Cassini Discovers a Kinematic
Spiral Ring Around Saturn

Science , 2005 November 25 Issue

Sébastien Charnoz (charnoz(at)cea.fr) 1
Carolyn Porco 2
Estelle Déau 1
André Brahic 1
Joseph Spitale 2
Guillaume Bacques 1
Kevin Baillie 1

1 : University Paris 7 France / CEA Saclay / CNRS
2 : CICLOPS Institute, Boulder, Colorado, USA
Material for medias (text, images, animations, contact, etc.)

Since Voyager (1980-81) the F ring is a very intriguing ring becauseof its very complex and changing shape. Its located at 140 000 km from Saturn’s center, 4000 km away from the edgeof the A Ring

The F ring is composed of a bright main ringlet called « the core » surrounded by diffuse ringlets called « strands ».

Cassini image of a portion of the F ring

The small satelliteon the right is Pandora

By doing a full map of the F ring at 360° (full turn) our team has shown that the « strands » are NOT different ringlets but are all connected into a single SPIRAL arm, doing at least 3 turns around Saturn.

On this map, the F ring is mapped at 360°. This map is repeated 2 timesto show clearly that the strands (spiral) are ALL connected together intoa single spiral. The map map shows that the spiral does at least 3 turns aroundSaturn.

Seen from above (~ Saturn North Pole) it would appear like this
(SKETCH NOT to scale!)

This is a sketch.
In reality, the spiralis so thin thatit would appear likesimple thin circle at realscale !The spiral is located at 140000 kmfrom Saturn, and itswidth is only ~ 800 km.

Link to Image(700Ko)

It is a brand new category of ring with no known equivalent in theSolar System.

It is NOT a fixed spiral, it rotates around Saturn :1 turn in ~ 15 hours

It illustrates again that the F ring is a very dynamical and changingobject.

It is very probable that such a structure (the spral) is ephemeral. The F ring itself is also suspected for long to be transient.

What is the cause of the spiral ?
How it could be formed ?

We think that a collision of the F ring core with a small moon could formthe spiral !

A SIMPLE IDEA

1. At the location of collision, material from the F ring core is scattered away

2. The released material spreads around Saturn

3. As a simple consequence of orbital motion, the material organize itself
In the shape of a spiral structure

Note : The rings are composed of billions of icy particles with centimeter size

We do not known exactly which moon could be responsible for this…

We have many candidates seen by Cassini :

Several putative moonlets seen by Cassini nearby the F ring.

This scenario has been investigated and comforted with numerical simulations

1. Let’s imagine a moonlet is approaching the ring

2. The moons crosses the ring and scatters material

3. As time goes by, the scattered particles goes away. Because of the gravity of Saturn, inner particles goes in the direction of satellite motion, outer particles goes in the opposite direction.

4. As a result of this motion, scattered particles organize into a spiralaround Saturn.

The phenomenon seen from above (Not to scale!)

	At the begining the material is scatteredfrom the F ring due tocollision The solid segmentsis the scattered material.

LINK TO MOVIE (3Mo) (thank you to www.animea.com)

As time goes by, the material spreads into a spiral shape around Saturn

In reality , the spiral is rotating around Saturn. Find below a more exact movie

Movie of a rotating Spiral (3Mo) (thx www.animea.com)

Now the question is :

Which satellite could have done this ??

We do not know exactly , but we have a suspect :

A recently discovered small object , S6, has been seen orbitingand crossing the F ring core.

It is very probable that this moonlet could be the cause of the spiral.

NOTE
In 2009, the big Satellite Prometheus will be crossing the F ring.
It is probable that it will create some new spiral around the ring !!

Stay tuned with Cassini !!!

CREDITS :

All Cassini images : NASA/JPL

Sketches and animations : SCIENCE

Saturn computers graphics and animations created by : ANIMEA (www.animea.com)

CONTACT :

Sébastien Charnoz

charnoz@cea.fr

Cassini Discovers a Kinematic Spiral Ring Around Saturn

Cassini Discovers a Kinematic
Spiral Ring Around Saturn