Two years ago, when NASA's Cassini Solstice spacecraft flew past the moon Dione, it noticed something familiar. Oxygen is present in Saturn's third-largest moon's exosphere (its extended, tenuous atmosphere), and according to research published this week, Cassini's hi-tech "nose" had sniffed it.
Obviously, the first thing that springs to mind when discussing oxygen is that it's a pretty important component for life on Earth. But Dione, a barren and icy world, possesses few attributes that would make it suitable for life as we know it.
Although it is known to be composed of significant quantities of water ice, there is no indication — unlike sister Saturn moon Enceladus — that there is any sub-surface aquifer of liquid water. Liquid water is key to the evolution of life.
So why is the discovery of oxygen in Dione's exosphere important? If Dione's got it, then perhaps its sibling moons also have it, giving us a tantalizing clue as to the possibility of life on the natural satellites around Saturn and Jupiter.
"Some of the other moons have liquid oceans and so it is worth looking more closely at them for signs of life," Andrew Coates, of University College London and lead scientist of the study, told BBC News.
It is thought the oxygen is being produced via interactions between Saturn's powerful radiation belts and Dione's water ice. The radiation breaks the water molecules down, liberating oxygen into the moon's exosphere.
This most recent discovery will no doubt give a boost to scientists lobbying for sending missions to the gas giant's satellites to search for alien life as, like the presence of liquid water, the presence of oxygen could support microscopic lifeforms on other, more habitable moons.
The Cassini research has been published in the journal Geophysical Research Letters.
Images: Top: Dione hangs above Saturn's magnificent rings. Bottom: Dione emerges from behind its sibling Titan's hazy atmosphere. Credit: NASA/JPL/Space Science Institute. For more spectacular views from Cassini, visit the Cassini Imaging Central Laboratory for Operations (CICLOPS) website.