Chemistry and Astrobiology of Oceans on icy Galilean satellites

Interpretations of Galileo spacecraft data are consistent with the presence of a subsurface ocean and have stimulated new ideas about the habitability of Jovian icy satellite Europa. These data include the detection of induced magnetic field caused by currents in a subsurface conductive material [Kivelson et al. 2000], detection of non-ice species in colored and disrupted surface areas [McCord et al., 1999], as well as shifting and tilting of icy blocks in several places (see Galileo NASA image of the Conamara region; colored areas are represented by non-ice material that could have been delivered from the subsurface ocean). 

Galileo electromagnetic data for Ganymede and Callisto, together with the composition of non-icy surface materials on Ganymede, provide indirect evidence for deep layers of liquid water on these satellites as well.  These data raise questions about the formation, survivability, chemical composition, and habitability of all three icy satellites of Jupiter.

In GEOPIG, major research is focused on chemistry of the oceans, chemical processes at oceanic floors, physical-chemical aspects of formation of the oceans, evolution of oceanic chemistry throughout the history, as well as evaluation of chemical sources of energy for potential life. Our major method is theoretical thermodynamic analysis, which include calculation of equilibrium speciation and reaction-path modeling in water-rock-gas type multicomponent systems, and development of phase diagrams. One of our goals is to explain formation of chemical compounds (e.g., sulfates, carbon dioxide) observed on the satellites' surfaces in terms of aqueous endogenic processes. Results of our modeling are compared with chemical, mineralogical and isotopic patters of carbonaceous chondrites, which could be considered as meteoritic analogs for the Galilean satellites. 

Ongoing research projects:

  • Chemical models for formation of oceans on Europa and other icy Galilean satellites. We propose that alteration of water with reduced solar nebular components lead to formation of hydrogen, which escapes into space. Escape of hydrogen from icy satellites caused oxidation of silicate mantles and could have lead to formation of oxidized sulfate-carbonate fluids, which form oceans. Leaching of sulfates from carbonaceous chondrite type material in not likely because of secondary nature (parent body) of sulfates in chondrites. We collaborate with Dr. William McKinnon (Washington University in St. Louis) on this work. Some results are published by Zolotov and Shock [2000a, 2001a; 2001b; 2001c; 2002a; 2003c].
  • Chemical composition and the oxidation state of present-day ocean on Europa. We perform mass-balance calculations, develop phase diagrams, and perform equilibrium calculations in multicomponent systems to evaluate equilibrium speciation on ocean water and sediments. This work also allows us to infer chemical disequilibria in the ocean and at the ocean-rock interface that could be used by non-photosynthetic life to gain energy for metabolism. Some results are published [Zolotov and Shock 2001a; 2001c; 2002b; 2003a].
  • Biogeochemical cycles of S, C, and Fe in the Europan ocean. We use thermodynamic calculations, published data on reaction kinetics, and known microbial metabolic reactions to evaluate abiotic and possible biologic pathways of elements on Europa. Preliminary results are published by Zolotov and Shock [2000b].
  • Hydrothermal activity as a source of chemical energy for microbial life in Europan ocean. In the framework of this project, we evaluated energy that could support sulfate-reducing organisms in a hydrothermally formed ocean on Europa [Zolotov and Shock 2003a; 2003b].

Publications:

Glein, C. R., Zolotov, M. Yu., and Shock, E. L. (2007) Hydrothermal Geochemistry as the Source of Plume Gases on Enceladus, XXXVIII Lunar and Planet. Sci., [CD-ROM], abstract 1251.

Zolotov, M. Yu., and Shock, E. L. (2006) Chemical Evolution of Europa’s Ocean: Insights from Chondrites, Europa Focus Group, Workshop 5, Moffett Field, California, February 27-28, 2006, abstracts, 135-136.

Zolotov, M. Yu., Krieg, M. L., Shock, E. L., and McKinnon, W. B. (2006) Chemistry of a Primordial Ocean on Europa, Astrobiology, 6(1), p. 162.

Zolotov, M. Yu., Krieg, M. L., Shock, E. L., and McKinnon, W. B. (2006) Chemistry of a Primordial Ocean on Europa, XXXVII Lunar and Planet. Sci., [CD-ROM], abstract 1435.

Zolotov, M. Yu., Owen T., Atreya S., Niemann H., and Shock, E. L. (2005) An Endogenic Origin of Titan’s Methane, Eos Trans. AGU, 86(52), Fall Meet. Suppl., Abstract P43B-O4, Invited.

Zolotov, M. Y., and Shock, E. L. (2004) A Model for Low-Temperature Biogeochemistry of Sulfur, arbon, and Iron on Europa. J. Geophysical Research, [Planets] 109, E06003, doi: 10.1029/2003JE002194.

Zolotov, M. Yu., Shock, E. L., Barr, A. C., and Pappalardo, R. T. (2004) Brine Pockets in the Icy Crust of Europa: Distribution, Chemistry, and Habitability. In Workshop on Europa’s Icy Shell: Past, Present, and Future, 100-101, LPI Contribution No. 1195, Lunar and Planetary Institute, Houston.

Zolotov, M. Y., and Shock, E. L. (2003a) Energy for Biologic Sulfate Reduction in a Hydrothermally Formed Ocean on Europa, Journal of Geophysical Research, [Planets] 108, E4, 5022, 10.1029/2002JE001966.

Zolotov, M. Yu., and Shock, E. L. (2003b) Autotrophic Sulfate Reduction in Hydrothermally Formed Ocean on Europa. Astrobiology 2, No. 4, 514.

Shock, E. L., McKinnon, W., and Zolotov, M. Yu. (2003c) Habitability of Icy Galilean Satellites. Seventh Exobiology Principal Investigators Science Conference, NASA Ames Center.

Zolotov, M. Yu., and Shock, E. L. (2003c) Aqueous Oxidation of Parent Bodies of Carbonaceous Chondrites and Galilean Satellites Driven by Hydrogen Escape, XXXIII Lunar and Planet. Sci., [CD-ROM], abstract 2047.

Zolotov, M. Yu., Shock, E. L. and McKinnon, W. B. (2002a) Effects of Early Water-Rock Chemical Interactions on Interior Structures, Physical Properties, and Heat Balances of Galilean Satellites. Eos Trans. AGU, 83 (47), Fall Meet. Suppl., F839.

Zolotov, M. Yu., and Shock, E. L. (2002b) The Speciation of Sulfur in an Ocean on Europa, XXXIII Lunar and Planet. Sci., [CD-ROM], abstract 1531.

Zolotov, M. Yu., and Shock, E. L. (2001a) Composition and Stability of Salts on the Surface of Europa and their Oceanic Origin. Journal of Geophysical Research, [Planets] 106, 32815-32828.

Zolotov, M. Yu., and Shock, E. L. (2001b) Geochemical Constraints on the Oxidation States of the Europan Ocean and Mantle, XXXII Lunar and Planet. Sci., [CD-ROM], abstract 2025.

Zolotov, M. Yu., and Shock, E. L. (2001c) A Hydrothermal Origin for the Sulfate-Rich Ocean of Europa, XXXII Lunar and Planet. Sci., [CD-ROM], abstract 1990.

Zolotov, M. Yu., and Shock E. L. (2000a) The Oxidation State of Europa and Other Galilean Satellites. Eos Trans. AGU, 81, No. 48, F790.

Zolotov, M. Yu., and Shock, E. L. (2000b) A Microbial Cycle for Organic Carbon and Sulfur in the Vicinity of the Oceanic Floor on Europa. First Astrobiology Science Conference, April 3-5, 2000, California, NASA Ames Research Center, 17.