On the Chemical Composition of
Europa‘s Icy Shell, Ocean and
Unterlying Rocks
M. Yu. Zolotov (Arizona State University)
J. S. Kargel (University of Arizona)
By Isabella Kraus
Overview
• Introduction
• Composition of Icy Shell
 Brine, Salt and Gas Inclusions
• Chemistry of the Ocean-Rock System
 Basic Geochemistry of Ocean-Rock Interaction
 Salinity of Oceanic Water
• Chemical Evolution of the Water Layer
 Geochemistry of a Primordial Ocean
• Conclusion
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Introduction
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Introduction
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Introduction
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Introduction
• outer shell  dominated by water ice
• ocean  contains sulphate, Mg, Na, and Cl as major solutes
• ocean  evolved from a reduced Na-Cl solution toward a Mg
sulphate ocean
• Radioactive decay + tidal heating  melting icy shell
• chemical information  sparse at present
• surface oxidants (O2, H2O2) and possible H2SO4 hydrate  are
likely products of radiolysis and photolysis
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Introduction
• current icy shell  formed through freezing of oceanic water
• oceanic composition  affected by freezing from above, dissolution
of minerals in underlying rocks, mineral precipitation, degassing
processes and loss of volatiles to space
• Radiolysis, vapour cycling, gardening of the surface materials and
injection of material from Io  produced surface materials
• affected the composition of the deeper icy shell + ocean
• degassing of H2, N2, S and C volatiles  from the icy shell 
influenced the composition and oxidation state
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Introduction
• Mineral and/or organic precipitation  isolated the
suboceanic silicate crust from the ocean  influenced the
nature of ocean-rock interaction
• Euopa’s moment of inertia  composition and mineralogy of
the interior
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Composition of Icy Shell
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Composition of Icy Shell
• non-ice within the icy shell  geological structure of the shell
• tectonic processes  caused by tidal motions and/or
convection
• geologically young age of the surface  reflects the time of
significant ice melting/removal
• non-ice material  concentrated in the upper part of the
current (thick) shell
• a thicker shell  disrupted less often and slower freezing
would have led to less-efficient capture of oceanic solutes
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Brine, Salt and Gas Inclusions
• icy shell  contain salt, brine and gas inclusions
• formation  solutions/gases formed in the icy shell
• upper ice layer  radiolytically formed O2 and CO2
• typical “oceanic” inclusion  solids + contain aqueous (brine)
and gas phases
• brine/salt inclusions  contain abiotic or biogenic organic
molecules
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Brine, Salt and Glas Inclusions
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Brine, Salt and Glas Inclusions
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Brine, Salt and Glas Inclusions
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Chemistry of the
Ocean-Rock System
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The nature of suboceanic rocks
• differentiated interior  Fe or Fe-FeS core + silicate mantle
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upper parts of the mantle  resisted melting
 affected by silicate due to gravitational instability
tidal heating  silicate melting and suboceanic volcanism
uppermost mantle layers  never affected by volcanism
suboceanic rocks  presented by accreted chondritic-type
materials
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The nature of oceanic sediments
• sizeable fraction  Io’s particles ejected by impacts
• carbonaceous-chondrite-type fragments ejacted from outer
irregular satellites of Jupiter
• space materials  late heavy bombardment
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Salinity of Oceanic Water
•  mass of dissolved salts per specified mass of aqueous
solution
•  balance of mineral dissolution, secondary precipitation and
ionic exchange
• freezing  larger effect on oceanic salinity than evaporation
•  affected by thickness of the icy shell, the ocean and
permeable rocks
• Reflect  history, composition and oxidation state
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Salinity of Oceanic Water
• maximum  correspond to eutectic compositions
• Freezing  leads to near eutectic salinities of several
hundreds of g/kg
• lower limits  assuming saturation with respect to sparingly
soluble secondary minerals in suboceanic rocks
• thin icy shell ( 50-160 km thick ocean)  not consistent with
extremely high salinities at the salt saturations
• correspond to near-complete freezing
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Salinity of Oceanic Water
• low tidal activity  freezing of the icy shell, increasing salinity
of oceanic water, mineral precipitation and exsolution of
dissolved gases
• higher salinities  depress freezing temperatures + imply
colder oceanic water
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Chemical Evolution of
the Water Layer
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Geochemistry of a Primordial Ocean
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warming  by radioactive decay  more melting of ice
composition  formation subject to low-temperature (0°C)
composition of aqueous fluids  dissolution of minerals
very early fluids  low pH
• some of the models  there is not much subsequent waterrock interaction
• other models  there is extensive water-rock interaction
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Conclusion
chemical information  sparse
models suggest:
1) Hydration + oxidation in the upper parts of the mantle
2) preferential accumulation of Cl, Br, I and Na in a water ocean
3) alkaline pH of ocean-entering fluids  reactions with minerals
4) oceanic sediments  affected by the degree of freezing of the water shell
5) low-temperature redox disequilibria among solutes, solids, and gases
6) accumulation of carbonate in the outer layers of the body
7) escape of low-solubility volatiles (H2, N2, CH4 noble gases) into space
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Literatur
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http://commons.wikimedia.org/wiki/File:Europa-moon.jpg
http://commons.wikimedia.org/wiki/File:PIA01130_Interior_of_Europa.jpg
http://de.wikipedia.org/wiki/Europa_%28Mond%29
http://www.google.at/search?q=jupiter+system&source=lnms&tbm=isch&sa=X&ei
=oYXBUbDOCo3bsgaF0IDABw&ved=0CAcQ_AUoAQ&biw=1045&bih=516#facrc=_
&imgrc=3LRknAoiYgjRAM%3A%3BNQ8K4zi61frTrM%3Bhttp%253A%252F%252Fw
ww.seasky.org%252Fsolarsystem%252Fassets%252Fanimations%252Fsystem_menu_jupiter.jpg%3Bhttp%25
3A%252F%252Fwww.seasky.org%252Fsolar-system%252Fjupitermenu.html%3B910%3B450
Buch: Europa (On the Chemical Composition of Europa‘s Icy Shell, Ocean, and
Underlying Rocks)
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Danke für Ihre Aufmerksamkeit!