The Galilean moons of Jupiter 3.5 g/cc 3.0 g/cc1.9 g/cc1.8 g/cc

Last time …. Io Innermost Galilean moon Heavy tidal heating – orbital resonance Active Sulfur volcanos

Europa Water Ice surface! Most recent estimate: crust ~ 19 km thick (Structure: gravity and magnetic field data) NOT REAL

Ganymede NASA 2014 (Structure: gravity and magnetic field data + Keck scope measurements of Aurora shifts)

Callisto Parts of surface quite old

Galilean satellites: Io: Volcanically active! Tidal heating from Jupiter drives the active geology. The origin of the tidal effect is its eccentric orbit, caused by orbital resonance with Europa and Ganymede. Europa, Ganymede and Callisto: Ice tectonics! All three are likely to have internal oceans of water. On Ganymede and Callisto the source of heating is somewhat of a mystery (tidal effects not enough). These three moons combined may contain more liquid water than earth!!

Titan Natural color/smog (Organo-Nitrogen) 1.9 g/cc

Dense atmosphere ! 1.4 x earth 95% N 2 5% CH 4, etc. Thick atmo. Used to be thought of as biggest moon, now Ganymede is bigger. Cassini IR/false color Kraken Mare ?

‘Shangri-La’ plains/desert of dark smog particles Icy highlands Adiri as seen by Huygens

Kraken mare Ligeia mare Methane Lakes!!

Transient feature in Ligeia mare! Waves? Gasses released? Summer  Buoyant solids?

Huygens's descent Images are flattened (360° Mercator)

Landing site: dry (methane) river bed.

Jovian rings Saturn thru a bad scope

“I discovered another very strange wonder, which I should like to make known to their Highnesses..., keeping it secret, however, until the time when my work is published.... the star of Saturn is not a single star, but is a composite of three, which almost touch each other, never change or move relative to each other, and are arranged in a row along the zodiac, the middle one being three times larger than the lateral ones, and they are situated in this form: oOo.” Galileo, 1610

Christiaan Huygens, Opera varia (Lyon, 1724

equinox solstice Tilt: 27°

Rings are a common feature of ALL Jovian worlds!

Jupiter Keck Galileo from the backside

Jupiter

Hubble Uranus

Neptune

Saturn’s rings

A B C Cassini Encke Major features: GAPS BANDS

APOD 7/23/04 Saturn's Rings in Natural Color Mostly water-ice reflecting sunlight … Thinner portions darker (Like the gaps) Some unknown dark dirt …. Outgassing of trace elements Why the colors?

Mostly frozen water Ring thickness: “tens of meters” Particles sizes: 1 cm – 10 m (10 cm most abundant) Est. total mass ≈ 3 × kg ( ≈ ¾ Mimas ) Saturn’s rings:

Relationship to moons and rings:

What causes all the structure? Moons do a lot … Resonance orbits cause gaps Sheppard moons can confine/concentrate rings Moons can simply plow gaps Moons can add material

A) Orbital resonance (remember Io?)

Mimas Kepler’s law

At what radius would something orbit at to have half the period of Mimas? (0.630) × (185,540 km) = 117,000 km Inner edge of Cassini division: Huygens gap Mimas’ orbit

Mimas 2:1 resonance orbit Every 2 nd orbit, each bit of dust in the Cassini orbit gets an outward kick at same place.

The A Ring's outer edge is maintained by a destabilizing 7:6 resonance with the moon Janus.

B) Sheppard moons Sheppard movie Sheppard movie (

The Encke and Keeler gaps within the A Ring are cleared by the embedded moonlets Pan and Daphnis, respectively: C) Moons can clear gaps in rings ( 1:1 resonances )

Daphnis churns up the edges of the Keeler Gap Daphnis: 8 km Keeler gap: 42 km

The Encke gap and Pan Pan: 14 km Encke gap: 325 km Close-up of the Encke Gap. The central ringlet is coincident with Pan's orbit. (Wik)

D) Moons can also be the source of rings

Enceladus and E-Ring Black dot Enceladus Plume jets from the moon Enceladus supplying vapor to the E ring

Cryo-volcanic plumes on Enceladus

Imaginative picture of the day:

Anthe partial Ring (20⁰ long.) Anthe ( 10:11) and Methone ( 14:15) resonance with Mimas micrometeoroid impacts? Ring Arcs

Lot’s of unknown processes…

Streamer channels caused by Prometheus in the F-ring

Ring spokes?

Ring origins? Most other sources: Our book: Ring particles can’t be old, they’re constantly being worn down New particles must be constantly created from moonlets Moonlets big enough to survive 4.5 billion years of sandblasting Rings are old, remnants of the early days Tidal forces of big planets … Keeps/kept particles from forming moons Broke up larger proto-moons that got too close

The Roche Limit An object held together only by gravitational forces – Unstable within Roche’s limit Objects held together by chemical forces (ice/rock) are tougher (Tuft’s)