ISKOKIN TITAN SUN ƘARA GUDU DA KASHI ƊAYA CIKIN UKU A KWANAKI 27

Titan, wata mafi girma na Saturn, yana da sararin sama mai kauri — bar 1.45 a saman ƙasa — wanda aka yi da kusan kashi 98% na nitrogen da 2% na methane, tare da dukkan sinadaran nitrile da hydrocarbon. Yana juyawa a hankali, sau ɗaya a kowane kwanakin Duniya 15.9. Duk da haka sararin samansa yana juyawa fiye da kima (superrotation): iskoki suna zagaye dukkan watan da sauri fiye da yadda jikinsa mai ƙarfi ke juyawa.

Da farko an gano waɗannan iskoki a kaikaice, sannan aka tabbatar da su ƙasa da kilomita 150 ta ma’aunin Doppler na aikin Cassini–Huygens. Suna gauraya sinadarai tsakanin dare da rana, suna taimakawa wajen kama ƙwayoyin sinadarai a cikin guguwar sanyi ta sandar duniya, kuma ana tunanin suna siffanta tuddan yashin halitta na Titan. Amma auna su kusa da layin tsakiya yana da wahala: hanyar da ta dogara da taswirorin zafi na Cassini ba ta aiki a can.

Abin mamaki daga 2016–2017

Kallon da aka yi a baya da ALMA, babbar jerin na’urorin milimita/ƙasa da milimita ta Atacama a Chile, sun gano wani abu da ba a zata ba: tsakanin Agusta 2016 da Mayu 2017, iskar tsakiya a tsayin kusan kilomita 1,000 ta ragu da kashi 47%, daga mita 373 zuwa 196 a kowace daƙiƙa. Samfuran yanayi na Titan, waɗanda samansu ke tsayawa kusan kilomita 500, ba sa samar da irin waɗannan sauye-sauye.

Martin Cordiner na Cibiyar Tashin Sararin Samaniya ta Goddard ta NASA da abokan aikinsa daga Yale, Bristol, Caltech, Cibiyar Kimiyyar Na’urar Hangen Nesa ta Sararin Samaniya da wasu cibiyoyi sun yi niyyar kallon wani ƙaramin layi na sararin sama na tsawon lokaci mafi tsawo.

Karanta iska a cikin ƙwayar sinadari

Ƙungiyar ta lura da acetonitrile (CH₃CN), wata ƙwayar sinadari a sararin Titan, a sabbin ranaku biyar tsakanin Yuni 2022 da Mayu 2023, kuma ta sake nazarin ranaku biyu na ajiya daga 2016 da 2017. A gefe ɗaya na watan, gas ɗin yana zuwa gare mu; a ɗayan, yana nisanta. Ɗan ƙaramin sauyi a mitar layukan rediyonsa — tasirin Doppler — yana ba da saurin iska.

Ma’aunin ya fi jin daɗi a kusan tsayin kilomita 250, a cikin kewayon kilomita 200 zuwa 490 — saman stratosphere da ƙasan mesosphere. Ranakun bakwai sun mamaye kusan cikakken lokaci na Titan, daga ƙarshen kaka ta kudu zuwa ƙarshen damina ta sanyi ta kudu.

Masu sauri, kuma masu canjawa

• Iskoki mafi sauri koyaushe suna cikin kusan digiri 10 na layin tsakiya, har zuwa mita 240 ± 26 a kowace daƙiƙa a Agusta 2016.
• Daga 2016 zuwa Yuni 2022, iskar ƙananan latitude ta rage gudu a hankali da kashi 46%, zuwa mita 130 a kowace daƙiƙa.
• Sannan ta yi ta hawa da sauka tsakanin kusan mita 130 da 170 a kowace daƙiƙa, da tsalle-tsalle na kusan mita 40 a kowace daƙiƙa.
• Tsakanin 12 ga Afrilu da 9 ga Mayu 2023 — kwanakin Duniya 27 kacal, ƙasa da kwanakin Titan biyu — ta tashi daga mita 120 zuwa 159 a kowace daƙiƙa, ƙarin kashi 33%. A cikin waɗannan makonni, iskokin manyan latitude sun tsaya daram.

Marubutan sun kira wannan karon farko da aka gano sauye-sauye masu ƙarfi masu ci gaba a iskokin tsakiyar Titan a cikin lokaci na kusan wata ɗaya ko ƙasa da haka.

A 2022–2023 yanayin iskar ya kuma nuna ɓangarori biyu: zirin kusa da layin tsakiya da zirin na biyu tsakanin digiri 40 da 60 kudu — guguwar iskar damina ta sanyi (winter jet) da samfura ke hasashe kuma Cassini ya gani.

Abin da samfuran suka rasa

Samfuran zagayawar yanayi na zamani guda biyu, TitanWRF da TAM, sun sake samar da sauyin yanayi na lokaci-lokaci a hankali: dogon raguwa, sannan ƙarin matsakaici. A manyan latitude, saurin iskokinsu ya kusanci abin da aka lura da kusan kashi 30%.

Amma samfuran suna sanya iskoki mafi sauri a manyan latitude na lokacin sanyi, kusan digiri 40 zuwa 50 kudu, kuma iskokinsu na tsakiya sun yi jinkiri har sau biyu, gibin ya fi girma kusa da solstice. Babu ɗayansu da ya kama tsalle-tsallen ba-zata na wata-wata, aƙalla a matsakaicinsu na shekaru goma. Dukansu suna ba da sakamako iri ɗaya duk da cewa TAM kaɗai ke haɗa gizagizan methane da ruwan sama, wanda ke nuna cewa al’amuran danshi ba su da tasiri sosai a waɗannan tsayi.

Raƙuman iska a sararin da ke juyawa a hankali

Marubutan sun ba da shawarar cewa sauye-sauyen ba-zata suna fitowa ne daga rashin daidaiton sararin sama. A cikin kwaikwayo, raƙuman da ake kira rashin daidaiton Rossby–Kelvin suna ɗaukar ƙarfin juyawa (angular momentum) zuwa layin tsakiya kuma suna tafiyar da juyawa fiye da kima; raunana na ɗan lokaci zai iya bayyana raguwar gudu ba-zata. Kusa da solstice, bayanan kuma suna nuna alamun ƙarfin juyawa yana sauka ƙasa, daga tsayi zuwa ƙasa.

Shawararsu ga masu gina samfura: a ɗaga saman samfuran Titan daga kusan kilomita 500 zuwa kusan kilomita 1,000, a inganta tsarin layukansu na tsaye, kuma a ci gaba da kallo da ALMA. Guguwar iska ta tsakiya mai sauyawa sosai a saman watan da ke juyawa a hankali, kamar yadda suka lura, gwaji ce ga sauran sararin sama masu juyawa fiye da kima, a Tsarin Rana da bayansa.