The View From Saturn: Images from the Cassini spacecraft

Tuesday 21st August 2012

Prof Carl Murray from Queen Mary University of London admitted at the start of his talk that "I've got one of the best jobs in the world". He came to tell us about "The View from Saturn" and concentrated mainly on Cassini which is a NASA spacecraft currently in orbit around the gas giant. He is involved with the imaging instruments on Cassini known as the Imaging Science Subsystem (ISS) which consists of both a wide-angle and narrow-angle CCD camera.

The second largest planet in our Solar System has been studied by many ancient cultures including the Babylonians. However, it was not until the invention of the telescope that the rings were spotted when Galileo, in 1610, noted the appearance of what he thought to be two moons on each side of the planet. Later, another famous astronomer Christian Huygens improved upon his observations by using a telescope with greater magnification and saw a solid ring.

Huygens also discovered Saturn's largest moon Titan and in time other large moons were discovered as imaging technology improved. Titan is the second largest moon is the Solar System and is a very unusual moon in that it has an appreciable atmosphere and liquid on its surface. Apart from Earth it is the only other body to have a dense nitrogen-rich atmosphere.

However, it is a very inhospitable place with surface temperatures hovering around -180 C and with methane lakes and rain. Its atmosphere rotates faster than its surface and it has a permanent atmospheric vortex at its south pole. Pictures of the surface were obtained when a probe called Huygens, which had hitched a ride there on the Cassini spacecraft, sent back data. It saw a dark plain covered in rocks and pebbles which were made of water ice.

Perhaps one of the most fascinating aspects of the Saturnian system is the mini solar system of small moons and rings. There are over 60 moons circling the planet in and around the nested sets of rings and Prof Murray's interest lies in Saturn's F Ring.

This ring of mainly water ice is the outermost discrete ring and most dynamic with its features changing within a timescale of hours. Discovered in 1979 by the Pioneer 11 spacecraft, it is just a few hundred kilometres wide and is maintained by two shepherd moons. These moons, Prometheus and Pandora orbit just inside and outside it and effectively corral it into its slender ring-like shape. When examined more closely it appears to consist of two parts: a core ring structure surrounded by a spiral strand.

Sometimes Prometheus' orbital path actually enters the inner edge of the F Ring repeatedly and pulls a stream of material from within it, leaving a set of dark channels within the ring. It is not only the larger moons that can disrupt the rings shape. Smaller objects orbiting within the ring itself known as "snowballs" can pull out a bright stream of material from the ring. Researchers have dubbed these protrusions "mini-jets".

This article was written for the club news column of the Stratford Herald. The actual lecture explained the subject at a deeper level.