Tuesday, September 22, 2009

NASA’s Cassini orbiter has sent back remarkable images from Saturn, revealing that the planet’s famous rings are far more bumpy than expected.

Astronomers previously thought that the rings were almost completely flat, with changes in height of only a few metres. However analysis of the new images show ridges up to 4 kilometres tall, similar in height to the Rocky Mountains or the Alps.

The images were taken around the planet’s equinox on August 11, when the Sun was directly over Saturn’s equator and caught the rings edge on. A similar equinox occurs today (September 22) on Earth. But whilst equinoxes occur twice a year on Earth, Saturn takes around 29.7 Earth years to orbit the Sun so the events are much rarer.

With the light from the Sun reaching Saturn’s rings at such a low angle, scientists were able to measure the shadows cast by bumps on the rings and discover their surprising height. As Cassini project scientist Bob Pappalardo put it: “It’s like putting on 3-D glasses and seeing the third dimension for the first time. This is among the most important events Cassini has shown us.”

Some of the ring features are known to be caused by Saturn’s moons, but others are harder to explain. “To understand what we are seeing will take more time, but the images and data will help develop a more complete understanding of how old the rings might be and how they are evolving,” said Linda Spilker, Cassini deputy project scientist.

Cassini was launched in 1997, and entered orbit around Saturn in 2004. It is part of the Cassini-Huygens joint mission between NASA, the European Space Agency and the Italian Space Agency.