Astronomija

Ali obstaja razlog, da sta bila v tako kratkem času v sončnem sistemu najdena dva medzvezdna predmeta?

Ali obstaja razlog, da sta bila v tako kratkem času v sončnem sistemu najdena dva medzvezdna predmeta?


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`Oumuamua so odkrili 19. oktobra 2017, 2I / Borisov pa 30. avgusta 2019. Ali se je kaj spremenilo glede opazovalnih tehnik ali opreme, ki so omogočile iskanje teh predmetov v manj kot dveh letih?

Težko verjamem, da v zadnjih desetih ali dvajsetih letih skozi notranji sončni sistem ni šlo nobenega medzvezdnega predmeta, kar sta nato nenadoma storila čisto blizu.

Zavedam se, da je neverjetno težko najti tako majhne, ​​temne predmete, ki se premikajo tako hitro, še posebej, če so zunaj ekliptike in je skozi njih še veliko več, ki pa še niso bili odkriti. Bi to morali označiti za čisto srečo?


K temu, da sta se ti dve opazovanji zgodili tako blizu, največ prispevata sposobnost in zanimanje.

Naša sposobnost opazovanja takšnih predmetov se vedno povečuje. Ko smo ga videli, se je naše zanimanje povečalo in smo izgledali težje, tj. veliko več sredstev za potrebna opazovanja, ki bi identificirala take predmete. Naslednjega smo videli kmalu zatem.

Tukaj verjetno ne bo kaj posebnega, samo politika znanstvenega financiranja.

Mogoče sta bila to dva predmeta, ki sta naključno prešla skozi sončni sistem skoraj istočasno, vendar bomo morali pred takšno odločitvijo še veliko opazovati takšne dogodke.


V sončnem sistemu bi lahko bilo zdaj na stotine medzvezdnih asteroidov in komet, ki bi jih lahko preučevali

19. oktobra 2017 je bil zaznan prvi medzvezdni objekt & # 8211 z imenom 1I / 2017 U1 (alias 'Oumuamua) & # 8211, ki ga je mogoče opazovati v našem Osončju. V naslednjih mesecih so izvedli več nadaljnjih opazovanj, da bi zbrali več podatkov o njegovi sestavi, obliki in možnem izvoru. Namesto da bi razblinil skrivnost okoli resnične narave & # 8216Oumuamua & # 8211 je komet ali asteroid? & # 8211 ta prizadevanja so jo uspela le še poglobiti.

V nedavni študiji sta harvardski profesor Abraham Loeb in Shmuel Bialy & # 8211 podoktorski raziskovalec iz Smithsonian Center for Astrophysics (CfA) & # 8211 to skrivnost obravnavala s predlogom, da je & # 8216Oumuamua morda zunajzemeljsko sončno jadro. Na podlagi tega sta Loeb in Amir Siraj (študent Harvardskega dodiplomskega študija) izvedla novo študijo, ki je pokazala, da je v našem Osončju mogoče zaznati na stotine & # 8220‘Oumuamua podobnih & # 8221 predmetov.

Študija, ki opisuje njihove ugotovitve, se je nedavno pojavila na spletu in jo trenutno objavlja Mesečna obvestila Royal Astronomical Society. Študijo sta vodila Amir Siraj, dodiplomski študent Harvardskega oddelka za astronomijo in prof. Abraham Loeb & # 8211 Frank B. Baird mlajši profesor znanosti na univerzi Harvard in predstojnik oddelka za astronomijo Harvarda.

Oumuamua, kot se je pojavil s pomočjo teleskopa William Herschel v noči na 29. oktober. Univerza Queen & # 8217s Belfast / William Herschel

Ko je Oumuamua prvič zaznal teleskop Panoramic Survey and Rapid Response System-1 (Pan-STARRS-1) na Havajih, znanstveniki niso bili prepričani, kaj je to. Sprva so mislili, da je predmet medzvezdni komet, vendar so opazovanja Evropskega južnega observatorija (ESO) in drugih astronomov pokazala, da ima visoko gostoto in da se hitro vrti (kar je bolj skladno z asteroidom).

Vendar pa so ločena opazovanja, izvedena z ESO-jevim zelo velikim teleskopom v Čilu in teleskopom Williama Herschela v La Palmi, pokazala, da so spektri predmetov & # 8217s skladni z ledeno sestavo. Medtem ko & # 8216Oumuamua ni naredil plinaste ovojnice ali repa, medtem ko je najbližje prehajal Sonce, je iz našega Osončja pospešil kot komet.

Na podlagi opazovanj, izvedenih z Vesoljski teleskop Hubble, je mednarodna ekipa astronomov ugotovila, da je do povečanja hitrosti verjetno prišlo zaradi sončnega ogrevanja, zaradi česar se bodo vse zamrznjene hlapne snovi (npr. voda, ogljikov dioksid, amoniak, metan itd.) sublimirale in odzračevale njegovo površino (alias. izplinjevanje).

A kot je poudarila še ena raziskovalna skupina, če bi bilo za pospeševanje resnično odgovorno izpuščanje, bi to povzročilo tudi hiter razvoj vrtenja "Oumuamua" (ki ni bil opažen). Loeb in Shmuel Bialy (v študiji, ki je bila objavljena oktobra 2018) sta ponudila precej zanimivo nasprotno razlago.

Kot je profesor Loeb po elektronski pošti pojasnil za Universe Today:

& # 8220Naš prvi medzvezdni gost se je zdel čuden in za razliko od vsega, kar smo že videli. Ko smo se tega zavedali, je bil gost že odšel s podobo, ki je bledela v temno ulico, zato nismo imeli priložnosti še enkrat pogledati njegovih skrivnostnih lastnosti. Podatkov imamo malo, nazadnje pomanjkanje zaznavanja s strani vesoljskega teleskopa Spitzer, kar pomeni, da je „Oumumua majhna in vsaj desetkrat bolj sijoča ​​od tipičnih asteroidov v Osončju.

& # 8220Nimamo fotografije `Oumuamua, vendar se je njena svetlost zaradi odsevne sončne svetlobe spreminjala za faktor 10, ko se je občasno vrtela vsakih osem ur. To pomeni, da ima Oumuamua skrajno obliko s svojo dolžino, ki je vsaj 5-10 krat večja od predvidene širine. Poleg tega je analiza njegovega premikanja ugotovila, da bi bilo v najvišjem stanju vzbujanja, kot se pričakuje od njegovega burnega potovanja, če bi imel geometrijo, podobno palačinkam. Izvedena oblika je bolj ekstremna kot pri vseh asteroidih, ki smo jih prej videli v Osončju in imajo razmerje osi največ 3. & # 8221

V bistvu sta Bialy in Loeb upoštevala možnost, da bi lahko bila "Oumuamua dejansko lahko jadro, oblika vesoljskih plovil, ki se za pogon poganjajo s sevalnim tlakom - podobno kot Preboj Starshot (Svetovalni odbor, kateremu je predsednik prof. Loeb), se trenutno razvija. Izračunali so tudi njegovo verjetno obliko, debelino, razmerje med maso in površino ter ali bo tak objekt lahko preživel medzvezdno potovanje.

Na koncu je študija pokazala, da bi bilo takšno vesoljsko plovilo tehnično izvedljivo, vendar obstaja preveč neznank o & # 8216Oumuamua, da bi zagotovo rekli, da gre za vesoljsko plovilo. Na koncu so ugotovili, da & # 8216Oumuamua, ne glede na to, ali je bila naravno prisotna ali ne, predstavlja povsem nov razred medzvezdnih predmetov in da bi morali v prihodnosti iskati še več takšnih predmetov.

Projekt Starshot, pobuda, ki jo sponzorira fundacija Breakthrough Foundation, naj bi bila prva medzvezdna plovba človeštva. Zasluga: breakthroughinitiatives.org

To priporočilo deloma temelji na prejšnjih raziskavah, ki so pokazale, da je naš Osončje v svoji zgodovini verjetno zajel na tisoče takšnih medzvezdnih predmetov. Temu so kmalu sledili astronomi, ki so v bližini Jupitra locirali medzvezdni objekt, za katerega se je zdelo, da je v retrogradni orbiti okoli Sonca & # 8211, kar kaže na to, da prihaja iz drugega zvezdnega sistema in da ga je ujel naš.

Na podlagi vsega tega sta se Siraj in Loeb odločila raziskati orbitalne lastnosti zajetih medzvezdnih predmetov v Osončju, da bi ugotovila, koliko predmetov, podobnih & # 8216Oumuamua. Zaradi svoje študije so izvedli dinamične simulacije sistema Jupiter-Sonce in naključne začetne pogoje, da bi določili orbite, ki bi jih imeli takšni predmeti.

Nato so rezultate teh simulacij primerjali s podatki, pridobljenimi z anketo Panoramic Survey Telescope and Rapid Response System (Pan STARRS). Kot je navedel Loeb:

& # 8220To daje približno en tak predmet (velikosti sto metrov) na prostornino, ki jo določa gibanje Zemlje okoli Sonca. Skupaj mora vsak planetarni sistem v svoji življenjski dobi odstraniti približno 10 ^ <15> takih predmetov & # 8230 Od teh je majhen delček ujet v Osončju, saj predmeti prehajajo blizu Jupitra in izgubljajo energijo s svojo gravitacijsko interakcijo z njim. Sistem Sonce-Jupiter deluje kot ribiška mreža, ki kadar koli sprejme nekaj tisoč ujetih predmetov. Predmeti se sčasoma izločijo iz sistema, novi pa se zajamejo in tako je stalno prebivalstvo.

Ta diagram prikazuje orbito medzvezdnega asteroida 'Oumuamua, ko prehaja skozi Osončje. Zasluge: ESO / K. Meech et al.

Skratka, ugotovili so, da danes v našem Osončju verjetno obstaja na tisoče & # 8216Oumuamua podobnih predmetov in da bi jih bilo mogoče identificirati na stotine glede na njihove orbite. Izračunali so tudi, da bo Veliki sinoptični teleskop (LSST), ki je trenutno v fazi gradnje in bo predvidoma popolnoma operativen do januarja 2022, lahko odkril na desetine teh ujetih predmetov.

Siraj in Loeb sta v svoji študiji identificirala tudi štiri konkretne kandidate za ujete predmete, ki so jih morda že odkrile pretekle raziskave. Ti predmeti so označeni kot 2011 SP25, 2017 RR2, 2017 SV13 in 2018 TL6, ki se gibljejo od 8,26 do 23,65 AU za Sonce in krožijo okoli njega od 23,76 do 115 let.

& # 8220 Ker so ti predmeti ujeti, lahko letimo mimo njih, fotografiramo ali pristanemo na njihovi površini, & # 8221 je dodal Loeb. & # 8220To nam bo omogočilo spoznavanje njihove strukture, sestave in izvora. Omogočil nam bo tudi boljše razmere v njihovih vrtcih zunaj Osončja. In končno, morda nam bo omogočil prepoznavanje predmetov umetnega izvora, kot je iskanje plastičnih steklenic na sicer neokrnjeni plaži. & # 8221

Posledice teh študij bi bile neizmerne. Ob predpostavki, da so takšni predmeti naravno prisotni, bo njihovo preučevanje razkrilo stvari o razmerah drugih planetarnih sistemov, kar bi nam lahko rešilo potrebo po pošiljanju medzvezdnih sond, ki bi jih neposredno raziskale. A kot je poudaril Loeb, bi bile posledice veliko večje, če gre dejansko za umetne predmete & # 8211, kot so razbitine tujih sond (kot so predlagali z & # 8216Oumuamua) & # 8211:

& # 8220To bo revolucionarno, saj bo pokazalo, da nismo sami in bo osvetlilo napredne tehnologije, ki presegajo našo. Ima potencial, da bo najpomembnejši rezultat v znanosti in tehnologiji v prihodnjih stoletjih. & # 8221

Bi lahko bila & # 8216Oumuamua medzvezdna sonda, ki jo je poslala zunajzemeljska inteligenca? Zasluge: ESA / Hubble, NASA, ESO, M. Kornmesser

Prihod in odhod & # 8216Oumuamua, medzvezdnega objekta, ki je nasprotoval razvrstitvi, je znanstvenike razumljivo navdušil. Toda še bolj vznemirljivo je vedeti, da v našem Osončju že obstajajo številni predmeti, kot je ta, in vedeti, kje bi našli nekaj za preučevanje. Toda dejstvo, da bomo to lahko storili v le nekaj letih? Zelo razburljivo!

Čeprav se izkaže, da ti predmeti NE predstavljajo težko pričakovane rešitve Fermijevega paradoksa, bo dejstvo, da bi nam lahko dali pogled od znotraj na druge zvezdne sisteme v naši galaksiji, izjemno znanstveno koristno.

Če želite poslušati profesorja Loeba o vseh znanstvenih najdbah, povezanih z & # 8216Oumuamua & # 8217s, in o tem, kaj bi lahko pomenile, si oglejte ta podcast (& # 8220Our Interstellar Visitor & # 8220) na After-On, ki ga je vodil romanopisec Rob Reid.


Uvod

Komet 2I / Borisov, znan tudi kot C / 2019 Q4 (Borisov), je 30. avgusta 2019 odkril Gennady Borisov v observatoriju MARGO na Krimu (MPEC 2019-R106). Njegova orbitalna ekscentričnost (3.356191 ± 0.000015) kaže, da objekt ni gravitacijsko vezan na Osončje, zaradi česar je prvi nedvoumen primer kometa, ki prihaja iz medzvezdnega prostora. To je šele drugi prepoznani primer majhnega telesa, ki vstopi v Osončje iz medzvezdnega prostora. Prvi tak primer, in sicer primera 1I / ′ Oumuamua, ki ga je 18. oktobra 2017 odkril teleskop Pan-STARRS 1, je bil na videz asteroidno telo brez pomanjkljivih zaznavnih znakov kometne aktivnosti 1. V nasprotju s tem je 2I / Borisov pokazal komo in njegovo prikazovanje je dalo edinstveno priložnost, da pridobi informacije o telesu, ki je na videz podobno kometom iz Osončja, sicer pa ni povezano z njimi. Večina dosedanjih opazovanj je bila namenjena pridobivanju spektrov kometa in merjenju emisij prahu in plinov, da bi določili sestavo materiala in jo primerjali s kometami sončnega sistema. Zlasti odbojni spektri v območju valovnih dolžin 0,49–0,92 μm kažejo rdečkast naklon 2, podoben naklonu drugih teles Sončevega sistema, vključno s kometi, Jupitrovimi trojanskimi asteroidi iz tako imenovanega D taksonomskega razreda 3 ter več kentavrov in transneptunskih objektov. 4 (zadnji dve kategoriji prikazujeta široko paleto barv, vključno - vendar ne omejeno na - telesa z izjemno rdečim spektralnim naklonom).

Meritve kometne linearne polarizacije zagotavljajo informacije o fizikalnih lastnostih delcev prahu kome, ki jih je težko dobiti z drugimi tehnikami opazovanja. Sončna svetloba, ki jo razpršijo prašni delci, je delno polarizirana, torej ima električno polje, povezano s sevanjem, prednostno ravnino nihanja. Polarizirani delež sevanja se spreminja glede na kot razprševanja in je odvisen od značilnosti razpršilnega medija, zlasti njegovega kompleksnega lomnega količnika (s tem kemične sestave) in morfologije, ki vključuje porazdelitev velikosti, obliko in strukturo razpršenih delcev . V planetarni znanosti se polarizacija meri kot tok, ki je pravokoten na ravnino Sonce-opazovalec (ravnina razprševanja) minus tok, vzporeden tej ravnini, deljen z vsoto dveh pretokov, ki se ta meritev običajno ponovi v različnih opisanih pogojih gledanja s tako imenovanim faznim kotom (kot med smermi proti Soncu in opazovalcu, gledano s tarče). Presenetljivo je, da površine brezzračnih predmetov (kot so Luna ali asteroidi) in atmosfere komete kažejo podobno odvisnost polarizacije od faznega kota. Zlasti je bilo ugotovljeno, da je linearna polarizacija pri majhnih faznih kotih (≤20 ∘) usmerjena vzdolž trosilne ravnine, ker je način merjenja polarizacije opisan kot negativna polarizacija. Pri večjih faznih kotih postane linearna polarizacija pozitivna, to je usmerjena vzdolž smeri, pravokotne na ravnino razprševanja, in narašča, dokler ne doseže svojega maksimuma pri faznih kotih ≃ 90–100 ∘. Hudič je v podrobnostih, razliko med različnimi vrstami teles Sončevega sistema, pa tudi med določenimi kometi ali asteroidi, je razvidno iz vrednosti in lokacije minimalne in največje polarizacije, iz vrednosti faznega kota, kjer se negativna polarizacija spremeni v pozitivni ali iz gradienta valovne dolžine polarizacije 5,6,7,8.

Izločanje značilnosti razprševalnega medija iz polarimetričnih rezultatov je težka naloga, saj zahteva modeliranje številnih pojavov sipanja svetlobe, kot so odsev, difrakcija, interferenca, skrivanje sence itd. Natančneje, negativna polarizacija, opažena za brezzračna telesa, ima za posledico predvsem iz tako imenovanega koherentnega povratnega razprševanja je prišlo do učinka večkratnega razprševanja med regolitnimi delci 9,10, medtem ko v kometnih atmosferah posamezno razprševanje in s tem lastnosti prašnih delcev sami določajo opaženo polarizacijo. Sestava, velikost in struktura delcev komete se razlikujejo ne samo od kometa do kometa, ampak tudi znotraj vsakega kometa se delci razlikujejo v bližini jedra in v repu, v curkih in komi iz okolice, blizu Sonca in daleč od njega 8 , 11. Za modeliranje opazovanj se uporabljajo intenzivni numerični izračuni 12,13 in laboratorijski podatki 14,15,16. Izjemen rezultat polarimetričnih preiskav je bila napoved, da je kometni prah izdelan iz agregatov submikronskih zrn 17, kar so kasneje potrdile in situ študije misije Rosetta 18 in vzorcev, ki jih je vrnila misija Stardust 19.

Tudi brez numeričnega modeliranja lahko nekatere informacije zlahka ugotovimo z zelo preprosto analizo fizike sipanja svetlobe. Na primer, svetloba, ki jo razprši površina z nizkim albedom ali kompleksni (agregirani) delci, je bolj polarizirana kot svetloba, ki jo razpršijo površine z višjim albedom ali agregirani delci (tako imenovani Umov učinek) 20, kot razpršilci z visokim albedom verjetneje povzročijo večkratno razprševanje, kar pa je odgovorno za učinkovitejšo depolarizacijo. Večjo pozitivno polarizacijo lahko povežemo tudi z manjšimi in tako Rayleigh podobnimi delci, medtem ko na svetlobo, ki jo razpršijo bolj zapleteni veliki agregirani delci, večkratno razprševanje bolj vpliva in je tako bolj depolarizirana. Pri kometah lahko polarizacijo kontinuuma močno spremenimo z molekularnimi emisijskimi črtami zaradi plinske komponente v komi in repu, zato je treba analizirati širokopasovne polarimetrične meritve ob upoštevanju spektralnih značilnosti predmeta ali še bolje z uporabo filtri, posebej izdelani za preprečevanje emisijskih vodov.

Natančne krivulje polarizacijske faze so bile pridobljene za številne komete in v širokem razponu faznega kota, v nekaterih primerih od 0 ∘ do več kot 100,, odvisno od ciljne oddaljenosti od Sonca in Zemlje v različnih okoliščinah 8 . Zato je najbolj zanimivo razumeti, ali ima komet, ki prihaja iz medzvezdnega prostora, enako polarimetrično vedenje, ki ga kažejo kometi Osončja, saj bi se lahko kometi, ki so se kopičili v drugih astrofizičnih okoljih, načeloma bistveno razlikovali od teles Sončevega sistema.

Tu poročamo o polarimetričnih opazovanjih, pridobljenih z zelo velikim teleskopom (VLT) Evropskega južnega observatorija (ESO), in dokazujemo, da se polarizacija medzvezdnega kometa 2I / Borisov precej razlikuje od tiste, ki jo na splošno opažamo pri kometih našega Osončja, z izjemna izjema, komet C / 1995 O1 (Hale-Bopp). Verjame se, da se je Hale-Bopp pojavil blizu našega Sonca le enkrat pred nedavnim pristopom leta 1997, zato je njegov material precej neokrnjen, vendar njegova polarimetrično homogena koma kaže na še bolj neokrnjeno naravo kometa 2I / Borisov.


Naš sončni sistem je morda ujel & # 8216alien & # 8217 komete

Ta članek lahko delite z licenco Attribution 4.0 International.

Nova teorija bi lahko razložila izvor medzvezdnih kometov.

Po najbolj priljubljeni teoriji, ki jo je predlagal nizozemski astronom Jan Oort, so orjaški planeti v zelo zgodnji fazi nastanka sončnega sistema razpršili predmete v zunanja območja daleč stran od sonca. Tam so ledene skale in prašni delci tvorili nekakšen oblak.

Mimoidoče zvezde lahko nato razpršijo te predmete nazaj v notranji sončni sistem, kjer jih opazujemo kot komete. Ti dolgotrajni kometi, ki prihajajo iz oblaka Oort, pogosto potrebujejo več kot 200 let, da krožijo okoli sonca.

Kometa Borisov pred oddaljeno spiralno galaksijo v ozadju, posneto s Hubblovim vesoljskim teleskopom 16. novembra 2019. (Zasluga: D. Jewitt / NASA / ESA)

& # 8220Predstavljamo drugi potencialni izvor takšnih kometov, & # 8221 pravi Tom Hands, podoktorski raziskovalec na Inštitutu za računalniške znanosti Univerze v Zürichu. & # 8220V relativno nedavni preteklosti jih je mogoče ujeti iz medzvezdnega prostora. & # 8221

Dva medzvezdna obiskovalca sta v zadnjih letih naslovila naslove. Leta 2017 so znanstveniki odkrili telo, podobno asteroidu, pozneje imenovano Oumuamua. Avgusta 2019 je amaterski astronom Genadij Borisov odkril komet, ki je prišel iz medzvezdnega vesolja in bo spet zapustil osončje. Oumuamua in komet Borisov sta ostanka nastajanja planetov v drugih sončnih sistemih, na enak način kot naj bi bili naši kometi in asteroidi ostanki nastajanja planetov v našem sončnem sistemu.

Po odkritju prvih dveh medzvezdnih predmetov sta Hands in Walter Dehnen z münchenske univerze z računalniškimi simulacijami preučevala, kako lahko medzvezdne predmete ujame naš sončni sistem.

& # 8220Ti potniki se tvorijo okoli oddaljenih zvezd, preden jih odvrnejo proti nam in potujejo dolga svetlobna leta, preden naletijo na Jupiter in jih ujamejo v sončni sistem, & # 8221 pojasnjuje Roke. & # 8220 Simulirali smo 400 milijonov takšnih teles, ko so se približali soncu in Jupitru. & # 8221

Raziskovalci so na podlagi podatkov misije GAIA uporabili realne hitrosti za te predmete in preučili, kako med seboj sodelujejo z Jupitrom na poti skozi sončni sistem. To delo so opravili na grozdu VESTA na Univerzi v Zürichu.

& # 8220 Uporabili smo napredno kodo, ki deluje na enotah za obdelavo grafike in ne na tradicionalnih računalniških procesorjih, da smo lahko v kratkem času simulirali tako veliko število predmetov, & # 8221 pojasnjuje Roke. & # 8220 Simulacije so skupaj uporabljale približno 70 grafičnih kartic, torej približno 140 dni, če bi uporabili samo eno kartico, in veliko, veliko dlje, če bi uporabili običajni procesor namiznega računalnika. & # 8221

Rezultati simulacij, ki so prikazani v Mesečna obvestila Royal Astronomical Society, razkrivajo, da v majhni manjšini primerov Jupiter spremeni usmeritve predmetov toliko, da postanejo vezani na sončni sistem.

& # 8220 Čeprav je verjetnost ujetja majhna, lahko teh tujih komet, ki krožijo okoli sonca, kroži od nekaj sto do sto tisoč, & # 8221 pravi astrofizik.

Ujeti predmeti so običajno na orbitah, ki so zelo podobne tistim pri dolgotrajnih kometih, ki jih je človeštvo opazovalo stoletja, kar kaže na to, da se skrivajo pred očmi.

& # 8220Če bi ga lahko prepoznali, bi imeli resnično možnost natančno preučiti sestavo materiala, ki nastane v drugih sončnih sistemih, & # 8221 pravi Hands.

V prejšnjem članku iz maja 2019 so Hands in sodelavci preučevali, kako tesne interakcije med zvezdami v njihovi rojstni kopici vplivajo na komete in asteroide, ki nastanejo okoli posamezne zvezde. Ugotovili so, da se lahko predmeti osvobodijo in zapustijo & # 8220prosto lebdeče & # 8221 v galaksiji ali druge & # 8220 ukradene & # 8221 druge zvezde. Zaradi tega so domnevali, da bi lahko Oortov oblak delno naselili predmeti, ki so nastali okoli drugih zvezd, nato pa jih je pred milijardami let zajelo sonce v svoji rojstni kopici.

Ta najnovejša študija raziskuje zajem prosto plavajočih asteroidov in kometov, ki jih je mehanizem, prikazan v prejšnji študiji, morda osvobodil matične zvezde.


6 Pan in Atlas

Ti dve Saturnovi luni imata veliko skupnega in sta dve najbližji luni svojega matičnega telesa. Ta dva dela tako posebna je dejstvo, da se zdi, da sta sama kopirala prstane Saturna in dobila obliko, ki je naravnost iz filma UFO B iz petdesetih let. Pan, ki je znan pod imenom & ldquoshepherd moon, & rdquo je ime dobil po bogu pastirjev, medtem ko je bil Atlas poimenovan po titanu, ki je & ldquoheld držal nebo na svojih ramenih, & rdquo, ker podpira Saturnove obroče.

Atlas, ki je bolj položen, je od droga do droga oddaljen le 19 kilometrov, čez pas pa 46 kilometrov. Podolgovatih ekvatorjev teh lun ni mogoče razložiti na enak način kot Haumea, saj se ne vrtijo dovolj hitro, da bi se izbočili. Hitro vrtenje ustvarja tudi enakomerno raztezanje in te lune zagotovo niso pravilne. Izkazalo se je, da je po številnih računalniških simulacijah pariška univerza našla odgovor: akrecijski diski. Ko se disk drobirja zavrti, se robovi konstrukcije izravnajo. Med nastajanjem Saturnovih & rsquos lun so se na drobnih lunah oblikovali nabiralni diski iz prahu iz Saturnovih & rsquos obročev, ki so se na koncu kopičili na njihovih ekvatorjih in ustvarili njihove ogromne, izbočene grebene.


Sorodno

Desetletje dolgo prizadevanje za pristanek na kometu se konča

Nova trojka eksoplanetov bi lahko namignila, kako nastajajo srednje veliki planeti

Vodna para, najdena na eksoplanetu, velikem kot Zemlja, 110 svetlobnih let od doma

Zgodnja Zemlja, ki so jo bombardirali kometi

Zdi se, da je to primer z medzvezdnim interloperjem, zdaj znanim kot 2I / Borisov, kometom, ki ga je 30. avgusta prvič opazil amaterski astronom Genadij Borisov, ki je odkritje naredil z domačim teleskopom na Krimu. Borisov je šele drugi potrjeni objekt, ki je v našo kozmično sosesko prodrl od zunaj.

»Ko gre za komete. že desetletja čakamo na medzvezdne, «pravi Piotr Guzik, astronom na Jagelonski univerzi na Poljskem. "To so uresničitve sanj za večino astronomov sončnega sistema."

V tednih po odkritju so se raziskovalci po vsem svetu trudili, da bi zbrali čim več informacij o svojem skrivnostnem gostu, preden jim je ta dal na voljo nekje jeseni 2020. Uničenje kemijske sestave in poti kometa bi nam lahko povedalo Znanstveniki pravijo, da veliko govori o kraju, iz katerega prihaja - in nam celo dovoli, da Zemljani primerjamo ta zvezdni sistem s svojim.

"Ta komet predstavlja še en planetarni sistem," pravi Karen Meech, astronomka z Inštituta za astronomijo Univerze na Havajih. »Vprašanje je, ali je podobno ali drugače? Zame je to ena najbolj vznemirljivih stvari. "

Naš zapis o odkrivanju ob strani, medzvezdni predmeti verjetno ves čas vohljajo po našem soncu, pravi Malena Rice, astronom z univerze Yale. Ti deli kozmičnega šrapnela so naravni stranski produkti nasilnega pojmovanja planetarnih sistemov okoli galaksije. Po njenem mnenju je povsem naravno, da se drobni predmeti premaknejo iz ene soseske v drugo - ponavadi so premajhni in zatemnjeni, da bi jih videli s teleskopi, ki jih imamo.

Toda leta 2017 so znanstveniki nepričakovano opazili podolgovato 'Oumuamua, ko je oddaljila od našega sonca. Oblika in hitrost poti vesoljske skale sta astronomom povedala, da je bila zagotovo izpuščena iz drugega planetarnega sistema. Toda čas je bil izklopljen: Škiljenje po hitrem odhodu Oumuamua ni dalo veliko koristnih informacij, njegove čudne lastnosti pa so nekatere astronome oklevale, da bi ga označili za pravi komet.

Vtis umetnika ʻOumuamua, prvega znanega medzvezdnega predmeta, ki je prešel skozi sončni sistem. Zasluga za sliko: ESO / M. Kornmesser

V nasprotju s predhodnikom pa je bil Borisov opažen na dohodni del bivanja sončnega sistema. Raziskovalci ocenjujejo, da se bo najbližje Soncu in Zemlji približal decembra letos, preden bo oboje postavil v vzvratno ogledalo in izginil nekje prihodnje leto. "Zdaj ga nekoliko dlje gledamo," pravi Michele Bannister, planetarni astronom na Queen's University v Belfastu.

Številni znanstveniki ostajajo previdni s samo nekaj opažanji o Borisovu pod pasom. Toda zaenkrat se zdi, da predhodni rezultati podpirajo zanimivo idejo: zunaj sončne korenine kometa so morda najbolj eksotična stvar pri tem.

Za razliko od "Oumuamua" gre nedvomno za komet, ki je presenetljivo podoben tistim, ki izvirajo iz našega sončnega sistema, pravi Guzik, ki je skupaj s svojimi kolegi danes objavil poročilo o Borisovu Astronomija narave. Smučarski rock ima vso potrebno opremo za razvrstitev, vključno s svetlim repom in mehkim, svetlečim haloom, imenovanim koma - oba stranska produkta ledu, ki se pod sončno toploto sublimira v plin. In s svojim rdečkastim odtenkom bi se brez težav zlil v tipično kometno linijo.

Borisov je lahko sestavljen tudi iz znanih sestavin. Podatki, ki so jih zbrali Meech in njeni sodelavci, kažejo, da Borisova komina vsebuje cianogene - strupene spojine ogljika in dušika, ki so tudi običajne sestavine naših kometov. "To je običajno prva stvar, ki jo vidite v katerem koli kometu našega sončnega sistema," pravi Meech. "Cianogene preprosto vlečejo ven."

2I / Borisov, posnela Hubble & # x27s Wide Field Camera 3. Zasluge za slike: D. Jewitt in D. Bamberger, Wikimedia Commons

Druga skupina je prav tako pobrala sledi dvoatomskega ogljika (dva atoma ogljika, povezana skupaj) v svojem plinastem pokrovu. Poročajo, da je podpis razmeroma šibek in bi Borisov uvrstil v kategorijo kometov, ki so osiromašeni z ogljikom, če bi bil prisoten našemu soncu.

Glede na to, kako čudna je bila Oumuamua, je narava za pešce Borisova nekaj vrgla, pravi Guzik. V mnogih pogledih pravi: "to je samo komet normalnega videza."

Toda veliko o Borisovu ostaja skrivnostno. Za razliko od 'Oumuamua, ki ji ni bilo kome in je imela zlahka zaznavno obliko in velikost, je ta novinec zagrnjen v oblak plina, zato je njegovo pravo obliko težko ločiti od daleč. Guzikove ocene kažejo, da znaša približno miljo čez, vendar bi se te številke še vedno lahko spremenile. Bannister pravi, da prava zajeta Borisova "nikakor ni gotova stvar".

Ko se komet s sončno toploto približa osebno in osebno, lahko začne razkrivati ​​svoj osebni pridih. Lahko začne oddajati nove vrste plina - ali pa se razbije na koščke. "To bi bilo res zabavno, če bi se," pravi Bannister.

Če pa lastnosti Borisov še naprej odsevajo lastnosti domačih kamnin, je to še vedno velika stvar, pravi Bannister. Tako kot naši kometi je tudi Borisov verjetno precej spodobna časovna kapsula od zore planetarnega sistema. Z divjo sorto, za katero je znano, da je tam zunaj v kozmosu, pravi, kakšne so verjetnosti, da je druga medzvezdna vesoljska skala, ki nas je obiskala, naredila le nekaj drugega, kot da je dvignila ogledalo?

"To je fascinantno," pravi Bannister. »Pomeni, da imajo procesi, ki so tvorili telesa v našem lastnem sistemu, stopnjo univerzalnosti. da je to, kar se je zgodilo tukaj, podobno kot drugje. "

Kje točno je »drugje«, pa je drugo vprašanje. Določitev korenin Borisova pomeni natančen obratni načrt njegove poti skozi galaksijo - naloga, ki zahteva natančno spremljanje gibanja v naslednjih nekaj mesecih. To ni enostavno, pravi Meech. Veliko stvari lahko zmoti komet z neposredne poti, od gravitacije večjih teles, do curkov plina, ki izvirajo iz same skale, ki lahko deluje kot potisniki na vesoljskem plovilu.

Koncept umetnika 2I / Borisov. Prispevek slike: NASA / JPL

Zemljevid galaksije prav tako ni statičen. Borisov potuje že vsaj mnogo milijonov let, zvezde pa so se premikale po njem. "Ko jo zasledujete nazaj v času, morate uro previti nazaj in postaviti zvezde nazaj, kjer so bile, ko je [komet] minil," pravi Meech.

Zaradi vse te negotovosti bi se moralo veliko stvari postaviti v vrsto, da bi astronomi lahko trdno ocenili, pravi Meech. Zelo mogoče je, da bomo nikoli vedeti, od kod prihaja Borisov. »To morda be possible if we get really lucky, and it was ejected recently by a nearby star that was measured with Gaia [an ongoing effort to map the Milky Way],” she says. “But I think the probability that all those things happen is negligible.”

That’s no reason to despair, though. Noticing two interstellar invaders in the past two years is a sign that there’s a lot more to come—especially now that astronomers know to look. And with Chile’s upcoming, ultra-sensitive Large Synoptic Survey Telescope slated to start surveying the skies in 2022, Rice says, “we should expect a goldmine of these objects, relative to what’s been seen in the past.”

In the end, it’s a matter of us humans cluing in to what the universe has to offer, Bannister says. “This is all a natural outcome of how planetary systems form and evolve,” she says. “These objects are just bobbing through. Occasionally, we get lucky. and one of them lands on our shores.”

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Why the Chinese want pangolins

Much of the blame lies in East and Southeast Asia, especially China. Since the 1950s, China has periodically released variations on something called the Chinese Pharmacopoeia. This is a huge tome that acts both as a legal document outlining all the state sanctioned drugs and a recipe book for do-it-yourself Traditional Chinese medicine. The Pharmacopoeia is updated every five years, and it's massively influential in directing what the everyday person buys, makes, and takes as medicine.

The problem is that the Pharmacopoeia lists a series of endangered or vulnerable animal species in its recipe section. It has an injection made with goat horns and a bear's gall bladder. It calls for leopard and tiger bones to be steeped in rice wine to make health drinks. (There are now only 450 wild leopards left in China.) And, unfortunately for pangolins, a whole range of pills require their scales and/or blood.

Much was made of a hopeful claim, coming from Chinese state media, that their latest (2020) release of the Pharmacopoeia "did not include pangolins" and that they were being "upgraded to a second-class protected animal." Yet, closer examination reveals that this is not the entire picture. While pangolins are no longer considered a "key ingredient," they are still listed as treatments for blood circulation and abdominal pain. The 2020 Pharmacopoeia is undoubtedly bolje, but in no way can we say the Chinese are suddenly absolved of blame for pangolin trafficking.


Update on Near-Earth Objects

While initial reports from the Minor Planet Center in Cambridge, Mass., categorized object 2013 US10 as a very large near-Earth asteroid, new observations now indicate that it is, in fact, a long-period comet, and it is now designated C/2013 US10 (Catalina). The comet was discovered by the Catalina Sky Survey near Tucson, Ariz., on Oct. 31, 2013, and linked to earlier pre-discovery Catalina observations made on Sept. 12. The initial orbit suggested this object is a large, short period, near-Earth asteroid, as reported here yesterday. An updated orbit, issued today by the Minor Planet Center, removed the September 12 observations that belong to another object and include earlier pre-discovery August and September observations made by the Catalina Sky Survey, the ISON-HD observatory in Russia and Hawaii's Pan-STARRS group. The new orbit indicates that this object is in a long-period, near parabolic orbit about the sun. Furthermore, observations made last night at the Canada-France-Hawaii telescope indicate the object is showing modest cometary activity, which means that yesterday's rough estimate for the object's size (about 12 miles, or 20 kilometers) must now be completely revised. A new size estimate is not yet available, but the object could very well be much smaller than yesterday's estimate.

Surprising Recent Discoveries of Three Large Near-Earth Objects
5. november 2013

Two surprisingly large Near-Earth Asteroids have been discovered in just the last week or so, as well as a third moderately large asteroid which, surprisingly, has also gone undetected until now, even though it can pass close enough to Earth to be classified as "potentially hazardous." Not since 1983 has any near-Earth asteroid been found as large as the approximately 12-mile (20-kilometer) size of the two new large ones. In fact, there are only three other known near-Earth asteroids that are of comparable size or larger than the two new large ones.

It is important to note that none of these three new large near-Earth asteroids can come close enough to Earth to represent a near-term threat to our planet.

The first of the new large near-Earth asteroid discoveries is named 2013 UQ4, and it is perhaps the most unusual. This approximately 12-mile (19-kilometer) wide object was spotted by the Catalina Sky Survey on Oct. 23 when the asteroid was 270 million miles (435 million kilometers) away from Earth. Not only is this object unusually large, it follows a very unusual, highly inclined, retrograde orbit about the sun, which means it travels around the sun in the opposite direction of all the planets and the vast majority of asteroids.

The only objects usually found in retrograde orbits are comets, which suggests that 2013 UQ4 may be the remains of an old comet that no longer possesses the near-surface ices required for it to become active while near the sun. Comets that have exhausted most, or all, of their volatile ices do not spew dust during sweeps through the inner-solar system like their less-seasoned, more hyperactive space kin. Without the telltale comet tails or atmospheres, dead comets look like, and in fact for all practical purposes are, asteroids.

As reported on Circular No. 9262 of the International Astronomical Union, the Massachusett's Institute of Technology's Richard Binzel, David Polishook and Rachel Bowens-Rubin observed this object on October 31 with NASA's 3-meter Infrared Telescope Facility in Hawaii and determined this object belongs to the so-called X-type spectral class and exhibits no obvious comet-like activity. This implies about a 4 percent reflectivity, from which they estimate a diameter of approximately 12 miles (19 kilometers).

The second very large near-Earth object, named 2013 US10, was discovered on October 31 by the Catalina Sky Survey. While the reflectivity of this object has not yet been determined, and hence its diameter is still uncertain, it is also likely to be about 12 miles (20 kilometers) in size. Only three near-Earth asteroids (1036 Ganymed, 433 Eros and 3552 Don Quixote) are of comparable size or larger.

Why has it taken so long to discover these large near-Earth asteroids? The delay in discovering 2013 UQ4 is more easily understood because it has a very long orbital period that has kept it out of Earth's neighborhood for centuries. But the delayed discovery of 2013 US10 is a bit harder to explain, since current population models suggest that almost all near-Earth asteroids of this size and orbit should have already been found. A contributing factor may be that this object's orbit does not allow it to get closer than 50 million miles (80 million kilometers) of Earth's orbit, so the asteroid seldom gets close enough to Earth to become easily detectable. However, NASA-supported telescopic surveys are now covering more sky and looking "deeper" than they ever have before, and in fact, 2013 US10 was first detected where it spends much of its time, well beyond the orbit of Jupiter.

The third of the recent discoveries is the approximately 1.2-kilometer (two-kilometer) near-Earth asteroid 2013 UP8, found on Oct. 25 by the Pan-STARRS group in Hawaii. This asteroid can approach quite close to Earth's orbit, within 3.4 million miles (5.5 million kilometers), which makes it a "potentially hazardous asteroid" (PHA). 2013 UP8 is in the top 5th percentile of the largest PHAs, most of which were found much earlier during NASA's asteroid survey program. Like the other new discoveries, this asteroid has gone undetected for a long time because it has not approached Earth closely for decades. But the increasingly capable NASA-supported asteroid surveys finally found this object while it was still at a large distance from Earth, well beyond the orbit of Mars.

NASA's Near-Earth Object Program at NASA Headquarters, Washington, manages and funds the search, study and monitoring of asteroids and comets whose orbits periodically bring them close to Earth. JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena.


Osončje

Take a trip through the Solar System, passing the Sun, the nine planets, moons and asteroids.

Imagine you were on a starship deep within interstellar space, heading toward the solar system where Earth resides. As you approached from tens of billions of miles away, the Sun would appear to grow ever brighter. Eventually you would detect Earth as a faint pinpoint of light. If you observed for long enough, you would notice that Earth follows a wide path around the Sun. You would also see, at various distances from the Sun, eight other objects of various sizes. You might detect that many of these planets are circled by still smaller objects&mdashtheir moons. In the space between the orbits of two of the planets, Mars and Jupiter, you would see thousands of very small "planets," or asteroids, also revolving around the Sun. You might even spot a few comets, their long, streaming tails slicing across the planetary orbits.

Sonce

The Sun lies at the very heart of our solar system. It is a typical star, one of the 150 billion in the Milky Way galaxy. Because the Sun is much closer to us than is any star, it seems many, many times larger than the more distant bodies. Its disk appears about the size of a full Moon.

Compared with the other stars of our galaxy, the Sun is an average-size star. But it is giant compared with even the largest planets. Its diameter of 865,278 miles (1.39 million kilometers) is more than 100 times greater than that of Earth. Even though it is of gaseous composition, the Sun weighs more than 300,000 times as much as Earth. Its surface temperature is 9,945° F (5,507° C). At its center, the temperature may reach as high as 25,000,000° F (14,000,000° C)&mdashhot enough to smash atoms and generate energy through a process called nuclear fusion. Each second, the Sun converts 661 billion tons of hydrogen into 657 billion tons of helium. In the process, 4 billion tons of matter are converted to pure energy. This energy initially takes the form of deadly gamma rays, but by the time it bubbles to the surface of the Sun, the energy has been transformed into a torrent of light, illuminating the planets and nurturing the many forms of life on Earth.

Children of the Sun

The nine planets, in order of their distance from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. The planets all lie in about the same orbital plane, and they orbit the Sun in the same direction. This suggests that the solar system is a relic of a vast disk of dust and gas that surrounded the Sun as it formed 4.6 billion years ago. In the first few million years after the Sun ignited, major planets, ranging from several thousand to tens of thousands of miles across, formed within this gaseous disk. The largest chunks of leftover debris became trapped in the gravitational fields of the newly formed planets, and began orbiting them as moons. Gravity pulled the smaller chunks to the surfaces of the planets and moons. Many of the craters that pepper the surfaces of these bodies are relics of this early period of intensive bombardment by interplanetary debris.

The solar system has two types of planets. The tiny rock, or terrestrial, planets all lie close to the Sun, like campers huddled around a bonfire. The immense outer planets&mdashJupiter, Saturn, Uranus, and Neptune&mdashlie in the colder reaches of the solar system. They consist mostly of liquid and gas. The farthest planet from the Sun, Pluto, though still called a planet, may not be one after all. Recent evidence indicates that it may be the last remaining "fossil" of a population of thousands of "icy dwarf" bodies that once inhabited the solar system. These icy dwarfs were either absorbed into the major planets or tossed out of the solar system altogether.

We have used robot spacecraft to fly by, orbit, and even land on, eight of the nine planets of our solar system. Probes have transmitted spectacular close-up pictures of all the planets (except Pluto), and in the process have revolutionized our understanding of how the celestial objects in our solar system evolved. The manned Apollo expeditions to the Moon, in the late 1960s and early 1970s, returned with the very first samples of rock collected from another world. Some of the Moon rocks were found to be 4.5 billion years old, providing additional evidence that the formation of the planets and moons accompanied that of the Sun.

Lune

A moon is any natural body that orbits a planet. There are more than 90 known moons in our solar system. The majority of them orbit the giant planets Jupiter and Saturn, and are little more than huge, airless balls of ice, ranging from hundreds to more than a thousand miles across. One of the largest moons, Saturn's Titan, is so big (3,449 miles, or 5,550 kilometers, in diameter) that it retains its own atmosphere of nitrogen. Mars has some of the smallest moons, a pair called Deimos and Phobos, each no bigger than an asteroid, which indeed they may have been at one time.

Asteroidi

In the 18th century, astronomers calculated astrophysical laws that predicted they would find an as-yet-unseen planet between Mars and Jupiter. And they eagerly searched the skies for it. On the night of January 1, 1801, the Italian astronomer Giuseppe Piazzi discovered a small celestial body, which he took to be a planet, in the space between the orbits of Mars and Jupiter. This body, which was later called Ceres, was found to have a diameter of only 623 miles (1,002 kilometers). Over the years, many more small, planetlike bodies were found in the gap between Mars and Jupiter&mdasha region of space dubbed the Asteroid Belt. Today, some 30,000 of these small bodies are discovered every year, and more than 210,000 are known to exist in our solar system. Some even have moons of their own.

These small bodies are now known as minor planets, or asteroids. The orbits of some extend beyond the Mars-Jupiter gap. But their combined mass is only a fraction of Earth's.

Astronomers once thought that asteroids were the fragments of a big planet that once orbited the Sun in a path between Mars and Jupiter and then broke apart for unknown reason. But in recent years, scientists have come to believe that asteroids are probably debris from throughout the solar system that never coalesced to form a planet.

Kometi

Comets are among the strangest members of the solar system. Instead of moving as the planets do, in nearly circular orbits in the same direction, comets revolve around the Sun in very elongated ellipses, and from every conceivable direction. Much of the time they are so far away from the Sun that they are invisible even to our largest, most powerful telescopes.

Today, astronomers know that comets are members of the Sun's family. Many "long-period comets" may originate in a vast shell of icy debris called the Oort cloud, 50,000 times farther from the Sun than is Earth. Others, particularly those known as "short-period comets," come from the Kuiper Belt, a region 30 to 100 times farther from the Sun than is Earth. Both clouds contain trillions of icy comet bodies that are gravitationally bound to the Sun.

When astronomers first discover a comet, it usually appears as a faint, diffused, fuzzy star, with a dense, starlike center and a veil-like region, known as its koma. As the comet approaches the Sun, its coma becomes brighter, as more and more material vaporizes off the surface of the comet's solid, icy nucleus. When they are some 100 million miles (160 million kilometers) from the Sun, some comets begin to show a tail streaming behind them, pointing directly away from the Sun. Comet tails consist of very thin gases that fluoresce, or glow, under sunlight, as well as a fine stream of dust particles. This material is forced away from the Sun by the pressure of sunlight and the solar wind.

Meteors

Comets eventually break up into particles, which are sometimes seen entering Earth's atmosphere as meteors. Meteors &mdash some of which originate in comets, and others as chunks from asteroids, moons, or other planets&mdashrange in size from specks the size of a pinhead to huge stones weighing many tons. We become aware of meteors only through the bright light produced when they collide with air molecules in our atmosphere. Most meteors disintegrate once they strike the atmosphere. Those that reach the ground are called meteorites. Most meteorites are fragments of asteroids, but a small number of them may have come from the Moon or Mars.

Early Ideas of the Solar System

The ancient Greek philosophers did not realize that Earth itself is a planet, or wanderer in the heavens (which, incidentally, is what planeta means). Earth, they thought, hung motionless at the very center of the universe. They believed that each of the five planets they had seen (Mercury, Venus, Mars, Jupiter, and Saturn) were attached to concentric, invisible crystal spheres. The Moon and the Sun were attached to other spheres. These crystalline spheres, set one within the other, revolved around Earth, carrying with them the heavenly bodies. This theory could not explain certain phenomena, however.

For one thing, the planets do not move at an even rate across the sky. At certain times, they move more rapidly than at others. An even greater mystery was the observation that a planet such as Mars occasionally ceases its apparent eastward motion among the stars and reverses itself to head westward for a time. To explain this "retrograde motion" of the planets, early astronomers invented a complicated system of "epicycles." They held that each planet traveled along the circumference of a small circle, the center of which traveled along the circumference of a larger circle. Earth, it was maintained, was at the center of the larger circle.

This model of the universe prevailed for more than 1,000 years. In the first half of the 16th century, however, Polish astronomer Nicolaus Copernicus revived an idea that had been first proposed by the Greek philosopher Aristarchus of Samos&mdashthat the Earth and other planets move around the Sun. This system was called the heliocentric theory, since it placed the Sun (helios, in Greek) at the center of the universe.

Motions of the Planets

It required a lifetime effort on the part of several great astronomers to prove the Copernician heliocentric system. The 16th-century Danish nobleman Tycho Brahe made a long and accurate series of observations of the planets. Johannes Kepler, a German disciple of Brahe, drew up three laws of planetary motion that still hold true today. Kepler also improved on the Copernician model, which maintained that the planets move in circular orbits around the Sun. This belief led to inaccuracies in predicting planetary positions. Kepler was able to show, instead, that orbits are ellipses, rather than true circles.

While Kepler was refining his theories, Italian inventor and scientist Galileo Galilei used the telescope, a recent Dutch invention, to gather additional evidence supporting Copernicus'theory. The telescope allowed Galileo to see the phases of Venus, which proved that it orbited the Sun, not Earth. Galileo also saw four tiny moons orbiting the distant planet Jupiter, in perfect accordance with Kepler's laws of motion.

The research of Kepler and Galileo clearly explained the nature of the planets'movements around the Sun, but neither scientist understood the force that governed these movements. This force was first revealed in 1687, when the great English scientist Isaac Newton presented his law of universal gravitation. This law states that every particle of matter in the universe attracts every other particle. This force of gravitation increases with the mass of an object, and depends on the distance between two objects. Newton showed mathematically that this is truly a universal law, since it applies not only to objects upon the Earth, but to heavenly bodies as well. The law of universal gravitation explains why planets, asteroids, and meteors keep orbiting the Sun, which is by far the most massive object in the solar system.

Using the law of universal gravitation, we can now analyze the motions of the planets with great accuracy. We can account for the small deviations that arise as one planet affects the orbit of another.

It was the study of such deviations that led directly to the discovery of the planet Neptune. After Uranus had been discovered by Sir William Herschel in 1781, careful studies showed that it did not follow the orbit predicted by the law of universal gravitation. This led young Englishman John Couch Adams and French astronomer Urbain-Jean-Joseph Leverrier to conclude that Uranus was being attracted by another planet even more distant from the Sun. Both men calculated the position in the sky of the unknown planet without ever having seen it. On September 23, 1846, on the basis of Leverrier's calculations, German astronomer Johann Gottfried Galle located Neptune.

Astronomers suspected the existence of Pluto because of the disturbances of motion they had seen in the orbits of Uranus and Neptune. Such deviations suggested that the two planets were being gravitationally tugged by yet another unseen body. Pluto was discovered in 1930 after a yearlong detailed search by astronomers at Flagstaff Observatory in Arizona.

In 1978 astronomers discovered that Pluto has at least one moon, which they called Charon. By plotting the moon's six-day orbit, astronomers were able to calculate the mass of Pluto, which turns out to be only 1 /500 that of Earth. Pluto's orbit is rather unusual, taking a path some 17 degrees inclined to the plane taken by the other planets. Pluto's orbit is also highly elliptical, so much so that Pluto moves inside Neptune's path for about 20 years out of its 248-year orbit.

Because of Pluto's puny size, its solid icy surface, and its peculiar elongated orbit, many astronomers have begun to debate its status as an actual planet. It may, in actuality, be the largest of a new class of relatively large icy bodies beyond the orbit of Neptune, or maybe even a strange type of comet. In 1999, however, the International Astronomical Union tabled such debate and ruled that, until other evidence becomes available, Pluto will remain classified as the solar system's ninth planet.


Poglej si posnetek: The Planet Song for Kids (December 2022).