Cassini sees collisions of moonlets in Saturn’s ring
BY DR EMILY BALDWIN
ASTRONOMY NOW
Posted: June 9, 2008

The rapid changes in Saturn’s F ring can be attributed to small moonlets embedded within the ring causing perturbations and collisions, say a team of UK-led scientists who published their findings in Nature last week.

The dynamic structure of Saturn's F ring. It is thought that nearby "shepherd" moon Prometheus, as well as objects embedded within the ring itself, cause these interesting features through gravitational pertubations and collisions. Image: NASA/JPL/Space Science Institute.

Saturn’s dynamic F ring, which lies 3,400 kilometres beyond the edge of the main ring system, has long been of interest to planetary scientists because its features change on timescales ranging from just a few hours to several years. It is also probably the only location in the Solar System where large scale collisions happen on a daily basis, and studying these processes gives insight into the early stages of planet formation when collision events were rife.

Images shot by Cassini in 2006 and 2007 show the evolution of a series of jet-like structures emanating from the F-ring as a result of collisions between small nearby moonlets within the core of the ring. A 5 kilometre object discovered by Cassini in 2004 is the best candidate to explain some of the largest jets seen in the images.

“Previous research has noted the features in the F ring and concluded that either another moon of radius about 100 kilometres must be present and scattering the particles in the ring, or a much smaller moonlet was colliding with its constituent particles,” says Professor Carl Murray of Queen Mary London. “We can now say that the moonlet is the most likely explanation and even confirm the identity of one culprit.”

Evidence for embedded satellites in the core of Saturn's F ring. These images were taken between September 2006 and May 2007. A fan shaped structure can be seen in the large image (a). Image: from Murray et al (Nature 453, 5 June 2008).

The F ring and all the nearby objects are being continually perturbed by encounters with the shepherding moon Prometheus, and the existence of sheared jets of material produced by collisions between objects embedded within the

F ring allows the Cassini scientists to detect the event even if the collisions cannot directly be seen. An incredible array of patterns is produced by these collisional events, including a new set of features nicknamed “fans” – a sequence of sheared channels with a common point of intersection – produced by the gravitational effect of small (~1 kilometre) satellites orbiting close to the F ring core.

“Large scale collisions happen in Saturn’s F ring almost daily – making it a unique place to study,” says Dr Sébastien Charnoz of Université Paris 7 / CEA Saclay. “We can now say that these collisions are responsible for the changing features we observe there.”

Cassini is now preparing for an extended two year mission (see 'Cassini primed for extended tour of Saturn'), adding to its previous successful four year odyssey in the Saturnian playground.

Our latest 132-page Astronomy Now special edition is an extravaganza of astronomy for the year ahead, with a complete 30-page guide to observing the planets, moon, meteor showers, two solar eclipses, and the deep sky in 2010.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

This special publication features the photography of British astro-imager Nik Szymanek and covers a range of photographic methods from basic to advanced. Beautiful pictures of the night sky can be obtained with a simple camera and tripod before tackling more difficult projects, such as guided astrophotography through the telescope and CCD imaging.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Explore the Universe with these new versions of the award-winning Starry Night Software. Available now from the Astronomy Now Store.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Astronomy Now is pleased to announce the publication of Exploring Mars. The very best images of Mars taken by orbiting spacecraft and NASA's Spirit and Opportunity rovers fill up the 98 glossy pages of this special edition!
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

This new poster features some of the best pictures from NASA's amazing Mars Exploration Rovers Spirit and Opportunity.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE