...a new report in the Jan. 27 (year 2000) issue of the journal Nature concludes that Europa does indeed contain plenty of biological fuels, thanks to billions of charged particles that constantly rain down from neighboring Jupiter.
This relentless bombarbment of radiation "should produce organic and oxidant molecules sufficient to fuel a substantial Europan biosphere," writes Christopher Chyba, associate professor (research) of geological and environmental sciences.

According to Chyba, when these ions slam into the icy surface of the moon, chemical reactions are likely to occur, transforming frozen molecules of water and carbon dioxide into new organic compounds such as formaldehyde.
It turns out that one of the most common bacteria on Earth, Hyphomicrobium, survives on formaldehyde as its sole source of carbon, and Chyba believes that similar formaldehyde-feeding microbes could be alive and swimming in Europa's subsurface ocean.

But Chyba notes that the oxidant and organic molecules formed on Europa's frigid surface "are biologically relevant only if they reach the ocean."

a team from the University of Hawai'i, the Jet Propulsion Laboratory, the U.S. Geological Survey, and STI Inc. may have given us our first glimpse at the chemical composition of that ocean. Using data obtained by the Near-Infrared Mapping Spectrometer (NIMS) carried by Galileo, Thomas McCord (U. Hawai'i) and his colleagues examined darker regions on the surface and compared the spacecraft data to numerous chemical compounds. Their analysis indicates that the darker areas are most likely composed of deposits of salty minerals such as sulfates and carbonates. McCord and his associates believe that the minerals formed when ocean water erupted onto the surface and then evaporated, leaving behind salty deposits. They hope that further research will allow them to determine the chemical composition of Europa's hidden ocean and assess the likelihood that life could have formed in it.

Europa has a complicated surface. It has brighter and darker regions, is crisscrossed by ridges and troughs, and large pieces of the crust appear to have rotated. The mottled nature of the surface is seen clearly in images of an entire hemisphere. In spite of these variations, however, the surface is made up mostly of water ice. The brownish areas appear to be mixtures of ice and something else. Tom McCord and his colleagues wanted to find out what that something else is.

Close-up views of the surface show even more complexity. Some regions are appropriately called "chaotic terrain," such as the Conamara region shown in the image below. Large chunks of the crust have been disrupted, tilted, and rotated. The appearance resembles icebergs somewhat, leading mission scientists to conclude that the thin crust floated on a layer of water or slush, an underground ocean. Movement of the water in the ocean placed stresses on the solid crust, causing huge pieces to break, move, and possibly sink. It is not known if the ocean exists at present or if the surface features reflect conditions billions of years ago.