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. There could be creatures either the size of great white whales or creatures even bigger.