Lecture 11: Moons & Rings

Lecture 11: Moons & Rings

1. what are trojans

   • moons that share the same orbit as the planet and the sun

2. Mars

   • - Both are close enough to be tidally locked. - Small and irregular shaped - Similar in color and density to carbonaceous asteroids. - They may be captured asteroids.
   • Phobos
   • Deimos

3. Jupiter

   • - Have similarities to terrestrial planets: orbits have low eccentricity - Density decreases as distance from Jupiter increases - May have been formed from Jupiter's accretion disk
   • Io
     • - Densest Jupiter's moon and the most geologically active object in the solar system - Many active volcanoes, some white large. - Can change surface features in a few weeks - No craters: they fill in too fast. Io has the youngest surface of any solar system object. - Very close to Jupiter and experiences gravitational forces from Europa. Huge tidal force that heats the core and provide energy for volcanoes.
     • Tidal heating
       • - Io's orbit is slightly eccentric because of the orbital resonance with Europa and Ganymede and the recurring gravitational tugs. - The forces from Jupiter raise tidal bulges on Io: these go up and down depending on how far Io is to Jupiter. - These also occur on Europa but not as much cuz Europa is further away from Jupiter
     • Volcanoes & How plasma torus are formed
       • - Numerous volcanoes throw sulphur into space - These sulphur atoms interact with Jupiter's magnetosphere and become ionized - The ions are then trapped to form a plasma torus around Jupiter. - The energetic particles in the plasma torus form a belt of intense radiation
   • Europa
     • - Surface is water ice with no craters. - There may be liquid water below the ice. - Tidal forces from interaction with Jupiter, Io and Ganymede stress and crack the ice. - Tidal heating might be an important factor: interior may be warm enough to have liquid water.
     • - Surface layers slide past each other. - Friction heats the crust and causes it to expand and form a ridge - Melting ice collapse the ridge centre. - Interior ice or water may flow out from these cracks and freeze on the surface.
   • Ganymede
     • - Largest moon in the solar system - Icy body - Very weak magnetic field - May have more water than Europa - Some evidence of early plate tectonics.
     • - Similar to Earth's moon but instead of ________, __________ lunar rocks, water ice lava, water flowed and froze to form the flat regions - Interior heat probably caused seismic activities in the past - Magnetic field means probably the interior is liquid
   • Callisto
     • - Similar in composition to Ganymede - No plate activity observed - Surface is ol and heavily cratered
     • - Interior is undifferentiated - probably too cold for that to happen - Impact that caused the Valhalla impact crater threw up ripples on the surface. - Impact heated the surface so it could deform more easily - Before the ripples cuts subside, the surface froze the ripples in. Heavy cratering suggests not much seismic activities.
     • Valhalla

4. Saturn

   • - 62 moons with confirmed orbits - Most are made of ice - Some interact with the ring system
   • Titan
     • - Atmosphere is thicker and denser than Earth - Composed mainly of nitrogen and methane. - Sunlight breaks up methane and cause chemical reaction in the atmosphere. This create orange haze the hide the surface. Deeper in, clouds of methane form and rain on the surface
     • - Can use infrared but still best to land on it. - rocks are pebble size with sign of erosion - surface is an mixture of water and hydrocarbon ice.
   • Other moons
     • - Mimas, Enceladus, Tethys, Diona, Rhea and Iapetus - all tidally locked - meaning they all have leading and trailing side
     • Shepherd moons
       • - smaller moons of Saturn that orbits in the rings system - gravitational interactions define the outer edges of a ring - the co-orbital moons Janus and Epimetheus share the same orbit.
     • Enceladus
       • - orbits within the E-ring - icy body and may have liquid water under its surface - seismically active with cryovolcanoes (colder than lava) - heated water from the interior escapes the surface in jets. Some water falls back down as snow and some adds to the rings of Saturn. - cryovolcanoes clustered at the south pole near the stripes
       • Cryovolcanoes
         • - water from interior breaks through the icy surface and then cools down and solidifies (usually occurs further out when it's colder) - as such low temp, liquid water do not exist - internal heat melts the ice and causes pressure to build up - liquid water may then escape from cracks onto surface.

5. Why rings?

   • - rings usually occur too close to a planet for a moon to form - tidal force would tear it apart. - generally occur inside a circle called Roche limit - may be leftover from planet formation - may be made of material blasted off moons by micrometeorites - made of particles that mostly are water ice and some may be dust. - edges and division in rings are sometimes the result of resonance
   • Roche limit

6. Rings & Moons

   • - rings occur when particles bunch up at some orbital radius - moons within a ring can clear its orbit of material - ring particle are forced out, forming a gap. - Another moon on the other side of the ring can do the same. these two moons on either side are shepherd moons - more distant, massive moons can also cause resonance in a ring ad push particles out of a particular orbit - moons with volcanic activity can also release a large amount of particles to form a ring - these particles bunch up around the orbit of the source moon
   • Shepherd moons & Moons with volcanic activities

7. Jupiter' ring

8. Saturn's rings

   • - main rings are within Roche limit - largest rings extend far beyond the Roche limit
   • Gaps and divisions
     • - gaps are narrow separations within named rings - divisions are wider separations within named rings - gaps and divisions are often caused by moons close by - orbital resonances with a moon can clear out a gap in a ring - the gap is an orbit that is unstable because of interaction with the moon - Shepherd moons close to the edge of a ring can also create a clear ring - material that stray out of the ring is thrown back in, ejected out or accreted onto the moon
     • What happens to materials that stray out of a ring?
   • Arcs and dust
     • - arcs are partial rings that do not go all the way around - some rings are made of particles that come off moons.  EXAMPLE: Enceladus - materials coming off through its cryovolcanoes populate the E ring. this is usually in the form of small particles - snowflakes. micrometeorites can also eject particles from a moon into space - i.e. the other moons also help to populate the E ring. - some arcs are also made from materials that is ejected off a moon but they are formed because the materials dissipates too quickly
   • Radial spikes
     • - radial spikes formed and dissipated quickly - could be seasonal phenomenon: usually when Saturn approached its equinox
   • Saturn's largest ring
     • the Phoebe ring is a diffuse ring of dust just inside the orbit of the Phoebe moon. - ring particles are blasted off the surface of Phoebe by micrometeorites - ring materials moving inwards towards Saturn strike the leading surface of Iapetus - leading to two-tone color
   • Shepherd moon & F ring
     • - Prometheus and Pandora shepherd the F ring - gravitational interactions with the ring material keep it within a clear ring - material that stray out is thrown back in, ejected out or accreted into the moons - Prometheus also creates kinks and knots in the F ring

9. Uranus' rings

   • - number of thin rings 9 narrow main rings, 2 dusty rings, 2 outer rings - more complex ring system then Jupiter and Neptune but simpler than Saturn - main rings are narrow and consist of mainly dark macroscopic particles
   • Stellar Occultation

10. Neptune's rings

    • - 5 rings: 3 narrow rings, 2 wide rings
    • Adam Ring Arcs
      • - arcs were found in Adam rings - arcs are regions in the rings where particles are clustered together