Jupiter (Galileo) Saturn (Cassini)

Uranus (Hubble) Neptune (Voyager)

Everything You Need to Knowabout Ring Dynamics

• Newton: Force = Mass x Acceleration

• Law of Gravity

• Collisions

• Light-scattering Physics

Main ring

Dark side = High “phase angle”: emphasizes tiny dust grains

“Halo”

“Gossamer ring” discovery

Two “Gossamer” rings

Dusty rings must be sustained by source bodies(seen or unseen)

A B C

Encke Gap Cassini Division

D F

Lit side = Low “phase angle”: emphasizes large bodies

EG

Enceladus

Earth!

Unique high-phase view!F

“Geysers” on Enceladus= the source of the E ring

Cassini On-line Resources

• Cassini Main Site– http://saturn.jpl.nasa.gov/

• The latest raw images (cool!)– http://

saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm

• Imaging Team Web Site– http://ciclops.org/

The “Opposition Surge”on Saturn’s rings.

This appears exactlyopposite to the directionto the Sun, at phaseangle 0°.

The size of the surge isa measure of how rough the particles are.

gammaeta

lambda

epsilon

beta

alpha

6, 5, 4

delta

The main rings of UranusImaged by Voyager 2

Low phase = big particles

The rings of Uranus at high phase > dust belts!

Uranus in HST

Long exposures reveal rings

Overlaying frames shows moons

Processing shows new rings!

Mab & the mu ring

nu ring

Liberté

FraternitéEgalité

Courage

Leverrierring

Adamsring

Neptune’s Changing Arcs

• The arcs can now be detected by Hubble and ground-based telescopes.

• Since 1989, the leading arcs have advanced forward and faded.• Gravity effects of the nearby moon Galatea help to confine the

arcs– …but the model is in trouble!

Fun with Rings (1)

Vertical Ripples

D ring ripples that have been winding up since 1984!

Fun with Rings (2)

Satellite “Wakes”

Wavy edge of EnckeGap suggests anembedded moon.

Colorenhancementreveals “spiral” structure.

Perturbedcentralringlet

The discoveryof Pan

in a sequenceof five

Voyager images

A spectacularview of

the Pan wakefrom Cassini

direction to Pan

Pan Imaged at Fine Resolution by Cassini

The Discovery of Daphnis in the Keeler Gap:The wake is highly distorted

Fun with Rings (3)

Saturn’s Pathological F Ring

Ophelia

Cordelia

Two moons “shepherd” theepsilon ring of Uranus

Pandora

Prometheus

Distant Voyager approach image:Is the F ring shepherded too?

A Selection of Cassini Images

Prometheus produces a “wake” pattern just like Pan

The aftermath of a ring impact?

A recent, new feature 200 km inward from the central ring

2007: A Good Yearahead for Ring Science…

Cassini Extended MissionJuly 2008–June 2010

Sample TourScience planning is proceeding.Note that this period includes the equinox on August 11, 2009!

New Horizons at JupiterFebruary 28, 2007

The first images ofJupiter from New Horizons

Range is 1 AU

Sample planned imagesduring the

New Horizons flyby