Amaplanethi amancane ku-astronomy yanamuhla
Igama elithi iplanethi encane lizwakala lilula—njengokungathi lisho nje “iplanethi encane.” Kodwa kusayensi yezinkanyezi yanamuhla, iplanethi encane iyisigaba sesayensi esinencazelo edalwe yimpikiswano ende, intuthuko kwezobuchwepheshe bokubuka, kanye nezinguquko endleleni abantu abadweba ngayo iSistimu Yelanga. Kusukela ekuqaleni kwekhulu lama-21, amaplanethi amancane abe ngomunye wemibono ethakazelisa kakhulu ngoba akhona kuleso sikhala “esiphakathi”: hhayi iplanethi enkulu njengoMhlaba, kodwa futhi hhayi nje idwala elincane njengama-asteroid amaningi. Ukuba khona kwawo kusiza ososayensi ukuqonda umlando wokwakheka kweSistimu Yelanga, ukufuduka kwamaplanethi amakhulu, kanye nokwakheka kwemizimba ebandayo emaphethelweni esistimu yethu.
Ukusuka “eplanethini” kuya “eplanethini encane”: ushintsho encazelweni
Emakhulwini eminyaka, incazelo yeplanethi iye yathuthuka kanye nolwazi lwabantu. Isibonelo, iPluto, yayibhekwa njengeplanethi yesishiyagalolunye selokhu yatholakala ngo-1930. Kodwa-ke, ngawo-1990 nasekuqaleni kwawo-2000, amatheleskopu anamandla kakhulu kanye nokuhlolwa kwesibhakabhaka okuhlelekile kwaqala ukuthola izinto eziningi ezifana nePluto eKuiper Belt—isifunda esingaphezu kweNeptune esicebile ngemizimba ebandayo. Ukutholakala kwezinto ezifana neQuaoar, iSedna, futhi ikakhulukazi i-Eris (enobunzima obufana noma obukhulu kancane kunePluto) kwaphakamisa umbuzo oyisisekelo: uma iPluto iyiplanethi, ingabe zonke izinto ezifanayo kufanele zibizwe ngamaplanethi?
Ngo-2006, i-International Astronomical Union (IAU) yasungula incazelo esemthethweni yeplanethi. Ngokwale ncazelo, iplanethi kumele: (1) izungeze iLanga, (2) ibe nesisindo esanele ukugcina isimo esicishe sibe yindilinga (ukulingana kwe-hydrostatic), kanye (3) "nokusula indawo yayo ezungezile" yezinto ezifanayo. I-Pluto ihlangabezana nezidingo ezimbili zokuqala, kodwa ayihlangabezani nesidingo sesithathu ngoba indawo yayo ezungezile igcwele izinto ze-Kuiper Belt futhi ithintwa amandla adonsela phansi e-Neptune. Ngakho-ke, i-Pluto yahlukaniswa kabusha njengeplanethi encane.
Iyini iplanethi encane?
Ngokusho kwe-IAU, iplanethi encane iyindikimba yasezulwini:
1. Ukuzungeza Ilanga.
2. Inesimo esicishe sibe yindilinga ngenxa yamandla ayo adonsela phansi.
3. Ayikaze “ihlanze” indawo yayo yokuzungeza.
4. Akuyona isathelayithi (hhayi inyanga yenye iplanethi).
Iphuzu "lokuhlanza indawo ezungezile" liwumehluko obalulekile. Amaplanethi amakhulu afana noMhlaba noma iJupiter alawula imijikelezo yawo ngamandla adonsela phansi: asusa, abambe, noma asakaze ezinye izinto, ashiye indawo ezungezile "icacile". Ngakolunye uhlangothi, amaplanethi amancane abelana ngesifunda sawo nezinye izidalwa ezincane eziningi. Lokhu akuyona nje indaba yobukhulu, kodwa kunalokho ukubuswa kwamandla okujikeleza.
Izibonelo zamaplanethi amafushane aziwayo
Kuze kube manje, i-IAU iyaqaphela amaplanethi amaningana amakhulu ama-dwarf, yize uhlu lwabazongenela ukhetho luqhubeka lukhula ngokutholwa okusha.
1. I-Pluto
I-Pluto isalokhu iyiplanethi encane edume kakhulu. Itholakala e-Kuiper Belt futhi inomjikelezo ojikelezayo ogobile uma kuqhathaniswa nendiza ejikelezayo yamanye amaplanethi. I-Pluto iphinde ibe nohlelo lwesathelayithi oluyinkimbinkimbi, oluhlanganisa i-Charon, olukhulu kakhulu kune-Pluto—kangangokuthi ivame ukubhekwa njengohlelo “lwamaplanethi amabili”. Umsebenzi we-New Horizons (2015) wembule ubuso be-Pluto obusebenzayo ngokwejiyoloji, obunamathafa e-nitrogen aqandisiwe kanye nezinqubo ezifana nenguqulo yomhlaba obandayo “ye-glaciation.”
2. ICeres
I-Ceres iyiplanethi encane ebhandeni le-asteroid eliphakathi kwe-Mars ne-Jupiter. Ihlukile ngoba iseduze kakhulu kunezinye iziplanethi ezincane kakhulu ngale kwe-Neptune. Umsebenzi we-NASA we-Dawn uthole ubufakazi bokuthi usawoti, iqhwa, kanye nomsebenzi ongaba khona we-cryovolcanic (uhlobo "lwentaba-mlilo yeqhwa") esikhathini esidlule. I-Ceres inikeza izinkomba ezibalulekile zokuthi ibhande le-asteroid aligcini nje ngokwakhiwa ngamatshe omile, kodwa futhi ligcina amanzi kanye nezinto eziguquguqukayo.
3.Eris
I-Eris ikude kakhulu neNeptune futhi yayiyisici esibalulekile encazelweni entsha yeplanethi. Icishe ifane ngobukhulu nePluto, kodwa umjikelezo wayo ukude kakhulu futhi awuvamile. I-Eris inenyanga ebizwa ngokuthi i-Dysnomia. Ngenxa yebanga layo elikhulu, ulwazi oluningiliziwe mayelana nobuso bayo lulinganiselwe, kodwa kukholakala ukuthi icebile ngamaqhwa njenge-methane ne-nitrogen.
4. Haume
I-Haumea iphawuleka ngesimo sayo eside, okucatshangwa ukuthi ibangelwa ukujikeleza kwayo okusheshayo kakhulu. Iphinde ibe nezindandatho ezincane kanye nezinyanga eziningana. I-Haumea iyisibonelo sokuthi amaplanethi amancane angaba nezici zomzimba ezingezona "izindilinga ngokuphelele," kodwa asahlangabezana nezidingo zokulingana kwe-hydrostatic ngaphakathi kwemingcele ethile.
5. Ukwakha
I-Makemake nayo ihlala e-Kuiper Belt. Le nto iyathakazelisa ngoba ubuso bayo bukhanya kakhulu, okubonisa ukuthi kuneqhwa eliningi. I-Makemake inesathelayithi okungenani esisodwa esitholiwe, esiza ososayensi ukulinganisa ubukhulu bayo.
Kungani amaplanethi amancane ebalulekile kusayensi yezinkanyezi yanamuhla?
Amaplanethi amancane avame ukubhekwa “njengezinsalela” ezivela ekwakhekeni kwamaplanethi—izitini zokwakha ezingazange zibe amaplanethi aphelele. Kodwa yingakho eyigugu kangaka. Amaplanethi amaningi amancane ahlala ezindaweni ezibandayo, “ezilondolozayo”, okuvumela izinto zawo ukuthi zigcine ulwazi lwamakhemikhali nolwezinto ezibonakalayo oluvela ohlelweni lwelanga lokuqala.
Ngaphezu kwalokho, izifundo zamaplanethi amafushane zisiza ukuhlola amamodeli okufuduka kwamaplanethi amakhulu. Inkolelo-mbono yanamuhla isikisela ukuthi iJupiter, iSaturn, i-Uranus, neNeptune kungenzeka ukuthi zashintsha izikhundla endaweni yonke yokuqala, zakha i-Asteroid Belt kanye ne-Kuiper Belt. Ukusatshalaliswa kwemizila yamaplanethi amafushane—ukuthambekela, ukuzwakala, kanye nokungajwayelekile—kunganikeza “isinyathelo” salesi senzakalo sokufuduka.
Amaplanethi amancane aphikisana nomqondo wokuthi imizimba emincane ihlala "ifile" ngokwejiyoloji. I-Pluto ne-Ceres zibonisa izimpawu zokusebenza, kungaba ngenxa yokushisa kwangaphakathi, ukusebenzisana kwamaza, noma i-chemistry yeqhwa eyinkimbinkimbi. Ngamanye amazwi, amaplanethi amancane ayizindawo zemvelo zokufunda ijiyoloji yezwe elibandayo kanye nokwenzeka kwezindawo ezisekela izinto eziphilayo.
Amaplanethi amancane kanye nentuthuko yezobuchwepheshe
Intuthuko kwezinkanyezi zanamuhla—kusukela kumakhamera e-CCD azwelayo kuya ezinhlolovo ezenzakalelayo kuya kuma-telescope asemkhathini—yenza ukutholakala kwamaplanethi amafushane kube yinto engenzeka kakhulu. Izinhlolovo ezifana ne-Pan-STARRS kanye namaphrojekthi okusesha izinto ze-trans-Neptunian ziyasiza ekutholeni abantu abasha abangaphandle kweSistimu Yelanga.
Uma sibheka phambili, i-Vera C. Rubin Observatory (ene-Legacy Survey yayo ye-Space and Time/LSST) kulindeleke ukuthi iguqule ukusesha izinto ezincane, ezikude. Izazi zezinkanyezi eziningi zibikezela ukuthi inani lamaplanethi amancane angakhula kakhulu, ikakhulukazi e-Kuiper Belt nasezindaweni ezihlakazekile zediski. Lokhu kuvula nethuba lokuthi kube khona “iPlanet Nine” ecatshangelwayo—hhayi iplanethi encane, kodwa iplanethi enkulu engakatholakali—okukhona kwayo okuye kwacatshangwa kusukela kumaphethini okuzungeza kwezinto ezikude. Uma le mbono ilungile, iplanethi encane enomjikelezo omkhulu ingaba yisihluthulelo sokufakazela leli phuzu.
Impikiswano kanye nekusasa lokuhlukaniswa ngezigaba
Nakuba incazelo ye-IAU isiza ekwenzeni kube lula ukuhlukaniswa, impikiswano ayixazululwanga ngokuphelele. Abanye ososayensi bathi incazelo "yokucacisa umjikelezo" incike kakhulu endaweni (isibonelo, e-Kuiper Belt, kungaba nzima kakhulu "ukucacisa umjikelezo" ngenxa yobuningi bezinto). Kukhona futhi impikiswano mayelana nokuthi incazelo yeplanethi kufanele isebenze kuphela ezintweni ezizungeza iLanga, njengoba kutholakale izinkulungwane zamaplanethi angaphandle ezungeza ezinye izinkanyezi.
Naphezu kwempikiswano yamagama, amaplanethi amafushane aseyisigaba esizinzile nesikhiqizayo. Axhumanisa ucwaningo lwamaplanethi, ama-asteroid, ama-comet, kanye nezinto ezishintsha i-Neptunian ohlakeni olulodwa lokuqonda ukuvela kweSistimu Yelanga.
I-Penutup
Amaplanethi amancane kakhulu kwezinkanyezi zanamuhla awagcini nje “ngokungqubuzana okukhulu.” Ayizingobo zomlando wendawo yonke, imihlaba eyingqayizivele enezindandatho, izinyanga, imimoya emincane, kanye nomsebenzi wejiyoloji ongaba khona. Kusukela kuCeres e-Asteroid Belt kuya ku-Pluto no-Eris emaphethelweni eSolar System, amaplanethi amancane andisa indlela esicabanga ngayo “ngeplanethi” futhi aqinisekisa ukuthi iSolar System ihluke kakhulu kunalokho okwakucatshangwa ngekhulu lama-20. Ngezizukulwane ezintsha zamateleskopu kanye nemisebenzi yasemkhathini yesikhathi esizayo, amaplanethi amancane azoqhubeka nokuba semkhanyeni—okusiza ukuphendula imibuzo emikhulu mayelana nemvelaphi, amandla, kanye nokwehlukahlukana kwemihlaba ezungeze iLanga.
Uma uthanda, ngingangeza ingxenye ethi “uhlu lwamaplanethi amafushane nezici zawo” ngendlela yethebula, noma ngibhale inguqulo ethandwa kakhulu yalesi sihloko yabafundi besikole samabanga aphezulu.
