1. Jovian Planet Rings

2. The Rings of Saturn From Earth, they look solid.
concentric rings & Cassini division
From within the rings, we would see many individual particles
size ranges from boulders to dust
reflective H2O ice (snowballs)
many collisions keep ring thin

3. From spacecraft flybys, we see thousands of individual rings separated by narrow gaps
Cassini
Division

4. Saturn’s rings are very thin, in some cases less than 100 meters thick.
The rings are not solid sheets but are made up of small particles of water ice or water-ice mixed with dust. 33

5. Three distinct rings are visible from Earth, and were named (outer to inner) A, B, and C. Additional rings were detected by spacecraft and named D, E, F, … H.
Prominent gaps in the rings are also named, e.g., Cassini Division, Encke Division, … 33

6. The largest division between rings is known as the Cassini division.
This space is caused largely by the gravity of Mimas acting synchronously (2:1 resonance) on the orbital path of nearby ring particles.
Some other ring features are explained by the presence of small shepherd moons.
Mimas 33

7. The F ring: Confined by Shephard Satellites Prometheus
and Pandora
The A ring
Voyager
Cassini

8. The other ring systems: fewer particles, smaller in extent, darker particles

9. Jupiter’s Rings Voyager I discovered a thin ring around Jupiter.
Voyager from
“behind” Jupiter
Jupiter’s Rings
Voyager I discovered a thin ring around Jupiter.
The ring is close to Jupiter, extending to only about 1.8 planetary radii.
The ring is thought to be replenished from the small moonlets within or near it.

10. Rings of Uranus & Neptune
The rings of Uranus and Neptune and are made of particles which are darker and smaller than that of Saturn.
The Uranian rings are narrow, a few of which are clearly confined by shepherding moons.
The Neptunian rings vary in width and are confined by resonances of some of the moons.

11. Roche Limit
The Roche limit is the minimum radius at which a satellite (held together by gravitational forces) may orbit without being broken apart by tidal forces.
Saturn’s rings are inside Saturn’s Roche limit, so no moons can form from the particles.
Source of ring material

12. Origin of Planetary Rings
Within 2 or 3 planetary radii of a planet (the Roche Limit), tidal forces will be greater than the gravity holding a moon together.
A moon which wanders inside the Roche limit will be torn apart.
Matter from the mini-nebula at this distance will not form moon.
Rings can not last the age of the Solar System.
Particles will be ground to dust by micrometeorite collisions.
Atmospheric drag will cause ring particles to fall into planet.
There must be a source to replenish ring particles.
gradual dismantling of small moons by collisions, tidal forces, etc.
The appearance of ring systems must change dramatically over millions or billions of years.

13. Jupiter’s Galilean Satellite’s

14. Jovian Planets have Numerous Moons
small moons (< 300 km across)
not spherical
probably captured asteroids
Medium/large moons
formed like planets out of the “mini-Solar nebulae” surrounding the Jovian planets

15. Are the large moons are too small for active geology to occur?
No!
terrestrial planets made mostly of rock; Jovian moons mostly ice
Ices melt at lower temperatures than rock.
less heating is required to have molten cores
volcanism and tectonics can occur
There is another heat source.
tidal heating plays a more important role
There is very little erosion due to lack of substantial atmospheres with the exception of Titan.

16. The Jovian Moons
The moons of Jupiter become less dense as you get farther from Jupiter
“mini Solar System”
Gravitational tidal heating keeps the interiors of the inner moons hot.

17. Io’s Volcanoes Io
The most volcanically active world in the solar system.

18. Io  Jupiter’s tidal forces flex Io like a ball of silly putty.
friction generates heat
interior of Io is molten
Volcanoes erupt frequently.
sulfur in lava accounts for yellow color
surface ice vaporizes and jets away
Evidence of tectonics & impact cratering erased. 

19. The Io Torus Io loses volcanic gases into space.
ions of Sulfur, Oxygen, Sodium form a donut-shaped belt of charged particles, called the Io torus
they follow Io’s orbit & are a source of charged particles for the auroras of Jupiter

20. Europa: An ice-covered world

21. Icebergs

22. ice cliffs

23. Grooves
&
channels

24. Jupiter’s Europa Has tidal heating, similar to IO but weaker
Has a young cracked water ice crust perhaps only a few kilometers thick
Thought to have a warm ocean of salty liquid water below its crust.
life?

25. Salty - Europa has a magnetic field
Europa’s interior warmed by tidal heating. Internal structure derived from measurements taken by spacecraft in the Jovian system.
Based on Galileo spacecraft measurements of the strength of gravity over different positions of Europa and theoretical modeling of the interior.
Salty - Europa has a magnetic field

26. Sub-Crust
Ocean . . . .
First New Ocean
Since Balboa

27. Life in the
Ocean?
Conditions are consistent with the presence of volcanic vents (black smokers) at bottoms of ocean. Life could have developed there. . . . .

28. Missions to Europa

29. Ganymede

30. Ice-covered moon

31. Ganymede Largest moon in the solar system
Clear evidence of geological activity
Tidal heating expected - but is it enough?
Largest moon
Figure might work better if there were one with out the callouts.

32. Ganymede
Wrinkles due to tectonic movement in ice crust in (distant) past - possible water deep below?

34. Ganymede Cratering Ocean? Heat source
Dark areas: cratering upon cratering  several byr old
Bright areas: far fewer craters and grooves
Explanation: “lava” (i.e., water) eruptions followed by freezing
Ocean?
Magnetic field  convecting core
Part of magnetic field varies with Jupiter’s rotation  electrically conducting interior (brine?)
Salts found on the surface
Heat source
Less tidal heating than Europa (larger distance from Jupiter)
Large mass  more radioactivity
Much less heat than in Europa  thick crust (>150 km?)

35. Callisto

36. Callisto “Classic” cratered iceball.
No tidal heating - no orbital resonances.
But it has magnetic field! This is not understood.

37. Scarp close up
Callisto
Possible water deep?

38. Callisto
Cratering
Heavily cratered everywhere  no water gushing to the surface
Gravity
Undifferentiated: mix of ice and rock throughout
Induced magnetic field
Exists  underground ocean? Not clear.
Heat source?
Does not participate in the tidal resonance
Radioactive decay: only possibility for heating of interior

40. Given our discussion of tidal synchronization of the rotation and orbital periods, what might this say about planets and stars?
(red) nothing
(yellow) planets close to stars will have synchronized rotations
(green) planets far from stars will have synchronized rotations
(blue) it will depend upon the composition of the planet

41. Given our discussion of tidal synchronization of the rotation and orbital periods, what might this say about planets and stars?
(red) nothing
(yellow) planets close to stars will have synchronized rotations

42. Enceladus
Titan

44. Titan

45. Titan Huygens spacecraft landed on surface
Cassini spacecraft has made several close flybys
2nd largest moon
Only moon with a substantial atmosphere

46. Saturn’s Titan
atmosphere denser than Earth’s but very cold (100K) and composed mostly of N2 and methane (CH4)
Completely enshrouded in smog-like clouds
Methane acts like water (liquid).
Few craters on the surface.
Surface eroded by liquids
Methane/Ethane lakes

47. Huygens Probe

48. On the surface! “Rocks” of ice?

49. View from Huygens Spacecraft during descent to surface

52. Hydrocarbon lakes
River gully?
Coastline?

54. Cold, windy, surface like wet clay, ice “rocks”

56. Dunes
Earth
Titan

57. Physical Characteristics
Size
Among moons, second only to Ganymede (measured by surface, not atmosphere)
Mass
Almost double that of our Moon
Density: 1.9 gm/cm3  equal mixture of rock and ice
Thought to be differentiated: rocky core of silicates with a crust of water ice

58. Surface Gross features: Few impact craters  surface 130-300 Myr old
Tectonics: thin features for hundreds of miles
Cryo-volcano:
30 km volcano observed on Titan, including caldera inside
Magma would be mainly CH4 & H2O
Energy?: tidal heating or radioactivity
Erosion:
Huygens saw round ice pebbles
Sinuous channels: liquids
East-west dunes near equator with sharp western boundaries: super-rotating winds

59. Atmosphere Pressure: 1.5 bar Surface temperature: - 180C (-290F)
Composition: 9298% N2 + 26% methane (CH4)
Constantly smoggy: UV breaking up CH4 into radicals
Radicals combine to form complex hydrocarbons: C2H6, C2H2, HCN, C6H6

60. Possible Earthlike Processes
Tectonics
Weather, including rain (methane)
Erosion by winds and liquids
Formation of complex organic compounds
Greenhouse effect
Volcanism (molten water, not rock)
But: all at a much lower temperature