na mimo. Ali jih lahko nocoj ujamemo na nebu? Tu je oblačna pokritost nad Evropo in ZDA, ki jo vidijo vremenski modeli:

Številne novice v zadnjem času imenujejo ta dogodek & lsquoBožična zvezda & rsquo, vendar še zdaleč ni to. Nadalje vam bomo razložili, kaj pravzaprav je božična zvezda.

Kljub temu je tak dogodek skoraj enkrat v življenju. To & rsquos zagotovo!

KAJ JE BOŽIČNA ZVEZDA

Tako kratko, ko bomo slišali & lsquoBožično zvezdo & rsquo, pričakujemo, da bomo videli zelo svetlo zvezdo, ki sija.

Jupiter in Saturn sta planeta, torej niti ene same zvezde! Ne bodo blizu nobenega križišča ali celo združevanja v en sam predmet, zato med njima ni & lsquotouching & rsquo.

Spodnja črta, Velika konjukcija Jupitra in Saturna je morda videti kot ena sijoča ​​božična zvezda, vendar tehnično ni & rsquot.

Vendar je v preteklosti nekaj razlag o božični zvezdi.

  • Pojasnilo 1: Božična zvezda je bila eksplozija nove ali supernove
  • Pojasnilo 2: božična zvezda je bila komet
  • Pojasnilo 3: Božična zvezda je bila zveza Jupitra in Saturna
  • Pojasnilo 4: božična zvezda je bila mirujoča točka Jupitra
  • Pojasnilo 5: Božična zvezda je bila zveza Jupitra, Regula in Venere
PLANETI JUPITER in SATURN

Največji od dveh velikanov je planet Jupiter, ki je tudi najsvetlejši objekt za Soncem, Luno in Venero na našem nočnem nebu. To je 5. planet od Sonca.

Planet Saturn je nekoliko manjši in tudi nekoliko zatemnjen od Jupitra, a hkrati tudi 2. največji v našem planetarnem sistemu. Saturn je skoraj dvakrat oddaljen od Jupitra.

Saturn je šesti planet, oddaljen od sonca. Saturn potrebuje skoraj 30 let, da kroži (da obide) sonce, Jupiter pa 1,5-krat manj, približno 12 let.

Če želite bolj tehnične in hellip

Obdobje Saturn & rsquos 29,65 let pomnoženo z Jupitrom & rsquos 11,86 let znaša 351,65. Če to vrednost delimo z razliko v zvezdičnih obdobjih, dobimo 19,76 leta.

Zato približno vsakih 20 let Jupiter dohiti Saturn, gledano z Zemlje. Torej je & lsquomeeting dogodek & rsquo obeh velikanov reden dogodek. Toda večinoma si niso tako blizu, dogodek pa se zgodi zunaj nočne vidljivosti z Zemlje in še posebej ne blizu božičnega časa kot letos.

Nocoj bo nebo videlo zelo svetlo povezavo obeh planetov, & lsquovery & rsquo bosta blizu. Bu astronomsko gledano je to še vedno velika razdalja.

Jupiter in Saturn se bosta resnično zdela zelo blizu, vendar sta dejansko oddaljena 734.000 milijonov km.

V astronomiji z besedo veznik opisujemo srečanja planetov in drugih predmetov na nebu. Uporaba izraza Velika konjunkcija je bila znana kot srečanje velikanskih planetov Jupiter in Saturn, saj sta dva največja planeta v našem sončnem sistemu.

OBLAKA OBLAKE PO EVROPI IN ZDRUŽENIH DRŽAVAH

Toda ali boste imeli jasno nebo za opazovanje Velike konjukcije velikanov? Tu je kratek pogled na oblačnost po evropski in severnoameriški celini.

Združene države

Nocoj v velikem delu ZDA pričakujejo zelo dobre pogoje opazovanja. Zdi se verjetno, da bo po zahodnem, srednjem zahodu in jugovzhodu države večinoma jasno nebo.

Oblačne razmere bi morale omejiti ogled Velike konjukcije v Teksasu, delih Floride, severu in severozahodu ZDA ter Velikim jezerom s severovzhodom.

Evropi

Žal še vedno stabilen vremenski vzorec s široko nizko oblačnostjo ne bo omogočal tako dobrih opazovanj po Evropi. Zdi se, da so najboljši pogoji le v delih južne Španije, mogoče tudi v osrednjem Sredozemlju in morda v zahodni Poljski.

V drugih regijah je zelo verjetno oblačno nebo z veliko vlage in tudi padavin.

KAKO OPAZOVATI VELIKO KONJUNKCIJO

Tukaj je opis, kako lahko nocoj, 21. decembra, gledate ali fotografirate Veliko konjunkcijo.

Poiščite odprt prostor kot polje. Za najboljša opazovanja se odmaknite od mestnih luči, da se izognete svetlobnemu onesnaženju. Čeprav je Velika konjukcija urbano prijazen dogodek, sta oba dovolj svetla. Jupiter in Saturn sta zelo svetla planeta, zato ju je mogoče videti celo iz večine mest po svetu.

Poglejte proti zahodu nad obzorjem, takoj po sončnem zahodu. Če želite poiskati planete, poiščite najsvetlejšo piko na nebu (običajno bi napisali & lsquostar & rsquo, a naj se & rsquos izognemo temu citiranju), to bo Jupiter. In planet Saturn bo na njegovi levi strani.

Planeti bodo dokaj nizko na obzorju in svetli, zato ne bi smeli imeti veliko dela.

Pogled na jugozahod 21. decembra. Vir: Zemeljsko nebo

Z majhnim teleskopom ali daljnogledom lahko vidite naše orjake na nebu, poleg tega pa bi morali videti tudi nekatere Jupitrove in rsquosove lune skupaj s planeti.

Če nameravate fotografirati dogodek, boste potrebovali objektiv 200 ali 300 mm, da posnamete fotografijo planetov in morda lun Jupiter & rsquos v zbirajoči se temi po sončnem zahodu.

ZAKLJUČEK

Ogromna planeta Jupiter in Saturn bosta imela svojo veliko konjunkcijo 21. decembra, na dan decembrskega solsticija in začetek astronomske zime. Velikani bodo na našem nebu vidno bližje, kot so bili rsquove od leta 1226 (pred skoraj 800 leti).

Nocoj bosta Jupiter in Saturn oddaljena le 0,1 stopinje.

* UŽIVAJTE * svoj večer in opazovanja obeh planetov. Svoja opažanja lahko poročate naši skupini za poročanje in razpravo na Facebooku in če jih ujamete, jih bomo z veseljem delili z našimi bralci!

Kot bi rekli astronomi in astrofotografi & ndash ČISTO NEBO!

Don & rsquot ne zamudite priložnosti za lepo darilo za svoje prijatelje, družino ali koga posebnega & hellip Vremenski koledar bi lahko bil popolno darilo zanje & ndash glej spodaj:


Analiziranje soncu podobnih zvezd, ki jedo planete, podobne Zemlji

SLIKA: To je umetnikova predstava o skalnatem planetu, ki ga gravitacijska sila plinskega velikana potisne v svojo zvezdo. Poglej več

Zasluge: Keith Wood, univerza Vanderbilt

Nekatere Soncu podobne zvezde so "zemelci". Med svojim razvojem zaužijejo velike količine skalnatega materiala, iz katerega so narejeni 'zemeljski' planeti, kot so Zemlja, Mars in Venera.

Trey Mack, podiplomski študent astronomije na univerzi Vanderbilt, je razvil model, ki ocenjuje učinek takšne prehrane na kemično sestavo zvezde, in jo uporabil za analizo dveh zvezd dvojčkov, ki imata oba svoja planeta.

Rezultati študije so bili objavljeni na spletu 7. maja v Astrofizični časopis.

"Trey je pokazal, da lahko dejansko natančno modeliramo kemični podpis zvezde, element za elementom, in ugotovimo, kako se ta podpis spremeni z zaužitjem planetov, podobnih Zemlji," je povedal Vanderbilt, profesor astronomije Keivan Stassun, ki je nadzoroval študij. "Po pridobitvi spektra visoke ločljivosti za določeno zvezdo lahko ta podpis dejansko podrobno zaznamo, element za elementom."

Po mnenju astronomov bo ta sposobnost bistveno prispevala k razumevanju astronomov procesa nastajanja planetov in pomagala pri nenehnem iskanju zemeljskih eksoplanetov.

Najprej nekaj ozadja: Zvezde sestavljajo več kot 98 odstotkov vodika in helija. Vsi drugi elementi predstavljajo manj kot 2 odstotka njihove mase. Astronomi so vse elemente, ki so težji od vodika in helija, samovoljno opredelili kot kovine in poimenovali "kovinskost", ki se nanaša na razmerje relativne številčnosti železa in vodika v kemični sestavi zvezde.

Od sredine devetdesetih let, ko so astronomi razvili sposobnost zaznavanja zunajsolarnih planetov v velikem številu, je bilo več študij, ki poskušajo povezati kovino zvezd z nastankom planetov. V eni od takih študij so raziskovalci iz Nacionalnega laboratorija Los Alamos trdili, da so zvezde z visoko kovinskostjo bolj verjetno, da bodo razvile planetarne sisteme kot tiste z nizko kovinskostjo. Druga študija je zaključila, da najdemo vroče planete velikosti Jupitra pretežno krožijo zvezde z visoko kovinskostjo, manjše planete pa krožijo zvezde s široko paleto kovinskih vsebin.

Na podlagi dela soavtorja Simona Schulerja z Univerze v Tampi, ki je razširil preučevanje kemijske sestave zvezd nad njihovo vsebnost železa, je Mack pogledal na številčnost 15 specifičnih elementov glede na sonce. Zanimali so ga predvsem elementi, kot so aluminij, silicij, kalcij in železo, ki imajo tališča nad 1.200 stopinj Celzija (600 stopinj Celzija), ker so to ognjevzdržni materiali, ki služijo kot gradniki zemeljskih planetov.

Mack, Schuler in Stassun so se odločili, da bodo to tehniko uporabili za binarni par, ki gosti planete, imenovan HD 20781 in HD 20782. Obe zvezdi bi se morali zgostiti iz istega oblaka prahu in plina, zato bi morali obe začeti z enakimi kemičnimi sestavami. Ta binarni par je prvi odkriti, kjer imata obe zvezdi svoja planeta.

Obe zvezdici v binarnem paru sta pritlikavi zvezdi razreda G, podobni Soncu. Eno zvezdo tesno obkrožata dva planeta velikosti Neptuna. Drugi ima en planet velikosti Jupitra, ki sledi zelo ekscentrični orbiti. Zaradi razlik v njihovih planetarnih sistemih sta dve zvezdi idealni za preučevanje povezave med eksplanetami in kemijsko sestavo njihovih zvezdnih gostiteljev.

Ko so analizirali spekter obeh zvezd, so astronomi ugotovili, da je bila relativna številčnost ognjevzdržnih elementov bistveno večja kot pri soncu. Ugotovili so tudi, da višja kot je temperatura taljenja določenega elementa, večja je bila njegova številčnost, trend, ki služi kot prepričljiv podpis zaužitju zemeljskega kamnitega materiala. Izračunali so, da bi moral vsak od dvojčkov porabiti dodatnih 10-20 zemeljskih mas kamnitih materialov, da bi ustvaril kemične podpise. Natančneje, videti je, da je zvezda z planetom velikosti Jupitra pogoltnila dodatnih deset zemeljskih mas, medtem ko je zvezda z dvema planetoma, velikima Neptun, odstranila dodatnih 20.

Rezultati podpirajo trditev, da sta kemična sestava zvezde in narava njenega planetarnega sistema povezani.

"Predstavljajte si, da je zvezda prvotno oblikovala skalnate planete, kot je Zemlja. Poleg tega si predstavljajte, da je oblikovala tudi planete plinskih velikanov, kot je Jupiter," je dejal Mack. "Kamniti planeti nastajajo v regiji blizu zvezde, kjer je vroče, plinski velikani pa v zunanjem delu planetarnega sistema, kjer je hladno. Ko pa se plinski velikani popolnoma oblikujejo, začnejo migrirati navznoter in tako kot počne, njihova gravitacija začne vleči in vleči notranje kamnite planete. "S pravilno mero vlečenja in vlečenja lahko plinski velikan zlahka prisili kamniti planet, da se potopi v zvezdo. Če v zvezdo pade dovolj kamnitih planetov, jo bodo odtisnili s posebnim kemijskim podpisom, ki ga lahko zaznamo. "

Po tej logiki je malo verjetno, da bi kateri od binarnih dvojčkov imel zemeljske planete. Na eni zvezdi oba planeta v velikosti Neptuna krožita okoli zvezde precej blizu, na tretjini razdalje med Zemljo in Soncem. Na drugi zvezdi se pot do planeta velikosti Jupitra pase na zvezdo in jo pripelje bližje od orbite Merkurja na točki najbližjega približevanja. Astronomi domnevajo, da je razlog, da je zvezda z dvema planetoma velikosti Neptuna zaužila več zemeljskega materiala kot njen dvojček, ta, da sta bila oba planeta učinkovitejša pri potiskanju materiala v svojo zvezdo, kot pa je bil en planet velikosti Jupitra pri potiskanju materiala v svojo zvezdo .

Če se kemijski podpis zvezd G razreda, ki pogoltnejo kamnite planete, izkaže za univerzalen, "bomo lahko, ko bomo našli zvezde s podobnimi kemičnimi podpisi, sklepali, da se morajo njihovi planetarni sistemi zelo razlikovati od našega in da so najverjetneje primanjkuje notranjih kamnitih planetov, "je dejal Mack. "In ko najdemo zvezde, ki nimajo teh podpisov, potem so dobri kandidati za gostovanje planetarnih sistemov, podobnih našemu."

Dodal Stassun: "To delo razkriva, da je vprašanje, ali in kako zvezde tvorijo planete, dejansko napačno. Zdi se, da je resnično vprašanje, koliko planetov, ki jih naredi zvezda, se izogne ​​usodi, da bi jih pojedla njihova starševska zvezda ? "

Raziskavo sta podprla donacija Nacionalne znanstvene fundacije AAG AST-1009810 in PAARE AST-0849736.

Obiščite Research News @ Vanderbilt, kjer boste našli več informacij o Vanderbiltu. [Opomba za medije: Vanderbilt ima 24-urni TV in radijski studio z namensko optično linijo in linijo ISDN. Use of the TV studio with Vanderbilt experts is free, except for reserving fiber time.] -VU-

Izjava o omejitvi odgovornosti: AAAS in EurekAlert! ne odgovarjamo za točnost objav novic, objavljenih na EurekAlert! s prispevanjem institucij ali za uporabo kakršnih koli informacij prek sistema EurekAlert.


Some sunlike stars eat Earthlike planets

Astronomers have identified the signature of Earth-eating stars. During their development, these stars ingest large amounts of the rocky material from which terrestrial planets – small, rocky planets like Mercury, Venus, Earth and Mars – are made.

Trey Mack, a graduate student in astronomy at Vanderbilt University, has developed a model that estimates the effect that such a diet has on a star’s chemical composition and has used it to analyze a pair of twin stars that both have their own planets.

The results of the study were published online May 7, 2014 in the Astrofizični časopis.

“Trey has shown that we can actually model the chemical signature of a star in detail, element by element, and determine how that signature is changed by the ingestion of Earthlike planets,” said Vanderbilt Professor of Astronomy Keivan Stassun, who supervised the study. “We can actually see the signature predicted by our model, in detail, element by element.”

This ability will add substantially to astronomers’ understanding of the process of planet formation as well as assist in the ongoing search for Earthlike exoplanets, according to the astronomers.

What if we could determine if a given star is likely to host a planetary system like our own by breaking down its light into a single high-resolution spectrum and analyzing it? A spectrum taken of the sun is shown above. The dark bands result from specific chemical elements in the star’s outer layer, like hydrogen or iron, absorbing specific frequencies of light. By carefully measuring the width of each dark band, astronomers can determine just how much hydrogen, iron, calcium and other elements are present in a distant star. The new model suggests that a G-class star with levels of refractory elements like aluminum, silicon and iron significantly higher than those in the sun may not have any Earthlike planets because it has swallowed them. (N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF)

First, some background: Stars consist of more than 98 percent hydrogen and helium. All the other elements make up less than 2 percent of their mass. Astronomers have arbitrarily defined all the elements heavier than hydrogen and helium as metals and have coined the term “metallicity” to refer to the ratio of the relative abundance of iron to hydrogen in a star’s chemical makeup.

Since the mid-1990’s, when astronomers developed the capability to detect extrasolar planets in large numbers, there have been several studies that attempt to link star metallicity with planet formation. In one such study, researchers at Los Alamos National Laboratory argued that stars with high metallicity are more likely to develop planetary systems than those with low metallicity. Another study concluded that hot Jupiter-sized planets are found predominantly circling stars with high metallicity while smaller planets are found circling stars with a wide range of metal content.

Building on the work of coauthor Simon Schuler of the University of Tampa, Mack took this type of analysis a step further by looking at the abundance of 15 specific elements relative to that of the Sun. He was particularly interested in elements like aluminum, silicon, calcium and iron that have melting points higher than 1,200 degrees Fahrenheit (600 degrees Celsius) because these are the refractory materials that serve as building blocks for Earthlike planets.

Mack and Stassun decided to apply this technique to the planet-hosting binary pair designated HD 20781 and HD 20782. Both stars should have condensed out of the same cloud of dust and gas and so both should have started with the same chemical compositions. This particular binary pair is the first one discovered where both stars have planets of their own.

Both of the stars in the binary pair are G-class dwarf stars similar to our sun. One star is orbited closely by two Neptune-size planets. The other possesses a single Jupiter-size planet that follows a highly eccentric orbit. The difference in their planetary systems make the two stars ideal for studying the connection between exoplanets and the chemical composition of their stellar hosts.

When they analyzed the spectrum of the two stars, the astronomers found that the relative abundance of the refractory elements was significantly higher than that of the Sun. They calculated that each of the twins would have had to consume an additional 10-20 Earth-masses of rocky material to produce the chemical signatures. Specifically, the star with the Jupiter-sized planet appears to have swallowed an extra 10 Earth masses while the star with the two Neptune-sized planets scarfed down an additional 20.

The results support the proposition that a star’s chemical composition and the nature of its planetary system are linked.

“Imagine that the star originally formed rocky planets like Earth. Further, imagine that it also formed gas giant planets like Jupiter,” said Mack. “The rocky planets form in the region close to the star where it is hot and the gas giants form in the outer part of the planetary system where it is cold. However, once the gas giants are fully formed, they begin to migrate inward and, as they do, their gravity begins to pull and tug on the inner rocky planets.

“With the right amount of pulling and tugging, a gas giant can easily force a rocky planet to plunge into the star. If enough rocky planets fall into the star, they will stamp it with a particular chemical signature that we can detect.”

Following this logic, it is unlikely that either of the binary twins possesses terrestrial planets. At one twin, the two Neptune-sized planets are orbiting the star quite closely, at one-third the distance between the Earth and the Sun. At the other twin, the Jupiter-sized planet spends a lot of time in the outer reaches of the planetary system but it’s eccentric orbit also brings It in extremely close to the star. The astronomers speculate that the reason the star with the two Neptune-size planets ingested more terrestrial material than its twin was because the two planets were more efficient at pushing material into their star than the single Jupiter-sized planet was at pushing material into its star.

“With the right amount of pulling and tugging, a gas giant can easily force a rocky planet to plunge into the star. If enough rocky planets fall into the star, they will stamp it with a particular chemical signature that we can detect.”

Following this logic, it is unlikely that either of the binary twins possesses terrestrial planets. At one twin, the two Neptune-sized planets are orbiting the star quite closely, at one-third the distance between the Earth and the Sun. At the other twin, the Jupiter-sized planet spends a lot of time in the outer reaches of the planetary system but it’s eccentric orbit also brings It in extremely close to the star. The astronomers speculate that the reason the star with the two Neptune-size planets ingested more terrestrial material than its twin was because the two planets were more efficient at pushing material into their star than the single Jupiter-sized planet was at pushing material into its star.


If Jupiter and Saturn Collide

The largest ocean in the Solar System exists in an unexpected place. It is unlike any ocean on Earth, or even like those on a promising lunar world like Europa. This ocean resides somewhere beneath the soft bitten-peach atmosphere of Jupiter, vaporous and crystal-colored, made not of water but of liquid hydrogen. The hydrogen becomes a liquid as both temperatures and pressures mount beneath Jupiter’s atmosphere. Like the sun, Jupiter is made mostly of hydrogen and helium.

This composition is what sets the four Jovian planets — Jupiter, Saturn, Uranus, and Neptune — apart from the four inner rocky planets. Enormous, billowing layers of gas surround small but dense cores. As dreamy as it would be to visit a planet like Saturn, any traveler would find that there is no surface on which to land their craft. Neither can they fly through the atmospheres of gas giants since the intense environment would lead to fatal malfunctions. Spacecraft entering would be melted and crushed, then inevitably vaporized before much time had passed. They are beautiful worlds indeed, but they echo like pieces of art in a shadowy museum: look but do not touch.

For this reason, and for the breadth of their distance from Earth, we haven’t yet been able to discern much of the inner life of planets like Saturn and Jupiter. It may be the case that when approaching Jupiter’s core electrons are forced off hydrogen atoms, causing the liquid ocean to become electrically conducting. The planet’s core may be either solid or perhaps more like a dense, thick collection of gas. It’s undoubtedly hot — up to 90,032 degrees Fahrenheit (50,000 degrees Celsius). Measurements by spacecraft reveal a diffuse core, something which may have resulted from a planet 10 times more massive than Earth colliding with Jupiter over 4.5 billion years in the past. This impact disrupted the core, spreading the heavy elements which should have been concentrated there. Jupiter’s powerful gravity increases the chances that an incoming body will result in a collision rather than a simple grazing event. As Jupiter is more massive than all other planets combined, it has a stronger gravitational attraction.

Second in planetary size and mass to Jupiter alone, Saturn may have sustained collisions early on in its formation as well. Its core is smaller than Jupiter’s and overall the planet has only about 30% of Jupiter’s mass. But, while both planets have rings, Saturn’s are far more impressive. They are made of shattered moons and asteroids, orbiting alongside gleaming shards of ice. Jupiter’s rings on the other hand are made largely of dust. Together they make up the Solar System’s two reigning planets.

Studies on whether or not they would collide at some point in the future have come back inconclusive. It’s not expected that such a collision would take place in a system that’s as developed and stable as ours. The planets are neither set to collide nor be ejected from the Solar System for a few billion years — about 10,000,000,000 — but neither can their orbits be perfectly predicted. Disruptions can come from events such as galactic tidal forces, asteroids, and stars passing near our system.

Out of curiosity, and inspired by their alignment this past December, I ran a physics-based universe simulator to see what would happen if Jupiter and Saturn collided.

Jupiter is already larger than some stars at 140,000 km versus 121,000 km for some of the smallest stars. With the added mass and material from Saturn, is it possible that the new cosmic body would become massive enough to sustain fusion and become a new star? Images from the simulation are shown below. The two planets first approached one another, the looming Jupiter bending Saturn’s rings with its gravitational pull, arching them, both planets heating up as they touched and then merged two swirling, sultry atmospheres into one.

The resulting new body has about 1.25 Jupiter masses, with a slightly larger radius and a much higher average temperature. On its own Jupiter has an average temperature of about -238 degrees Fahrenheit (-150 degrees Celsius). The collision resulted in a new average of 108 degrees Fahrenheit (42 degrees Celsius). The added mass, however, is nowhere near enough to make the new giant planet into a star. Mass, and not size, is the determining factor in whether or not a new star is formed. The more massive an object, the higher the internal pressures which can eventually cause nuclear fusion. Fusion happens when pressures override the repulsion between hydrogen nuclei and transform them into helium. This process is what creates the energy that powers stars. Even the least massive stars in the universe have at least 70 times the mass of Jupiter. This seems to be the threshold for nuclear fusion, though lower rates of metallicity require masses of 87 Jupiters and higher to produce a star. At just 1.25 Jupiter masses, our new object would have needed to accrue far more material to undergo stellification.

The new planet’s composition also changed, having greater amounts of iron, silicates, and hydrogen, as well as water which may have come in part from ice particles in Saturn’s rings. Much of the ring system was dispersed or consumed, though some did go into orbit around our new planet, giving it a faint likeness to the now absent Saturn.

It’s unclear, however, if our new and more massive planet would become a brown dwarf — failed stars which in fact appear red and not brown. The distinction between giant planets, brown dwarfs, and stars is still ill-defined. Jupiter could become a dim dwarf star if it could accrue more material from, for example, a passing cloud of interstellar gas. This larger and more massive planet, along with the missing presence of Saturn, could disrupt the orbits of other objects in the Solar System.

It wouldn’t be the first time a planet in our Solar System goes missing. Some research suggests that a fifth Jovian planet existed between Jupiter and Neptune at some early point in our system’s formation. It was later ejected and erased from our night sky, just as the ancient world that collided with Earth and created our moon was also erased, preserved now only by the stony, cool orb of moonlight in the late dark. Together Jupiter and Saturn played an important part in the creation of life on Earth. Their gravity kept our planet safe from many of the disasters which could have wiped out the very first organisms, or otherwise made conditions unfavorable for us to emerge at all. Losing them and creating a new world would not only change the landscape of our Solar System, but would also destroy intimate artifacts from the story of mankind.


Could Jupiter become a star?

Galileo at Jupiter. Credit: NASA

NASA's Galileo spacecraft arrived at Jupiter on December 7, 1995, and proceeded to study the giant planet for almost 8 years. It sent back a tremendous amount of scientific information that revolutionized our understanding of the Jovian system. By the end of its mission, Galileo was worn down. Instruments were failing and scientists were worried they wouldn't be able to communicate with the spacecraft in the future. If they lost contact, Galileo would continue to orbit the Jupiter and potentially crash into one of its icy moons.

Galileo would certainly have Earth bacteria on board, which might contaminate the pristine environments of the Jovian moons, and so NASA decided it would be best to crash Galileo into Jupiter, removing the risk entirely. Although everyone in the scientific community were certain this was the safe and wise thing to do, there were a small group of people concerned that crashing Galileo into Jupiter, with its Plutonium thermal reactor, might cause a cascade reaction that would ignite Jupiter into a second star in the Solar System.

Hydrogen bombs are ignited by detonating plutonium, and Jupiter's got a lot of hydrogen.Since we don't have a second star, you'll be glad to know this didn't happen. Could it have happened? Could it ever happen? The answer, of course, is a series of nos. No, it couldn't have happened. There's no way it could ever happen… or is there?

Jupiter is mostly made of hydrogen, in order to turn it into a giant fireball you'd need oxygen to burn it. Water tells us what the recipe is. There are two atoms of hydrogen to one atom of oxygen. If you can get the two elements together in those quantities, you get water.

In other words, if you could surround Jupiter with half again more Jupiter's worth of oxygen, you'd get a Jupiter plus a half sized fireball. It would turn into water and release energy. But that much oxygen isn't handy, and even though it's a giant ball of fire, that's still not a star anyway. In fact, stars aren't "burning" at all, at least, not in the combustion sense.

Our Sun produces its energy through fusion. The vast gravity compresses hydrogen down to the point that high pressure and temperatures cram hydrogen atoms into helium. This is a fusion reaction. It generates excess energy, and so the Sun is bright. And the only way you can get a reaction like this is when you bring together a massive amount of hydrogen. In fact… you'd need a star's worth of hydrogen. Jupiter is a thousand times less massive than the Sun. One thousand times less massive. In other words, if you crashed 1000 Jupiters together, then we'd have a second actual Sun in our Solar System.

Jupiter as imaged by Michael Phillips on July 25th, 2009.

But the Sun isn't the smallest possible star you can have. In fact, if you have about 7.5% the mass of the Sun's worth of hydrogen collected together, you'll get a red dwarf star. So the smallest red dwarf star is still about 80 times the mass of Jupiter. You know the drill, find 79 more Jupiters, crash them into Jupiter, and we'd have a second star in the Solar System.

There's another object that's less massive than a red dwarf, but it's still sort of star like: a brown dwarf. This is an object which isn't massive enough to ignite in true fusion, but it's still massive enough that deuterium, a variant of hydrogen, will fuse. You can get a brown dwarf with only 13 times the mass of Jupiter. Now that's not so hard, right? Find 13 more Jupiters, crash them into the planet?

As was demonstrated with Galileo, igniting Jupiter or its hydrogen is not a simple matter.

We won't get a second star unless there's a series of catastrophic collisions in the Solar System.


Could the Planets in Star Wars Actually Support Life?

Če želite popraviti ta članek, obiščite Moj profil in nato Ogled shranjenih zgodb.

A scene of Tatooine from Star Wars: A New Hope. Lucasfilm

Če želite popraviti ta članek, obiščite Moj profil in nato Ogled shranjenih zgodb.

The Star Wars franchise always has been long on imagination. Fantastic creatures, giant spaceships, man-made death moons—the galaxy far, far away has them all. It also contains a rich array of planets, each with a unique environment. But one thing about those celestial bodies always stood out: the singular adjective—desert, ice, etc.—describing each of them.

Whereas Earth hosts a wide diversity of biomes, the planets of Star Wars boast far fewer climates and topographies. The ice planet Hoth never thaws. The desert planet Tatooine seems to never see rain or cold. Meanwhile, the forest moon Endor orbits the temperate zone of a gas giant and a diminutive Jedi master trains in a world covered by an unchanging bog.

While a world of sorcerers, faster-than-light travel, and fussy robots may not meet the standards of the hardest of hard sci-fi (why was the T-65 X-wing starfighter a long-range vehicle but the TIE Fighter wasn't?), seeing the mono-ecosystem worlds of Star Wars raises the question: Is a world with a single, homogenous weather pattern the exception or the rule? Earth has many environments, but does the rest of the universe look more like our home or Luke Skywalker's?

The first thing we should point out: In many cases, no one knows for sure. Scientists know there are more than 1,800 confirmed exoplanets out there, but in many cases, that's all they know. While that could change sooner rather than later, for now, science must speculate on their attributes based upon our solar system, what is known about planetary formation, and a few educated guesses.

"It's amazing that we've found all these extrasolar planets, but we know virtually nothing about them," says Greg Laughlin, professor of astronomy and astrophysics at the University of California, Santa Cruz and an exoplanet expert. "So there's still license to do whatever you want when it comes to fictional representation of habitable worlds. And I think there's no way to know if monolithic worlds are the rule, or if a planet is bouncing around between a lot of climatic patterns."

Just how much license does the Star Wars galaxy take with its many worlds? We talked to some planetary scientists to find out.

Monosystem: Puščava
Climate: Hot, arid

The first planet we "visit" in the original Star Wars trilogy is the desert world of Tatooine, a harsh planet where the surface has been scorched by binary stars and moisture must be farmed from the air. The idea of a desert world (seemingly) is revisited in Star Wars: The Force Awakens, but J.J. Abrams says the world seen in the teasers isn't Tatooine, but Jakku, which may or may not be an all-desert world.

Most coverage, however, points to Jakku being a desert planet. It certainly looks Tatooine-esque in the trailer and the upcoming Star Wars Battlefront videogame promises a DLC for the "Battle of Jakku," which EA says occurs on a "remote desert planet." We'll have to wait and see the game—and The Force Awakens—to know whether Jakku is a desert world or one of more varied terrain.

But if Jakku and Tatooine end up being twin—or nearly twin—worlds, they wouldn't be alone. Most astronomers agree desert worlds might be quite common. However, whether those desert planets would be viable places to live, as they are in the Star Wars universe, is another story. Is a planet without much water capable of sustaining indigenous life like Jawas, Tusken Raiders, and wamp rats?

"I don't remember seeing a lake or oasis on Tatooine, and maybe I missed it but it seems like an awfully dry place for people to live and it wasn't clear to me if they were growing crops," says Andrew Johnston, a geoscience researcher at the National Air and Space Museum. "And where were the crops and how were they irrigating them?"

Johnston says moisture-farming situations are certainly possible they're used in the Atacama Desert in South America, for instance. But to sustain a population of Jawas, Tuskens, farm boys, and bounty hunters, the planet would need some bodies of water. Otherwise it would be harsh, unforgiving, and all but lifeless.

We even have an example of it in our solar system, albeit one that's a little colder than Tatooine. "Mars is largely a desert world, but having an all desert world that has creatures that have grown up there and walk around is somewhat unusual," Johnston says. (And anyone who has read The Martian knows Mars isn't exactly an easy place to survive.)

However, with sufficient water, Laughlin thinks organisms on a planet like Tatooine might not only survive, but thrive.

"If I had to guess, and this is based not on science but just a hunch, Iɽ have to say that [Tatooine] is the most realistic depiction of a world in our galaxy," he says.

A desert world might have an advantage over a verdant planet, as desert worlds are more resistant to the harmful effects of global warming. As the stars they orbit grow hotter, the worlds are better able to rebound from increased luminosity.

That brings us to the most striking feature of Tatooine: its binary stars. But while the planet's double noon is striking, it's also plausible. We know of planets orbiting binary stars. Some orbit the common center of mass between pairs of stars, while others spend their time around just one of the stars in the system.

"The inference is that they were quite close together, and the planet was quite distant from the stars," Laughlin says. "That posts zero problems for habitability. As far as the planet is concerned, it's just getting mixed light from the two stars."

Could It Exist? Yes

Monosystem: Ice
Climate: Frigid

At the beginning of The Empire Strikes Back, we're taken to Hoth. It's a frozen wasteland, a remote and inhospitable planet the Rebellion chose because it was out of the way, far from where the Empire might look for them. It's a barren hellscape that looks like it will remain that way. But in reality, Hoth has more in common with Earth than you might think.


Why Are Jupiter and Saturn Spinning so Slowly?

Editor’s note: AAS Nova is on vacation this week. Normal posting will resume next week in the meantime, we hope you enjoy this post from Astrobites, a graduate-student-run organization that digests astrophysical literature for undergraduate students. The original can be viewed at astrobites.org.

Naslov: On the Terminal Rotation Rates of Giant Planets
Avtorji: Konstantin Batygin
First Author’s Institution: California Institute of Technology
Status: Published in AJ

The rotation periods of Jupiter and Saturn are 9.93 hours and 10.7 hours, respectively. Now, compared to our tiny Earth that lazes around on a 24-hour rotational period, you might think, “wow, those are some zoomy-bois.” However, our best theories of planet formation tell us that, based on how massive they were when they formed, they should really be doin’ a faster spin.

Fun fact alert: While the sun holds most of the solar system’s mass, Jupiter and Saturn hold the majority of our solar system’s angular momentum.

How Do You Form a Jupiter?

So let’s say you want to make a Jupiter, just for the heck of it. If you follow the rules of our understanding of general planet formation , there are three main steps. You start inside of a protoplanetary disk . There is some sort of gravitational instability where heavy metals can gravitationally collapse and start to form a metallic core. This core acquires a gaseous envelope which can then feed the newly forming planet. Once that gaseous envelope is about the size of the initial core, the planet enters a stage called runaway accretion. That just means that material around the planet falls quickly and efficiently, adding mass rapidly. And BAM — you have a Jupiter-like planet (technically called a Jovian planet). But, following this simple model, once the runaway process begins, the planet is accreting so much mass that our new Jupiter spins faster and faster and has no way to let go of any of its angular momentum. In this simple model, the surface of the planet can reach speeds that equal the escape velocity , which means that the planet breaks apart. That’s not great for planet formation. Plus, when we observe Jupiter and Saturn (and now that we’re gathering more and more data of Jovian planets outside of our solar system), we continue to see rotational velocities well below the planets’ escape velocities. So how in the heck do we slow down a young energetic planet? We turn to the answer that all astronomers look to in times of need: magnetic fields.

Setting Up the Problem of Slowing Down a Chonker Like Jupiter

Today’s paper attempts to lay the groundwork for solving this angular-momentum problem in Jovian-planet formation using magnetohydrodynamics. Big (scary) word, yes, but put more simply, this paper creates a semi- analytic model of a newly forming Jovian planet with a strong magnetic field, and it then explores how the field might slow the planet down. The model breaks the problem into two parts: the circumplanetary disk and the planet itself. Each part of this problem has equations that describe key parameters, such as the temperature, density, and abundance of metals in the surrounding envelope. For the planet part, the author calculates a magnetic field strength based on a typical luminosity of young exo-Jovian planets and uses these properties to calculate the electric conductivity and magnetic induction of the system, which would produce the forces that affect the speed of planet rotation. “Running” this model consists of calculating each of these equations over a series of time steps so that one can further understand how each of these factors change and affect each other as the planet forms.

How the Giant Chonker Was Slowed Down

The results of the model are illustrated in Figure 1 below. The finding of this paper is that if we consider the Jovian protoplanet to have a significant magnetic field, that field will invoke a force in the opposite direction of the rotation of both the circumplanetary disk and the planet itself. Basically, the magnetic field couples to the surrounding disk. Since there is now a force in the opposite direction of the original motion, the planet slows its spin. Angular momentum leaves the system as material feeding the planet gets kicked out of the system and back into the surrounding protoplanetary-disk environment.

Figure 1: An illustrative view of planet formation and the effect of magnetic fields (red lines). We are taking a look inside a protoplanetary disk, with the host star to the left, zooming in on a Jupiter-like planet being formed. The planet has its own circle of influence, the edges of which correspond to the purple regions. We can see that material flows onto the planet from above, and that material can only fall onto the planet if it is very nearly falling directly down. Material that falls just off to the side gets added to the de-cretion disk and thus shucked off into the gaseous nebula. The planet slows down via magnetic-field induction that invokes a force in the opposite direction of the original Keplerian rotation, which is the same direction as the planet is rotating. [Batygin 2019]


Poglej si posnetek: Da Li Možemo Živeti Na Drugim Planetima? (Oktober 2022).