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Chap e
Is he Ocean o Enceladus in a
P imi i e E olu iona y S age?
Ka he ine Villa icencio Vale o, Emilio Ramí ez Juidías
and Aina À ila Bosch
Abs ac
Enceladus has a subsu ace ocean in he Sou h Pole ha has been in e ed due o
he p esence o wa e apo and o he molecules like molecula hyd ogen and ammo-
nia de ec ed by he Cassini mission om he ejec ion o ma e ial h ough he plumes
in ha egion. The chemical composi ion o his ocean could gi e some in o ma ion
abou he e olu iona y s age o he icy moon i i s componen s a e ound o be simila
wi h he aqueous chemis y o he p imi i e oceans on Ea h du ing glacial pe iods.
He e we p esen a compa a i e geochemical analysis be ween he ocean o Enceladus
and he aqueous composi ion o he oceans on Ea h du ing he Snowball E en , in
o de o igu e ou i he e a e simila species, how he in e ac ion o he me abolic
p ocesses be ween hem wo ks and i , in he u u e, hose molecules could e ol e
making possible he eme gence o li e.
Keywo ds: ocean, snowball e en , aqueous chemis y, species, li e
1. In oduc ion
Enceladus, one o he moons o Sa u n, p esen s a global ocean benea h he ice
shell [1]. The exis ence o ha ocean was sugges ed because o he wa e apo
de ec ed by he Cassini mission, h ough he ejec ion o ma e ial om he plumes
loca ed in he sou h pole [2, 3]. The expulsion o ma e ial om he wa e plumes could
be ela ed o hyd o he mal ac i i y [4], whe e ice pa icles a e hea ed due o he idal
de o ma ion [5] and expelled o he su ace. E idence ha hose pa icles a e associ-
a ed o hyd o he mal ac i i y a e he silica e sal s esidues ound a he E- ing [6], and
he small size o he nanopa icles o ha ing. Bo h cha ac e is ics indica e ha he
possible liquid wa e wi hin he ocean laye was p e iously in con ac wi h a ho
silica e en i onmen [7].
The Ion and Neu al Mass Spec ome e (INMS) ins umen on boa d o he
Cassini mission also de ec ed ammonia and some aces o o ganic molecules like
benzene [8]. Ammonia is one mo e clue o he p esence o liquid wa e . Residuals
om ammonia a e ni ogen-bea ing and oxygen-bea ing molecules ha , in combina-
ion, could con e in o amino acids like i happens on Ea h [9]. O he de ec ed
species we e H2O and CO2[10]. The me abolic in e ac ion be ween hese la e wo
1
species, h ough me hanogenesis, can o m me hane. I was also de ec ed molecula
hyd ogenH2by he Cassini spacec a [11]. The e we e also ound some species wi h
compounds o ca bon, ni ogen, oxygen and sul u [8, 12, 13]. The in e ac ion
be ween molecula hyd ogen and some ca bona es wi hin he ocean p oduce a chem-
ical ins abili y ha cons i u es an ene gy sou ce ha may suppo li e [11].
The Cosmic Dus Analyze (CDA) aboa d o he Cassini mission de ec ed wa e
ice, o ganic molecule, and siliceous ma e ial [14]. The e we e also de ec ed concen-
a ions o Na, and some sodium sal s like NaCl, NaHCO3and Na2CO3indica ing he
p esence o liquid wa e [15, 16]. To main ain his liquid wa e in o he global ocean,
he idal dissipa ion could be conside ed as an ene gy sou ce ha come om inside
Enceladus [17]. Tidal hea ing also ac s in he solid co e p o oking high empe a u es
in o he hyd o he mal ac i i y [18]. The hyd o he mal ac i i y c ea es con ec ion
columns ha p oduce a dynamic mo emen in he ocean anspo ing he hea in o
he ice shell om he co e [19]. The dissipa ion o he hea linked o he gas a ios
p esen in he wa e plume could de e mine he s a e o he hyd o he mal ac i i y [7].
Acco ding o Woods [20], a hyd o he mal sou ce o gas could explain he dis ibu ion
o hyd ogen in he wa e plume. In his sense, i mus be emphasized ha he abundance
o hyd ogen de ec ed is simila o some aces o ola ile compounds like ca bon dioxide,
me hane, and ammonia [8]. Labo a o y simula ions [7] sugges ed ha , in Enceladus, he
molecula hyd ogen is a p oduc o in e nal eac ions. E idence o he in e nal p oduc-
iono molecula hyd ogenis hehigh a ioo H
2=H2O which canno come om a gas
apped in he ocean, because o i s high concen a ion, and i canno also come om he
emnan s o a o ma ion en i onmen , due o he low a io o He=H2[21].
The geochemical sys em o he ocean o Enceladus could be composed mainly
byNa2O -HCl-CO2-H2O. The concen a ion o CO2in he plumes is assumed o be he
same ha may be ound in he dissol ed molecules o he subsu ace ocean. I s
p esence sugges s a basic pH o he ocean o Enceladus. The es ima ion o his pH is
based on he s udy o he he modynamic equilib ium, conside ing he empe a u e
close o 0°C, he p essu e a 1 ba , he ca bon dioxide ac i i y, he chlo ide concen-
a ion, and he dissol ed ino ganic ca bon HCO3=CO32. Acco ding o Glein e al.
[22], he pH is 12.15 1.15.
Ca bona es and bica bona es ions CO32=NaCO3a e also p esen in he ocean
[23] and could come om soluble ca bona e mine als, o med h ough he eac ion o
a apped CO2and silica mine als du ing wa e - ock di e en ia ion. I he ocks o he
ocean eac wi hCO2, i is easible he ca bona ion p ocess o high wa e - ock a ios
[24]. The me al concen a ion in he seawa e is o med by phyllosilica es and
hyd oxide mine als, ha need an acid in o de o hyd olyze and being inco po a ed
in o ca bona e mine als [23].
CO2=H2O a io in he plume o Enceladus is simila o he a io ound in he
seawa e on Ea h [23], whe e heCO2ac i i y is con olled by al e a ion o mine als,
assuming ha wa e - ock in e ac ions a e he main d i ing o ce o he pH as well as
he composi ion o he ocean. On Enceladus, he se pen iniza ion is assumed o be he
esul o mine als al e a ion [25], h ough a hyd olysis o p ima y mine als con aining
i on and magnesium which p oduc is he hyd ogen. This p ocess is usually associa ed
wi h ul ama ic ocks (<45% o SiO2and high Mg - Fe con en ), which eac ion ha
akes place is he oxida ion by wa e o Fe(II) and Fe(III) in mine als such as oli ine
and py oxene. The p oduc o his eac ion is he molecula hyd ogen.
The p esence o hyd ogen can o m linea chains o hyd oca bons like me hane
CH4 om he chemical eac ion be ween CO2and H2. This me hane could be p esen
2
As onomy and Plane a y Science - F om C yo olcanism o Black Holes and Galac ic E olu ion
in low concen a ions in o he ocean o Enceladus [26]. E idence o his, i is he
o ma ion o cla h a es ha a e able o ap ce ain molecules, which hen, would ise
o he su ace and e en ually dissocia e and en ich he plume wi h me hane. Me hanol
was also de ec ed by he Cassini mission; i is possible ha his compound has a
biological o igin [27]. I was ound ha he CH3OH=H2O a io has ce ain co ela ion
wi h bio ic ac i i y a ound he hyd o he mal en s. The concen a ion o me hanol
de ec ed in he a mosphe e is high, which gi es a clue abou ha his specie is o med
benea h he ice shell be o e being expelled in o he a mosphe e. These o ganic com-
pounds de ec ed could be conside ed as a building block o li e o e en by-p oduc s o
li e [28].
On Ea h, he i s signs o li e came om he A chean oceans whe e he oxida i e
eac ions we e a p oduc o he in e ac ion be ween molybdenum and henium [29].
The e we e only aces o oxygen be o e he G ea Oxygen E en bu hen, a e i , he
pho osyn he ic ac i i y led o an inc emen o his elemen [30]. The e olu ion o
oxygen in he a mosphe e and oceans wen h ough i e s ages [31]. Du ing he
C yogenian age, he a mosphe e and he shallow oceans had an inc ease o oxygen.
The oxygen concen a ion was s agnan in ha e a, and subsequen ly i had an inc e-
men ha con inued a e he nex million yea s and migh ha e culmina ed a ound
he Ca boni e ous age. Du ing glacial pe iods, he concen a ion o CO2in he a mo-
sphe e d opped and, be o e he eme gence o pho osyn he ic li e, he ca bon dioxide
was mo e abundan in he a mosphe e han nowadays [32].
Abundance o CO2in he a mosphe e du ing ha ime would be a consequence o
a ca bon-silica e cycle du ing millions o yea s ha a e changed he Snowball e en s
condi ions [33]. The concen a ion o oxygen was low in he oceans du ing he Snow-
ball pe iods. The wa e had a high le el o acidi y due o he high concen a ion o CO2
in he a mosphe e [32]. The ice-co e ed condi ions on Ea h we e al e ed because o
he mel ing o he ice c us ha ook place due o he inc ease o he empe a u e by
olcanoes ac i i y, which educed he p esence o CO2in he a mosphe e and p o-
oked he eme gence o liquid wa e [34]. The high olcanic ac i i y igge ed he
ex ensi e p esence o hyd o he mal en s du ing he C yogenian age [35–37].
Nowadays, hyd o he mal sys ems can be classi ied as black smoke s and los ci y
sys ems. The i s one, a e cha ac e ized by he black smoke ha ises om he
chimney-like ocky o ma ions, whe e seawa e is in con ac wi h he magma cham-
be s and eme ges wi h an acid pH 2–3, a high con en o dissol ed me als such as Fe
(II) and Mn (II), a a ie y o gases o igina ed om olcanic ac i i y like CO2,H
2S, H2,
CH4and also wi h high empe a u es up o 405°C. In con as , in he los ci y sys ems,
he wa e ha ci cula es ough he en s is no in con ac wi h he magma, ins ead, i
is hea ed by con ec ion om he man le and by exo he mic chemical eac ions
be ween he luid and he su ounding ocks eaching empe a u es o 200°C [35].
The ock ha in e ac s wi h he luid is domina ed by low-silica i on and magnesium
ich mine als, p o oking he me hanogenesis by se pen iniza ion o he hyd ogen and
he educ ion o ca bon dioxide in he ocean. In his case, he pH o he luid is basic
9–11, i has dissol ed gases likeH2,CH
4, low-mass o hyd oca bons, and a low
dissol ed CO2.
Simila i ies could be ound along wi h he ancien oceans on Ea h du ing he
Snowball E en s and he cu en condi ions o he ocean on Enceladus. He e we
p esen a compa a i e geochemis y analysis o bo h oceans. We also desc ibe a
chemical me abolic p ocess based on nume ical simula ions ha could ake place
wi hin he global ocean o Enceladus, in o de o in e i he cu en condi ions o ha
3
Is he Ocean o Enceladus in a P imi i e E olu iona y S age?
DOI: h p://dx.doi.o g/10.5772/in echopen.104862
ocean could e ol e o c ea e he building chains o li e. Du ing glacia ions ages, he
ice-co e ed Ea h allowed o main aining he liquid wa e benea h he ice c us , and
subsequen ly ha liquid wa e eme ged o he su ace by he ho spo s o hyd o he -
mal en s once he high concen a ion o CO2s a ed changing he condi ions o he
a mosphe e [38]. On Enceladus, he e a e hin s ha indica e he p esence o liquid
wa e , such as he hyd a ed sodium sal s de ec ed by he Cassini mission. The molec-
ula hyd ogen ound also gi es clues abou a hyd o he mal ac i i y benea h he ice
shell. We aim o in e a possible e olu iona y s age o he ocean o Enceladus ha
could make possible he eme gence o li e.
2. S udy a ea
Models o he in e nal s uc u e o Enceladus e eals an ocean on a e age 26–
31 km in dep h below an ice laye be ween 21 and 26 km o hickness [39]. Salini y
geochemis y simula ions o he ocean o Enceladus show alues nea ly simila o
Ea h, a ound 20 g/kg [40, 41]. The quan i y o wa e apo ejec ed om he plumes
is a ound 150–300 kg/s [42]. This ejec ion o pa icles supply he composi ion o he
ing E o Sa u n, wi h <10% o he ma e ial ca ching in o i , also sugges ing a liquid
o igin [43, 44]. Figu e 1 shows he dis ibu ion o he plumes along he sou h pole o
Enceladus.
Figu e 1.
Digi al ele a ion model (DEM) o he plumes called “Tige s ipes”loca ed in he sou h pole o Enceladus. I was
used he images aken by he Cassini Mission. This DEM was de eloped using he so wa e TopoCal 2022
.9.0.811.
4
As onomy and Plane a y Science - F om C yo olcanism o Black Holes and Galac ic E olu ion

Benea h he sou h pole he composi ion o he pa icles is mainly sal ich, implying
ha hose sal s a e la ge han sal -poo g ains and hey a e expelled wi h lowe escape
eloci y. The escape speed o pa icles om he plumes in Enceladus is on a e age
1.85–2.25 km/s, acco ding o he measu es om he dus y plume by he lyby o he
Cassini spacec a [45]. Figu es 2 and 3show he longi udinal (y axis) and ans e sal
(x axis) heigh p o iles o he plumes o Enceladus om Figu e 1. The longi udinal
axis o Figu e 2 p esen s a adius in he cen al plume o 190 m, besides, he ans-
e sal axis o Figu e 3 shows a adius o 90 m. The dis ibu ion o he issu es along
he plumes seems o be aligned in he y axis.
3. Ma e ials and me hods
In his esea ch, we used he da a o he molecula species de ec ed by he INMS
ins umen on boa d o he Cassini Mission. The spec al signa u es we e encoded
acco ding o Ramí ez-Juidías e al. [46]. Then, he e we e selec ed he common
spec al lines p esen in he ocean o Enceladus and in he seawa e o he oceans on
Ea h. Based on he spec al lines, i was applied da a mining in o de o ex ac he
Figu e 2.
Ele a ion p o ile o he DEM om op o bo om.
Figu e 3.
Ele a ion p o ile o he DEM o he cen e om le o igh .
5
Is he Ocean o Enceladus in a P imi i e E olu iona y S age?
DOI: h p://dx.doi.o g/10.5772/in echopen.104862
concen a ion o species de ec ed in he ma e ial ejec ed om he plumes. Table 1
shows some o he species p esen in he ocean o Enceladus and he seawa e o he
oceans on Ea h [47] wi h hei concen a ion in g/kg. Each specie was ex apola ed
o he geochemical p ocesses associa ed o he ac i i y o CO2and H2O wi hin he
ocean [22].
Acco ding o he me hod pa en ed by Ramí ez-Juidías e al. [46], he da a mining
p ocess was ca ied ou h ough he applica ion o modi ied gene ic algo i hms, i e a-
i ely analyzing a la ge amoun o da a h ough a p ocess simila o gene ic mu a ion,
in o de o ex ac he a iables ha a e hen used o ob ain he concen a ions (g/kg)
o species in he ocean o Enceladus, using he wa eleng hs be ween 0.35 and 1 μm
om he spec al da a aken by he VIMS ins umen .
The encoding model de eloped o ob ain hese concen a ions consis s in
building a ec o o size equals o he numbe o i e a ions o execu e. The k h-o de
o he ec o ep esen s he wo k ha is done in he k h-posi ion. In his case, a
popula ion o al e na i e solu ions is se led o a ce ain numbe o ch omosomes,
ha ep esen he na u al sequence in which he a iables (spec al signa u es) a e
p og ammed.
The p ocess o planning and p og amming equi ed o he ex ac ion o he
concen a ions o species is usually conduc ed by applying a h ee-le el model called
espec i ely S a egic App oach, Tac ical App oach and Ope a ional App oach. This
model can be eplica ed using machine lea ning.
Species Enceladus concen a ion (g/kg) Ea h concen a ion (g/kg)
BOHðÞ
40,008
BOHðÞ
30,019
B 0,067
Ca2þ0,412
Cl7076 19,353
CO322867 0,016
F0,013
HCO30,031 0,107
Kþ0,399
Mg2þ1284
Naþ7343 10,784
NaCl 0,024
NaCO31788
NaHCO30,015
NaOH 0,008
OH0,038
SO420,1–0,01 2713
S 2þ0,008
Table 1.
Concen a ion o species in he ocean o Enceladus and in he seawa e o he oceans on ea h.
6
As onomy and Plane a y Science - F om C yo olcanism o Black Holes and Galac ic E olu ion
4. Resul s and discussion
Sodium ion and Chlo ine a e he mos abundan species in he ocean o Enceladus.
Figu e 4 shows he concen a ion o bo h species in mol pe kg o H2O. The quan i y
o mol is calcula ed in unc ion o he CO2ac i i y. Naþis p esen in concen a ions
a ound 0.800 mol/kg while he concen a ions o Cla e cons an , a ound 0.400 mol/
kg. Figu e 5 also shows ha he e a e p esen some ca bona es CO32, bica bona e
HCO3and sul a e SO42.CO
32has a concen a ion on a e age 0.075–0.030 mol/kg
which ends o dec ease wi h he ac i i y o CO2. HCO3p esen s an inc emen om
0.020 o 0.070 mol/kg and SO42has a concen a ion be ween 0.01 and 0.1 mol/kg.
The concen a ions o salini y and chlo ini y a e ela i ely cons an in he cu en
e es ial oceans. The a e age concen a ion om he seawa e wi h a pH o 8.1 and
empe a u e o 25°C a e de ailed in Table 1. Geological in o ma ion ex ac ed om
sedimen a y laye s e eals ha deep oceans we e in a educed s a e ill he end o he
Paleop o e ozoic e a. I on and calcium sul a e p obably played as educed agen s wi h
he oxygen con e ing FeO in o Fe2O3, and p ecipi a ing CaSO4. Du ing he
Figu e 4.
Sodium ion and chlo ine p esen in he ocean o Enceladus. The concen a ion o species a e calcula ed in unc ion
o he CO2ac i i y.
Figu e 5.
Some ca bona es, bica bona es, and sul a e p esen in he ocean o Enceladus. The concen a ion o species a e
calcula ed in unc ion o he CO2ac i i y.
7
Is he Ocean o Enceladus in a P imi i e E olu iona y S age?
DOI: h p://dx.doi.o g/10.5772/in echopen.104862
C yogenian e a he concen a ion o sulpha e could ise o le els simila o he ecen
ones, a ound 23 mol/kg o H2O [47].
Table 2 shows ew key species p esen in he ocean o Enceladus and in he
seawa e o he oceans on Ea h. Sodium ion and Chlo ine a e he mos abundan
species in bo h oceans. The oceans on Ea h a e sal ie wi h a pH o 8.1 on a e age,
while he ocean o Enceladus is mo e basic, a ound pH 12.2. The ocean o Enceladus
has mo e dissol ed ino ganic ca bon han he ocean on Ea h. On Enceladus, he
p edominan ca bona e is CO32while on Ea h is he bica bona eHCO3. The abun-
dance o CO32in he ocean o Enceladus could be due o he se pen iniza ion o he
molecula hyd ogen. The concen a ion o sul u in he ocean o Enceladus is a iable
compa ed o he one p esen on Ea h.
Two scena ios can be conside ed o calcula e he amoun o sulpha e ha could be
oxidized on he ocean o Enceladus. The lowe concen a ion o SO42, 0.01 g/kg,
displayed in Table 2, akes place only in aqueous educ an s en i onmen s whe e HS
eac s wi h he oxidan s, while in he la ge concen a ion 0.1 g/kg, some mine als a e
conside ed as a sou ce o educ an s. The concen a ion o sulpha e in he ocean o
Enceladus is below o he cu en amoun o sulpha e ound on he oceans on Ea h
bu , his concen a ion could ha e been smalle du ing he Snowball e en s, being
close o he cu en quan i ies on he ocean o Enceladus.
The p edominan concen a ion o ino ganic ca bona e species ound in he ocean
o Enceladus, se he ocean as no compa ible wi h li e excep o he me hane
de ec ed ha can be a p oduc o he me hanogenesis o he ca bon dioxide and he
hyd ogen. Would i be possible ha he species de ec ed in he ocean o Enceladus
e ol e o c ea e he chains o li e? how we e he chemical condi ions o he p imi i e
e es ial oceans be o e ising li e? In o de o igu e ou which simila i ies could be
ound be ween he e es ial oceans and he ocean o Enceladus, i is necessa y o
unde s and he e olu ion o he ancien aqueous geochemis y o he oceans in he
p imi i e Ea h.
Du ing he i s s age o o ma ion o Ea h, i was bomba ded by hyd ous as e -
oids mainly ype Cl chond i es b inging wa e , o ganic molecules, and chond i ic
mine als. Tec onic ac i i y acili a ed o di e si y he mine alogy along he c us ,
inc easing he ma ic con en o he op laye s h ough he e up ion o ho basal ic
la as. Chond i ic ma e ial has been also de ec ed in he plumes o Enceladus [14, 21],
ha is why, i could be possible o in e ha his ma e ial can be se led in he sea loo
o i s ocean [48].
O ganisms canno de ise chemical p ocesses by hemsel es, hey mus copy na u-
al eac ions, adap hem, and op imize hem h ough ime. Phospho yla ion is he
addi ion o a phospha e g oup in o a p o ein, being he main mechanism o
Species Enceladus concen a ion (g/kg) Ea h concen a ion (g/kg)
Cl7076 19,353
CO322867 0,016
HCO30,031 0,107
Naþ7343 10,784
SO420,1 - 0,01 2713
Table 2.
Concen a ion o species p esen in he seawa e o he oceans on ea h and in he ocean o Enceladus.
8
As onomy and Plane a y Science - F om C yo olcanism o Black Holes and Galac ic E olu ion
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