Rings of intrigue

SATURN’S rings may be vintage jewellery as old as the solar system, and they’re practically sparkling with water ice, according to data from Nasa’s Cassini spacecraft.

The findings, released last week in the Astrophysical Journal, give planetary scientists a window into the solar system’s birth and development, and show that the formation of at least one of the planet’s 62 known moons may have been a little more complicated than thought.

Launched in 1997, the Cassini mission spacecraft is now on its third lifetime exploring Saturn’s complex system and still turning up remarkable new information about the ringed gas giant.

Data from the spacecraft’s visual and infrared mapping spectrometer have revealed how water ice and shades of colour are spread through Saturn’s system. Finding an abundance of water ice – too much to have been deposited by icy comets ramming into the planet or its moons – the team of Italian and American scientists realised that the ice must hail from around when the solar system first formed, more than four billion years ago.

The colours Cassini mapped allowed the researchers to trace local interactions in the planet’s system. In Saturn’s inner neighbourhood, the geyser moon Enceladus whitewashes the nearby moons with fine particles from its plumes. Around the outskirts, far-off moon Phoebe (possibly a stray planetesimal captured from the Kuiper belt)

stains its nearby peers like Iapetus and Hyperion with reddish dust. Meteoroids also seem to be staining parts of the main ring system red.

The researchers came across one big surprise: Prometheus, Saturn’s long, potatoshaped moon, shares a reddish hue with some nearby ring particles – even though the surrounding moons are all white-toned. Perhaps Prometheus was created from the ring particles, the scientists said.

Astronomers generally believe that Saturn’s rings are formed from the smashedup remains of larger bodies. But it now seems that moon creation and destruction could be a two-way street. – Los Angeles Times/McClatchy-Tribune Information Services

Ringed giant: a long-distance view of Saturn taken by the Cassini spacecraft upon its approach in 2004. The discovery of water ice in the planet’s rings is an important clue to the birth of the solar system.