differentiation may have been, or what elements of biological interest may have been lost to space as that differentiation took place.

Chemosynthesis may have occurred either at the present or in the past. Terrestrial chemosynthetic organisms take advantage of sluggish oxidation-reduction reactions as energy sources. Many redox reactions remain far from equilibrium owing to kinetic constraints, and life has evolved many ways of taking advantage of redox disequilibria involving iron, sulfur, carbon, nitrogen, manganese, arsenic, uranium, and other redox-sensitive elements. Redox reactions may also supply the chemical energy that could drive organic synthesis or the processing of organic compounds into primitive versions of biomolecules.

One test of whether Europa can support life is to identify whether there are sources of chemical energy available that are sufficient to drive metabolism. Measurements of the nature and abundance of chemical species within the water, the extent of any redox disequilibrium, and the abundance, if any, of organic molecules will help to determine the biological potential within the ocean.

REFERENCES

1. J.D. Anderson et al., "Europa's Differentiated Internal Structure: Inferences from Two Galileo Encounters," Science 276: 1236, 1997.

2. J.D. Anderson et al., "Europa's Differentiated Internal Structure: Inferences from Four Galileo Encounters," Science 281: 2019, 1998.

3. C. Allen et al., "Airborne Radio Echo Sounding of Outlet Glaciers in Greenland," International Journal of Remote Sensing 18: 3103, 1997.

4. D.J. Drewry, Antarctica: Glaciological and Geophysical Folio, Scott Polar Research Institute, Cambridge, U.K., 1983.

5. V.V. Bogorodsky, C.R. Bentley, and P.E. Gudmandsen, Radioglaciology, D. Reidel Publishing Co., Dordrecht, the Netherlands, 1985.

6. K.M. Golden et al., "Inverse Electromagnetic Scattering Models for Sea Ice," IEEE Transactions on Geoscience and Remote Sensing 26: 1675, 1998.

7. C.F. Chyba, S.J. Ostro, and B.C. Edwards, "Radar Detectability of a Subsurface Ocean on Europa," Icarus 134: 292, 1998.

8. M.G. Kivelson et al., "Discovery of Ganymede's Magnetic Field by the Galileo Spacecraft," Nature 384: 537, 1996.

9. M.G. Kivelson et al., "Europa and Callisto: Induced or Intrinsic Fields in a Periodically Varying Plasma Environment," Journal of Geophysical Research, submitted 1998.

10. T. Denk, G. Neukum, T.B. McCord, G.B. Hansen, C.A. Hibbits, P.D. Martin, and the Galileo Team, "Candidate Surface Materials of the Icy Galilean Satellites That Might Be Distinguished by the Galileo SSI Camera," abstract, 29th Lunar and Planetary Science Conference, Lunar and Planetary Institute, Houston, Texas, 1998.

11. A.L. Lane, R.M. Nelson, and D.L. Matson, "Evidence for Sulphur Implantation in Europa's UV Absorption Band," Nature 292: 38, 1981.

12. K.S. Noll, H.A. Weaver, and A.M. Connella, "The Albedo Spectrum of Europa from 2200 Å to 3300 Å," Journal of Geophysical Research 100: 19057, 1995.

13. T.B. McCord, G. Hansen, F.P. Fanale, R.W. Carlson, D. Matson, T.V. Johnson, W. Smythe, J.K. Crowley, P.D. Martin, A. Ocampo, C.A. Hibbits, J.C. Granahan, and the NIMS Team, "Salts on Europa's Surface Detected by Galileo's Near Infrared Mapping Spectrometer," Science 280: 1242, 1998.

14. J.S. Lewis, "Satellites of the Outer Planets: Their Physical and Chemical Nature," Icarus 15: 174, 1971.

15. J.S. Kargel, "Brine Volcanism and the Interior Structures of Asteroids and Icy Satellites," Icarus 94: 368, 1991.

16. J.S. Kargel, "Brine Volcanism and the Interior Structures of Asteroids and Icy Satellites," Icarus 94: 368, 1991.

17. B.M. Jakosky and E.L. Shock, "The Biological Potential of Mars, the Early Earth, and Europa," Journal of Geophysical Research 103: 19359, 1998.



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