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Pluto - huidige teorieë oor die geologiese aard daarvan?

Pluto - huidige teorieë oor die geologiese aard daarvan?


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Die beelde van New Horizons van Pluto sal meer as 'n jaar neem om uit die ruimte te kom, met 'n paar saamgeperste beelde as voorskou.

Nasa het inligting rakende die geologies onaktiewe sone voorgehou, maar daar was geen inligting oor die vorming van die plato's en die berge oor die moontlike geologies aktiewe sones nie.

Watter kragte kan geotermiese aktiwiteit van watter aard op Pluto dryf? Wat kan geleer word uit die teorieë van die mane van Jupiter en Saturnus om aktiwiteit in Pluto te verstaan? Wat is die teoretiese temperatuur van die middel van die dwergplaneet?


Geotermiese aktiwiteit kan ontstaan ​​uit 'n kombinasie van:

  1. Resthitte van planeetvorming: Tydens die vorming van 'n planeet kan die helfte van die potensiële energie in die moedergebied van stof en gas teoreties omgeskakel word na kinetiese energie --- dit staan ​​bekend as die viriale stelling. Die kinetiese energie van die deeltjies vertaal na 'n temperatuur.

  2. Interne radioaktiwiteit: Ongeveer die helfte van die hitte van $ 4,5 keer 10 ^ {13} $ W wat uit die binneland van die aarde kom, word aangedryf deur radioaktiewe verval. Moet Pluto dieselfde hoeveelheid radioaktiewe materiale in sy samestelling hê? Sommige sal dit aanvaar, maar ander sal sê dat die swaarder radioaktiewe materiale tydens die vorming van die middelpunt van die sonnestelsel moes val en dus meestal in die binneste planete sou bestaan. Let daarop dat geotermiese aktiwiteit op Mars nou gestaak is, ondanks die feit dat dit baie groter is (Mars het 'n radius van $ 3400 $ km, terwyl die van Pluto $ 1200 $ is), so 'n kombinasie van resthitte en radioaktiewe verval is miskien onwaarskynlik in die geval van Pluto.

  3. Gety-effekte: Getykragte is basies van toepassing wanneer 'n deel van 'n planetêre liggaam mettertyd 'n veranderende swaartekragveld ervaar (sien getyverhitting) --- 'n aantal prosesse kan dit veroorsaak:
    • die maan het 'n elliptiese baan;
    • ekstra mane in die omgewing (relevant vir Io);
    • die maan se wentelperiode en die rotasieperiode van die planeet word nie gesinchroniseer nie;
    • nie-eenvormige digtheid in die planeet.

Met verloop van tyd moet die New Horizons-missie meer lig werp op hierdie $ 3 $ moontlikhede.

Let daarop dat die geotermiese aktiwiteit op Pluto waarskynlik eksplisiet verwys na stowwe soos stikstof, metaan, ensovoorts, waar baie minder energie benodig word om aktiwiteit aan te dryf; dit wil sê, die vermoë om silikate te smelt is lankal verby.


Pluto

Pluto (klein planeetbenaming: 134340 Pluto) is 'n dwergplaneet in die Kuiper-gordel, 'n ring van liggame anderkant die baan van Neptunus. Dit was die eerste en grootste voorwerp van die Kuiper-gordel wat ontdek is. Nadat Pluto in 1930 ontdek is, is dit tot die negende planeet van die son verklaar. Begin in die negentigerjare word sy status as 'n planeet bevraagteken na die ontdekking van verskeie voorwerpe van soortgelyke grootte in die Kuiper-gordel en die verspreide skyf, waaronder die dwergplaneet Eris. Dit het daartoe gelei dat die Internasionale Astronomiese Unie (IAU) in 2006 die term "planeet" formeel omskryf het - Pluto uitgesluit en herklassifiseer as 'n dwergplaneet.

Pluto is die negende grootste en tiende massigste voorwerp wat direk om die Son wentel. Dit is die grootste bekende trans-Neptuniese voorwerp volgens volume, maar is minder massief as Eris. Soos ander voorwerpe van die Kuiper-gordel, is Pluto hoofsaaklik gemaak van ys en rots en is dit relatief klein - 'n sesde van die massa van die maan en 'n derde van sy volume. Dit het 'n matige eksentrieke en skuins baan waartydens dit wissel van 30 tot 49 sterrekundige eenhede of AU (4,4-7,4 miljard km) vanaf die son. Dit beteken dat Pluto van tyd tot tyd nader aan die son kom as Neptunus, maar 'n stabiele baanresonansie met Neptunus voorkom dat hulle bots. Lig van die son neem 5,5 uur om Pluto op sy gemiddelde afstand (39,5 AU) te bereik.

Pluto het vyf mane wat bekend is: Charon (die grootste, met 'n deursnee van net meer as die van Pluto), Styx, Nix, Kerberos en Hydra. Pluto en Charon word soms as 'n binêre stelsel beskou, omdat die bary-sentrum van hul wentelbane nie binne een van die liggame lê nie.

Die Nuwe horisonne ruimtetuie het op 14 Julie 2015 'n vlieg van Pluto uitgevoer en die eerste en tot dusver enigste ruimtetuig geword om dit te doen. Tydens sy kort vlug, Nuwe horisonne het gedetailleerde metings en waarnemings van Pluto en sy mane gedoen. In September 2016 het sterrekundiges aangekondig dat die rooibruin kap van die noordpool van Charon bestaan ​​uit tholiene, organiese makromolekules wat bestanddele kan wees vir die ontstaan ​​van lewe, en geproduseer word uit metaan, stikstof en ander gasse wat vrygestel word uit die atmosfeer van Pluto. en 19 000 km (12 000 myl) na die wentelbaan oorgedra.


Toegangsopsies

Kry volledige joernaaltoegang vir 1 jaar

Alle pryse is NETPryse.
BTW sal later by die betaalpunt gevoeg word.
Belastingberekening sal tydens die betaalpunt gefinaliseer word.

Kry tydsbeperking of volledige artikeltoegang op ReadCube.

Alle pryse is NETPryse.


Kode wat verband hou met die implementering van metodes wat in hierdie studie aangebied word, sal op redelike versoek aan die ooreenstemmende outeur verskaf word.

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Intrilligator, D. S. & amp Smith, E. J. Mars in die sonwind. J. Geophys. Res. 84, 8427–8435 (1979).

Riedler, W. et al. Magnetiese velde naby Mars: eerste resultate. Aard 341, 604–607 (1989).

Lundin, L. Ionversnelling en uitvloei van Mars en Venus: 'n oorsig. Ruimte wetenskap. Ds. 162, 309–334 (2011).

Dong, Y. et al. Seisoenale wisselvalligheid van Mars-ioon ontsnap deur die pluim en stert van MAVEN waarnemings. J. Geophys. Res. Ruimte Fis. 122, 4009–4022 (2017).

Jakosky, B. M. & amp Phillips, R. J. Mars se vlugtige en klimaatsgeskiedenis. Aard 412, 237–244 (2001).

Mangold, N., Baratoux, D., Witasse, O., Encrenaz, T. & amp Sotin, C. Mars: 'n klein aardse planeet. Astron. Astrofis. Ds. 24, 15 (2016).

Baumjohann, W., Blanc, M., Fedorov, A. & amp Glassmeier, K.-H. Huidige stelsels in planetêre magnetosfere en ionosfere. Ruimte wetenskap. Ds. 152, 99–134 (2010).

Ramstad, R., Barabash, S., Futaana, Y., Nilsson, H. & amp Holmström, M. Global Mars – solar wind coupling and ion escape. J. Geophys. Res. Ruimte Fis. 122, 8051–8062 (2017).

Nilsson, H., Barghouti, I. A., Slapak, R., Eriksson, A. I. & amp André, M. Uitvloeiing van warm en koue ione: ruimtelike verspreiding van ioonverwarming. J. Geophys. Res. Ruimte Fis. 117, A11201 (2012).

Li, K. et al. Uitvloei van koue ione gemoduleer deur die insette van die windenergie en die kanteling van die geomagnetiese dipool. J. Geophys. Res. Ruimte Fis. 122, 10658–10668 (2017).

Arridge, S. A. & amp Martin, C. J. in Elektriese strome in Geospace and Beyond (reds. Keiling, A., Marghitu, O. & amp Wheatland, M.) 191–205 (Wiley, 2018).

Chapman, S. & amp Ferraro, V. C. A. 'n Nuwe teorie oor magnetiese storms. Terr. Magn. Atmos. Elekt. 36, 77–97 (1931).

Axford, W. I., Petschek, H. E. & amp Siscoe, G. L. Stert van die magnetosfeer. J. Geophys. Res. 7, 1231–1236 (1965).

Volland, H. 'n Halfempiriese model van grootskaalse magnetosferiese elektriese velde. J. Geophys. Res. Ruimte Fis. 78, 171–180 (1973).

Ganushkina, N. Yu., Liemohn, M. W. & amp Dubyagin, S. Huidige stelsels in die Aarde se magnetosfeer. Ds Geophys. 56, 309–332 (2018).

Cloutier, P. A. & amp Daniell, R. E. Ionosferiese strome geïnduseer deur sonwindinteraksie met planetêre atmosfeer. Planeet. Ruimte wetenskap. 21, 463–474 (1973).

Daniell, R. E. & amp Cloutier, P. A. Verspreiding van ionosferiese strome geïnduseer deur die sonwindinteraksie met Venus. Planeet. Ruimte wetenskap. 25, 621–628 (1977).

Luhmann, J. G. Deurdringende grootskaalse magnetiese velde in die Venus-nagkant-ionosfeer en die implikasies daarvan. J. Geophys. Res. 97, 6103–6121 (1992).

Acuña, M. H. et al. Magnetiese veld- en plasma-waarnemings by Mars: aanvanklike resultate van die Mars Global Surveyor Mission. Wetenskap 279, 1676–1680 (1998).

Gringauz, K. I. 'n Vergelyking van die magnetosfere van Mars, Venus en Aarde. Ann. Ruimte Res. 1, 5–24 (1981).

Li, L., Xie, L., Zhang, Y. & amp Liu, T. Modelondersoek van huidige stelsel en invloed van die korsvelde op die grootskaalse struktuur van huidige velle by Mars. Planeet. Ruimte wetenskap. 86, 80–85 (2013).

Vernisse, Y., Riousset, J. A., Motschmann, U. & amp Glassmeier, K. H. Simulasies van sterwind en planetêre liggame: ionosfeerryke struikelblokke in 'n super-Alfvéniese vloei. Planeet. Ruimte wetenskap. 137, 64–72 (2017).

Jakosky, B. M. et al. Die Mars atmosfeer en vlugtige evolusie (MAVEN) missie. Ruimte wetenskap. Ds. 195, 3–48 (2015).

Connerney, J. E. P. et al. Die MAVEN magnetiese veld ondersoek. Ruimte wetenskap. Ds. 195, 257–291 (2015).

Dunlop, M. W., Southwood, D. J., Glassmeier, K. H. & amp Neubauer, F. M. Analise van data van meerpuntmagnetometer. Adv. Ruimte Fis. 8, 9–10 (1988).

Escoubet, C. P., Fehringer, M. & amp Goldstein, M. The Cluster mission. Ann. Geophys. 19, 1197–1200 (2001).

Burch, J. L., Moore, T. E., Torbert, R. B. & amp Giles, B.-L. Magnetosferiese multiskaaloorsig en wetenskaplike doelstellings. Ruimte wetenskap. Ds. 199, 5–21 (2015).

Dubinin, E. et al. Plasma-eienskappe van die grenslaag in die magnetiese sfeer van die Mars. J. Geophys. Res. Ruimte Fis. 101, A12 (1996).

Luhmann, J. G., Ledvina, S. A. & amp Russell, C. T. Geïnduseerde magnetosfere. Adv. Ruimte wetenskap. 33, 1905–1912 (2004).

DiBraccio, G. A. et al. Die gedraaide konfigurasie van die Mars-magnetotail: MAVEN waarnemings. Geophys. Res. Lett. 45, 4559–4568 (2018).

Fillingim, M. in Elektriese strome in Geospace and Beyond (reds. Keiling, A., Marghitu, O., & amp Wheatland, M.) 445–458 (Wiley, 2018).

Opgenoorth, H. J. et al. Ionosferiese geleidings op die dag by Mars. Planeet. Ruimte wetenskap. 58, 1139–1151 (2010).

Dubinin, E. et al. Plasma-omgewing van Mars soos waargeneem deur gelyktydige MEX-ASPERA-3 en MEX-MARSIS waarnemings. J. Geophys. Res. 113, A10217 (2008).

Halekas, J. S. et al. Vloei, velde en kragte in die interaksie tussen die wind en die son van Mars. J. Geophys. Res. Ruimte Fis. 122, 11320–11341 (2017).

Lyons, L. R. & amp Speiser, T. W. Ohm se wet vir 'n huidige blad. J. Geophys. Res. 90, 8543–8546 (1985).

Dubinin, E. et al. Die effek van sonwindvariasies op die ontsnapping van suurstofione vanaf Mars deur verskillende kanale: MAVEN waarnemings. J. Geophys. Res. Ruimte Fis. 122, 11285–11301 (2017).

Chai, L. et al. Die geïnduseerde wêreldwye lusmagnetiese veld op Mars. Astrofis. J. Lett. 871, L27 (2019).

Chai, L. et al. 'N Geïnduseerde wêreldwye magnetiese veld wat rondom die magnetostaart van Venus loop. J. Geophys. Res. Ruimte Fis. 121, 688–698 (2016).

Dubinin, E. et al. Toroïdale en poloïdale magnetiese velde by Venus. J. Geophys. Res. 87, 19–29 (2013).

Marquette, M. L. et al. Outokorrelasiestudie van sonwindplasma en IMF-eienskappe soos gemeet deur die MAVEN-ruimtetuig. J. Geophys. Res. Ruimte Fis. 123, 2493–2512 (2018).

Halekas, J. S. et al. Die son wind ioon ontleder vir MAVEN. Ruimte wetenskap. Ds. 195, 125–151 (2015).

McComas, D. J., Spence, H. E., Russell, C. T. & amp Saunders, M. A. Die gemiddelde magneetvelddrapering en konsekwente plasma-eienskappe van die Venus magnetotail. J. Geophys. Res. Ruimte Fis. 91, 7939–7953 (1986).

Liemohn, M. W. et al. Ionosferiese beheer van die asimmetrie van die dagbreek-skemer van die Mars-magnetotail-stroomblad. J. Geophys. Res. Ruimte Fis. 122, 6397–6414 (2017).

Riousset, J. A. et al. Elektrodinamika van die Mars-dinamostreek naby magnetiese knoppies en lusse. Geophys. Res. Lett. 41, 1119–1125 (2015).


Inhoud

Ontdekking

In die 1840's het Urbain Le Verrier Newtonse meganika gebruik om die posisie van die destyds onontdekte planeet Neptunus te voorspel nadat hy steurings in die baan van Uranus geanaliseer het. [15] Daaropvolgende waarnemings van Neptunus in die laat 19de eeu het gelei dat sterrekundiges bespiegel dat Uranus se baan deur 'n ander planeet buiten Neptunus versteur word.

In 1906 het Percival Lowell - 'n welgestelde Bostonian wat in 1894 Lowell Observatory in Flagstaff, Arizona, gestig het - met 'n uitgebreide projek begin op soek na 'n moontlike negende planeet, wat hy 'Planet X' genoem het. [16] Teen 1909 het Lowell en William H. Pickering verskeie moontlike hemelse koördinate vir so 'n planeet voorgestel. [17] Lowell en sy sterrewag het sy soektog uitgevoer tot sy dood in 1916, maar dit was tevergeefs. Onbekend vir Lowell, het sy opnames twee dowwe beelde van Pluto op 19 Maart en 7 April 1915 vasgelê, maar dit is nie erken vir wat dit was nie. [17] [18] Daar is veertien ander bekende voorafgaande waarnemings, waarvan die vroegste op 20 Augustus 1909 deur die Yerkes-sterrewag gemaak is. [19]

Percival se weduwee, Constance Lowell, het 'n regstryd van tien jaar met die Lowell-sterrewag gevoer oor die nalatenskap van haar man, en die soeke na Planet X het eers in 1929 hervat. Planet X opspoor na die 23-jarige Clyde Tombaugh, wat pas by die sterrewag aangekom het nadat Slipher onder die indruk was van 'n voorbeeld van sy astronomiese tekeninge. [20]

Tombaugh se taak was om die naghemel stelselmatig in pare foto's af te beeld, dan elke paar te ondersoek en vas te stel of enige voorwerpe verskuif het. Met behulp van 'n knipvergelyker skuif hy vinnig heen en weer tussen die aansigte van elk van die plate om die illusie van beweging te skep van voorwerpe wat die posisie of voorkoms tussen foto's verander het. Op 18 Februarie 1930, ná bykans 'n jaar se soektog, ontdek Tombaugh 'n moontlike bewegende voorwerp op fotografiese plate wat op 23 en 29 Januarie geneem is. 'N Foto van minder gehalte wat op 21 Januarie geneem is, het die beweging help bevestig. [21] Nadat die sterrewag verdere bevestigende foto's gekry het, is die nuus oor die ontdekking op 13 Maart 1930 aan die Harvard College Observatory getelegrafeer. [17]

Pluto moet nog 'n volle baan van die son voltooi sedert sy ontdekking, aangesien een Plutoniese jaar 247,68 jaar lank is. [22]

Die ontdekking het opslae regoor die wêreld gehaal. [23] Lowell Observatory, wat die reg gehad het om die nuwe voorwerp te benoem, het meer as 1 000 voorstelle van regoor die wêreld ontvang, wat wissel van Atlas tot Zymal. [24] Tombaugh het Slipher aangemoedig om vinnig 'n naam vir die nuwe voorwerp voor te stel voordat iemand anders dit doen. [24] Constance Lowell voorgestel Zeus, dan Percival en uiteindelik Konstansie. Hierdie voorstelle is buite rekening gelaat. [25]

Die naam Pluto, na die Romeinse god van die onderwêreld, is voorgestel deur Venetia Burney (1918–2009), 'n elfjarige skoolmeisie in Oxford, Engeland, wat geïnteresseerd was in klassieke mitologie. [26] Sy het dit voorgestel in 'n gesprek met haar oupa Falconer Madan, 'n voormalige bibliotekaris aan die Bodleian-biblioteek van die Universiteit van Oxford, wat die naam deurgegee het aan astronomieprofessor Herbert Hall Turner, wat dit aan kollegas in die Verenigde State gekabel het. [26]

Elke lid van die Lowell-sterrewag is toegelaat om op 'n kortlys met drie moontlike name te stem: Minerva (wat al die naam vir 'n asteroïde was), Cronus (wat reputasie verloor het deur voorgestel te word deur die ongewilde sterrekundige Thomas Jefferson Jackson See) , en Pluto. Pluto het 'n eenparige stem ontvang. [27] Die naam is op 1 Mei 1930 aangekondig. [26] [28] Na die aankondiging het Madan Venetia £ 5 (gelykstaande aan 300 GBP, oftewel 450 USD in 2014) [29] as beloning gegee. [26]

Die finale keuse van die naam is deels aangehelp deur die feit dat die eerste twee letters van Pluto is die voorletters van Percival Lowell. Pluto se astronomiese simbool (, Unicode U + 2647, ♇) is toe geskep as 'n monogram wat saamgestel is uit die letters "PL". [30] Pluto se astrologiese simbool lyk soos dié van Neptunus (), maar het 'n sirkel in die plek van die middelste punt van die drietand ().

Die naam is gou deur die breër kultuur omhels. In 1930 is Walt Disney blykbaar daardeur geïnspireer toe hy vir Mickey Mouse 'n hondegenoot met die naam Pluto bekendgestel het, hoewel Disney-animator Ben Sharpsteen nie kon bevestig waarom die naam gegee is nie. [31] In 1941 noem Glenn T. Seaborg die nuutgeskepte element plutonium na Pluto, in ooreenstemming met die tradisie om elemente na pas ontdekte planete te noem, na uraan, wat na Uranus vernoem is, en neptunium, wat na Neptunus vernoem is. [32]

Die meeste tale gebruik die naam "Pluto" in verskillende transliterasies. [h] In Japannees het Houei Nojiri die vertaling voorgestel Meiōsei (冥王星, "Star of the King (God) of the Underworld"), en dit is geleen aan Chinees, Koreaans en Viëtnamese (wat eerder "Sao Diêm Vương" gebruik, wat afgelei is van die Chinese term 閻王 (Yánwáng), as 'minh' is 'n homofoon vir die Sino-Viëtnamese woorde vir 'donker' (冥) en 'helder' (明)). [33] [34] [35] Sommige Indiese tale gebruik die naam Pluto, maar ander, soos Hindi, gebruik die naam van Yama, die God van die dood in die Hindoe en Boeddhistiese mitologie. [34] Polinesiese tale gebruik ook die inheemse god van die onderwêreld, soos in Māori Whiro. [34]

Planeet X weerlê

Nadat Pluto gevind is, het die floutheid en die gebrek aan 'n oplosbare skyf die idee dat dit Lowell se Planet X was, betwyfel. [16] Die ramings van Pluto se massa is gedurende die 20ste eeu afwaarts hersien. [36]

Massa ramings vir Pluto
Jaar Massa Skat deur
1915 7 Aarde Lowell (voorspelling vir Planet X) [16]
1931 1 Aarde Nicholson & amp Mayall [37] [38] [39]
1948 0,1 (1/10) Aarde Kuiper [40]
1976 0,01 (1/100) Aarde Cruikshank, Pilcher en amp. Morrison [41]
1978 0.0015 (1/650) Aarde Christy & amp Harrington [42]
2006 0.00218 (1/459) Aarde Buie et al. [43]

Sterrekundiges het die massa aanvanklik bereken op grond van die vermeende effek daarvan op Neptunus en Uranus. In 1931 is die berekening van Pluto ongeveer die massa van die aarde, met verdere berekeninge in 1948 wat die massa tot ongeveer die van Mars afgebring het. [38] [40] In 1976 bereken Dale Cruikshank, Carl Pilcher en David Morrison van die Universiteit van Hawaii vir die eerste keer die albedo van Pluto en vind dat dit ooreenstem dat dit vir metaanys beteken dat Pluto buitengewoon helder moes wees vir sy grootte en kan dus nie meer as 1 persent van die aarde se massa wees nie. [41] (Pluto se albedo is 1,4-1,9 keer dié van die Aarde. [2])

In 1978 het die ontdekking van Pluto se maan Charon vir die eerste keer die meting van die massa van Pluto toegelaat: ongeveer 0,2% dié van die aarde, en heeltemal te klein om die verskille in die baan van Uranus te kan verantwoord. Daaropvolgende soektogte na 'n alternatiewe Planet X, veral deur Robert Sutton Harrington, [44] het misluk. In 1992 gebruik Myles Standish data van Voyager 2 'se vlieg van Neptunus in 1989, wat die ramings van Neptunus se massa met 0,5% afwaarts hersien het - 'n bedrag wat vergelykbaar is met die massa van Mars - om die swaartekrageffek daarvan op Uranus te herbereken. Met die nuwe syfers wat bygevoeg is, het die teenstrydighede en daarmee saam die behoefte aan 'n planeet X verdwyn. [45] Vandag is die meerderheid wetenskaplikes dit eens dat Planet X, soos Lowell dit gedefinieer het, nie bestaan ​​nie. [46] Lowell het in 1915 'n voorspelling gemaak van die baan en posisie van Planet X wat taamlik naby aan Pluto se werklike baan was, en Ernest W. Brown se bevinding op daardie tydstip het ná die ontdekking van Pluto tot die gevolgtrekking gekom dat dit toevallig was. [47]

Klassifikasie

Vanaf 1992 is daar baie liggame ontdek wat in dieselfde volume as Pluto wentel, wat wys dat Pluto deel is van 'n bevolking voorwerpe genaamd die Kuiper-gordel. Dit het sy amptelike status as 'n planeet kontroversieel gemaak, en baie het gevra of Pluto saam met of afsonderlik van sy omliggende bevolking oorweeg moet word. Museum- en planetariumregisseurs het soms kontroversie geskep deur Pluto uit te laat van die planetêre modelle van die sonnestelsel. In Februarie 2000 vertoon die Hayden Planetarium in New York 'n sonnestelsel-model van slegs agt planete, wat byna 'n jaar later opslae gemaak het. [48]

Ceres, Pallas, Juno en Vesta het hul planeetstatus verloor nadat baie ander asteroïdes ontdek is. Net so is voorwerpe wat al hoe nader aan Pluto is, in die Kuiper-gordelstreek ontdek. Op 29 Julie 2005 kondig sterrekundiges by Caltech die ontdekking aan van 'n nuwe trans-Neptuniese voorwerp, Eris, wat aansienlik massiewer was as Pluto en die mees massiewe voorwerp wat sedert Triton in 1846 in die Sonnestelsel ontdek is. Die ontdekkers en die pers was aanvanklik het dit die tiende planeet genoem, hoewel daar destyds geen amptelike konsensus bestaan ​​of dit 'n planeet genoem moet word nie. [49] Ander in die astronomiese gemeenskap beskou die ontdekking as die sterkste argument om Pluto as 'n minderjarige planeet te herklassifiseer. [50]

IAU-klassifikasie

Die debat het in Augustus 2006 tot 'n punt gekom met 'n IAU-resolusie wat 'n amptelike definisie vir die term "planeet" geskep het. Volgens hierdie resolusie is daar drie voorwaardes om 'n voorwerp in die sonnestelsel as 'n planeet te beskou:

  1. Die voorwerp moet om die son wentel.
  2. Die voorwerp moet massief genoeg wees om deur sy eie swaartekrag afgerond te word. Meer spesifiek, sy eie swaartekrag moet dit trek in 'n vorm wat gedefinieer word deur hidrostatiese ewewig.
  3. Dit moes die omgewing rondom sy baan skoongemaak het. [51] [52]

Pluto voldoen nie aan die derde voorwaarde nie. [53] Die massa daarvan is aansienlik minder as die gesamentlike massa van die ander voorwerpe in sy baan: 0,07 keer, in teenstelling met die aarde, wat 1,7 miljoen keer die oorblywende massa in sy baan is (die maan uitgesluit). [54] [52] Die IAU het verder besluit dat liggame wat soos Pluto aan kriteria 1 en 2 voldoen, maar nie aan kriterium 3 voldoen nie, dwergplanete genoem sal word. In September 2006 het die IAU Pluto, en Eris en sy maan Dysnomia, opgeneem in hul Minor Planet Catalog, wat hulle die amptelike klein planeetbenamings "(134340) Pluto", "(136199) Eris" en "(136199) Eris I gegee het. Dysnomie ". [55] As Pluto by sy ontdekking in 1930 opgeneem is, sou hy waarskynlik 1164 aangewys word na aanleiding van 1163 Saga, wat 'n maand tevore ontdek is. [56]

Daar was weerstand in die astronomiese gemeenskap teen die herklassifikasie. [57] [58] [59] Alan Stern, hoofondersoeker by NASA's Nuwe horisonne sending na Pluto, bespot die IAU-resolusie en verklaar dat "die definisie stink, om tegniese redes". [60] Stern beweer dat, volgens die terme van die nuwe definisie, Aarde, Mars, Jupiter en Neptunus, wat almal hul wentelbane met asteroïdes deel, uitgesluit sou word. [61] Hy het aangevoer dat alle groot bolvormige mane, ook die Maan, ook as planete beskou moet word. [62] Hy het ook verklaar dat omdat minder as vyf persent van die sterrekundiges daarvoor gestem het, die besluit nie verteenwoordigend van die hele astronomiese gemeenskap was nie. [61] Marc W. Buie, toe by die Lowell-sterrewag, het 'n beroep op die definisie gedoen. [63] Ander het die IAU ondersteun. Mike Brown, die sterrekundige wat Eris ontdek het, het gesê: "deur hierdie hele gekke, sirkusagtige prosedure is die regte antwoord op die een of ander manier gestruikel. Dit kom al lank. Die wetenskap korrigeer uiteindelik, selfs wanneer sterk emosies betrokke is. " [64]

Die openbare ontvangs van die IAU-besluit was gemeng. In 'n resolusie wat in die Kaliforniese staatsvergadering ingedien is, word die IAU-beslissing 'n "wetenskaplike dwaalleer" genoem. [65] Die Huis van Afgevaardigdes in New Mexico het 'n resolusie geneem ter ere van Tombaugh, 'n jarelange inwoner van die staat, wat verklaar het dat Pluto altyd as 'n planeet beskou sal word terwyl hy in die Nieu-Mexikaanse lug is en dat Pluto Planet Day op 13 Maart 2007 was. . [66] [67] Die Senaat van Illinois het in 2009 'n soortgelyke resolusie aangeneem op grond daarvan dat Clyde Tombaugh, die ontdekker van Pluto, in Illinois gebore is. In die resolusie word beweer dat Pluto deur die IAU 'onregverdig afgegradeer is tot 'n' dwerg-planeet '.' [68] Sommige lede van die publiek het ook die verandering verwerp en verwys na die meningsverskil in die wetenskaplike gemeenskap oor die kwessie, of om sentimentele redes. , met die feit dat hulle Pluto nog altyd as 'n planeet geken het en sal voortgaan om dit te doen ongeag die IAU-besluit. [69]

In 2006 het die American Dialect Society in sy 17de jaarlikse stem-tot-jaar-stem gestem geploeter as die woord van die jaar. Om te "pluto" is om iemand of iets te degradeer of te waardeer. [70]

Navorsers aan beide kante van die debat het in Augustus 2008 by die Johns Hopkins University Applied Physics Laboratory bymekaargekom vir 'n konferensie wat rugbysprekke oor die huidige IAU-definisie van 'n planeet ingesluit het. [71] Met die titel "The Great Planet Debate", [72] het die konferensie 'n persverklaring na die konferensie gepubliseer wat aandui dat wetenskaplikes nie tot 'n konsensus kon kom oor die definisie van planeet nie. [73] In Junie 2008 het die IAU in 'n persverklaring aangekondig dat die term "plutoid" voortaan gebruik sou word om te verwys na Pluto en ander planeetmassa-voorwerpe wat 'n halfas-as het wat groter is as dié van Neptunus. die term het geen noemenswaardige gebruik gesien nie. [74] [75] [76]


Pluto en sy botsingsbaan in ons sonnestelsel

Daar is nog net ure om te gaan voordat die New Horizons-ruimtetuig op Dinsdag 14 Julie (ongeveer 22:00 AEST) verby Pluto sal skeur, wat ons die eerste beeld van die raaiselagtige dwergplaneet gee.

As dit verby vlieg, sal die sewe instrumente aan boord elke oomblik van hul vlugtige ontmoeting vasvang.

In die daaropvolgende maande sal die data na die aarde terugsak en belangrike leidrade bied om die verhaal van ons sonnestelsel en evolusie saam te stel.

Maar wat weet ons al van Pluto en sy plek in ons sonnestelsel?

Die meeste wetenskap is oor die algemeen eksperimenteel. As u wil uitvind hoe iets werk, kan u dit met 'n hamer slaan, dit in 'n proefbuis kook of deur 'n ingewikkelde doolhof laat loop - u kry die idee.

Sterrekunde is daarenteen 'n waarnemingswetenskap. Ons kan nie regtig eksperimenteer nie (behalwe deur slim gebruik van rekenaars). In plaas daarvan versamel ons waarnemings en gebruik dit om die verhaal saam te stel oor hoe, wanneer, waarom en waar iets gebeur het.

Die heelal is dus 'n misdaadtoneel, en sterrekundiges is die speurders wat die leidrade ondersoek. Pluto, en sy broers in die ruimte anderkant die planete, is veral belangrike leidrade vir sterrekundiges wat ons sonnestelsel en die verlede bestudeer.

Sterrekunde, 'n waarnemingswetenskap, plaas sterrekundiges in die rol van speurders wat die heelal rondom ons probeer ontwrig. xkcd, CC BY-NC-SA

Pluto - 'n hemelse vreemde bal

In die jare sedert dit in 1930 ontdek is, het sterrekundiges baie oor Pluto geleer. Dit was 'n baie ongewone voorwerp.

Dit is baie reflekterend en straal 'n sagte atmosfeer uit as dit die naaste aan die son is. Daarbenewens het dit 'n familie satelliete, insluitend die bek Charon, 'n bietjie meer as 1 200 km in deursnee, dit is net meer as die helfte van die Pluto-grootte.

Pluto en Charon, soos voorgestel deur New Horizons op 8 Julie 2015. NASA-JHUAPL-SWRI

Die baan van Pluto & # x2019 is duidelik nie-sirkelvormig of eksentriek nie. Op sy naaste aan die son ('n afstand van 4,44 miljard km) gaan Pluto binne die baan van Neptunus, terwyl dit amper drie miljard kilometer verder weg is.

Die baan van Pluto & # x2019 word ook ongeveer 17 grade gekantel of geneig tot die vlak van die sonnestelsel. Pluto dwaal ver bo en ver onder die ander planete tydens elke 248-jarige baan.

Die eienaardighede eindig nie daar nie. As u paaie met Neptunus kruis, kan u verwag dat Pluto uiteindelik naby daardie planeet sal kom en moontlik selfs daarin kan neerstort. Maar dit vermy so 'n lot as gevolg van iets wat 'n gemiddelde-resonansie genoem word.

Die baan van Pluto & # x2019 duur ongeveer 50% langer as dié van Neptunus & # x2019's (164 jaar). Pluto voltooi dus twee volle ronde van die son ongeveer die tyd wat dit Neptunus neem om drie te voltooi. Dit voorkom noue ontmoetings tussen Pluto en Neptunus. Elke keer as Pluto die baan van Neptunus & # x2019 kruis, is Neptunus elders.

Dit werk so: op die eerste baan slaan Pluto Neptunus tot op die punt waar hul wentelbane kruis, en die twee vermy 'n groot botsing. Teen die tyd dat Pluto 'n ander baan voltooi het, het Neptunus anderhalf jaar voltooi, wat beteken dat dit nou voor Pluto voorafgaan, en 'n botsing word weer vermy. Na nog 'n Plutonian-jaar keer die twee terug na waar hulle begin het, en die dans begin weer.

Omdat Neptunus drie wentelbane voltooi in die tyd wat Pluto twee voltooi, sê ons dat hulle vasgevang is in 3: 2-gemiddelde-resonansie. En dit is hierdie resonansie wat die sleutel is tot die begrip van die vorming van die sonnestelsel.

Pluto En Planeet Formasie

Ons huidige beste teorie is dat die sonnestelsel gevorm word uit 'n gas- en stofryke protoplanetêre skyf - baie soos dié waargeneem rondom jong sterre in die Orion-newel.

Hubblecast 32: The Proplyds in the Orion Nebula

Vir planete, dwergplanete en ander verskillende puin wat in so 'n omgewing moet vorm, moet die skyf dinamies koud wees, met ander woorde so plat soos 'n pannekoek.

In daardie scenario bots die klein stukkies stof en ys op die skyf teen so 'n lae spoed dat dit aanmekaar kan plak, eerder as om mekaar uitmekaar te slaan.

Snel vorentoe ontelbare botsings oor 'n paar tien miljoene jare en 'n planetêre stelsel word gebore.

Dit is 'n verrassend suksesvolle model en pas die leidrade wat ons waarneem, beter as enige van sy mededingers. Maar met die eerste oogopslag lyk dit asof die eienaardige wentelbaan van Pluto die verhaal weerspreek. As Pluto so gevorm het, waarom beweeg hy dan op so 'n eksentrieke en skuins baan?

En Pluto is nie alleen nie. Ons weet nou van 'n groot aantal voorwerpe buite die baan van Neptunus, waarvan baie ook vasgevang is in resonansie met Neptunus en beweeg op skuins en / of eksentrieke wentelbane. Hulle is beslis nie wat u kan verwag van 'n bevolking wat gebore is uit 'n dun, koue skyfie materiaal nie.

Die hellingsbaan van die sonnestelsel en klein liggame, buite Saturnus & # 39; s baan. Wikimedia, CC BY-SA

En so het ons 'n idee in die vorm van die eksentrisiteite en neigings van Pluto en die ander Plutinos. Maar wat beteken dit?

Pluto as die maatstaf van migrasie

Namate ons modelle van planeetvorming meer gesofistikeerd geraak het, is die eenvoudige prentjie wat ons planete op hul huidige wentelbane gevorm het, omvergewerp.

Op grond van die bewyse wat in die sonnestelsel en die klein liggaamsbevolking bevries is, dink ons ​​nou dat Jupiter, Saturnus, Uranus en Neptunus migreer terwyl hulle groei, en versprei om hul huidige verspreide argitektuur te bereik.

Veral Neptunus was 'n groot swerwer, met sommige modelle wat daarop dui dat dit tussen een en twee miljard kilometer nader aan die son gevorm het as wat ons dit tans sien. Maar hoe kan ons dit vertel?

Die antwoord? Pluto & # x2019 se eienaardige wentelbaan en die van die Plutinos.

Die bewys vir die groot reis van Neptunus & # x2019

Terwyl die planete gevorm het, met Neptunus baie nader aan die son as vandag, was daar 'n magdom puin (planeetdiere) verder buite. Terwyl Neptunus gevoed het en die materiaal die naaste daaraan verslind, het dit materiaal na binne uit hierdie trans-Neptuniese streek versprei en in die proses na buite begin dryf.

Neptune & # x2019 se Great Dark Spot en sy metgesel helder vlek soos vasgelê deur Voyager 2. NASA

Namate Neptunus beweeg het, het die ligging van sy resonansies ook gedoen. Voorwerpe is gevang toe die planeet na buite gevee het, gedwing om in die slotstap met die reus te beweeg.

Namate dit verder gereis het, het Neptunus meer voorwerpe verstrik. Sodra dit gevang is, het min ontsnap, en die res is onverbiddelik na buite gedra en voor die reuse-planeet gevee. Terwyl hulle gedruk is, het die krag wat hulle gedryf het, hul wentelbane opgewek en hul eksentrisiteite en neigings verhoog.

Uiteindelik het die migrasie van Neptunus byna opgehou, en die bevolking van Plutinos was bevrore soos wat ons vandag waarneem - die leidraad wat die omvang van die vinnige opmars van Neptunus onthul.

'N Goed gereisde raaisel

Dit bring ons terug na Pluto. Vanuit sy baan en die skakel na Neptunus kan ons sien dat Neptunus nader aan die son moes gevorm het en dan na buite moes beweeg.

Dit beteken ook dat Pluto nader aan die son moes gevorm het as sy huidige baan. Ons kan skat waar dit tot 'n sekere mate gevorm het op grond van die huidige opwinding daarvan.

En dit is hier waar ons by die held van die uur kom - die New Horizons-ruimtetuig. Die metings wat die sonde in die komende ure maak wanneer dit Pluto verbygaan, moet ons 'n onafhanklike maatstaf gee van waar dit gevorm is, en 'n belangrike nuwe leidraad by die mengsel voeg.

Sal dit ons teorieë ondersteun, of sal ons weer van vooraf moet begin? We will have to see what the data reveals, and that’s part of the beauty and thrill of the observational detective missions such as these.

Jonti Horner is Vice Chancellor&aposs Senior Research Fellow at University of Southern Queensland.
Jonathan P. Marshall is Vice Chancellor&aposs Post-doctoral Research Fellow at UNSW Australia.

This article was originally published on The Conversation. Read the original article.


How Does Position Affect Geology?

The goal of the study was to compare and contrast the geological features between Mercury and Pluto. These two bodies were chosen due to their extreme orbital radius differences in relation to the sun, with their overall size being quite similar. The data for this study was obtained by focusing on two particular satellite missions: MESSENGER, which explored Mercury, and New Horizon, which explored Pluto. Through this data the geological similarities and differences were compared.

(Image from: https://www.engadget.com/2015/09/13/solar-system-simulation-music/)

Mercury is approximately 100 times closer to the Sun than the dwarf planet Pluto. Pluto has an orbital radius of approximately 5,913,000, 000 kilometers from the sun while Mercury has a radius of 57,900,000 kilometers[1] They are similar in regards to their size, with Mercury having a diameter of 4,878 km, Pluto’s being 2,274 km. Comparing this to the diameter of Earth, (12,756 km) shows these planets are quite small in comparison. Pluto and Mercury are similar in the sense they are both composed of hard materials. However, their geological characteristics are very different: Mercury has no atmosphere with extreme weather fluctuations, while Pluto maintains extremely cold temperatures and is covered by various elemental ices.

Recent explorations, such as New Horizon’s 2015 fly-by of Pluto and the 2011-2015 MESSENGER exploration of Mercury have provided a plethora of new information of these formerly elusive entities, including a clearer picture of how their distance to the Sun affected their formation and geology. For the purposes of clarity, we will first discuss the individual characteristics of Mercury and Pluto, and then briefly compare the two, while considering how the extreme differences in distance from the Sun may have affected their current states.

Mercury: The Innermost Planet

Moler, 04/06/2016 – Ephemeris Mercury – Mercury Makes its Spring Appearance in the West – Plus Jovian Moon Hijinx, http://scholar.aci.info/view/149e1a4c20f4e24013c/153ea2ff10a00014c45

The temperature of Mercury demonstrates extreme fluctuations depending on where the planet is in its elliptical orbit. Mercury’s closest orbital radius is 47 million kilometers from the sun and 70 million kilometers from the sun at it’s farthest orbital radius. [2] Due to Mercury’s proximity to the sun, it can reach temperatures as high as 430 degrees Celsius during the day. [3] Due to the lack of an atmosphere, Mercury has difficulty retaining heat. This causes a large temperature fluctuation between night and day, with Mercury’s nighttime temperature reaching lows of -170 degrees Celsius. [4]

These extreme temperature fluctuations have caused the planet to be very dense, and its composition includes sulfur and iron in the core, while its crust and mantle are made primarily of silicate. [5] Much of what we know about Mercury comes from the Mariner 10 mission in 1973, where approximately 45 percent of Mercury’s surface was observed, and subsequent radar observations indicate that the planet may have water ice at both its north and south poles, made possible by deep craters that maintain frigid temperatures.

(Image from: http://www.space.com/18301-mariner-10.html)

The MESSENGER mission revealed that volcanic material and dried lava flows cover the majority of the planet’s surface, which is a strong indication of historic volcanic activity. [6] This mission also showed the surface to contain enigmatic flat and shallow bright spots, which scientists suggest form when volatile material from the surface was eroded due to solar wind.

The Particulars of Pluto

Much of what we know about Pluto comes from NASA’s New Horizons mission, which was launched with the purpose of exploring Pluto and the Kuiper Belt. It was launched shortly after Pluto lost its classification as a planet, and was intended to explore both the newly designated dwarf planet and the other objects that lay more than a billion miles beyond Neptune’s orbit. [7] The New Horizons team has been diligently publishing their findings in a variety of academic journals since July 2015, which has provided invaluable information regarding the dwarf planet’s geography and atmospheric components.

Image from: (http://www.nasa.gov/feature/putting-pluto-s-geology-on-the-map)

Pluto has some very interesting geological features, ranging from its composition, to its mountainous landforms, and an interesting atmospheric makeup. Mountains can be seen rising 2-3 km above their surroundings, and are likely composed of water-ice bedrock. [9] This can not be said with any certainty, however scientists have concluded this to be the most likely explanation, as there are limited materials that would allow mountains to form and maintain their shapes over millions of years in the temperatures that Pluto is subject to.

Methane ice is common at high altitudes and on what is known as the “winter hemisphere,” which contributes to some of Pluto’s more unusual landforms. [10] There is substantial

Image from: (http://www.nasa.gov/feature/putting-pluto-s-geology-on-the-map)

compositional variation throughout the planet, and evidence of a water-ice rich crust, a relatively young surface, wind streaks, and other curious characteristics. [11] The New Horizon’s encounter was invaluable in collecting this data, and indicates that other small planets deep in the Kuiper Belt could have similarly complex geological histories, while the diversity of Pluto’s geology and long-term activity raises questions about how Pluto it has remained tectonically active so long after its formation. [12] One theory about this tectonic activity is the partial freezing of a subsurface ocean may be driving recent extensional tectonic activity on Pluto (Hammond et al., 2016). The lack of compressional features that would be caused by the ocean freezing, and subsequent volume contraction, suggest that the subsurface ocean on Pluto may still be present (Hammond et al., 2016).

The atmosphere on Pluto is primarily composed of Nitrogen, however there are traces of methane and carbon dioxide, the amounts of which change daily. [13] Scientists have also indicated that there may be an unidentified cooling agent in the atmosphere, which is affecting the lower-than-expected nitrogen opacity at high altitudes. [14] The Plutonian atmosphere is a bluish haze, which is likely the result of very small particles with scattering properties. [15]

Finally, it is interesting to note that when Pluto is closest to the Sun in its orbit, its atmosphere forms a cloud around it. At its furthest point from the Sun, its atmospheric gases (nitrogen, carbon monoxide, and methane ices) create glaciers and snow. [16]

Comparing the Extremes

Mercury and Pluto are both part of our solar system and thus have many similarities. However, their positions in the solar system give rise to many differences as well. The areas in which these differences can be found are size/density, planetary temperature, atmosphere, and terrain.

Mercury and Pluto share a commonality in that they are both very small in comparison to the other planets. However, Mercury is still twice the size of Pluto. The diameter of Mercury is 4,879.4 km, while Pluto’s diameter is only 2,360 km. For comparison, while Mercury is 38% of Earth’s diameter, Pluto is only 18% of the diameter of Earth. The density of Mercury is also much higher. Mercury is comprised of rock and metal with a density of 5.427 g/cm 3 , while Pluto is ice and rock with a density of around 2 g/cm 3 .

Image obtained from http://pics-about-space.com/mercury-size-compared-to-other-planets?p=3

Mercury is comprised of rock and metal with a density of 5.427 g/cm 3 , while Pluto is ice and rock with a density of about 2 g/cm3. Because Pluto is smaller and less dense than Mercury, it has a much lower force of gravity. While you would feel 38% the force of Earth gravity standing on the surface of Mercury, you would experience only 5.9% of Earth gravity on Pluto.

While the surface of Mercury is dominated with impact craters, Pluto’s surface demonstrates both cratered and smooth regions. Basaltic rock is present on the surface of Mercury due to widespread volcanism. Mercury has very dense core implying solid core being iron rich. Just like Earth we have noticed that mercury’s true magnetic poles shift over time (dynamo effect). Similar to Earth, Mercury is thought to have an exterior crust 100-200m thick, a mantle 600 km thick, and an inner core 1,800 km radius.

Scientists also suspect that Pluto’s internal structure is differentiated, with the rocky material having settled into a dense core surrounded by a mantle of water ice. The diameter of the core is believed to be approximately 1700 km, 70% of Pluto’s diameter. Thanks to the decay of radioactive elements, it is possible that Pluto contains a subsurface ocean layer that is 100 to 180 km thick at the core–mantle boundary.

In contrast to Mercury’s lack of atmosphere, Pluto has a thin atmosphere consisting of nitrogen (N2), methane (CH4), and carbon monoxide (CO), which are in equilibrium with their ices on Pluto’s surface. However, the planet is so cold that during part of its orbit, the atmosphere congeals and falls to the surface. The average surface temperature is 44 K (-229 °C), ranging from 33 K (-240 °C) at aphelion to 55 K (-218 °C) at perihelion.

Image from http://www.universetoday.com/13861/pluto/

Pluto has a moderately eccentric and inclined orbit, which ranges from 29.657 AU (4.4 billion km) at perihelion to 48.871 AU (7.3 billion km) at aphelion. Pluto has an orbital period of 247.68 Earth years, meaning it takes almost 250 years to complete a single orbit of the Sun. Meanwhile, its rotation period (a single day) is equal to 6.39 Earth days. [17] Like Uranus, Pluto rotates on its side, with an axial tilt of 120° relative to its orbital plane, which results in extreme seasonal variations. At its solstices, one-fourth of its surface is in continuous daylight, whereas another fourth is in continuous darkness.

When it comes to temperature, Mercury and Pluto are very different but also share frigidly cold nighttime temperatures. Temperatures on Mercury’s surface can reach 800 degrees Fahrenheit (430 degrees Celsius). Because the planet has no atmosphere to retain that heat, nighttime temperatures on the surface can drop to -280 degrees Fahrenheit (-170 degrees Celsius). [18] This nighttime temperature is only roughly 100 degrees Fahrenheit warmer than Pluto! Pluto is very cold! The temperature on Pluto ranges from -387 to -369 Fahrenheit (-233 to -223 Celsius).

How did the distance from the Sun affect the geology of Mercury and Pluto?

It is well established at this point that the greater the distance of an object from the Sun, the slower its orbit. [19] In addition, the idea well established that the planetary distance from the Sun directly influenced composition—the Terrestrial planets that are close to the Sun had much of their gasses evaporated by the Sun’s heat, leaving the particles to bind tightly together as rock and metal, while planets further away were able to retain their gaseous nature as the heat was less intense.

Pluto appears to fit outside of this hypothesis, as it is primarily ice and rock, until a few things are considered. First, the distance from the Sun and the temperatures on Pluto are so low, that most of its gasses (atmospheric and otherwise) tend to freeze, creating glaciers and ice mountains. Second, the running theory about Pluto’s formation is very different than those of the other planets. Instead of a bunch of tiny particles coming together, with the gravity and orbit lining up just right, to form a massive ball of particles, Pluto is thought to be the result of two big blocks of ice colliding. [20] The distance from the Sun is conducive to its primary composition of various ices, and one can speculate that its slow orbital speed is directly connected to the presence of different glaciers and the composition of its atmosphere.

Concluding Thoughts

Mercury and Pluto are the “bookends” of the solar system. Because of this, they provide a good opportunity to understand how celestial position in the solar system can affect geological makeup. They share similarities in that they are the two smallest planets (or dwarf planet, in Pluto’s case), and share extremely cold night temperatures, despite Mercury’s proximity to the Sun, as well as both being very dense. Due to how close it is to the Sun, Mercury has no atmosphere, while Pluto’s atmosphere forms a cloud around the dwarf planet when it is closer to the Sun, and the atmospheric gasses freeze to form glaciers and mountains when it is at its furthest.

Based on these observations, the distance from the Sun is not the only factor determining the geological composition and makeup of these celestial bodies, although there is a significant effect. The comparison is not exact, partly due to incomplete knowledge and preliminary information, and partly because Mercury and Pluto have very different compositional origins and current classifications. Black and white observations on this subject are not particularly useful, because there are so many factors that go into the geological and compositional aspects of a planet—for example, like Mercury, Pluto also does not have an atmosphere and is known for its extreme temperature fluctuations, despite being further from the Sun than Mercury, and the planets in between them having different features altogether. However, it is useful to use distance as an indicator for certain geological factors.

[1] Enchanted Learning, WWW Document, http://www.enchantedlearning.com/subjects/astronomy/planets/.

[2] Nasa, Mercury: In Depth, WWW Document, (http://iphone22.arc.nasa.gov/public/iexplore/missions/pages/solarsystem/mercury.html)

[6] N.M. Short, Planetary Geology, pp 287-289.

[8] All figures from the table are taken from the Pluto Fact Sheet, http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html

[10] Surface Compositions across Pluto and Charon: New Horizons Science Team, March 2016

[11] Surface Compositions across Pluto and Charon: New Horizons Science Team, March 2016

[12] Surface Compositions across Pluto and Charon: New Horizons Science Team, March 2016

[13] Surface Compositions across Pluto and Charon: New Horizons Science Team, March 2016

[14] The Pluto System: Initial results from its exploration by New Horizons – New Horizons Team, October 2015

[15] The Pluto System: Initial results from its exploration by New Horizons – New Horizons Team, October 2015


Pluto - a celestial oddball

In the years since it was discovered in 1930, astronomers have learned a great deal about Pluto. It’s turned out to be a very unusual object.

It is highly reflective, exuding a tenuous atmosphere when closest to the sun. In addition, it has a family of satellites, including the behemoth Charon, a little over 1,200km in diameter it is just over half Pluto’s size.

Pluto and Charon, as imaged by New Horizons on July 8, 2015. NASA-JHUAPL-SWRI

Pluto’s orbit is distinctly non-circular, or eccentric. At its closest to the sun (a distance of 4.44 billion km), Pluto passes within the orbit of Neptune, while at its most distant it lies almost three billion kilometres further away.

Pluto’s orbit is also tilted, or inclined, by about 17 degrees to the plane of the solar system. Pluto wanders both far above and far below the other planets during each 248-year orbit.

The oddities don’t end there. Crossing paths with Neptune, you might expect Pluto to eventually come close to that planet, potentially even crashing into it. But it avoids such a fate due to something called a mean-motion resonance.

Pluto’s orbit takes around 50% longer than that of Neptune’s (164 years). Pluto therefore completes two full laps of the sun in around the time it takes Neptune to complete three. This prevents close encounters between Pluto and Neptune. Every time Pluto crosses Neptune’s orbit, Neptune is elsewhere.

It works like this: on the first orbit, Pluto beats Neptune to the point their orbits cross, and the two avoid a collision by a huge distance. By the time Pluto completes another orbit, Neptune has completed one and a half, meaning that it now precedes Pluto, and a collision is again avoided. After another Plutonian year, the two return to where they started, and the dance begins again.

Because Neptune completes three orbits in the time Pluto completes two, we say that they are trapped in 3:2 mean-motion resonance. And it is this resonance that is key to our understanding the solar system’s formation.


Surface and Atmospheric Readings

The surface temperature of Pluto is currently under debate. Two results have been published: about 40 ° K (-233 ° C -388 ° F) and about 55 ° K (-218 ° C -361 ° F). The first value is similar to the temperature on Triton, Neptune's largest moon the latter is more consistent with Pluto's lower albedo. In either case, it is very cold. Water ice on Pluto is harder than steel is at room temperature! Misconceptions exist about how dark it would seem for an astronaut on Pluto. Despite the planet's remote distance, the Sun would appear to have the brightness of about 70 full Moons on Earth. Combine this with the bright, icy surface and one would have no problems navigating the surface.

On June 9, 1985, Pluto passed in front of a star. Rather than blinking out, the starlight gradually dimmed due to refraction by an atmosphere. Too dense to be methane alone, the atmosphere was suspected to contain nitrogen and carbon monoxide. Both have since been identified on Pluto's surface, with nitrogen comprising about 97 percent of the ground material. From details of precisely how the starlight faded, scientists believe there is a temperature increase close to the surface, much like on Earth. Pluto's atmospheric pressure is only a few millionths that of Earth, and the atmosphere actually may "frost out" with increasing distance from the Sun.

The Hubble Space Telescope has been used to measure the size of Charon's orbital radius, about 19,500 kilometers (12,090 miles, or approximately 1.5 Earth diameters). Densities have also been calculated: 1.8 to 2.0 grams per cubic centimeter (112 to 125 pounds per cubit foot) for Pluto and 1.6 to 1.8 grams per cubic centimeter (100 to 112 pounds per cubit foot) for Charon. From the density, scientists can infer the internal composition, a roughly 50-50 mix of rock and ice.


“The Death of Mars” –Did a Pluto-Size Asteroid Ignite Ancient Climate Change?

In the mid-1980s, a group of American archaeologists pored over satellite images trying to understand what had become of the Mayan civilization that had once ruled over Mexico’s Yucatan Peninsula, discovered a pattern: a near-perfect ring of sinkholes -cenotes- about 200 kilometers across, encircling the Yucatecan capital, Merida, and port towns of Sisal and Progreso. A pattern created by an ancient asteroid explosion that one young NASA scientist thought may yield clues to the lost ocean and atmosphere of Mars.

Defining Event in the History of Planet Earth

When the researchers presented their findings to fellow satellite specialists at a scientific conference in Acapulco, Mexico, in 1988, one scientist in the audience, Adriana Ocampo , then a young planetary geologist at NASA, saw not just a huge ring, but a bullseye –the impact crater of an asteroid that hit with the force of 10 billion Hiroshima nuclear bombs that scarred the planet in ways still being revealed 66 million years on. An impact that ended the reign of dinosaurs and opened a pathway for the emergence of the human species. “It gave us a leg up to be able to compete, to be able to flourish, as we eventually did,” she said.

“It was perhaps the defining event in the history of planet Earth,” University of Washington planetary scientist Mark Richards wrote in an email to The Daily Galaxy .

The ‘Aha!’ Moment

Today, the center of the bullseye is buried a kilometer below a tiny town called Chicxulub Puerto. “As soon as I saw the slides that was my ‘Aha!’ moment. ‘This is something amazing, ‘This could be it’,” Ocampo, later director of NASA’s Lucy mission, told the BBC. “I was really excited but I kept cool because obviously you don’t know until you have more evidence. They didn’t even know what I was talking about!” she laughed, three decades later.

The key to her ‘Aha! moment’ had been an intuition she’d picked up after working with a legendary figure in space science, Eugene Shoemaker. Shoemaker is a pioneering American geologist who helped found the field of planetary science and remains the only person whose ashes are buried on the Moon. Shoemaker instructed Ocampo that near perfect circles were unlikely to have been caused by other terrestrial forces, and could provide clues to Earth’s geological development.

Mexico’s Chicxulub Crater is “a natural laboratory because of its similarities to what we can find on other planets like Mars where humans can’t go,” Ocampo said of debris discovered from asteroid impacts on Mars compared with ejecta from the Chicxulub Crater.

The satellite images revealed similarities that indicate that Mars must once have had a much thicker atmosphere than it does now – one closer to the atmosphere that supports life on Earth. “It’s important for us to know what happened in the past to be prepared for the future,” Ocampo said. “It provides a really good insight into what has happened in the geological evolution of Mars.”

Today, Mars is a frigid desert world with a carbon dioxide atmosphere 100 times thinner than Earth’s. But evidence suggests that in the early history of our solar system, Mars’ surface likely hosted an ocean as deep as the Mediterranean Sea. As the planet’s atmosphere thinned, however, most of the ocean was lost to space. The remainder of the water is locked in the Martian ice caps.

Mystery of the Two-faced Nature of Mars

Astronomers from UC Santa Cruz, Caltech and MIT proposed that a giant asteroid or comet the size of Pluto, more than 1,200 miles in diameter – sped toward ancient Mars at up to 21,600 miles an hour, crashed at a steep slant into the planet about 3.9 billion years ago, and blasted out the huge elliptical scar measuring 5,300 miles across that now forms all of the planet’s northern lowlands, while leaving the southern highlands relatively undamaged. An impact so big that it has left half the red planet at a lower elevation.

If the theories are right, it blasted out the biggest crater that any planet has ever survived. It was a convulsion far bigger than the one that drove the dinosaurs to extinction on Earth. One region of the surface is the huge oval-shaped scar of the impact itself, covering more than a third of the Martian surface and including all the vast low-lying lands of the planet’s far north. The other is the even larger highland region to the south, marked by deep canyons, high mountains and the remains of giant volcanoes.

NASA’s Mars Reconnaissance Orbiter and Mars Global Surveyor have provided detailed information about the elevations and gravity of the Red Planet’s northern and southern hemispheres. The mystery of the two-faced nature of Mars has perplexed scientists since the first comprehensive images of the surface were beamed home by NASA spacecraft in the 1970s. A giant northern basin that covers about 40 percent of Mars’ surface, sometimes called the Borealis basin, is the remains of a colossal impact early in the solar system’s formation, the new analysis suggests. At 8,500 kilometers (5,300 miles) across, it is about four times wider than the next-biggest impact basin known, the Hellas basin on southern Mars.

An accompanying report calculated that the impacting object that produced the Borealis basin must have been about 2,000 kilometers (1,200 miles) across. That’s larger than Pluto. Researchers speculate that Borealis basin — which spans a size on Mars comparable to the combined areas of the continents of Asia, Europe and Australia– could have once held an Ocean. This would have been in the planets infancy, before Mars lost so much of its atmosphere and the Ocean either sublimated away or froze beneath the surface.

Mars bears the scars of five giant impacts shown in image above, including the ancient giant Borealis basin (top of globe), Hellas (bottom right), and Argyre (bottom left). A NASA-funded team at SwRI discovered that Mars experienced a 400-million-year lull in impacts between the formation of Borealis and the younger basins .(University of Arizona/LPL/Southwest Research Institute).

Scientists have detected frozen water on the surface of the red planet. Martian seas could have disappeared when the planet was bombarded by smaller meteors that changed its atmosphere and dried it out, said Ocampo.

New 2021 findings by NASA’s Mars Curiosity rover, which continues to explore the base of Mount Sharp (officially Aeolis Mons), a mountain several kilometers high at the center of the Gale crater, using the telescope on the ChemCam instrument, has discovered that the Martian climate alternated between dry and wetter periods, before drying up completely about 3 billion years ago, according to a French-US team headed by William Rapin, CNRS researcher at the Institut de Recherche en Astrophysique et Planétologie.

The Daily Galaxy, Jackie Faherty , astrophysicist, Senior Scientist with AMNH via BBC and NASA Solar System. Jackie was formerly a NASA Hubble Fellow at the Carnegie Institution for Science.

Editor’s Note: this article has been edited with new content and updated on May 15, 2021.

Image top of page: This view of Mars is a composite of images taken by the Mars Global Surveyor spacecraft in April 1999. The northern polar cap and encircling dark dune field of Vastitas Borealis are visible at the top of the globe. White water-ice clouds surround the most prominent volcanic peaks, including Olympus Mons near the western limb, Alba Patera to its northeast, and the line of Tharsis volcanoes to the southeast. East of the Tharsis rise can be seen the enormous near-equatorial gash that marks the canyon system Valles Marineris. NASA/JPL/Malin Space Science Systems

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