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In my fiktiewe wêreld het ek alle parameters gekies om die Heuwelsfeer van my planeet te maksimeer. Die planeet het drie keer die Aarde se massa en is geleë in 2 AE vanaf sy ster, wat 1,4 keer massiewer is as ons son.
Ek neem aan dat daar meer planete op die stelsel is, maar om sodoende die minimum interaksie met my planeet te hê.
Ek wil drie mane hê op 'n resonansie van 1: 2: 4. Ek wil ook:
- die eerste een wat so groot soos ons maan na die hemel was
- die tweede 1,5 keer groter
- en die derde, die helfte van ons maan.
Om dit te bereik, het ek aangeneem:
- die eerste maan het 1,1 maanstraal,
- die tweede 2.3
- en die derde 1.1.
Hul wentelbane is 18, 36, 72 dae.
Ek gee nie regtig om vir hul digtheid nie, en ek het aangeneem dat hulle baie is
- 1 maanmassa (waarskynlik rotsagtig)
- 3 maanmassa (water- of yswêreld)
- 0,3 maanmassa (waarskynlik yswêreld)
Ek dink dat ekstensiteite kleiner as 0,05 en 'n helling gelyk aan nul moet wees om stabieler te wees.
Ek is nie seker oor die draai van my mane nie. Is daar 'n kans dat die gety toegesluit word?
Dit is my poging om die maksimum stabiliteit van die stelsel te bewerkstellig. Watter parameters moet ek heroorweeg om dit stabieler te maak? Ek is bereid om byna alles, selfs die resonansie, te verander, maar ek wil hê dat dit vanaf my planeet sigbaar moet wees op 'n soortgelyke manier as wat die maan met die aarde is.
Hou in gedagte dat hierdie vraag oor 'n fiktiewe wêreld vir 'n fantasieverhaal gaan, dus selfs die minimum moontlikhede vir die senario kan gebeur. Enige idees?
P.S. Ek het 'n soortgelyke vraag oor worldbuild.stackexchange gevra, maar hulle het my ook hierheen gerig vir 'n beter antwoord.
Niks in u beskrywing klink wild onwaarskynlik nie. Ek sal net 'n paar van u eiendomme uitbrei om seker te maak dat dit sinvol is.
Die planeet het drie keer die aarde se massa
Ek neem aan dat u nuwe planeet aardagtig is in samestelling en digtheid. Dit impliseer dat die radius ongeveer $ R_p ongeveer 1.4 moet wees: R_ oplus $. Laat ons dit opsy sit om later te gebruik.
Kom ons kyk nou na jou mane.
- die eerste een wat so groot soos ons maan na die hemel was
- die tweede 1,5 keer groter
- en die derde, die helfte van ons maan.
Om dit te bereik, het ek aangeneem:
- die eerste maan het 1,1 maanstraal,
- die tweede 2.3
- en die derde 1.1.
As u die eerste maan wil hê, moet u so groot soos ons huidige maan in die lug wees en u sê dat dit 'n fisiese straal van $ R_ {M1} = 1.1 : R_ {M} $ het. Ons huidige maan is gemiddeld ongeveer $ 30 : arcsec = 8.73 times10 ^ {- 3} : rad $. U kan die afstand, $ d_ {M1} $, bereken, die maan moet vanaf die planeet wees om dieselfde skynbare grootte as ons maan te hê met die volgende vergelyking.
$$ d = frac {R} {tan ( delta / 2)} $$
Gebruik $ R_ {M1} $ vir $ R $ en $ 8,73 times10 ^ {- 3} : rad $ vir $ delta $, u maan moet $ d ongeveer 4 times10 ^ 8 : m = 44.5 : R_p $. U eerste maan moet ongeveer 44,5 planeetstrale wees. Vergelyk dit met die maan se afstand van ongeveer 60 planeetstrale.
Nou wil ons weet hoe lank dit sal duur voordat so 'n maan wentel, gegewe die planeet se massa, die massa van die maan en baanafstand. U kan dit kry uit die derde wet van Kepler.
$$ P = sqrt { frac {4 pi ^ 2} {G (M_p + M_ {M1})} d ^ 3} $$
Ons kan sê $ M_p = 3 : M_ oplus $ (soos u gespesifiseer het) en ons het $ d $ netnou bereken. Ons hoef slegs die massa van die maan te spesifiseer. U het die gewenste massa vir u mane voorsien, so ons is gereed. Let op $ G = 6,67 times10 ^ {- 11} m ^ 3kg ^ {- 1} s ^ {- 2} $ is die gravitasiekonstante. Ek vind dat $ P_ {M1} = 1,44 times10 ^ 6 : s = 16 : dae $.
Kom ons stop nou eers hier. Ons het 'n punt bereik waar u getalle in konflik is. Gegewe u planeet en die skynbare grootte, massa en radius van u eerste maan, het ons gevind dat dit binne 16 dae om die planeet sal moet wentel. As u die resonansie van 1: 2: 4 wil behou, moet u ander mane binne onderskeidelik 32 en 64 dae wentel.
Ek sal nie die res van die wiskunde deurgaan nie, ek laat dit aan u oor. Maar wat u kan doen as u wil verseker dat alles in ooreenstemming is met die regte fisika, is dat ek weet hoe lank my oorblywende twee mane moet wentel (dit wil sê, u weet $ P $ daarvoor), op watter afstand moet hulle baan (dws, wat is die waarde van $ d $ vir hulle)? Werk Kepler se derde wet agteruit om dit te kry. Gegee dan die gewenste skynbare groottes in die lug, bepaal dan hoe groot dit fisies moet wees deur die hoekgroottevergelyking agteruit te werk. U kry nuwe strale vir die maan. U kan dan seker maak dat die nuwe massa en radius vir u mane ooreenstem met die digthede wat ooreenstem met die gewenste maansoorte. As u derde maan byvoorbeeld 'n ysmaan gaan wees, moet dit 'n digtheid van $ sim1 : g / cm ^ 3 $ hê. U kan met u getalle speel totdat u 'n stelsel kry wat ooreenstem met u vereistes en die vergelykings pas.
'N Belangrike opmerking: al hierdie vergelykings gebruik MKS-eenhede. Massas moet in kilogram ($ kg $), afstande en groottes in meter ($ m $), tyd in sekondes ($ s $) en hoeke in radiale ($ rad $) wees.
Ek sien geen rede waarom dit nie sou werk nie. Die binneste Galilese mane is in 'n 1: 2: 4-resonansie, dus dit is duidelik 'n stabiele wentelkonfigurasie. Hulle kan almal getyvergrendel word as u wil, maar die planeet self kan nie met almal opgetel word nie. As die planeet tydelik gesluit was, sou dit waarskynlik met die binneste maan toegesluit word.
Ook opmerklik dat die Galilese mane almal eksentrisiteit minder as 0,01 en hellings minder as 0,5 grade het.
Mane kan help om planete stabiel te bly lank genoeg om lewenslank te vorm
Die maan is meer as net die aarde se vennoot in die ruimte - dit het moontlik gehelp om die aarde se stabilisering genoeg te maak om gasvry te word vir die ontwikkeling van komplekse lewensvorme.
'N Nuwe studie dui daarop dat groot mane ook rondom verre planete vir lang tye kan vorm en stabiel kan bly, wat moontlik kan help om uitheemse lewe te ontwikkel.
Navorsers stel voor dat as die onlangs ontdekte rotsagtige vreemde planeet Kepler-62f 'n maan het, die maan langer as 5 miljard jaar kan duur, miskien lank genoeg om die ontwikkeling van die komplekse lewe te help bevorder. Die ondersoekers het hul bevindings in die Internasionale Tydskrif vir Astrobiologie.
Oor die afgelope twee dekades het sterrekundiges die bestaan van meer as 1 700 planete buite die sonnestelsel bevestig, en hulle kan binnekort die bestaan van duisende sulke eksoplanete bewys. Van besondere belang is verre planete in bewoonbare sones; die streke rondom sterre is net warm genoeg sodat wêrelde vloeibare water op hul oppervlaktes kan besit, aangesien daar feitlik oral op die aarde vloeibare water is.
Kunstenaar se opvatting van die super-Aarde Kepler-62f, wat volgens sommige sterrekundiges 'n misleidende term is omdat hierdie wêrelde nader aan Neptunus is. Krediet: NASA
Om komplekse lewensvorme te ondersteun, benodig 'n wêreld meer as net 'n baan binne sy bewoonbare sone. Dit benodig waarskynlik ook 'n klimaat wat stabiel bly oor lang tydperke. Een belangrike faktor wat 'n wêreldklimaat beheer, is die skuinsheid, ook bekend as aksiale kanteling, wat te doen het met die hoeveelheid wat sy rotasie-as gekantel is in verhouding tot die pad wat dit om sy ster neem.
Aardseisoene hang byvoorbeeld af van die aksiale kanteling, want die hoeveelheid lig wat die noordelike en suidelike halfrond tref, wissel met die manier waarop die noordelike en suidelike halfrond na of weg van die son wys.
Die aksiale kanteling van die aarde is gestabiliseer met behulp van die swaartekrag van sy groot maan, wat ongeveer 'n kwart van die deursnee van die aarde is.
& # 8220As die aarde nie die maan gehad het nie, sou die aksiale kanteling van die aarde vinnig verander het en sou die klimaat van die aarde dikwels verander het, & # 8221 het hoofstudieskrywer Takashi Sasaki, 'n planetêre wetenskaplike aan die Universiteit van Idaho, gesê. .
Daarenteen het Mars relatief klein mane en sy aksiale kanteling het oor lang periodes aansienlik verander en chaoties gewissel op 'n 100 000 jaar tydskaal. Hierdie wankels in Mars se aksiale kanteling kan help om te verklaar waarom groot ondergrondse ys sakke ver van die Red Planet se pale ontdek is. In die verre verlede sou die Mars & # 8217-as teen 'n aansienlik meer ekstreme hoek gekantel kon wees as nou, en yskappe kon oor die hele planeet kom. Selfs nadat Mars se aksiale kanteling minder ekstreem geword het, het hierdie ys ver van die pale oorleef, beskerm deur daaropvolgende lae stof.
Aansig van 'n planetêre stelsel gesien vanaf Kepler-62f. Krediet: Danielle Futselaar / SETI Instituut
'N Planeet waarvan die aksiale kanteling soos Mars baie wissel, sal moontlik nie lank genoeg 'n gunstige klimaat handhaaf vir die ontwikkeling van komplekse lewensvorme nie. Dit het byvoorbeeld ongeveer 3,8 miljard jaar geduur voordat die lewe op die 4,6 miljard jaar oue aarde ontwikkel het van eensellige organismes tot meersellige lewe soos plante, diere en swamme.
& # 8220Omdat die aarde 'n stabiele klimaat op lang termyn gehad het, het die lewe op die aarde tyd gehad om van enkele selle tot komplekse lewensvorme te ontwikkel, & # 8221 Sasaki.
Aangesien die maan 'n belangrike rede is waarom Aarde lankal 'n relatiewe stabiele klimaat gehad het, is die maan een van die belangrikste faktore in die evolusie van komplekse lewensvorme op aarde, het hy gesê.
Sasaki en sy kollega Jason Barnes het probeer verstaan hoe lank mane rondom rotsagtige planete in bewoonbare gebiede kan duur, gegewe verskillende massas en samestellings van mane, planete en sterre. Hulle het gefokus op stelsels waar mane 5 miljard jaar kon duur, met die veronderstelling dat so 'n duur lank genoeg is om komplekse lewens te ontwikkel.
Hul model het verklaar hoe 'n planeet of maan se swaartekrag toeneem in verhouding tot toenemende massa. Daarbenewens het hul berekeninge rekening gehou met hoe swaartekraggetyekragte groter is hoe nader twee liggame aan mekaar is. Die swaartekrag van 'n ster van die planeet kan ook die verhouding tussen die wêreld en sy maan beïnvloed.
Mars & # 8217 moon Phobos soos gesien deur die Mars Express-ruimtetuig. Krediet: G. Neukum (FU Berlyn) et al., Mars Express, DLR, ESA
Drie potensiële scenario's was moontlik. Eerstens kan 'n maan al hoe nader aan sy planeet kom totdat dit uitmekaar breek of met sy gasheer bots, soos voorspel word dat Mars & # 8217 moon Phobos ongeveer 50 miljoen jaar van nou af sal doen. Vervolgens kan 'n maan al hoe verder wegkom totdat hy van die planeet ontsnap. Laastens kan 'n maan 'n stabiele afstand van sy planeet bereik, soos die geval is met die dwergplaneet Pluto & # 8217s moon Charon.
Die tempo waarmee 'n maan nader of verder van sy planeet af kom, hang af van die mate waarin die getykragte wat hulle op mekaar uitoefen, verdraai en hul draaitempo vertraag. Aangesien die baan van die maan dit mettertyd verder van die aarde af geneem het, het die tempo van die maan afgeneem tot op die punt dat dit nou altyd net een kant na die aarde wys. Uiteindelik sal die Aarde ook sy tempo van spinasie stadig vertraag om altyd net een kant na die Maan te wys.
'N Kunstenaar se konsep van Pluto, gesien vanaf die oppervlak van een van sy mane. Pluto is die groot skyf in die middel van die beeld. Charon is die kleiner skyf aan die regterkant. Beeldkrediet: NASA, ESA en G. Bacon (STScI)
Die mate waarin 'n maan en sy planeet die getykragte versprei wat hulle op mekaar uitoefen, berus baie op die massa, samestellings en strukture van daardie liggame. Die manier waarop getye in water in die vlak seë van die aarde rondloop, versprei groot hoeveelhede energie. Planete sonder oseane of met diep oseane sal minder gety-energie as die aarde versprei.
Die navorsers het vier tipiese samestellings van die planeet ondersoek: Aardagtige planete wat bestaan uit 67 persent meestal silikongebaseerde rots en 33 persent ysterplanete met 50 persent rots en 50 persent ysplanete met 100 persent rots en planete met 100 persent yster. Hierdie planete was 'n tiende tot tien keer die massa van die aarde en wentel om die bewoonbare sones van sterre wat wissel van 40 persent tot die massa van die son.
Die wetenskaplikes het bevind dat sterre met minder as 42 persent van die son en die massa miskien nie goeie plekke is om na komplekse lewe te soek nie, want mane kan nie langer as 5 miljard jaar in hierdie stelsels oorleef nie. Dit is omdat die bewoonbare sones nader aan sterre is wat dowwer en laer massas het as in helder sterrestelsels met 'n hoër massa. Byvoorbeeld, in sonnestelsels met sterre van 40 tot 50 persent van die son en die massa, is die bewoonbare afstand ongeveer 'n kwart van die afstand tussen die son en die aarde. Aangesien hierdie planeetmaanstelsels so naby aan hul gasheersterre is, steur die swaartekrag van hul sterre die planeetmaanstelsels te veel om die mane om hul planete te bly, het Sasaki gesê.
New Horizons LOng Range Reconnaissance Imager (LORRI) saamgestelde beeld wat die opsporing van Pluto se grootste maan, Charon, toon. Toe hierdie beelde op 1 en 3 Julie 2013 geneem is, was die New Horizons-ruimtetuig nog ongeveer 880 miljoen kilometer van Pluto af. Op 14 Julie 2015 sal die ruimtetuig slegs 12 500 kilometer (12 500 kilometer) bokant Pluto se oppervlak verbygaan, waar LORRI kenmerke van die grootte van 'n sokkerveld sal kan raaksien. Krediet: NASA / Johns Hopkins University Laboratory Physics Laboratory / Southwest Research Institute
Hierdie bevinding is in stryd met die oortuiging dat laermassa-sterre goed is vir bewoonbare planete omdat hulle langer leef as sterre met 'n hoër massa, wat hulle moontlik meer tyd gee om te ontwikkel. Byvoorbeeld, terwyl die leeftyd van 'n planeet met 'n massa van twee keer die massa van die son ongeveer 1,2 miljard tot 1,3 miljard jaar is, is die leeftyd van 'n ster met die helfte van die massa van die son ongeveer 80 miljard jaar, het Sasaki gesê. Hy het egter opgemerk dat ons resultate toon dat sterre met klein massa nie goeie ouersterre vir bewoonbare planete is nie. & # 8221
Vir sterre wat meer as 42 persent van die massa van die son is, hang dit af van faktore soos die samestelling van die planeet en hoe goed die gety-energie versprei, of 'n maan oorleef. 'N Maan het 'n langer leeftyd hoe hoër die digtheid van sy gasheerplaneet.
Die navorsers het ook ondersoek ingestel na die vooruitsigte vir mane in die Kepler-62-stelsel, wat op 'n afstand van 1200 ligjaar van die aarde 'n ster het wat koeler en kleiner is as die son, sowel as twee planete in die bewoonbare sone: Kepler -62e en Kepler-62f. Die planete is onderskeidelik 1,4 en 1,6 keer die deursnee van die aarde.
Die diagram vergelyk die planete van die binneste sonnestelsel met Kepler-62, 'n vyf-planeetstelsel ongeveer 1200 ligjaar van die aarde in die sterrebeeld Lyra. Krediet: NASA / Ames / JPL-Caltech
Die wetenskaplikes het bevind dat Kepler-62e bykans geheel en al uit 'n hoë digtheidsmateriaal, soos yster, moet saamgestel word om 'n maan wat meer as 5 miljard jaar lank wentel. Hulle het ook ontdek dat Kepler-62f langer as 5 miljard jaar 'n maan kan hê as dit verskillende samestellings het, veral as die oseane of slegs diep oseane afwesig is, wat die planeet minder getye sal laat verdwyn. energie.
In die toekoms, in plaas daarvan om na mane rondom planete op aarde in bewoonbare sones te kyk, het Sasaki gesê dat hulle graag mane rondom reuse-planete in bewoonbare sones wil ondersoek.
& # 8220As 'n reuse-planeet in 'n bewoonbare gebied 'n groot genoeg maan het, kan daar lewe op die maan wees, 'het Sasaki gesê. & # 8220 Om die gunstige omstandighede vir bewoonbare mane te vind, is 'n rigting wat ons kan inslaan. & # 8221
Wat u beskryf, is 'n skelm planeet met mane. Dit is 'n planeet wat nie om enige ster wentel nie, of dit uit sy oorspronklike sonnestelsel geskiet is of in die eerste plek nooit tot 'n sonnestelsel behoort het nie. Dit sal nie gepas beskryf word as 'n sonnestelsel nie, want daar is geen ster nie, maar u kan 'n skelm planeet hê met mane wat om hom wentel. 'N Skelm planeet kan miskien sy eie stelsel beskryf word, aangesien dit nie tot enige sonnestelsel behoort nie.
Skelm planete is van nature donker en koud, omdat hulle van geen ster beduidend geïsoleer word nie. Sterretjie, hoewel swak, is egter steeds lig, dus sal die planeet nie heeltemal pikswart wees nie. Enige hitte sal van aardwarmte of radioaktiewe aktiwiteite op die planeet self moet kom, aangesien daar geen beduidende eksterne energiebron soos die son is nie. Skelm planete wat nie hul eie interne energiebronne het nie, sal dood wees. Ek sou nie sê dat dit onmoontlik is om op 'n skelm planeet te lewe nie, maar ek sou verwag dat die kans baie laer sou wees as gevolg van baie laer oorvloed beskikbare energie.
'N Enkele groot planeet en 'n enkele groot ster wat wentel? Geen.
Wikipedia het 'n lys van sterre-uiterstes. Hierdie ster is die kleinste, 7% van die massa van ons son. (Dus ongeveer $ 7 * 10 ^ <28> $ kg)
Hierdie planeet is die grootste, 20 * keer die massa van jupiter (ongeveer $ 3,7 * 10 ^ <28> $ kg)
Dit is baie naby aan mekaar, hulle wentel om 'n punt 2/3 van die afstand van die son tot die planeet.
Maar kan ons 'n planeet kry met 'n ster wat daaromheen wentel?
Ja, daar is 'n paar presiese konfigurasies wat 'n massiewe planeet in die middel het en 'n groot son om hom wentel.
Die eenvoudigste is drie massiewe planete en 'n klein son. Die klein son het twee keer die gewig van elke planeet en al drie planete het dieselfde gewig. Die klein son en twee van die groot planete deel 'n baan met die twee planete naby mekaar. Die magte moet ophou en die groot planeet in die garsentrum van die stelsel laat.
Let daarop dat dit nie 'n sonnestelsel genoem word nie - tegnies.
Die lewe op die planeet sal baie soos die son in die middel was en die planeet daaromheen wentel. Ironies genoeg, as hulle bewus is van normale sonnestelsels, kan dit 'n rukkie neem om te besef dat die son nie die middelpunt is nie)
Dit is hoogs onwaarskynlik dat hierdie stelsel natuurlik sal voorkom - miskien het 'n supernova 'n stuk gaswolk geblaas en 'n ring van die gas gevorm wat die ster en twee gasreuse gevorm het? Dit is 'n bietjie strek. Miskien is die liggame presies op die regte manier vasgevang, of het buitelanders dit dalk gebou. Dit sou ook miljoene jare lank nie stabiel wees nie, dit sou mettertyd verval.
Kan ons dit effens stabieler doen?
As ons die planeet laat beweeg, maar voldoen aan die & quotat the center & quot-vereiste deur niks nader aan die middelpunt as die planeet te hê nie, kan ons 'n effens meer stabiele stelsel hê deur die groot planeet in 'n stywe wentelbaan rondom niks te hê (dws. & quotat the center & quot), met die son in 'n wentelbaan om daardie onderlinge sentrum.
Enorme gasreus wat vinnig draai.
Kyk na die gloeiende lug van Io!
Hierdie skrikwekkende siening van Jupiter se maan Io in verduistering (links) is deur die NASA se Galileo-ruimtetuig verkry terwyl die maan in Jupiter se skaduwee was. Gasse bokant die oppervlak van die satelliet het 'n spookagtige gloed opgelewer wat op sigbare golflengtes (rooi, groen en violet) gesien kon word. Die lewendige kleure, wat veroorsaak is deur botsings tussen Io se atmosferiese gasse en energiek gelaaide deeltjies wat in Jupiter se magneetveld vasgevang was, is nog nie voorheen waargeneem nie. Die groen en rooi emissies word waarskynlik geproduseer deur meganismes soortgelyk aan dié in die poolgebiede van die Aarde wat die aurora, of noord- en suidlig, voortbring. Helderblou gloed dui op die terreine van digte pluime van vulkaniese dampe, en dit kan plekke wees waar Io elektries aan Jupiter gekoppel is.
Io het verskillende soorte aurora. Dit word vervaardig deur interaksies met Jupiter. Jupiter het 'n geweldige magneetveld en gee baie straling af in die vorm van gelaaide deeltjies. Uiteindelik dink ek dat die energie wat dit aanvuur, die rotasie-momentum van die Jupiter is en miskien die oorblywende kondenswarmte toe dit gevorm is.
U sentrale planeet is 'n enorme gasreus, 20 keer so groot soos Jupiter. Sy groot massa en vinnige rotasie genereer groot magnetiese velde. U mane het ook magiese veld en atmosfeer - hierdie mane is die grootte van die aarde. Hulle het ook magnetiese velde wat hulle nodig het om hulle te beskerm teen die bestraling wat deur hul reus uitgestraal word. Die gelaaide deeltjies spat teen die magnetiese velde van die maan en verlig die lug net soos Jupiter se deeltjies die lug van Io verlig.
Net 'n gasreus
In die algemeen kan u so 'n stelsel hê. As u na die Jupiter-stelsel kyk, is dit omtrent sy eie & quotSolarystem & quot. U het 'n klomp mane rondom 'n sentrale voorwerp met 'n stuk puin wat rondvlieg.
Dit kan net van nature in die middel van nêrens wees. 'N Mens kan redeneer dat so 'n stelsel net soos of een is. Net kleiner en met 'n mislukte ster in die middel.
Maar hoe kry jy lig?
Goeie vraag. Ek wil sê, aangesien die gasreus die middel van nêrens is, sal dit waarskynlik geen lig op sigself uitstraal nie. As dit sou gebeur, is dit 'n Mini Star. Een manier om 'n bietjie lig te kry, is dus om 'n planeet BAIE naby die gasreus te hê. In werklikheid so naby dat dit dubbeld smelt vir die getykragte. Maar selfs dit sou regtig donker wees. Om nie te praat dat so 'n noue planeet binne 'n baie kort tydjie in die gasreus sou val nie.
U kan probeer om met Meta te gaan en om die een of ander rede 'n lewensvorm te hê op die Gasreus wat bioluminescerend is. Afhangend van die grootte van die Gasreus wat genoeg lig vir iets kan skep. Maar ek is nie stil seker waarom enige lewensvorm sou besluit om daardie weg te gaan in die duisternis van die interstellêre ruimte nie. Miskien as gevolg van een of ander Aurora, maar selfs dit is 'n ware streep, want waar kom die Aurora vandaan?
Maar ek sou steeds aanvaar dat 'n bioluminescerende gasreus waarskynlik die beste opsie is om enige hoeveelheid lig te kry. Al is dit nog steeds amper niks. So 'n gasreus sal waarskynlik skaars meer helder wees as of maan.
Jou hoofbron van energie in so 'n stelsel is in elk geval nie lig nie. Dit is die getykragte. En die eerste lewe op aarde het regtig nie lig nodig gehad nie, maar dit kan heel moontlik nog begin. Maar ek sien nie hoe die lewe ingewikkeld sal raak as elke maan rondom die gasreus 'n bevrore ysbal is nie.
Die beste plekke om uitheemse lewe in ons sonnestelsel te soek
Venus
Ligging: 108 miljoen kilometer van die son af
Voordele: Mag oseane al lank beskerm
Nadele: Hellish warm op die oppervlak, wolke van gekonsentreerde swaelsuur
Missies beplan: DAVINCI + (bekendstelling 2026, nie bevestig nie)
U sou onder 'n rots op 'n verre planeet moes woon om die nuus in September 2020 oor die onverwagte - en nog onverklaarde - ontdekking van die gasfosfien in die atmosfeer van Venus mis te loop.
In Oktober was daar twyfel oor die vraag of fosfien regtig opgespoor is, maar in elk geval is daar 'n onvoorspelbare chemie in die Venus-atmosfeer. Miskien kan dit selfs biochemie wees - is die fosfine 'n tekenende teken van die Venus-lewe?
Die probleem met Venus, ten minste vir astrobioloë, is dat dit 'n ware helse wêreld is. Die planeet word versmoor in 'n buitengewone dik atmosfeer van koolstofdioksied, wat 'n kragtige kweekhuiseffek skep. Die oppervlaktemperatuur is meer as 460 ° C: warm genoeg om lood te smelt.
Soos u na hoër hoogtes styg, word die temperatuur koeler (net soos deur bergklimmers op aarde ervaar), en ongeveer 55 km is die temperatuur en druk soortgelyk aan die aarde se oppervlak: T-hempweer. Maar die druppels wat die wolke hier uitmaak, is gekonsentreerde swaelsuur - baie ekstremer as wat 'n geharde lewe op aarde kon oorleef.
Miskien het die Venusiese lewe - as dit bestaan - ontwikkel om veel hoër suurgehalte te verdra as ons wispelturige landerye, en het dit opgetrek vanaf die ou oseaan in die wolklaag voordat die planeet sy wegholkweekeffek ondergaan het.
Dit maak nie saak hoe onwaarskynlik die vooruitsig op lewe in 'n biosfeer uit die lug op Venus kan wees nie, die ontdekking het beslis belangstelling gewek in die verdere verkenning van die planeet. Gelukkig is daar al 'n missie wat deur NASA se Discovery-program oorweeg word.
Aan die begin van 2020 was DAVINCI + op die kortlys en sou dit reeds in Mei 2026 van stapel gestuur kon word as dit gekies is. Die missie sal 'n sonde in die Venusiese atmosfeer vrystel wat met sy sensitiewe spektrometerinstrumente metings sal neem soos dit valskerm val.
Dr Melissa Trainer, 'n ruimtewetenskaplike by die NASA Goddard Space Flight Centre, het gehelp om DAVINCI + voor te stel. "Uiteindelik kry ons 'n duidelike beeld van die mengsel van gasse deur die atmosfeer vanaf die wolktoppe tot by die oppervlak," sê sy.
Byvoorbeeld, DAVINCI + sal gedetailleerde metings van waterdamp in die atmosfeer doen, en sal dus hopelik onthul hoeveel water die planeet verloor het deur sy geskiedenis, en vir hoe lank dit 'n uitgebreide oseaan sou besit. En met enige geluk sal dit tot die bodem van die fosfien-raaisel kom.
"Ek dink dit is dringend om nou terug te keer na ons susterplaneet Venus en die regte meetinstrumente saam te neem sodat ons kan ontsyfer wat in sy atmosfeer aangaan," sê Trainer.
Ligging: 228 miljoen kilometer van die son af
Voordele: Uitgebreide bewyse van antieke vloeibare water, organiese molekules, energiebronne
Nadele: Uiters koue en droë oppervlak
Missies beplan: Tianwen-1, Al Hamal, deursettingsvermoë (onderweg) Rosalind Franklin (bekendstelling in 2022)
Terwyl sommige 19de-eeuse sterrekundiges hulself dalk oortuig het dat hulle kanale sien wat die oppervlak van Mars kruis, het ons eerste close-up-blik op die Rooi Planeet met vlieggesondes in die 1960's duidelik dat die Marsoppervlak 'n gevriesdroogde woestyn was .
Mars het 'n dun atmosfeer, wat beteken dat dit buitengewoon koud is. Vloeibare water is nie stabiel oor die grootste gedeelte van die oppervlak nie, en dit word ook in ultravioletstraling van die son gebad.
Maar Mars was nie altyd so onherbergsaam nie - daar is uitgebreide tekens van antieke riviervalleie, delta's, mere en moontlik selfs 'n oseaan oor sy noordelike halfrond, wat dui op 'n warmer, natter oer-Mars. Het die lewe begin tydens hierdie vroegste fase van die planeet se geskiedenis, en kan 'biosignatures' van hierdie mikrobes in sedimentêre neerslae bewaar bly?
Wetenskaplikes wat belangstel in die kans op lewe op Mars, ondersoek ekstreme omgewings hier op aarde en ondersoek watter soort mikro-organismes in staat is om te oorleef. Dr Claire Cousins is 'n astrobioloog aan die Universiteit van St Andrews.
"Terwyl nêrens op aarde presies soos Mars kan wees nie, is daar plekke wat genoeg ooreenkomste het om waardevolle vergelykings te maak," sê sy. 'As u 'n gevoel wil hê van hoe die beendroë Mars-oppervlak vandag is, kan u na die Atacama-woestyn in Chili gaan. Alternatiewelik, om die omgewing van die vroeë Mars te verstaan - ongeveer drie tot vier miljard jaar gelede - kan u vulkanies aktiewe plekke soos Ysland bestudeer. ”
Mars is nie net opwindend nie, want dit lyk asof dit een keer 'n bewoonbare omgewing vir die lewe aangebied het, maar omdat dit ons planetêre buurman is, is dit relatief maklik om met robotprobes te kom en te verken. In Julie 2020 is nie minder nie as drie afsonderlike missies na Mars van stapel gestuur: China se Tianwen-1-baan en rover, die Verenigde Arabiese Emirate se Al Amal-baan, en NASA se nuutste motorgrootte-rover, Perseverance.
En wanneer die lanseringsvenster volgende keer in 2022 open, stuur die Europese Ruimteagentskap (ESA) en die Roscosmos van Rusland hul eie robot, die ExoMars-rover Rosalind Franklin.
Cousins is ook lid van die kameraspan vir ExoMars. 'Die volgende rovers wat Mars toe gaan, sal die chemie van Marsrotse in ongelooflike besonderhede ondersoek. Dit is belangrik, want ons probeer bewyse vind van 'n klein mikroskopiese lewe wat 'n paar miljard jaar gelede geleef het - nie maklik nie! ' sy sê.
"Ons sal op soek wees na spoorhoeveelhede organiese materiaal wat agterbly deur mikro-organismes wat die hele tyd bewaar is."
Enceladus
Ligging: Saturnusstelsel 1 400 miljoen kilometer van die son af
Voordele: Ondergrondse see, organiese chemie, energiebronne
Nadele: Verseël onder ys dop
Missies beplan: Geen tans gekies nie
Enceladus, een van Saturnus se mane, is 'n klein sneeubal van 'n wêreld. Die deursnee daarvan sal gemaklik tussen Londen en Edinburgh pas, die geringe swaartekrag kan nie aan 'n betekenisvolle atmosfeer vasklou nie en die oppervlak is hard bevrore ys. Astrobioloë het dit nie meer gedink nie, tot 'n verrassende ontdekking in 2005.
Die Cassini-sonde het gesien dat breuke naby die suidpool van die maan glinsterende geisers waterys in die ruimte uitstoot. Met verloop van tyd het die uitstorting van hierdie yskristalle die E-ring rondom Saturnus opgebou, en daar word geglo dat hulle gespuit word uit 'n groot hoeveelheid vloeibare water wat onder die ysige kors van die maan lê.
Na hierdie wonderlike ontdekking is Cassini beveel om laag oor die oppervlak van Enceladus te vlieg en reguit deur hierdie diffuse waterstrale te dompel om die samestelling daarvan te ontleed. Daar is gevind dat die fonteine natrium en korrels silika-ryke sand bevat - Enceladus se see is sout, en dit is belangrik, want dit beteken dat die water in kontak moet wees met die rotsagtige kern van die maan om minerale op te los.
Cassini het ook eenvoudige organiese verbindings soos formaldehied en asetileen, asook 'n paar groter molekules opgespoor. Dit is nie tekens van lewe nie, maar is net die soort voorgangerschemie wat as belangrik beskou word in die ontwikkeling van biologie.
Toe, in April 2017 - kort voordat die missie in 'n dramatiese duik in die verpletterende atmosfeer van Saturnus geëindig het - kondig die Cassini-span die ontdekking aan van moontlike hidrotermiese aktiwiteit op Enceladus se seebodem.
Hidrotermiese openinge vorm oases vir mikrobiese lewe in die donker dieptes van die Aarde se oseane, en die waterstofgas wat in die pluime van Enceladus opgespoor word, is 'n voedselbron wat lewenslank beskikbaar is. Op die aarde verkry sekere mikrobes die energie wat hulle nodig het deur waterstof met koolstofdioksied te kombineer en dan metaan te produseer.
Dit lyk dus asof Enceladus al die nodige vakkies aanmerk om 'n bewoonbare lewensomgewing te bied: vloeibare water, organiese verbindings en energiebronne.
Verskeie robotopdragte vir die nadere ondersoek is die afgelope paar jaar voorgestel. Enceladus Life Finder (ELF) en Enceladus Life Signatures and Habitability (ELSAH) missies is albei voorgestel aan die mees onlangse ronde van NASA se New Frontiers Program, maar verloor Dragonfly.
Explorer of Enceladus en Titan (E2T) is voorgestel as 'n gesamentlike ESA-NASA-missie, maar in Mei 2018 was dit nie 'n kortlys vir die jongste ronde van ESA se Cosmic Vision-program nie. Die kompetisie is fel vir die befondsing van ruimtemissies, maar daar is genoeg opgewondenheid oor Enceladus dat ons beslis gou genoeg daarheen sal terugkeer.
Lees meer oor buitenaardse weë:
Europa
Afstand vanaf die aarde: Jupiter-stelsel 778 miljoen kilometer van die son af
Voordele: Ondergrondse see, moontlike organiese chemie, moontlike energiebronne
Nadele: Verseël onder ys dop
Missies beplan: JUICE (2022 bekendstelling), Europa Clipper (2024 bekendstelling)
Ruimtesondes het aan die lig gebring dat die oppervlak van Europa, een van Jupiter se mane, relatief vars en jonk is. Dit word deur min impakkraters getref, wat beteken dat die maan geologies aktief is. Europa is deurkruis met lang frakture vanwaar die maan se oppervlak gestrek en gebuig word deur die kragtige swaartekrag van Jupiter.
Die Galileo-baan het ook opgemerk dat die maan Jupiter se magneetveld verwring. This implied that a magnetic field was being created within Europa by an electrically conductive substance – an ocean of salty water beneath Europa’s surface being the ideal candidate.
There even appear to be regions where this ocean may have melted through to the surface, breaking off icebergs, before rapidly freezing over again with exposure to the cold of outer space. Therefore, in terms of the potential habitability of Europa, we know it harbours a great subsurface ocean of liquid water.
But that’s just about all we can be sure of. We don’t know how thick the ice shell on top of the ocean is, or what organic chemistry may be there, or whether there is any hydrothermal activity on the seafloor, or whether the pH or saltiness of the seawater is suitable for life.
If this ocean is habitable, then Europa offers much better prospects for extraterrestrial life surviving today than Mars (which is now exceedingly cold and dry), but the moon is tricky to explore with robotic probes.
Europa is much further away than Mars or Venus, it orbits within the intense radiation belt of Jupiter, and the moon has no atmosphere for parachuting to the surface. And even if we can get a hardy probe safely down onto the face of Europa, it might need to drill or melt down through many kilometres of rock-hard ice to reach the subsurface ocean.
In some respects, Enceladus would be much easier to check for life because it is conveniently squirting its seawater out into space for us – a probe could swoop through this water plume to collect a sample before looping back to the Earth for analysis. There is hope for Europa, however, after the Hubble Space Telescope spotted what seems to be water plumes erupting from near the moon’s south pole.
ESA’s Jupiter Icy Moons Explorer (JUICE) is launching in 2022, but will only make two flybys of Europa, whereas NASA’s Europa Clipper will make multiple passes of the moon and should launch in 2024. If the Europa Lander mission receives funding it could launch in 2025 and will be able to scoop 10cm into the surface ice to test for signs of life.
Titan
Distance from Earth: Saturn system 1,400 million kilometres from the Sun
Pros: Geologically active, organic chemistry
Cons: Very cold, liquid hydrocarbons
Missions planned: Dragonfly (2027 launch)
Saturn’s largest moon, Titan, is enormous, larger even than the planet Mercury. When ESA’s Huygens descent probe parachuted down through Titan’s hazy orange atmosphere in 2005, it discovered a landscape with rolling hills, networks of river valleys, and smoothed pebbles strewn across the ground.
Flybys from the Cassini spacecraft subsequently found great lakes and signs of rain near the moon’s north pole. Titan is sodden wet and smothered with the sort of simple organic chemistry thought to have been important for the origin of life on primordial Earth – surely this is a surefire winner for hosting extraterrestrial biology?
The problem with Titan is that it is really cold. It orbits Saturn, nine times further from the Sun than the Earth and so only receives about 1 per cent the amount of solar warming. The surface is a numbing -180°C, and Titan’s rivers and lakes don’t slosh with liquid water, but liquid hydrocarbons like methane and ethane. This means that any life on the surface would have to be ethane-based rather than water-based, and molecules like DNA won’t work. Titan life would be truly alien.
Astrobiologists are keen to return to Titan. In June, NASA selected Dragonfly as the latest mission to be funded by its New Frontiers Program. Dragonfly is a truly innovative endeavour – where other planetary probes have involved a static lander or a rover to trundle slowly across the surface, Dragonfly is an octocopter drone.
Titan’s combination of low gravity and thick atmosphere makes it suited for exploration by air, and the craft will be able to fly faster than 30km/h, and take off and land vertically, giving it an unprecedented capability to pinpoint sites of interest.
Trainer is also deputy principal investigator on this mission. “While Dragonfly is not a life-detection mission, we are going after really fundamental questions about how far prebiotic chemistry may have progressed in this environment. We will characterise the products of millions of years of chemical synthesis, and search for biologically relevant molecules.”
Colonizing the Moon?
Darby Dyar, professor of astronomy and geology at Mount Holyoke College, says the moon is to people today what the New World was to Europeans 600 years ago. “They had been there a few times,” said Dyar, “but it took time to work up the courage to send people there to stay.”
It’s no fantasy. Scientists like Dyar have been working on the prospect of colonizing the moon for decades. “In my lifetime,” she said, “we will establish some kind of permanent station on the moon. Mind you, I plan to live another 50 years!”
Now Dyar is serving on the Solar System Exploration Research Virtual Institute. The “virtual” part refers to the fact that the monthly meetings and collaboration between team members takes place mostly through video-conferencing.
The project involves nine teams around the country, of which Dyar serves on three. She will be studying minerals on the moon and other airless bodies such as asteroids.
Among her tasks: Figure out how future residents on the moon can get at that chemical compound that is essential to human existence – water. No water, no life.
“The moon is a very dry place,” said Dyar. “That’s why it’s difficult to imagine living on it.”
The challenge is to find out where the water is and how to tap it, said Dyar. “We have to understand how water got to the moon, how much is still there, and how hard it would be to extract water for human consumption for a settlement,” she said.
Some water was formed at the same time as the moon was formed, she said, and is “locked” in its minerals in tiny amounts. It’s a concept that’s hard to understand for people who are used to water flowing freely.
Water would also come from comets that have crashed on the moon. Comets are made of ice, said Dyar, and the heat of the impact melts the ice. Some of the water is preserved in “permanently shadowed craters” where the sun cannot reach it.
“By far the most common way water gets to the moon is by solar wind,” said Dyar. “Solar wind is composed of highly charged particles, some of which are hydrogen ions that bond with microscopic particles. They are spraying the moon all the time, and sometimes they stick.” Hydrogen is one of the components of water – the “H” in H20.
Getting water from moon rocks would involve heating them in a still – a daunting process.
One reason for serious space exploration is global politics. Americans may think the moon is theirs because they were the first to plant a flag on it. No such thing, says Dyar. “Who owns the moon is still up for grabs,” she said.
The Outer Space Treaty of 1967, signed first by the major powers and subsequently by about 100 other countries, governs exploration and use of celestial bodies. Among the rules: No nuclear weapons up there.
Another reason for serious space exploration: “If an asteroid were to hit the earth, people could survive temporarily on the moon,” said Dyar.
She is referring to the kind of asteroid that killed the dinosaurs. “If you read the literature, it’s very pragmatic,” she said. “We all know the U.S. and other countries monitor the skies. What would we do?”
One of the three teams to which Dyar is assigned is based at Stony Brook University in New York. It studies how to extract as much information as possible from very small rock samples from outer space.
Many of the techniques that have been used for such analysis require a pretty big sample,” said Dyar, who serves as co-leader of this team, and a big sample is not always available. Mount Holyoke lab instructor and asteroid expert Tom Burbine is also on that team.
Another team, based at Brown University in Providence, R.I., works on how to identify minerals long-distance from an orbiting spacecraft. Dyar also has a lead role in this one. She and her Mount Holyoke students will train Brown faculty and graduate students on how to use complicated data processing equipment to conduct the research.
Dyar is a spectroscopist, which means that she analyzes of the distinct patterns that light makes when it bounces off surfaces.
The third team project, based at Johns Hopkins University in Baltimore, Md., studies how much hydrogen is trapped in minerals on the moon.
Though she holds the august academic title of Kennedy-Schelkunoff Professor of Astronomy at Mount Holyoke, Dyar is as lively and excited as a kid when she talks about her work.
“It’s a fun project,” she said. “You gotta remember—I started working on lunar samples in 1979. I’ve had a lifetime to get used to how amazing this is!”
Stable moons
Over nearly a decade of study, Kepler identified 10 exoplanets in orbit around nine pairs of stars. The planets lie close to their stars, zooming around in no more than seven Earth days. Each pair of stars is in a tight configuration, separated by only about a tenth of the distance between the Earth and sun, a number known as one Astronomical Unit (AU). The planets themselves orbit their stars' centers of mass at a distance of about one AU, making these worlds circumbinary. (Planets can also orbit a single star in a binary pair if the pair is far enough apart, the planet may act more like it is circling a single star.)
While the exomoons of planets that orbit a single star is awell-studied phenomenon, Hamers said, less work has been done for exomoons in binary systems. A handful of circumbinary worlds have been discovered using other telescopes, but the researchers in the new study were particularly interested in the newfound Kepler planets.
"We were curious which orbits of exomoons around these circumbinary planets would be dynamically stable," Hamers said.
The scientists ran multiple simulations of the moons of planets around stellar pairs. Results showed that stable simulated moons remained close to their planets, at about 0.01 AU apart, so that these moons were less affected by the gravity of the stellar pairs. Moons were also more stable when they circled more massive planets. The angle of the moon's path around the planet compared to the planet's path around the suns proved important, as well. When a moon circled at a 90-degree angle compared to the planetary path, the moon oscillated widely before becoming unstable, crashing into the planet or, on rare occasions, one of the stars.
What might it look like to stand on the moon orbiting a planet with two stars in the sky? That would depend strongly on the moon's orientation and rotation period, Hamers said. If the moon resembles the moons of Jupiter, its "day" will likely span several Earth days. The tight orbits of these exomoons mean they should whip around their giant planets over about 10 Earth days, he said.
"During the 'day' on the exomoon, there will be two stars visible in the sky, separated by about 40 degrees, which will noticeably move during the course of the 'day,'" Hamers said. "Also, there will be times that the binary stars eclipse each other, [with] only one star visible for a limited amount of time."
If all three objects travel along the same plane, the planet itself will obscure the stars roughly every 10 days. If they are tilted in relation to one another, however, eclipses may be avoided.
Although the new research did not directly hunt for exomoons, the findings could help aim future hunts for the tantalizing objects. By determining the regions around a circumbinary planet where an exomoon would be unable to survive, Hamers said, this research can help scientists discount ambiguous signals. Such misleading signals could be effects created by stellar activity or star spots.
The new findings also reveal the limits on exomoon stability around double stars depending on the ratio of the planet&rsquos mass to that of its stars. "This relation likely applies to any circumbinary system," Hamers said. However, he did add the caveat that the team focused on Kepler binaries the researchers didn't thoroughly investigate outside binaries.
Telescopes such as NASA's recently launched Transiting Exoplanet Survey Satellite and the upcoming European CHEOPS and PLATO spacecraft may be good for hunting down exomoons, Hamers said.
The research was detailed Nov. 1 in the journal Monthly Notices of the Royal Astronomical Society.
Moonless Earth Could Potentially Still Support Life, Study Finds
Scientists have long believed that, without our moon, the tilt of the Earth would shift greatly over time, from zero degrees, where the Sun remains over the equator, to 85 degrees, where the Sun shines almost directly above one of the poles.
A planet's stability has an effect on the development of life. A planet see-sawing back and forth on its axis as it orbits the sun would experience wide fluctuations in climate, which then could potentially affect the evolution of complex life.
However, new simulations show that, even without a moon, the tilt of Earth's axis — known as its obliquity — would vary only about 10 degrees. The influence of other planets in the solar system could have kept a moonless Earth stable. [10 Coolest New Moon Discoveries]
The stabilizing effect that our large moon has on Earth's rotation therefore may not be as crucial for life as previously believed, according to a paper by Jason Barnes of the University of Idaho and colleagues which was presented at a recent meeting of the American Astronomical Society.
The new research also suggests that moons are not needed for other planets in the universe to be potentially habitable.
As the world turns
Due to the gravitational pull of its star, the axis of a planet rotates like a child's top over tens of thousands of years. Although the center of gravity remains constant, the direction of the tilt moves over time, or precesses (as astronomers call it).
Similarly, a planet's orbital plane also precesses. When the two are in synch, the combination can cause the total obliquity of the planet to swing chaotically. But the gravity of Earth's moon has been shown to provide a stabilizing effect. By speeding up Earth's rotational precession and keeping it out of synch with the precession of Earth's orbit, it minimizes fluctuations, creating a more stable system.
As terrestrial moons go, Earth's moon is on the large size — only about a hundred times smaller than its parent planet. In comparison, Mars is over 60 million times more massive than its largest moon, Phobos.
The difference is substantial, and with good cause — while the Martian moons appear to be captured asteroids, scientists think that Earth's moon formed when a Mars-sized body crashed into the young planet, blowing out pieces that later consolidated as the lunar satellite — a satellite which affects the planet's tilt.
Scientists estimate that only one percent of any terrestrial planets will have a substantial moon. This means that most such planets are expected to experience massive changes in their obliquity.
The pull of the planets
While Earth's moon does provide some stability, the new data reveals that the pull of other planets orbiting the sun — especially Jupiter — would keep Earth from swinging too wildly, despite its chaotic evolution. [10 Extreme Planet Facts]
"Because Jupiter is the most massive, it really defines the average plane of the solar system," said Barnes.
Without a moon, Barnes and his collaborators have determined that Earth's obliquity would only vary 10 to 20 degrees over a half a billion years.
That doesn't sound like much, but the changes of 1 to 2 degrees the planet presently exhibits are thought to be partly responsible for the Ice Ages.
According to Barnes, the present shift is "a small effect, but in combination with Earth's present climate, it causes big changes."
Still, a 10-degree change is not a huge problem when it comes to life. "(It) would have effects, but not preclude the development of large scale, intelligent life."
Furthermore, if Jupiter were closer, Barnes explains, the Earth's orbit would precess faster, and the moon would actually make the planet fluctuate more wildly, rather than less.
"A moon can be stabilizing or destabilizing, depending on what's going on in the rest of the system," he said.
The benefit of a backspin
The team also determined that planets with a retrograde, or backward, motion should have smaller variations than those that spin in the same direction as their parent star, a large moon notwithstanding.
"We think the initial rotation direction should be random," Barnes said. "If it is, half the planets out there would not have problems with obliquity variations."
What determines which way a planet spins? He suspects that "whatever smacks the planet last establishes its rotation rate."
A 50/50 shot at retrograde precession, combined with the likelihood of other planets in the system keeping the planet from tipping on its side, means more terrestrial planets could be potentially habitable. Barnes ventured an estimate that at least 75 percent of the rocky planets in the habitable zone may be stable enough for life to evolve, though he notes that additional studies are needed to confirm or disprove that.
In comparison, the previous idea that a large moon was necessary for a constant tilt meant that only about 1 percent of terrestrial planets would have a steady climate.
"A large moon can stabilize (a planet)," Barnes said, "but in most cases, it's not needed."
This story was provided by Astrobiology Magazine, a web-based publication sponsored by the NASA astrobiology program.
Moons in Our Solar System that Could Support Extraterrestrial Life
The search for extraterrestrial life forms has to begin from our vicinity. The first logical assumption is our neighbor Mars, where scientists believe that liquid water existed billions of years ago. Climate changes stripped most of the Red Planet’s atmosphere, but there is a possibility that simple forms of life exist within the ice hidden under its rocky surface.
Some forms of life may still exist in our solar system on worlds other than Earth or Mars. While there aren’t too many candidates in the “golden zone”, where the temperature is just right for liquid water to exist, there are reasons to believe that alien organisms could live on some of the moons around us. The things that are the most important for these natural satellites to support life are liquid water, orbital stability, suitable atmosphere, favorable tidal effects, stable axial tilt and climate.
Europa
System: Jupiter
Diameter: 0.25 Earths (
90 % of our own Moon)
Mass: 0.008 Earths
Atmosphere: Very thin, mostly oxygen
Europa is one of the most exciting prospects for extraterrestrial life in the Solar System. First, because there is a vast ocean buried beneath its icy surface. Heating caused by the tidal forces of Jupiter keeps large portions of these oceans liquid. This effect may provide a source of energy for life, while vents on the seafloor could provide food. Plumes of water have been seen erupting 160 kilometers (100 miles) above the surface. Oxygen, hydrogen and other compounds could also be supplied to living organisms from the water-ice surface. This outer shell is constantly “bombarded” with radiation from the giant planet, but this could be a shield for any life below. While Europa is only one-fourth the diameter of Earth, its ocean may contain twice as much water as the oceans on our planet.
Enceladus
System: Saturn
Diameter: 0.04 Earths (500 kilometers / 300 miles)
Mass: 0.000018 Earths
Atmosphere: Mostly water vapor (also nitrogen, carbon dioxide)
The tiny natural satellite Enceladus is another top candidate for finding life. It does not only have an ocean beneath the surface, but scientists believe that the icy crust is also thinner compared to other worlds where life might exist. Additionally, it is actively and regularly firing out plumes of water from its south pole. This means that materials from the ocean are dumped on to the surface. So, studying it may not be beyond the realms of possibility. Data from the Cassini spacecraft even showed that materials form the ocean contained complex organic molecules, which may suggest that the ocean is habitable. Hydrothermal vents on the sea floor could also provide food for life.
Titan
System: Saturn
Diameter: 0.4 Earths (larger than Mercury)
Mass: 0.02 Earths
Atmosphere: Thick, mostly nitrogen (also methane, hydrogen)
Saturn’s largest moon has unique qualities that have not been observed anywhere else in the universe so far. Namely, Titan is the only satellite in our family of planets known to have a substantial atmosphere. Additionally, it is the only world besides Earth known to have a system of liquid rivers, lakes, and seas. It can even rain and snow. The twist is that the liquid is not water, but methane, ethane, and other hydrocarbons. Normally, water is the key element that should be present somewhere if we expect to find life, but what if it’s not actually necessary? Carbon is a primary component of all known life on Earth and is the second most abundant element in the human body by mass after oxygen. It is a unique element that can bond to nearly anything, creating a wide variety of molecular structures. Therefore, some scientists suggest that methane and other hydrocarbons could be used as a solvent for life on Titan and similar worlds instead of water. So, if life exists on Titan, it would be very different from anything we have ever known before.
Ganymedes
System: Jupiter
Diameter: 0.4 Earths
Mass: 0.025 Earths
Atmosphere: Very thin, mostly oxygen
The largest moon in the Solar System is also the only one to have a significant magnetic field. This is crucial for keeping life on Earth safe from radiation, so it could have a similar role on Ganymede as well. Because of this commonality, auroras can be observed on its poles just like the northern lights can be seen on our planet. Interestingly, research studies have shown that Jupiter’s massive satellite could have layers of ice and liquid water between its surface and core. Tidal forces from Jupiter could keep this water in a frigid liquid form, so perhaps life could have evolved underneath the surface.
Other potentially habitable moons
Callisto
This is the most distant of Jupiter’s four largest moons, which means less radiation than the others. It is believed that Callisto may also contain a subsurface ocean, potentially habitable by living organisms. Its atmosphere consists of carbon dioxide, hydrogen, and oxygen, making this moon more hospitable to life as we know it.
Triton
There is a possibility that Neptune’s largest moon is home to alien life. Scientists are not completely sure if an ocean exists beneath its frozen crust, but there are some cracks and volcanic features on this world which suggest it is warmed by tidal heating from its planetary companion. Even though the surface of Titan is one of the coldest places in the solar system, the inner heat and geological activity could potentially provide conditions for water to exist in liquid form.
Io
Io is the most volcanically active world in the entire Solar System, so at first glance, it doesn’t look very hospitable and habitable. However, it could have had liquid water in the past, which in combination with the heat could have supported life.
Dione
This icy moon which orbits around Saturn is also thought to have an ancient ocean under the surface. However, the crust could be thick as much as 100 kilometers. Still, some form of life could theoretically exist down there.
Charon
A canyon and suspected cryovolcanic activity may suggest that Pluto’s largest moon once had an ancient internal ocean of water and ammonia. Whether it could have been habitable, remains a mystery.
Wandering Promise: Study Says Moons of Rogue Exoplanets Could Be Habitable, Host Liquid Water
The cosmic universe is vast, with countless worlds scattered around billions of distant galaxies—each different and unique from the other. The planets beyond the bounds of our solar system are known as exoplanets, and astronomers have long suspected that some of them may hold the potential to host some forms of life.
Even among these, not all cosmic worlds are loyally bound to host stars! Some of them are rogue exoplanets, which wander the dark cosmic space without a host. The absence of a heat source excludes them from possessing suitable conditions to host life.
But, there is a twist! Some of these rogue planets have a natural satellite like the Moon to Earth. And it turns out, these moons or exomoons could be as warm and wet as Earth. For the first time, a recent study has determined that some of the exomoons of rogue exoplanets could hold habitable conditions.
How can exomoons be habitable?
Scientists from the University of Concepción in Chile explored the possibilities of life on exomoons, equivalent to Earth’s mass, orbiting the rogue gas giants of mass comparable to Jupiter. The researchers modelled the probability of such exomoons hosting an atmosphere composed of 90% carbon dioxide and 10% hydrogen over its evolutionary history.
They further looked into the possible presence of an atmosphere and liquid water to find the ideal exomoon candidate. Finally, to understand the formation of these two life-supporting conditions, the team explored cosmic radiation and the gravitational effect of the rogue exoplanet on the exomoon.
And this was when they decoded the conditions conducive to life! The authors of the study explain: “We find that, under specific conditions and assuming stable orbital parameters over time, liquid water can be formed on the surface of the exomoon. The final amount of water for an Earth-mass exomoon is smaller than the amount of water in Earth oceans, but enough to host the potential development of primordial life.”
Researchers reveal that cosmic radiation can help execute the chemical reaction required to form water by converting hydrogen and carbon dioxide. “The chemical equilibrium time-scale is controlled by cosmic rays, the main ionisation driver in our model of the exomoon atmosphere,” says the study. Moreover, the tidal force will act as the source to keep it liquid.
The world of exomoons
According to the observations in the study, the combination of two factors—cosmic radiation and the gravitational effect of the rogue planet—can create the settings just right enough to sustain liquid water and the atmosphere. On Earth, the heat helps to keep the process of photosynthesis going and help maintain the surface water in the liquid state.
The study highlights that there could be at least one rogue Jupiter-sized gas exoplanet for every star in our home galaxy: Milky Way. Earlier studies have estimated that there could be over 100 billion rogue exoplanets. There are high chances that many of them would have moved from their original location along with an exomoon.
The temperatures beyond the limits of a star system are incredibly frigid. Despite this, there are some known worlds where water has been discovered in liquid form. In fact, there are some icy moons in the solar system as well—like the Ganymede and Europa that orbit Jupiter and Enceladus that orbit Saturn—which are thought to host liquid oceans beneath the thick ice shells.
For decades, astronomers have speculated that Europa and Enceladus might host some form of alien life. The speciality of these worlds is the retention of water in liquid form due to the gravitational tug of respective planets. Likewise, a substantial amount of water could exist in the exomoon's atmosphere. With this study, the possibilities of exploring the world of exomoons become wide open in search of alien life.
The results of the study have been published in the International Journal of Astrobiology and can be accessed here.
Revealed: Why We Should Look For Ancient Alien Spacecraft On The Moon, Mars And Mercury According To NASA Scientists
From UFO crash sites on other planets and aliens “lurking” on asteroids to a permanent radio . [+] telescope on the far side of the Moon, a new NASA-funded study into the search for intelligent extraterrestrial life (SETI) details how future NASA missions could purposefully look for “technosignatures.”
From UFO crash sites on other planets and aliens “lurking” on asteroids to a permanent radio telescope on the far side of the Moon, a new NASA-funded study into the search for intelligent extraterrestrial life (SETI) details how future NASA missions could purposefully look for the “technosignatures” of advanced alien civilizations.
Described as evidence for the use of technology or industrial activity in other parts of the Universe, the search for technosignatures has barely begun, but could unearth something surprising without much additional spend, says the study.
After more or less ceasing its search for technosignatures in 1993 after pressure by politicians, NASA has become increasingly involved in SETI.
Published in the specialized journal Acta Astronautica, the study includes a list of what’s NASA missions could detect as observational “proof of extraterrestrial life” beyond Earth.
Perhaps most intriguingly, the paper suggests that interstellar probes might have been sent into the Solar System a long time ago, perhaps during the last close encounter of our Sun with other stars.
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Uitgelê: Waarom hierdie week se 'Strawberry Moon' so laag, so laat en so helder sal wees
The closest star to the Sun right now, Proxima Centauri, is over 4.2 light-years distant, but roughly every 100,000 years a star comes within nearly a light-year from the Sun. There have therefore been “tens of thousands” of opportunities for technologies similar to ours to have launched probes into our Solar System, according to the paper.
“Such artifacts might have been captured by Solar System bodies into stable orbits or they might even have crashed on planets, asteroids or moons,” reads the paper. “Bodies with old surfaces such as those of the Moon or Mars might still exhibit evidence for such collisions.”
The Moon, Mars, Mercury or Ceres could contain evidence of impacts or existing artifacts that may . [+] have been preserved for between millions or billions of years.
The paper’s nine suggestions for technosignature-hunting missions include:
Mission 1: search for crash sites on the Moon, Mars, Mercury or Ceres
The surfaces of these places are ancient and unchanging. Evidence of impacts or existing artifacts might be preserved for between millions and billions of years—so we should scan the Moon and Mars in ultra-high resolution.
Mission 2: look for pollution using Earth as a template
As recently published for NASA by the same authors, the JWST could find CFC gases—proof of civilization—around exoplanets if it was 10 times more common than on Earth. It could also find nitrogen dioxide (NO2), produced as a byproduct of combustion or nuclear technology.
Mission 3: search for Dyson spheres
A so-called “waste heat mission” to pick-up technological waste heat would require an all-sky survey using a space telescope with sensitivity at many infrared bands.
A permanent dish on the “radio-quiet” far side of the Moon would be free of contamination from human . [+] radio emissions, so enable super-sensitive searches. (Photo by NASA via Getty Images)
Mission 4: build a radio telescope on the Moon’s far side
The search for technosignatures so far has been conducted largely via radio astronomy—and continues to be so via the Breakthrough Listen project. However, a permanent dish on the “radio-quiet” far side of the Moon would be free of contamination from human radio emissions, so enable super-sensitive searches.
Mission 5: look for ‘lurkers’ on asteroids
We may be being watched by aliens concealed on resources-rich near-Earth objects (NEOs)—possibly even asteroids that orbit the Sun with Earth.
Mission 6: intercept missions to ‘interstellar interlopers’
‘Oumuamua for 2I/Borisov passed through the Solar System without us able to conclusively establish their nature and origins. So we should have an intercept mission ready to launch when a target next presents itself—and that could be soon after the Vera C. Rubin Observatory’s all-sky surveys begin later in 2021.
Illustration of Oumuamua. In 2017, astronomers discovered an object in the Solar System which seemed . [+] out of place. Its orbit is highly hyperbolic, not parabolic, which implies it originated outside of the Solar System and is just passing through. The interloper has been named Oumuamua Hawaiian for scout or messenger. Follow-up observations have revealed that Oumuamua is very oddly shaped, like a cigar, more elongated than any known Solar System object. Estimates put its size at 200 x 30 x 30 m, and its rotational period at 8.14 hours. An alternative possibility, however unlikely, has been mentioned in a scientific paper - that the object might actually be an alien spacecraft such as a solar sail (left).
Mission 7: search existing data
Such as objects in orbit around exoplanets, pollution in exoplanet atmospheres and the detection of night-time illumination on exoplanets.
Mission 8: conduct all-sky laser searches
Short laser pulses could be searched for in visible light and in wide regions of the infrared with a single instrument.
Mission 9: study small asteroids
Asteroids under 10m in diameter may be artificial, but we’ve never looked. Anything with very flat metallic surfaces will high reflectivity polarize reflected light.
Wishing you clear skies and wide eyes.
I'm an experienced science, technology and travel journalist and stargazer writing about exploring the night sky, solar and lunar eclipses, moon-gazing, astro-travel,
