Larry Niven must be getting a good chuckle out of this:

During its close fly-bys of Saturn's ring system, Cassini's instruments showed that the environment around the rings is an atmosphere composed mainly of oxygen molecules, similar to the atmospheres of Jupiter's moons Europa and Ganymede, the European Space Agency said in a statement.

"As water comes off the rings, it is split by sunlight; the resulting hydrogen and atomic oxygen are then lost, leaving molecular oxygen," said Andrew Coates, a co-investigator from University College, London.

No word yet on whether Cassini has imaged any integral trees.