MANYAN-DUNIYOYIN DA WATAƘILA BA SU WANZU BA

Ka’idar samuwar duniyoyi ta sanya rufi ga duniyoyin dutse. Tsakiyar da ke girma da ta wuce kusan nauyin Duniya 10 ba za ta iya kauce wa runaway gas accretion ba: tana jan gas daga faifan da ke kewaye da tauraronta matashi kuma ta zama duniya mai yawan gas. Kwaikwayon karo da zaizayewa suna ba da iyaka iri ɗaya. Ma’aunan duniyoyin gaske suna sanya sauyi daga dutse tsirara zuwa duniyoyi masu lulluɓin gas har ƙasa da haka, kusan nauyin Duniya 4 zuwa 5.

Duk da haka, a shekarun baya-bayan nan, wasu ƙalilan duniyoyi sun bayyana da yawan nauyi (density) irin na dutse da nauyin da ya wuce Duniya goma nesa ba kusa ba. Wasu masanan taurari suna kiransu “Mega-Earths” (Manyan-Duniyoyi). Bayyana su zai buƙaci tarihi na ban mamaki: karo na ƙarshe bayan faifan gas ya ɓace, ko tsakiyar tsofaffin manyan duniyoyi da aka cire musu lulluɓi.

Casey Brinkman da Nicolas Cowan, na Trottier Space Institute a Jami’ar McGill a Montreal, sun yi wata tambaya mafi sauƙi: shin da gaske waɗannan duniyoyi suna da wannan nauyi?

Auna duniya ta hanyar girgizar tauraronta

Yawancin waɗannan nauyaye sun fito ne daga radial velocities: yayin da duniya ke kewayawa, tana jan tauraronta gaba da baya, kuma hasken tauraron yana canza launi kaɗan ƙwarai. Girman wannan girgiza yana ba da nauyin duniyar.

Matsalar ita ce taurari ba su da natsuwa. Taurari masu aikin maganaɗisu (magnetically active) suna ɗauke da tabo masu duhu da facin haske da ke juyawa tare da tauraron. Suna ƙara hayaniya ga ma’aunan, kuma tabo da ke juyawa zuwa gani zai iya kwaikwayon — ko kumbura — siginar duniya.

Waɗanda ake zargi takwas, siffa ɗaya ta bai ɗaya

Su biyun sun fara daga NASA Exoplanet Archive kuma sun riƙe duniyoyi 333 ƙanana da radius na Duniya huɗu masu radius mai inganci da nauyin radial-velocity. Sun gano:

duniyoyi 4 masu yawan nauyi irin na dutse da fiye da nauyin Duniya 10: WASP-84 c, TOI-1347 b, TOI-2322 c da HD 63433 b.
ƙarin 4 da suka wuce iyakar kusan ba tare da lulluɓin hydrogen-helium ba: GJ 523 b, TOI-815 c, HD 18599 b da GJ 143 b.

Don auna aikin kowane tauraro mai masauki, sun yi amfani da wani ma’auni bisa hasken calcium da matakin waje mai zafi na tauraron ke fitarwa, wanda ke ƙara haske da ɗumamar maganaɗisu. Sama da ƙimar −4.75, ana ƙidaya tauraro a matsayin mai aiki. Ma’aunan haske daga aikin TESS suna kuma nuna kowane tauraro yana dusashewa da haskakawa yayin da tabonsa ke juyawa.

Sakamakon: duka takwas suna kewaya taurari masu aiki. Cikin taurari 37 da ke da duka nauyin duniya da ma’aunin aiki, 13 ne kawai masu aiki.

Damar daidaituwa

Idan Manyan-Duniyoyi sun bazu daidai-wa-daida, damar cewa huɗu na dutse duka sun faɗa kewayen taurari masu aiki za ta zama:

p = 13/37 × 12/36 × 11/35 × 10/34 = 0.01

Kusan 1%. Idan aka ƙara sauran huɗu, ta faɗi zuwa 0.0003.

Shin taurari matasa, masu aiki, kawai sun fi ƙwarewa wajen samar da Manyan-Duniyoyi? Marubutan ba su ga dalili ba. Gina ɗaya zai buƙaci ƙarin karo, ƙaura zuwa ciki zuwa zagaye na kwanaki 0.8 zuwa 20, kuma wataƙila cire wani kauri na yanayi (atmosphere) — duk waɗanda ke ɗaukar lokaci. Idan ma, waɗannan duniyoyi ya kamata su fifita taurari tsofaffi.

Inda nauyayen ke kuskure

Kowane ma’aunin asali ya yi amfani da Gaussian processes, wani kayan aikin ƙididdiga da ke kwaikwayon hayaniyar tauraro don a raba siginar duniya. Amma ƙirar da ta fi sassauci za ta iya shanye siginar da ba ta dace ba kuma ta samar da nauyaye masu girma fiye da kima. Lokutan suna da rauni:

A kewayen WASP-84, girgizar tauraron (kusan 13 m/s) ta fi siginar duniyar girma (7.7 m/s).
TOI-2322 yana juyawa cikin kwanaki 21.28; duniyarsa tana kewayawa cikin kwanaki 20.23.
HD 63433 b, mafi nauyi da nauyin Duniya 37, ba a gano ta kwata-kwata ba ta wata ƙungiya ta biyu, wadda ta sanya iyakar sama ta nauyin Duniya 21.
Uku daga cikin duniyoyin sun faɗi ƙasa da wani iyakar signal-to-noise da aka wallafa, wanda a ƙarƙashinsa aka san irin waɗannan ƙira ba su da aminci.

Marubutan sun tuna wani misali na baya: wata duniya wadda aka gano nauyinta ya kumbura ninki uku saboda wata siginar mai maimaitawa da ba a magance ba.

Babu ƙattai na dutse — a yanzu

Ƙarshensu: babu ƙwaƙƙwarar shaida ga duniyoyin dutse da suka wuce nauyin Duniya goma. Nauyayen radial-velocity na duniyoyin da ke kewayen taurari masu aiki sun cancanci shakka, “musamman idan wanzuwar irin waɗannan duniyoyi za ta ƙalubalanci fahimtarmu ta samuwar duniyoyi.” Sun ba da shawarar tsara lokutan kallo ta yadda za a ɗauki samfuri mai kyau na duka aikin tauraron da duniyar.

Hujjar ta ƙididdiga ce kuma ta dogara kan ƙaramin samfuri: duniyoyi takwas da taurari 37. Marubutan ba su sake yin daidaita nauyin asali ba.