Jupiter's moon Europa should have enough oxygen-rich water to support not only simple micro-organisms but also complex life, according to a University of Arizona researcher who studies ice flows on the frozen moon.

Judging by how quickly Europa's surface ice is replenished, Richard Greenberg estimates that enough oxygen reaches the subterranean ocean to sustain "macrofauna" — more complex, animal-like organisms.

Assuming Europa life forms would need as much oxygen as Earth-like fish, Greenberg estimates the moon's ocean has enough oxygen to support 6.6 billion pounds of macrofauna.

A key question about whether Europa can support life has been whether its suspected buried ocean contains adequate levels of oxygen.

Although scientists have found life on Earth around deep-ocean vents and hot springs that use sulfur or methane-based chemistry, it is unknown whether Europa's ocean floor sports similar features.

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Greenberg believes oxygen in Europa's ocean can arrive from energetic particles from the sun, despite the fact that the ocean is buried beneath a thick layer of ice. Analysis of Europa's surface, which is unusually smooth and crater-free compared to other bodies in the solar system, suggests that the top layer of ice is relatively young, just 50 million years old or so.

Greenberg outlines three possibilities for Europa's resurfacing: fresh material layers on top, opening cracks in the ice that fill with new material, and/or patches of ice that are disturbed and replaced with fresh material.

Based on estimates for the production of oxidizers at the surface, Greenberg says oxygen buildup in Europa's ocean is happening so quickly that it could exceed that of the Earth's oceans in a few million years.

"We do not have definitive evidence for the existence of a liquid ocean, but the information we do have is compelling," Arizona State University planetary geologist Ronald Greeley told Discovery News.

"If there is evidence for oxygenation, then the presence of oxygen would certainly increase the environmental conditions for life. It doesn't mean life is there," he added, " just that there might be free oxygen available to support biological processes."

Greenberg is scheduled to present his findings at the American Astronomical Society's Division for Planetary Sciences in Puerto Rico on Friday.