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Was komeet ISON in 'n Kepler-baan voordat dit verbrokkel het?

Was komeet ISON in 'n Kepler-baan voordat dit verbrokkel het?


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Was komeet ISON in 'n Kepler-baan voordat dit verbrokkel het? As dit so is, is dit moontlik dat Kepler-wentelbane mettertyd verander kan word deur die toename of afname in die massa hemelliggame? As ISON byvoorbeeld in 'n Kepler-baan was en hy massa verloor het, het dit sy baan behou en in sy wentelbaan gedisintegreer of verander dit sy spoor as gevolg van die verlies aan massa?


Op u eerste vraag, ja, dit was in 'n Kepler-baan (hierdie interaktiewe model wys hoe dit verskyn het). ISON het nooit 'n volledige baan om die son voltooi nie, want dit was die eerste keer dat dit uit die land gekom het Oort Wolk en dit het verbrokkel.

Verdere antwoord: die massa van 'n liggaam om 'n ander in die ruimte word nie beïnvloed nie. Onthou die eksperiment wat bewys dat twee voorwerpe op dieselfde snelheid val, ongeag die massa daarvan (hier word die eksperiment op die maan gemaak met 'n veer en 'n hamer) en onthou dat wentelbaan val net teen 'n sekere snelheid en hoek ten opsigte van 'n ander liggaam.


Het ons die laaste van komeet ISON gesien?

UPDATE 6 DESEMBER 2013. Toe komeet ISON op 28 November van sy noue ontmoeting met die son wegtrek, verhelder dit eers en verdof weer. ISON is dit al 'n paar dae vermis in aksie & # 8211 buite die gesigsveld van NASA-sonwaarnemende ruimtetuie & # 8211 en nog nie sigbaar vir aardse waarnemers nie, nie eers die Hubble-ruimteteleskoop nie. Daar word nou geglo dat komeet ISON weinig meer geword het as 'n reisveld van puin in die ruimte, wat steeds die pad van die oorspronklike komeet gevolg het.

Wetenskaplikes het oorspronklik gesê dat & # 8211 as dit nie gefragmenteerd was nie, as dit sy vaste stand gehou het kern of kern- en # 8211-komeet ISON sal weer sigbaar word in die hemel van die Aarde vanaf 3 Desember.

Dit het nie gebeur nie. Ons het tot dusver nog geen foto's van ISON na die perihelium gesien wat van die aarde geneem is nie. Deskundige amateurwaarnemers het op 2 Desember gesê dat ons waarskynlik eers om 12 Desember enige teken van komeet ISON sal sien.

Professionele waarnemers, wat op 6 Desember by die Johns Hopkins Universiteit (tuiste van die Hubble-ruimteteleskoop) bymekaargekom het, sê dat waarnemings met HST vir einde Desember beplan word. Een waarnemer skryf egter op 6 Desember:

'N Soektog na ISON-oorblyfsels vandag by IRTF het niks opgedoen nie. Dit bring 'n probleem na vore: waar wys ons Hubble om daarna te soek? Daar is hoop dat amateurs kan deurkom.

Vir diegene wat vra & # 8211 en ja, mense vra nog steeds & # 8211 Comet ISON sal beslis NIE in Desember vir die blote oog sigbaar word nie. Party bly steeds hoopvol dat amateur- en professionele sterrekundiges een of ander oorblyfsel van die komeet op foto's kan sien. Diegene met teleskope en goeie kameras sal sekerlik probeer om die bewegende afvalveld wat nou komeet ISON is, te rig.

Lees die artikel hieronder van die Comet ISON Observing Campaign vir inligting oor die komeet en sy lot na sy perihelie op 30 November: 'n spoor van vrae

As u regtig 'n komeet wil sien, probeer dan komeet Lovejoy! Dit is nou sigbaar vir die oog in donker lug en dit moet gedurende die hele Desember so bly: Hoe om komeet Lovejoy in Desember 2013 te sien

Komeet ISON het dus nie 'n komeet van die eeu geword nie en ook nie. Ons moet nog een hou!

Komeet ISON was opwindendegter. Dit was die opwindendste komeet in jare. Ons kan dit nou nie met ons oë sien nie, maar ons sitplek op die voorste ry op sy perihelium & # 8211 moontlik gemaak deur middel van ons ruimtetuig & # 8211 was skouspelagtig. Daarbenewens is daar baie interessante komeetwetenskap, aangesien sterrekundiges hul data in die komende weke en maande ontleed en publiseer.

Komeet ISON het die son op 28 November 2013 afgerond. Dit het kort na die perihelium verhelder. Maar teen 30 November het die komeet weer verdof.

Hoed vir NASA Goddard & # 8217s Karl Battams, wat die wêreld byna eiehandig oor hierdie komeet tydens perihelion ingelig het, beide via sy Twitter-feed @SunGrazerComets of via NASA se comet ISON Observing Campaign-webwerf.

In die vroeë aand van 28 November plaas hy die volgende woorde: Ons noem dit & # 8230, u het dit eers hier gehoor & # 8230, ons glo dat 'n klein deel van die kern van ISON oorleef het.

Maar toe is alle hoop verydel toe die komeet weer vervaag. Battams het die volgende getwiet:

Hier is twee beelde van komeet ISON wat ure van mekaar geneem is, aangesien die komeet byna die naaste aan die son was, wat 'n groot mate van verbrokkeling getoon het. Die komeet het op 27 November helder geword, maar dit het kort voor perihelion op 28 November weer vervaag, wat vir sy voortbestaan ​​niks goeds voorspel het nie. Beeld via ESA / NASA, aantekeninge deur Karl Battams.

Aan die einde van 2012, toe sterrekundiges wat groot teleskope gebruik, die komeet ISON eers ver, ver van die son af raakgesien het, kon hulle duidelik sien dat dit 'n groot komeet en a helder komeet. Sy grootte en helderheid so ver van die son af het veroorsaak dat hulle voorspel het dat dit in Desember 2013 skouspelagtig in ons lug kan wees.

Die aarde se eie beweging in 'n baan het die komeet in Junie en Julie agter die son laat gaan, maar toe dit vroeg in Augustus uit die son verskyn, was dit nie so helder soos wat baie mense gehoop het nie. Hierdie gebrek aan helderheid het veroorsaak dat die sterrekundige voorgestel het dat komeet ISON nie 'n komeet van die eeu sou wees nie, maar tog 'n aansienlike helder komeet in ons naghemel sou wees.

Toe hy in November 2013 sy perihelium op 28 November nader, het Comet ISON verskeie opwindende uitbarstings in helderheid gehad. Baie met 'n baie donker lug en goeie lugtoestande het dit met die oog gesien. Baie mense met gewone kameras en / of verkykers het dit vasgelê, of dit ten minste raakgesien, en hul foto's was ongelooflik. Klik hier vir die beste beelde van komeet ISON, vóór die dood.

Hierdie gif is pre-perihelion, maar dit is een van my gunsteling beelde van Comet ISON. Dit is die komeet ISON (groter en helderder) en komeet Encke van 19 tot 22 November 2013 soos gesien met die sonwind. Beeld via NASA. Beeld via Karl Battams / NRL / NASA-CIOC. Hier & # 8217; s waar ISON sou wees, as dit in ons lug verskyn het. Die komeet se weg het sedert die perihelium nie verander nie. Sal dit helder en maklik om te sien wees? Absoluut nie.

As dit teruggekom het as 'n helder komeet in aardse lug, sou komeet ISON in die oggendhemel gewees het, naby die plek waar die son langs u oostelike horison opkom. Naby die son in die ruimte = naby die son in die lug. Die rudimentêre grafiek hierbo toon aan waar dit in ons lug sou gewees het, gesien vanaf die Noordelike Halfrond. Nou is 'n baie beter kaart as hierdie nodig om die komeet te sien.

As u nog steeds Comet ISON wil sien, en u die nodige toerusting het, is my raad om die kundiges op skyandtelescope.com te volg. Op 2 Desember skryf senior redakteur en jarelange waarnemer van die hemelruim Alan MacRobert in sy artikel getiteld So It Ends for Comet ISON:

Soos ek Maandag skryf [Des. 2], hierdie totaal onaktiewe spook van ISON is die 8ste sterkte [ver buite sig met die oog alleen] en in sy helderste deel minstens ½ ° wyd, met geen vooruitsig vir enigiets anders as om verder te versprei en verdof nie.

Ter vergelyking, dit is omtrent so wyd soos en baie dowwer as die visuele voorkoms van die Pinwheel Galaxy M33 in Triangulum. M33 is berug daarvoor dat hy selfs deur ligbesoedeling in die nag uitgewis word, en laat dit nooit voor sonop staan ​​nie.

Eers omstreeks 12 Desember sal die vlieënde spook van ISON ver genoeg van die son af klim om redelik goed in 'n donker lug te wees voordat die dagbreek begin (en slegs vir noordelike breedtegrade). Teen daardie tyd sal die oorskot 2,5 keer verder van die son af wees as nou, en dus 2,5 vierkante of 6,2 keer (2 groottes) flouer as nou. En dit as ons aanneem dat die stofwolk op die een of ander manier daarin slaag om nie verder te verdwyn nie.

Geskoolde astro-beelders wat vandag se kameras en sagteware gebruik, werk amper wonderwerke om flou dinge uit die donker te trek. Ons sien daarna uit om te sien wat hulle hier kan doen. En die Hubble-ruimteteleskoop sal ook middel Desember kyk, wanneer die komeet uitgang bly van Hubble se no-pointing zone om die son. Maar Hubble kan nie wyeveldbeelde doen nie. Die hoop is dat 'n paar soliede, onaktiewe fragmente van die voormalige kern groot genoeg is om Hubble as klein puntjies op te spoor.

Daar het jy dit. Adios, ISON. Ons sal na die afskeidsfoto's kyk!


Inhoud

Churyumov – Gerasimenko is in 1969 ontdek deur Klim Ivanovich Churyumov van die Universiteit van Kiev se Astronomical Observatory, [26] wat 'n foto ondersoek wat op 11 September 1969 deur Svetlana Ivanovna Gerasimenko vir komeet Comas Solà blootgestel is aan die Alma-Ata Astrophysical Institute, naby Alma-Ata (nou Almaty), die destydse hoofstad van Kazakh Soviet Socialist Republic, Soviet Union. Churyumov het 'n komete-voorwerp naby die rand van die plaat gevind, maar aanvaar dat dit die komeet Comas Solà is. [27]

Nadat hy na sy tuisinstituut in Kiëf teruggekeer het, het Churyumov al die fotografiese plate van naderby ondersoek. Op 22 Oktober, ongeveer 'n maand nadat die foto geneem is, ontdek hy dat die voorwerp nie Comas Solà kan wees nie, want dit is ongeveer 1,8 grade van die verwagte posisie af. Verdere ondersoek het 'n dowwe beeld van Comas Solà opgelewer op sy verwagte posisie op die bord, wat bewys dat die ander voorwerp 'n ander liggaam is. [27]

Die komeet bestaan ​​uit twee lobbe wat deur 'n nouer nek verbind word, met die groter lob wat ongeveer 4,1 km × 3,3 km × 1,8 km meet (2,5 mi × 2,1 mi × 1,1 mi) en die kleinste ongeveer 2,6 km × 2,3 km × 1,8 km ( 1,6 my × 1,4 mi × 1,1 myl). [4] Met elke baan verloor die komeet materie, aangesien gas en stof deur die son verdamp word. Daar word beraam dat tans 'n laag met 'n gemiddelde dikte van ongeveer 1 ± 0,5 m per baan verlore gaan. [28] Die komeet het 'n massa van ongeveer 10 miljard ton. [5]

Die tweelobvorm van die komeet is die gevolg van 'n sagte botsing met 'n lae snelheid van twee voorwerpe en word 'n kontakbinar genoem. Die "terrasse", lae van die binnekant van die komeet wat tydens die bestaan ​​daarvan gedeeltelik gestroop is, is in verskillende rigtings in verskillende rigtings georiënteer, wat daarop dui dat twee voorwerpe saamgesmelt het om Churyumov – Gerasimenko te vorm. [29] [30]

Daar is 26 verskillende streke op Churyumov – Gerasimenko, waarvan elk vernoem is na 'n Egiptiese godgebiede, op die groot lob is vernoem na gode, terwyl die op die klein lob na godinne vernoem is. 19 streke is in die noordelike halfrond gedefinieer voor die ewening. [31] [32] Later, toe die suidelike halfrond verlig word, is nog sewe streke geïdentifiseer deur dieselfde benaming te gebruik. [33] [34]

Streek Terrein Streek Terrein Streek Terrein
Ma'at Stof bedek As Stof bedek Babi Stof bedek
Set Ontpit en bros materiaal Hatmehit Grootskaalse depressie Moer Grootskaalse depressie
Aten Grootskaalse depressie Hapi Glad Imhotep Glad
Anubis Glad Maftet Rotsagtig Bastet Rotsagtig
Serqet Rotsagtig Hathor Rotsagtig Anuket Rotsagtig
Khepry Rotsagtig Aker Rotsagtig Atum Rotsagtig
Apis Rotsagtig Khonsu Rotsagtig Bes Rotsagtig
Anhur Rotsagtig, taamlik bros Geb Rotsagtig Sobek Rotsagtig
Neith Rotsagtig Wosret Rotsagtig

Gates Edit

Kenmerke beskryf as hekke, tweeling prominensies op die oppervlak wat so genoem word vanweë hul voorkoms, [ opheldering nodig ] is vernoem na oorlede lede van die Rosetta span. [35]

Naam Vernoem na
C. Alexanderpoort Claudia Alexander
A. Coradini-hek Angioletta Coradini

Oppervlakteveranderings Wysig

Tydens Rosetta gedurende sy leeftyd is daar baie veranderinge op die komeet se oppervlak waargeneem, veral wanneer die komeet naby die perihelium was. [36] [37] [38] Hierdie veranderinge het evolusiepatrone van sirkelvormige vorms in gladde terreine ingesluit wat op 'n stadium 'n paar meter per dag groot geword het. [39] [40] Daar is ook waargeneem dat 'n breuk in die nekstreek groei in grootte rotse wat tien meter breed is, is verplaas. Soms beweeg dit meer as 100 meter en kolle van die grond is verwyder om nuwe kenmerke bloot te lê. 'N Aantal ineenstortende kranse is ook waargeneem. Een opvallende voorbeeld in Desember 2015 is vasgelê deur Rosetta se NAVCAM as 'n helder lig van die komeet. Rosetta wetenskaplikes het vasgestel dat 'n groot krans ineengestort het, wat dit die eerste grondverskuiwing op 'n komeet maak wat bekend is as 'n uitbarsting van aktiwiteite. [41] [42]

Cheops boulder Edit

Cheops is die grootste rotsblok op die oppervlak van die komeet en meet tot 45 meter. Dit is in die groter lob van die komeet geleë. Dit is vernoem na die piramide in Gizeh omdat die vorm soortgelyk is aan die van 'n piramide. [43] [44] [45]

Soos die ander komete van die Jupiter-familie, het Churyumov – Gerasimenko waarskynlik sy oorsprong in die Kuiper-gordel en is dit na die binnekant van die Sonnestelsel uitgestoot, waar die ontmoetings met Jupiter later sy baan agtereenvolgens verander het.

Tot 1840 was die komeet se periheliumafstand 4 AU (600 miljoen km), te ver vir die son om die kern te verdamp. In 1840 verander Jupiter die baan na 'n afstand van 3 AE (450 miljoen km), en later ontmoetings verminder die afstand verder tot 2,77 AE (414 miljoen km). [46]

In Februarie 1959 het 'n noue ontmoeting met Jupiter [47] Churyumov – Gerasimenko se perihelium na binne geskuif tot ongeveer 1,29 AU (193 miljoen km), waar dit vandag nog bly. [14] [46] In November 2220 sal die komeet ongeveer 0,12 AU (18 miljoen km) van Jupiter af gaan wat die perihelium na binne sal beweeg tot ongeveer 0,8 AU (120 miljoen km) van die son af.

Voor Churyumov – Gerasimenko se perihelie-gang in 2009 was die rotasietydperk 12,76 uur. Gedurende hierdie periheliedoorgang het dit afgeneem tot 12,4 uur, wat waarskynlik gebeur het as gevolg van wringkrag deur sublimasie. [8]

2015 perihelion Edit

Vanaf September 2014 [update] het Churyumov – Gerasimenko se kern 'n skynbare grootte van ongeveer 20. [3] Dit het op 13 Augustus 2015 in Perihel gekom. [48] [2] Van Desember 2014 tot September 2015 het dit 'n verlenging minder gehad as 45 grade van die son af. [49] Op 10 Februarie 2015 het dit deur sonkrag gegaan toe dit 5 grade van die son af was en 3,3 AE (490 miljoen km) van die aarde af was. [49] Dit het op 5 Mei 2015 die hemelse ewenaar oorgesteek en vanaf die Noordelike Halfrond die maklikste gesien. [49] Selfs direk na die perihelium toe dit in die sterrebeeld Tweeling was, het dit net helder geword tot omtrent die skynbare magnitude 12, en moes 'n teleskoop gesien word. [2] Vanaf Julie 2016 [update] het die komeet 'n totale grootte van ongeveer 20. [3]

Die Rosetta missie was die eerste missie wat 'n wentelbaan ingesluit het wat 'n paar jaar lank met 'n komeet vergesel het, asook 'n lander wat naby-data van die komeet se oppervlak versamel het. Die missie wat in 2004 van stapel gestuur is, het in 2014 by komeet 67P aangekom en in 2016 afgesluit met 'n aanraking op die komeet.

Voorafwerk Redigeer

As voorbereiding vir die Rosetta missie, is die Hubble-ruimteteleskoopfoto's wat op 12 Maart 2003 geneem is, deeglik ontleed. 'N Algehele 3D-model is saamgestel en rekenaargegenereerde beelde is geskep. [50]

Op 25 April 2012 is die mees gedetailleerde waarnemings tot op daardie tydstip met die Faulkes-teleskoop van 2 meter geneem deur N. Howes, G. Sostero en E. Guido terwyl dit in sy afelie was. [ aanhaling nodig ]

Op 6 Junie 2014 is waargeneem dat waterdamp teen ongeveer 1 liter per sekonde (0.26 US liter per sekonde) vrygestel is. Rosetta was 360,000 km (220,000 mi) van Churyumov – Gerasimenko en 3,9 AU (580 miljoen km) van die son af. [51] [52] Op 14 Julie 2014 is beelde geneem deur Rosetta het getoon dat die kern daarvan onreëlmatig is met twee duidelike lobbe. [53] Die grootte van die kern is geskat op 3,5 × 4 km (2,2 × 2,5 myl). [54] Daar is destyds twee verklarings vir sy vorm voorgestel: dat dit 'n kontakbinair was, of dat die vorm as gevolg van asimmetriese erosie die gevolg kon wees as gevolg van ys wat van sy oppervlak sublimeer om die lobvormige vorm agter te laat. [19] [17] Teen September 2015 het sendingwetenskaplikes vasgestel dat die kontak-hipotese ondubbelsinnig korrek was. [55] [30]

Rendezvous en 'n baan Redigeer

Vanaf Mei 2014, Rosetta se snelheid is verminder met 780 m / s (2 800 km / h 1700 mph) met 'n reeks skroewe. [17] [56] Grondbeheerders het gereël Rosetta met Churyumov – Gerasimenko op 6 Augustus 2014. [18] [19] Dit is gedoen deur te verminder Rosetta se relatiewe snelheid tot 1 m / s (4 km / h 2 mph). Rosetta het die baan op 10 September, ongeveer 30 km van die kern, binnegegaan. [18] [19] [57]

Landing Wysig

Afkoms van 'n klein lander het op 12 November 2014 plaasgevind. Philae is 'n robottoets van 100 kg (220 lb) wat met landingsgestel op die oppervlak neersit. [17] [58] Die landingsterrein is gedoop Agilkia ter ere van Agilkia-eiland, waar die tempels van Philae-eiland hervestig is nadat die konstruksie van die Aswan-dam die eiland oorstroom het. [59] Die versnelling as gevolg van swaartekrag op die oppervlak van Churyumov – Gerasimenko is vir simulasiedoeleindes geskat op 10 −3 m / s 2, [60] of ongeveer 1/10000 daarvan op Aarde.

Vanweë die lae relatiewe massa, was daar sekere tegniese oorwegings om op die komeet te land Philae geanker. Die sonde bevat 'n verskeidenheid meganismes wat ontwerp is om die lae swaartekrag van Churyumov – Gerasimenko te bestuur, insluitend 'n koue gasskroef, harpone, ysskroewe met 'n landing op die been, en 'n vliegwiel om dit georiënteerd te hou tydens sy afdaling. [61] [62] [63] Tydens die geleentheid kon die skroef en die harpone nie werk nie, en die ysskroewe het nie 'n greep gekry nie. Die lander het twee keer gebons en eers tot stilstand gekom toe hy vir die derde keer kontak gemaak het met die oppervlak, [64] twee uur na die eerste kontak. [65]

Kontak met Philae het op 15 November 2014 verlore gegaan weens die laer batterykrag. Die Europese Ruimtebedryfsentrum het op 14 Junie 2015 kortstondig weer kommunikasie opgestel en 'n gesonde ruimtetuig gerapporteer, maar die kommunikasie is kort daarna weer verlore. [66] Op 2 September 2016, Philae was geleë op foto's wat deur die Rosetta wentelbaan. Dit het in 'n kraak tot stilstand gekom met net sy lyf en twee bene sigbaar. Terwyl die ontdekking die kwessie van die lander se ingesteldheid oplos, laat dit ook die wetenskaplikes van die projek toe om die data wat dit van die komeet se oppervlak teruggee, behoorlik te kontekstualiseer. [67]

Fisiese eienskappe Redigeer

Die samestelling van waterdamp van Churyumov – Gerasimenko, soos bepaal deur die Rosetta ruimtetuig, is wesenlik anders as op aarde. Die verhouding van deuterium tot waterstof in die water van die komeet is vasgestel dat dit drie keer groter is as wat vir landwater gevind is. Dit maak dit onwaarskynlik dat water wat op die aarde voorkom, van komete soos Churyumov – Gerasimenko kom. [10] [68] [69] Die waterdamp word ook gemeng met 'n beduidende hoeveelheid formaldehied (0,5 gew.%) En metanol (0,4 gew.%), En hierdie konsentrasies val binne die algemene reekse vir sonnestelselkomete. [70] Op 22 Januarie 2015 het NASA berig dat die komeet tussen Junie en Augustus 2014 toenemende hoeveelhede waterdamp vrygestel het, tot tien keer soveel. [71] Op 23 Januarie 2015 het die joernaal Wetenskap 'n spesiale uitgawe gepubliseer van wetenskaplike studies wat verband hou met die komeet. [72]

Metings wat voorheen uitgevoer is Philae As die batterye onklaar geraak het, dui dit daarop dat die stoflaag tot 20 cm (8 duim) dik kan wees. Daaronder is harde ys, of 'n mengsel van ys en stof. Porositeit neem toe in die middel van die komeet. [73]

Daar is gevind dat die kern van Churyumov – Gerasimenko geen magnetiese veld het nie nadat metings gedurende die tyd geneem is Philae se afdaling en landing deur sy ROMAP - instrument en Rosetta se RPC-MAG instrument. Dit dui daarop dat magnetisme moontlik nie 'n rol gespeel het in die vroeë vorming van die Sonnestelsel nie, soos voorheen veronderstel is. [74] [75]

Die ALICE-spektrograaf aan Rosetta vasgestel dat elektrone (binne 1 km of 0,6 myl bo die komeetkern) wat geproduseer word deur fotoionisering van watermolekules deur sonstraling, en nie fotone van die son af soos vroeër gedink nie, verantwoordelik is vir die agteruitgang van water- en koolstofdioksiedmolekules wat uit die komeet vrygestel word kern in sy koma. [76] [77] Ook op die komeet is aktiewe kuile ​​wat verband hou met sinkgat-ineenstortings en moontlik met uitbarstings aanwesig. [78] [79]

Metings deur die COSAC en Ptolemeus instrumente op die Philae Die lander het sestien organiese verbindings geopenbaar, waarvan vier vir die eerste keer op 'n komeet gesien is, insluitend asetamied, asetoon, metielisosianaat en propionaldehied. [80] [81] [82] Astrobioloë Chandra Wickramasinghe en Max Wallis het gesê dat sommige van die fisiese eienskappe wat op die komeet se oppervlak bespeur word deur Rosetta en Philae, soos die organiese ryk kors, kan verklaar word deur die teenwoordigheid van buiteaardse mikro-organismes. [83] [84] Rosetta programwetenskaplikes het die bewering as 'pure spekulasie' afgemaak. [85] Koolstofryke verbindings is algemeen in die sonnestelsel. Nie een van die twee nie Rosetta ook nie Philae is toegerus om direkte bewyse van organismes te soek. [83] Die enigste aminosuur wat tot dusver op die komeet opgespoor is, is glisien, tesame met voorloper-molekules metielamien en etielamien. [86]

Vaste organiese verbindings is ook gevind in die stofdeeltjies wat deur die komeet vrygestel word. Die koolstof in hierdie organiese materiaal is gebind in 'baie groot makromolekulêre verbindings', analoog aan die onoplosbare organiese materiaal in koolstofagtige kondrietmeteoriete. Wetenskaplikes meen dat die waargenome komeetagtige koolstofagtige vaste stof dieselfde oorsprong kan hê as die meteoritiese onoplosbare organiese materiaal, maar minder veranderings gehad het voor of nadat dit in die komeet opgeneem is. [87]

Een van die mees opvallende ontdekkings van die missie tot dusver is die opsporing van groot hoeveelhede vrye molekulêre suurstof (O
2) gas wat die komeet omring. Huidige modelle van die sonnestelsel dui daarop dat die molekulêre suurstof moes verdwyn teen die tydstip waarop 67P geskep is, ongeveer 4,6 miljard jaar gelede in 'n hewige en warm proses wat sou veroorsaak dat die suurstof met waterstof reageer en water gevorm het. [88] [89] Molekulêre suurstof is nog nooit tevore in kometas aangetref nie. In situ metings dui aan dat die O
2 / H
2 O-verhouding isotropies in die koma is en verander nie stelselmatig met heliosentriese afstand nie, wat daarop dui dat die oer O
2 is tydens die vorming van die komeet in die kern opgeneem. [88] Hierdie interpretasie is betwis deur die ontdekking dat O
2 kan op die oppervlak van die komeet geproduseer word in watermolekule-botsings met silikate en ander suurstofbevattende materiale. [90] Opsporing van molekulêre stikstof (N
2) in die komeet dui daarop dat die kometkorrels gevorm word onder lae temperatuur toestande onder 30 K (-243 ° C -406 ° F). [91]

Op 3 Julie 2018 het navorsers beraam dat daar nie voldoende molekulêre suurstof op die oppervlak van komeet 67P gemaak kan word nie, wat die raaisel van die oorsprong daarvan uitbrei. [92] [93]

CAESAR was 'n voorgestelde missie vir die terugkeer van monsters wat daarop gemik was om terug te keer na 67P / Churyumov – Gerasimenko, regolit van die oppervlak te vang en terug te bring na die aarde. [94] [95] Hierdie missie het deelgeneem aan die NASA se New Frontiers-missie 4-keuringsproses, en was een van die twee finaliste in die program. [96] In Junie 2019 is dit oorgedra ten gunste van Naaldekoker. [97] [98]


Komeet ISON_Please.

Ongelukkig woon ek in 'n rooi sone aan die rand van 'n oranje sone. Miskien sal ek vanaand vir Lovejoy skiet en ISON spaar vir as / wanneer dit begin skyn.

Dankie vir die skakel na die kaarte!

Dit lyk asof Stellarium die omvang vir ISON en Lovejoy omkeer. Daar staan ​​dat ISON 6.18 en Lovejoy 8.97 is

http://cometchasing.skyhound.com/ sê ISON is tussen 8.1 en 7.7 en Lovejoy tussen 6.7 en 5.1

# 77 MessiToM

Dit lyk asof ek net nie my IS in die AM uit die bed sleep nie. Ek moes regtig gisteraand net 'n bietjie langer wakker gebly het vir liefdesvreugde.

Tony Flanders, ek geniet dit baie om u kommentaar in hierdie drade te sien!

# 78 Edward E

# 79 Edward E

Ek was besig om vandag (11/12) @ 04:00 van my huis af in 'n rooi zone waar te neem en het komeet Lovejoy reg van die vlermuis gevind en dit 30 minute lank gekyk, dan was daar komeet ISON, asseblief. Ek kon dit nie eens vind nie, nie in finder 6X50 (ou Edmond Sci Deluxe Finder) of in die 6 & quot f8 Refractor met 'n Meade 40 mm wye-oogoogstuk (30X 1.4d FOV) of die 25mm Orthoscopic (49X 1d FOV) nie. soveel vir, wel weet julle almal.

Een van die ligte aspekte van dinge is dat daar nog 'n komeet is wat aan die lys in die AM sky komet Komeet C / 2013 V3 (Nevski) is tussen Leo en kanker of Cancer en Leo. Hier is die skakel na 'n soekgrafiek vir die nuwe speler:

Die AM-lug word nogal druk met Solar Dust Bunnies (laaste 5 tel).

# 80 Astro_Girl

# 81 Tony Flanders

Komeet Ison is miskien helderder as die gemiddelde beer, maar selfs ek as 'n beginner-amateur-sterrekundige het geweet dat ek nie 'n & briljante, skitterende, verblindende en helder komeet in die lug & quot of die & quotcomet van die eeu & quot sou verwag soos mense dink hulle moet wees nie.

Selfs die mees optimistiese voorspellings sou Comet ISON op hierdie stadium nie skitterend gemaak het nie. Realisties genoeg was die beste wat ons middel November sou kon verwag, 'n komeet soos Lovejoy - flou sigbaar vir die blote oog vanuit donker plekke en baie indrukwekkend deur 'n verkyker.

Al die & quotComet of the Century & quot-dinge moes veronderstel wees om aan die einde van November en vroeg in Desember onmiddellik na die perihelium te gebeur. En in werklikheid is dit nog steeds moontlik dat dit vroeg in Desember 'n goeie blote oogvertoning kan lewer.

Komeet van die eeu? Dit was altyd besig om die feite te rek, selfs in die mees optimistiese scenario.

# 82 Edward E

Moenie toelaat dat die & teleurgestelde publiek & quot u entoesiasme krom nie. Hou aan om die publiek waar te neem en aan te toon wat u opwindend vind, en dra dit aan hulle oor. U entoesiasme sal deurskyn en ander inspireer om te stop, kyk, luister en vrae vir hulself te stel. Dan, & quotwie weet watter drome kan kom & quot. Sonder die amateur-sterrekunde-gemeenskap is ek bang dat die publiek sal vergeet dat daar iets in die lug is ná die donker, behalwe die maan.

Is dit u eerste komete wat u waargeneem het?

# 83 Edward E

# 84 mattyfatz

Ek het hierdie komeet 'n bietjie gelees. Dit lyk asof die hype veroorsaak is deur die omstandighede na die eerste ontdekking daarvan. Kort nadat dit raakgesien is, terwyl dit nog buite die baan van Mars was, het die komeet 'n stert gedraai. Dit is ongewoon dat 'n stert so ver voorkom. Daardie stert het intussen verdwyn, en is vervang deur 'n meer algemene tipe. Sterrekundiges dink dat aangesien hierdie komeet sy eerste reis vanaf die Oortwolk onderneem, dit 'n laag bestraalde ys en stof aan die buitekant gehad het wat hierdie vroeë stert gevorm het. Die meeste komete wat ons waargeneem het, is periodiek, en selfs al is daar 'n baan van 70 000 jaar
(soos Hyakutake byvoorbeeld) het hierdie aanvanklike buitenste laag ys en stof lank gelede afgewaai.
Dus, selfs as dit nie so briljant presteer as wat ons verwag het nie, is dit steeds 'n belangrike besoeker. Dit is 'n goeie kans om 'n komeet te sien wat sy eerste reis vanaf die Oort-wolk onderneem. As ek dit aan die publiek wys of dit aan nie-sterrekundige tipes verduidelik, probeer ek hierdie aspek van die komete-betekenis beklemtoon. As jy daaroor nadink .. Dit is regtig 'n komeet van baie eeue.

# 85 Dave Mitsky

Komeet ISON het pas 'n uitbarsting beleef en het volgens die verslag op http: //www.cloudynig tot die vyfde sterkte verhelder. 6194029 / bladsy.

'N Tydsverloopvideo van die komeet wat vanoggend styg, word op http://blog.cajunastro.com/?cat=6 geplaas

# 86 Tony Flanders

Dit is waarskynlik die enigste komeet wat ons ooit sal sien, wat sy eerste reis vanaf die Oort-wolk onderneem.

Ek dink nie dat dit reg is nie. Kometjies wat pas aangekom het, is baie algemeen.

Oor die algemeen is dit onmoontlik om seker te maak, want die verskil tussen 'n miljoen jaar baan en een wat vars van die oneindigheid af kom (die Oort-wolk tel as oneindig) is te klein om te meet. Wat die saak betref, kan ons gewoonlik nie die moontlikheid uitsluit dat hulle van buite die Oort-wolk, vanuit die interstellêre ruimte, aangekom het nie. Maar sover ek weet, is geen asteroïde of komeet ooit vir seker as 'n interstellêre besoeker bevestig nie.

Let daarop dat wentelbane versteur word deur die planete, veral Jupiter. Iets wat as 'n nuwe aankoms begin, kan dus as 'n periodieke komeet eindig - of heeltemal uit die sonnestelsel gestoot word.

# 87 BrooksObs

Dus, selfs as dit nie so briljant presteer as wat ons verwag het nie, is dit steeds 'n belangrike besoeker. Dit is waarskynlik die enigste komeet wat ons ooit sal sien, wat sy eerste reis vanaf die Oort-wolk onderneem. As ek dit aan die publiek wys, of dit aan nie-sterrekundetipes verduidelik, probeer ek hierdie aspek van die komete-betekenis beklemtoon. As jy daaroor nadink .. Dit is regtig die komeet van baie eeue.

In werklikheid is komete uit die Oort-wolk regtig nie so ongewoon nie. Ek het deur die jare heen gesien hoe baie van hulle kom en gaan. Dit is hoekom, as u na die regte mense luister, maande gelede al gehoor het dat ISON nooit moontlik sou ontwikkel as die eerste keer bekend gemaak nie (dus helderder as die volmaan). Eintlik presteer dit redelik soortgelyk aan die meeste van die vorige Oort Cloud-broers, behalwe miskien vir die grootste uitbarsting van vandag. Die komeet Kohoutek was 'n dinamiese & quotnew & quot-komeet, soos in die onlangse komeet Austin in 1989 albei aangekondig is dat dit waarskynlik komeet van die eeu sou word, wat ook nie gedoen is nie.

Net so kan die onverstoorde omwentelingselemente van 'n komeet voordat hy die wêreld van die planete binnegegaan word, bereken word met 'n lang genoeg waargenome baan van die baan. Selfs diegene met miljoene jaarperiodes kan 'n net waarneembare afwyking van e = 1.0 toon, en die meeste Oort Cloud-komete kan selfs effens hiperbolies wees. Daar word egter verwag dat 'n ware interstellêre komeet hoogs hiperbolies is en dit is nog nooit gesien nie.

# 88 sterreboerdery

Is ISON of Lovejoy op hierdie stadium dus helder genoeg om deur 'n 60 mm-refractor gesien te word (dieselfde as die $ 24,99-refractor-draad)? Die lug in my omgewing is * BLEEP *, en daarom is ek nie lus om die 70 myl heen-en-weer-reis na my donker plek te neem vir waarneming nie.

Ek sal waarskynlik in 'n plaaslike park moet oprig, wat ligte besoedeling in die omgewing sal hê.


Die komeet ISON kan disintegreer


Die voorspellings rakende die onsekere toekoms van Comet ISON word bevestig, al is dit nie ten minste bevestig deur die mees onlangse optiese waarnemings nie, het FACom in 'n verklaring gesê.

Ondanks die algemene skeptisisme en bewerings oor die feit dat die gerugte van die komeet ISON 'fizzling' baie oordrewe was, toon die komeet steeds 'n onverwagse gedrag wat komeetkundiges beveg om te verklaar.

Ag, wag, miskien beteken dit dat die aarde nou deur een van die fragmente getref kan word. . DOOOOM se rug

Dud? Miskien, miskien nie.
Die skrywer van die artikel het 'n boodskapsdraad oor die komete-yahoo-groep begin en daar moet gesê word dat ander amateur-sterrekundiges nie oortuig is van sy gevolgtrekkings nie.

Ignacio het ook 'n webblad waar u die ligkrommingsdata kan sien en self kan sien waarop hy sy idee gebaseer het.

ook. moenie 'n party pooper wees nie.

Daar is duisende hier op aarde wat wag op die eerste kontak en dors na vreemde kennis.


Dit is dus waarskynlik nie 'n ruimteskip nie.

Interessante bespreking aan die gang by die Yahoo Group wat u noem

As die komeet opbreek, is daar 'n geringe kans dat dit die aarde sal stort met meteoriete van die astrologiese terreine waaruit ek artikels gelees het. The majority of the debris will follow the same path and timing so we will not see any large meteors from this most likely. It is totally dependent on when it breaks up also. The risk is greater of it effecting earth if it breaks up than if it doesn't. There is not any good evidence to know what is going to happen. It may just go into the sun. From the articles I have read over the last three weeks, it appears that they are not sure what is going to happen, it is totally dependent on when it breaks up.

Even NASA has an article about this on the net, but you have to go through a different site to find it because the NASA site is conveniently is down. The first I saw of this was from the Australian astronomy site.

We may get a good light show out of this folks, instead of the earth getting peppered with comet dust that will not give us a show. It may be a very interesting time. Why fear something we can do nothing about. Enjoy the show if this happens, we may not have such a nice show for hundreds of years. This firework display is nothing to fear, unless a chunk lands on your home. The ground here will be covered with snow in January so I doubt if there will be forest fires. I just hope the cyanogens in the comet don't overload the atmosphere. I suppose I will stock up on grapefruit juice and stock a bunch of onions just in case, the thio sulfate helps the body deal with cyanogens.

We will know what is happening by late november as it goes around the sun. The show will be in January sometimes, whether it breaks up or not. If it doesn't break up, I suppose the comet dust will make the snow all dusty

I hate dirty snow, I like when it is white.

So if it breaks up don't panic, it is hard to enjoy the fireworks when you are upset. Chances are it will just be a good show.


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Comet ISON and the Best Studied Planetary System

This Thursday, the Solar System put on a celestial performance, and we had a front row seat to the spectacle. Long period Comet ISON made its closest approach to the Sun entering the Sun’s atmosphere. This sun-grazing comet was making its first entry into the inner Solar System after spending most of its lifetime in the outer reaches of the Solar System in the Oort Cloud (a spherical shell of icy bodies residing at

10,000-20,000 AU and the repository of long period comets). For most of the Solar System’s history ISON has resided out in the Oort Cloud, but the gravitational tug from a chance passing star or the gravitational pull from the gravitational tides with the center of the Milky Way nudged ISON onto an orbit straight for the Sun.

Comet ISON was discovered in November 2012 and has sometimes been touted as potentially being the ‘Comet of the Century’ with some predictions that it might become so bright to be visible with the naked eye if it survived perihelion (its closest approach to the Sun). Since ISON was discovered with such warning before perihelion, astronomers were able to organize observing campaigns with ground-based and space-based telescopes to study how the comet changes as it got ever closer and closer to the Sun. Planetary scientists and astronomers will be pouring over the data for months and likely many years to come.

On Thursday the spacecraft monitoring the Sun including Solar Dynamics Observatory (SDO) and Solar and Heliospheric Observatory (SOHO) were poised to capture ISON as it made it’s closest approach. Comets are a conglomeration of ice, rock, dust, and frozen gases, and many don’t survive the fiery perihelion passage the nucleus disintegrating with only dust and a rocky rubble pile remaining. It wasn’t sure if ISON would survive. It looks like something has indedeed survived perihelion passage, but ISON is providing more questions than answers. It appears to have completely lost its coma and tail which were blasted away as it skimmed the Sun’s million-degree corona. As you’ve probably seen the contradictory statements that ISON was dead and then alive (ISON is not behaving like any sungrazing comet seen before and if you were following twitter and the news reports you were seeing science in progress. Conclusions were changing as more data came down in live time). The current word on the street is that likely a small chunk of ISON’s nucleus made it through perihelion, but it’s still not 100% clear what survived. ISON appears to be behaving like a comet albeit a very small and dusty comet, but time will tell. Future observations over the coming days and weeks will confirm whether gas is being produced which would be the tell-tale sign that there is ice and frozen gases in from some part of the nucleus still around. If there is no gas, then it’s just a rubble of rock and dust left in orbit that will slowly dissipate. Chances are that at this point ISON won’t be naked eye visible but either way, ISON has left us with more learned about comets in the Oort Cloud and added many many many questions for astronomers and planetary scientists to solve while putting on a spectacular show for us.

Snapshots from SOHO’s C2 chronograph monitoring of the Sun showing Comet ISON after its closest approach with the Sun (left) and before (right) on its way to perihelion Image Credit:ESA/NASA/SOHO/Jhelioviewer

For full coverage and the latest on Comet ISON and how it is doing after it’s fiery encounter with the Sun, check out NASA Comet ISON Observing Campaign blog run by Karl Battams and the Planetary Society’s Comet ISON Live Blog by Emily Lakdawalla and Bruce Betts.

What am I doing talking about a comet on the Planet Hunters blog? I do have having a soft spot in my heart for icy outer Solar System bodies, that’s the area of research I worked on for my thesis, but Comet ISON is a good reminder that we should think about these exoplanets we’re finding with Kepler and Planet Hunters as members of a larger planetary system. The transiting planets are the ones we detect, but there is much more there that we don’t see. We know in some transiting exoplanet systems there are unseen (‘invisible’) non-transiting planets, perturbing the orbits of the transiting planets changing the timings and durations of the observed transits. There is also likely the building blocks of planet formation left over as debris hanging around in many of the planetary systems found in the Kepler field. Perhaps some of the material is trapped in belts like the asteroid belt and Kuiper belt in our own Solar System. Many of them likely have Oort Clouds (distant repository of icy bodies of their own). Debris disks likely the equivalent to our own Kuiper belt have been spotted around stars. One of the famous examples is Fomalhaut shown below.


Friday, December 13, 2013

Geminid Meteor Shower Peaks Tonight: Watch Live Online!

After a days-long lead-up, tonight, December 13/14, 2013, is finally the peak of the Geminid Meteor Shower , which means that tonight, more so than any before or after, should offer the most meteors streaking through the sky.

Every December, Earth passes through the stretch of space junk shed by a mysterious object called 3200 Phaeton , reaching the deepest concentration of debris tonight. According to some estimates, under ideal conditions (dark country skies), one can expect to see something in the range from 60-120 meteors per hour. The reason the meteors are called Geminids is because the meteors seem to radiate from the constellation Gemini. The best time to view the shower is in the wee hours of the nigh/early morning, when Gemini is at its highest.

If you plan to go out in the early morning, look in the West-Southwest and directly above Orion to spot Gemini, whose signature feature is bright stars Castor and Pollux within a 5 degrees of each other.

The best part: even if its cloudy, you can watch the meteor shower online! Go here to learn more about the shower, how to observe it, and for a link to the webcasts!

If you found this informative (or at least entertaining), help me pay my bills and check out my Examiner pages for space news, cleveland photography, national photography, and astronomy for more great stuff.

For something even better, follow this blog.


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August Skywatching: Is Comet ISON's Future Bright?

The potentially spectacular Comet ISON continues to be masked by the glare of the sun as July transitions into August, but the icy wanderer will come into view soon.

ISON, a " comet of the century " candidate that may put on a dazzling show when it zooms through the inner solar system later this year, was in solar conjunction on July 15, when it was located about 8 degrees due north of the sun. (Your clenched fist held at arm's length measures about 10 degrees.)

Ever since then, the sun has appeared to slowly move away to the east, leaving the comet behind. Since early December 2012, ISON has resided in the constellation of Gemini (The Twins). But Thursday (Aug. 1) marks the start of a new month — and, for ISON, a new constellation — as it crosses over into the boundaries of Cancer (The Crab). Still, this is all a moot point, because the comet continues to be invisible. [ Photos of Comet ISON: A Potentially Great Comet ]

Things will change during the next couple of weeks, however. On Aug. 10, Comet ISON will be 18.1 degrees from the sun and will begin rising above the east-northeast horizon before dawn. For mid-northern latitudes on the morning of Aug. 21, ISON will stand 6 degrees above the east-northeast horizon at the start of twilight. And by the end of August, the comet's altitude will double to 12 degrees by the time dawn begins to break, making it an easy target for skywatchers.

The question is, what, exactly, will observers see?

Brightness unchanged

When first sighted in late September 2012, Comet ISON was 625 million miles (1 billion kilometers) from Earth and 584 million miles (940 million km) from the sun. It was shining at magnitude 18.8 on the reverse scale astronomers use to measure the brightness of sky objects. (The lower the number, the brighter the object.)

That made the comet about 100,000 times fainter than the dimmest star that can be seen with the unaided eye. The comet continued to brighten slowly until the beginning of this year, and then simply stopped brightening when it reached magnitude 15.5.

Astronomers suspect that ISON is a "dynamically new" comet, meaning that it's making its first trip to the inner solar system from the distant Oort Cloud. This could explain the lack of change in ISON's brightness so far: If the comet had never been exposed to intense light and heat, it may have possessed, until recently, a thin coating of volatile material that vaporizes at a great distance from the sun. After this coating evaporated, the comet stopped brightening, scientists speculate.

But changes could be coming soon for ISON. Even as the comet remains hidden by the glare of the sun, it is streaking toward the "frost line" — the distance from the sun at which an object's water begins boiling off into space. [ Comet ISON's Perilous Journey Explained (Video) ]

ISON will cross the frost line, which lies about 230 million to 280 million miles (370 million to 450 million km) from the sun, within the next few weeks, scientists say. When this happens, frozen water locked within the comet's 3-mile-wide (4.8 km) nucleus should begin to sublimate (go from a solid to a gaseous state), blasting out jets of gas and dust, and placing the comet back on a brightening trend.

But just how bright will the comet be by the end of August?

Two possibilities

That's the big question that might provide a clue as to what ISON ultimately does when it zips 724,000 miles (1.17 million km) above the sun's surface on Thanksgiving Day (Nov. 28).

If the comet is no brighter than 13th magnitude by the end of August, it stands a fair chance of completely disintegrating, either en route to, or immediately after, it rounds the sun. The sungrazing Comet du Toit completely disappeared on its way toward its solar rendezvous in late December 1945. More recently, Comet Lovejoy somehow survived its close brush with the sun in December 2011, even managing to put on a good show for the Southern Hemisphere. But within weeks, it, too, vanished.

On the other hand, if ISON is brighter than 13th magnitude, I suspect it will remain more or less intact as it sweeps past the sun. Although the icy nucleus would not completely disintegrate, it might still fracture into several pieces — think of what happens when you pour hot tea into a cold cup.

If that ends up being the comet's ultimate fate, ISON might release a tremendous amount of dust, which could produce a spectacularly long and bright tail. Such was the case with the Great Comet of 1882 and comet Ikeya-Seki in 1965, both of which fragmented as they grazed the sun.

At least one astronomer has already declared that Comet ISON likely is already fizzling out.

"It is probable that it may disintegrate at or before reaching perihelion," Ignacio Ferrin, an astronomer at the University of Antioquia Institute of Physics in Medellin, Colombia, said in a statement Monday (July 29). (Perihelion is the point in an object's orbit when it's closest to the sun.)

Ferrin points out that ISON stopped brightening in January and compared it to another comet — C/2002 O4 Hönig — which remained at the same brightness for 52 days, after which it disintegrated with no observable residue.

"The future of comet ISON does not look bright," Ferrin concluded.

However, it should be pointed out that on Feb. 21, Ferrin issued a statement saying he felt there was a 75 percent chance that ISON "will become as bright as the full moon at perihelion." There was a 25 percent chance it might not get as bright as initially expected but "still will put (on) a good performance," Ferrin added.

This flip-flop highlights just how difficult it can be for anybody, even an expert, to predict how a comet will behave as it approaches the sun. Hopefully, we'll have a better idea of what to expect from ISON in our next update at the end of August. Stay tuned!


Special Topic: The Death of Comets

The tail remnant of Comet Elenin C/2010 X1 on October 22, 2011, as imaged by a remotely-controlled telescope in New Mexico. Courtesy Rolando Ligustri in Italy.

W hat happens to comets when they “die?” Our solar system has been around for 4.6 billion years, and, obviously, a large percentage of the comets that the solar system started off with are no longer with us. While many comets still remain in the reservoirs of the outer solar system, i.e., the Kuiper Belt and the Oort Cloud , once they begin making passages into the inner solar system and start becoming active their days, so to speak, are numbered. As it turns out, there are several mechanisms by which comets can meet their demise.

Many comets do not “die” but rather are ejected from the solar system and thus “exiled” into interstellar space. As discussed in previous “Special Topics” presentations, the comets that were initially kicked out into the Oort Cloud are only loosely held to the solar system, and passing stars and tidal forces from the overall G alaxy can either perturb comets into the inner solar system or eject them from the solar system completely, and it is likely that there are far more of the latter than there are the former. Comets that pass by the major planets, especially Jupiter, can also be perturbed into hyperbolic orbits and consequently ejected from the solar system , and this has in fact been observed on numerous occasions.

Any such exiled comet would roam through the G alaxy essentially forever. On occasion, such as with the interstellar Comet 2I/Borisov last year – a previous “ Comet of the Week ” – it might encounter another planetary system and pass through it, but after doing so it would once again head back out into the G alaxy and continue its wanderings.

An interstellar exile. I took this image of Comet 2I/Borisov on December 21, 2019 with the Las Cumbres Observatory facility at McDonald Observatory in Texas.

Some comets will meet a much more dramatic demise by impacting another object, and this has undoubtedly occurred many times throughout the solar system’s history. We have seen this once, in July 1994 when Comet Shoemaker-Levy 9 1993e – another previous “ Comet of the Week ” – impacted Jupiter. Earth has also certainly been impacted by comets from time to time, although hopefully this will not happen anytime within humanity’s near- to intermediate term future, and in the unlikely event that a threatening object were to be inbound the presently-operating survey programs should give us a long enough advance warming to take appropriate action , as discussed in previous “Special Topics” presentations.

Comets, being made up of various ices, are rather porous objects to begin with, and as they make repeated passages through perihelion they continuously lose a fraction of their material. Eventually, so much material is lost that there is really nothing left, and the comet essentially just “disappears.” Even through the half-century that I have been following comets there have been several periodic comets that have simply vanished and that are no longer making returns.

A comet destroyed by impact. This is an infrared image of the impact of nucleus “G” of Comet Shoemaker-Levy 9 into Jupiter on July 18, 1994, taken by Peter McGregor from Siding Spring Observatory in New South Wales. Image courtesy Mount Stromlo and Siding Spring Observatories.

Sometimes this disintegration process is accompanied by a fragmenting of the nucleus. A classic example of this is Comet 3D/Biela – a previous “ Comet of the Week ” – which, after being observed during several returns in the late 18 th and early 19 th Centuries, appeared as a “double comet” for two returns and then just vanished – with the exception of strong meteor showers that occurred for a few returns thereafter. Although not quite as dramatic as this, there have been a couple of more recent cases where a periodic comet has been observe d to fragment and then subsequently vanish. Since the fragmenting of a comet’s nucleus will expose previously-hidden ice to sunlight which will then start undergoing new activity, these fragmenting events are often associated with outbursts in brightness. Indeed, there have been a couple of recent cases where a short-period comet was discovered during an obvious outburst, and then disappeared after a few returns – or in a few cases was never seen again.

Many long-period comets also have been seen to disintegrate as they pass through perihelion. In general, the smaller a comet’s perihelion distance – and thus the more intense solar heating it experiences – and the smaller the nucleus, the more likely it is that it will not survive perihelion. The small spacecraft-discovered Kreutz sungrazers – discussed in last week’s “ Special Topics ” presentation – are a striking example of this. Over my years of observing comets there have been several that have proceeded towards perihelion – sometimes exhibiting outbursts as they do so – but then either didn’t reappear after perihelion or in some cases didn’t even make it to perihelion at all . In 1991 veteran comet observer John Bortle developed an empirical formula that utilizes a long-period comet’s perihelion distance and its absolute magnitude to predict whether or not it will survive perihelion: H_max = 7.0 +6 q , where H_max is the limiting absolute magnitude for survival (and q , as always , is the perihelion distance in AU). While the exact physical relationship between a comet’s absolute magnitude and the size of its nucleus is not something that can be firmly established, in general, the brighter the absolute magnitude, the larger the nucleus.

An image of a disintegrating comet: Comet SWAN C/2020 F8 on May 31, 2020, four days after its perihelion passage (heliocentric distance 0.43 AU). Courtesy Pierre Girard in England.

A recent dramatic example of a disintegrating long-pe riod comet is Comet ISON C/2012 S1, which is a future “Comet of the Week.” Another interesting recent example is Comet Elenin C/2010 X1, which passed through perihelion in September 2011 at a heliocentric distance of 0.48 AU. As the comet disappeared into twilight en route to perihelion it began to grow very diffuse as if it was starting to disintegrate, and when it passed through perihelion and theoretically should have been detectable with the coronagraphs aboard the NASA/ESA SOlar and Heliospheric Observatory ( SOHO ) spacecraft there was nothing to be seen, despite the fact that there should have been a strong brightness enhancement due to forward scattering of sunlight. When Comet Elenin emerged into the morning sky in October initially nothing was seen, however, once it climbed higher above the horizon CCD images began to show a thin wisp-like structure 10 to 20 arcminutes long. This was the comet’s tail, apparently created b y a dust ejection event just as the nucleus began to disintegrate it survived, while the comet itself did not.

We have seen some recent examples of this phenomenon during “Ice and Stone 2020.” As discussed in its own “ Comet of the Week ” P resentation, Comet ATLAS C/2019 Y4 began to disintegrate as it approached perihelion, and as it turned out nothing was seen afterward. Comet SWAN C/2020 F8, discussed within that same Presentation, also began to show signs of disintegration, and by the time of perihelion passage was nothing more than a “smear” of light that disappeared not too long thereafter.

A CCD image I took of (944) Hidalgo on January 13, 2005.

For several periodic comets, especially those with a high dust content, a different fate may be in order. While much of the dust that is ejected from a comet’s nucleus never returns to it, instead, continuing to travel around the sun in the comet’s orbit – and, as discussed in a future “Special Topics” presentation, producing meteor showers if that orbit passes close to Earth’s – some of that dust does settle back onto the nucleus. As seen from the “Brownlee particles” – discussed in a previous “ Special Topics ” presentation – this dust is very dark, and meanwhile, over time it coats more and more of the nucleus until eventually, it covers the entire nucleus. The comet at that point “shuts down” and becomes an inert object essentially indistinguishable from an asteroid.

Some of the known periodic comets appear to be “transition” objects on the way from being active comets to becoming “extinct.” The first such known object was Comet 28P/Neujmin 1, discovered in September 1913 by Grigorij Neujmin at the Simeis Observatory in Crimea despite favorable viewing geometry and passing 0.55 AU from Earth, it exhibited at most just a very small coma and a weak short tail no more than a few arcminutes long. It has an orbital period of 18 years and although recovered at all the subsequent returns, for most of those it has appeared entirely asteroidal, although it’s fair to say that the viewing geometry tended to be unfavorable during those returns. During the one somewhat favorable return it has had since then, in 1984, it exhibited at most just a very tiny coma, which was found to be entirely gaseous in content. Studies indicated that the comet’s nucleus is quite large – 21 km in diameter – but that only about 0.1% of its surface area is active.

An image I took of (944) Hidalgo on October 14, 2018 with the 2-meter Las Cumbres Observatory Faulkes Telescope North at Haleakala, Hawaii.

A handful of additional potential “transition” comets have been discovered during the intervening years, perhaps one of the more notable ones being 49P/Arend-Rigaux. Meanwhile, on October 31, 1920, the German-born astronomer Walter Baade, then working at Hamburg Observatory in Bergedorf, discovered a 13 th -magnitude apparent asteroid now known as (944) Hidalgo. This object was found to be traveling in a distinct elliptical and inclined orbit (eccentricity 0.65, inclination 43 degrees) with a period of close to 13.6 years its perihelion distance is close to 2 AU, but at aphelion, it travels out to 9.4 AU, almost as far as Saturn. The story is told that at first Baade was unsure whether to announce his discovery as a comet or as an asteroid, finally deciding upon the latter since he felt its unusual orbit would cause his fellow astronomers to pay closer attention to it.

Hidalgo has been extensively observed and studied at every subsequent return, the most recent of which was in 2018. It has never exhibited any kind of activity that can be considered “cometary,” although it is apparently very dark, as would be expected for an extinct, or dormant, cometary nucleus, and it is apparently quite large, almost 38 km in diameter.

Infrared image of (3552) Don Quixote obtained with the Spitzer Space Telescope on August 22, 2009. The stellar central condensation has been subtracted out, revealing the faint surrounding coma. Courtesy NASA/JPL-CalTech/ DLR/NAU.

Since Hidalgo’s discovery, many additional “asteroids” have been found traveling in cometary orbits, most of these discoveries having come within the past two decades as the comprehensive survey programs have become operational. Since they do not exhibit cometary activity they are not as easy to detect as are active comets, but their population must nevertheless be quite large, and in fact, in a 1994 paper planetary geologist Eugene Shoemaker and his colleagues estimated that, for every active Jupiter-family periodic comet, there may be as many as 18 or more inactive, or “extinct” such comets. At least some of these objects may be in shorter-period orbits like those of the Amor- and Apollo-type asteroids , and in fact in a 2008 paper Francesca DeMeo and Richard Binzel at MIT suggested that approximately 8% of the near-Earth “asteroid” population has a cometary origin. One recent and very interesting such object is 2015 TB145, discovered by the Pan-STARRS survey program in Hawaii, which passed just 1.3 lunar distances from Earth on October 31, 2015 it travels in a highly-elongated orbit (eccentricity 0.86) with a period of three years, and is very dark as a cometary nucleus would be expected to be.

Infrared image of (3552) Don Quixote obtained with the Spitzer Space Telescope on August 22, 2009. The coma has been subtracted out, revealing a faint tail. Courtesy NASA/JPL-CalTech/ DLR/NAU.

Occasionally one of these cometary “asteroids” is found to be exhibiting cometary activity at a very low level, indicating that they are not entirely “extinct” yet. A dramatic example is (3552) Don Quixote, discovered in 1983 by Paul Wild at Berne University in Switzerland it travels in an elongated orbit (eccentricity 0.71) with an orbital period of slightly under nine years. It had been recovered at every return since its discovery and had never exhibited cometary activity, until in 2013 when a team led by Michael Mommert (now at Northern Arizona University) announced that, in infrared data taken with the Spitzer Space Telescope during its return in 2009, Don Quixote exhibited a distinct coma and a faint tail roughly two arcminutes long. The Spitzer data is entirely consistent with sublimation of carbon dioxide and/or carbon monoxide , indicating that Don Quixote is indeed still exhibiting weak cometary activity. Mea nwhile, during Don Quixote’s most recent return in 2018 Mommert’s team detected a faint coma and a tail at optical wavelengths.

From an astronomical point of view, Halley-type comets, and even long-period comets, can also be considered as “periodic” comets, and thus a similar fate may await some of these objects as well. In February 1991 Rob McNaught at Siding Spring Observatory in New South Wales discovered the apparent asteroid now known as (5335) Damocles, which is traveling in a highly eccentric inclined orbit (eccentricity 0.87, inclination 62 degrees) with an orbital period of 41 years despite intense scrutiny, it was never seen to exhibit cometary activity. Then, in August 1996 the NEAT survey program in Hawaii discovered the apparent asteroid 1996 PW, which was found to be traveling in an almost parabolic orbit (eccentricity 0.99) with an approximate orbital period of 5600 years. It, too, never exhibited any cometary activity.

An example of a Damocloid. An image I took of A/2018 V3, a long-period object discovered by Pan-STARRS with an approximate orbital period of 1340 years, on August 20, 2019, with the Las Cumbres Observatory facility at the South African Astronomical Observatory.

With the advent of the comprehensive surveys, many more such objects, in both Halley-type and long-period orbits, have been discovered some of these even travel in retrograde orbits. Collectively, these objects are now referred to as “Damocloids .” Studies indicate that a small percentage of objects in the Oort Cloud may be asteroids in a physical sense and thus some of the Damocloids may indeed physically be asteroids, but it is likely that the large majority of them are extinct comets.

Despite all the ways that a comet can “die” and the large numbers of comets that have undoubtedly vanished over the lifetime of the solar system, the fact that even now, 4.6 billion years after the solar system formed, there still are as many comets as there are suggests that we will continue to see comets in our skies for as long as there are humans here to observe them. I have certainly found them to be fascinating objects to watch and study, and I hope that a t least a few “Ice and Stone 2020” participants will do so as well.