4.12 Jovian Moons Rings, Dwarf Planets PDF

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Professor: Dr. Read
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JOVIAN MOONS, RINGS, DWARF PLANETS Jovian Moons and Rings

Moons can be divided into three groups: ● Small moons (less than 300 km in diameter) ○ Most moons ○ Irregular in shape because gravity is too small to force them into a spherical shape; many have unusual orbits (some revolve backwards and are likely captured asteroids) ● Medium sized moons (300 - 1500 km in diameter) ● Large moons (greater than 1500 km in diameter) ○ Medium and large: ■ Miniature solar nebulae ■ Circular, equatorial, prograde orbits (as opposed to retrograde) ■ Most spherical and some have atmospheres, hot interiors, magnetic fields ● Voyager flybys ● Galileo ● Cassini

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Many moons are geologically active ○ Large amounts of ice ○ Interiors similar to terrestrials Impact cratering occurs on most moons Volcanism on some Tectonics on some ○ Erosion is rare bc of light or lack of atmospheres

Galilean Moons of Jupiter ● Galileo was the first to observe the moons of Jupiter with his telescope ● Io, Europa, Ganymede, and Callisto

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67 known moons of Jupiter Three inner Galilean moons orbit Jupiter in a 1:2:4 resonance

Galilean Moons of Jupiter - Io ● Voyager 1 Three scientists: - Peale - Cassen - Reynolds ● Rotational periods of Io, Europa, and Ganymede are in 1:2:3 resonance ○ Gives Io an elliptical orbit, creating tidal forces on its interior resulting in continuous tidal heating and an active planet ● Thermal energy ○ 24 tons of TNT every second to the interior ○ Energy makes its way to surface through crust weaknesses (volcanoes) spewing out sulfur gases and sulfur ■ Colourful ● Io is the most volcanically active object in the solar system with 300 active volcanoes ○ 10,000 tons of material per second ○ Repaving the surface (no impact craters) ● Io is the plasma torus that has formed in its orbit ○ Solar wind particles trapped in Jupiter’s magnetosphere and form volcanicallyejected charged particles ● Io has taller mountains than Earth Galilean Moons of Jupiter - Europa ● Smooth, covered by water ice a few km thick ○ Covers an ocean of liquid water (100 km deep) ○ Lines covering surface - fractures in the ice caused by tidal forces of Jupiter and other moons ● Brown areas are rocky deposits from meteoric impacts and/or from Europa’s interior ● Solid, rocky core Galilean Moons of Jupiter - Ganymede and Callisto (Fraternal Twins) ● Ganymede - largest moon in the solar system ● Castillo - similar in appearance ○ Impact craters, patterns of light & dark markings ● Tectonic action early in its formation (3 billion years ago) ○ Icy shield Moons of Saturn - Titan ● Saturn’s largest moon ○ 90% N (only world besides Earth where N is the dominant gas) ○ Ar, methane, and ethane but no O2 ○ Almost as large as Mars ● Hydrocarbon gases = greenhouse effect ○ Still cold -180°C

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Surface temperature = 1.5 bars (Earth is 1.0) No oxygen and the cold ○ Uninhabitable 2005: Cassini ○ Dropped a probe Huygens through the atmosphere of Titan ■ Existence of hydrological cycle similar to Earth’s ■ Methane evaporates from surface, condenses into clouds, rains onto surface ● rivers/streams very few craters on Titan's surface although there appears to be evidence for ice volcanoes temperature and wind variations indicating seasonal variations with wind speeds as high as 550 km/hr a wide variety of hydrocarbon molecules in the upper atmosphere including acetylene and hydrogen cyanide

Saturn’s Other Moons

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Over 50 named moons, 62 confirmed ○ Dione ○ Hyperion ○ Prometheus ○ Epimetheus ○ Mimas ○ Phoebe

Moons of Saturn - Enceladus ● Small ● “Alien world” ● Geologically dead ● Water vapour, nitrogen, carbon dioxide, methane, carbonates (acetylene, ethane,

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propane, formaldehyde) Deep oceans of water exist under icy surface

Moons of Uranus ● Small and numerous ● Named after sprites and spirits in Shakespearean plays ● Miranda, Ariel, Umbriel, Titania, Oberon - largest ○ Ice & rock ● Proteus ○ Mid-sized ● Miranda ○ Heavily cratered Miranda of Uranus

→ june 2014: 27 known moons of Uranus Moons of Neptune - Triton, Neptune’s Backward Moon ● Retrograde orbit inclined at 20° to Neptune’s equatorial plane with a high eccentricity ○ Half the mass of Europa ○ Likely a captured satellite (moon) ○ Cold ○ Reflective water ice ○ “Cantaloupe terrain” Neptune’s Moons

→ 14 known moons ● S/2004 N1 - new How many moons in our solar system? ● Earth - 1 ● Mars - 2 ● Jupiter - 67 ● Saturn - 61

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Uranus - 27 Neptune – 14

RINGS Saturn: Lord of the Rings ● All jovian planets have rings ● Ice rings = saturn ● First observed by Galileo ● Cassini Division ○ Dark band ⅔ of the way out from the inner edge ● Three distinct rings areas: (from outside in) a. A ring i. Encke gap: small gap near the outer edge (300 km wide) b. B ring c. C ring ● Vary in size ● Rings - 10,000 km from Saturn’s surface & extend out to 420,000 km from the surface ● THICKNESS: 100 m, less than 30 m in many locations ○ Football field covered in newsprint Origin of the Rings ● Moons move closer ○ Tidal bulge ○ Moon breaks into smaller chunks and pieces ○ Take up their orbit around a planet ● Tidal stability limit or Roche limit ○ french mathematician ○ Critical distance inside which the moon is broken apart ■ 2.4x the radius of the planet ■ Rely on other forces to hold them together such as interatomic forces (electromagnetic bonds) ■ Low density = likely to get torn apart by gravity ● Ring particles are constantly FALLING into the parent planet as upper atmosphere extends into the ring system ○ Smaller particles feel air “drag” and slow down to de-orbit ○ Others get knocked out of the system due to inter-ring collisions More Rings and Shepherd Moons ● Up to Ring G ● Ring E: ○ Outermost ○ Volcanism on the moon Enceladus

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A ring particle finding itself in this gap would be in a 1:2 resonance with Mimas ○ Repeated tugs ■ Each trip around Saturn would change into an elliptical one ■ Out of Cassini division

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Shepherd moons ○ Influence of small moons that orbit on either side ○ Gravity plays same role DWARF PLANETS Large planetesimals known as dwarf planets 5 official dwarf planets ○ 4 in Kuiper Belt ○ Pluto best known ○ 5th - Ceres, lies in the asteroid belt between Mars & Jupiter

What Defines a Planet? ● Pluto is not a planet ○ Not related to the Jovian or Terrestrial ○ “Icy worlds” ●

Eris and Pluto - largest objects in Kuiper Belt ○ Dwarf planets ○ Large enough for their gravities to have pulled them into spherical shapes ○ IAU

Pluto ● February 18th, 1930: Discovered by Clyde Tombaugh ● Really small compared to Earth, Uranus, Neptune

Planetary Data - Pluto

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Orbit is eccentric Spends 20 of its almost 250-year orbit inside the orbit of Neptune Moon: Charon ○ 1/10th of the mass ○ Named after mythical boatman ○ Charon used to discover Pluto is 1/400th of Earth’s mass ○ Pluto’s rotational axis is almost in its orbital plane (rotates backwards) THREE planets rotate backwards: ○ Venus, Uranus, Pluto Pluto’s moons: ○ Formed at the same time form a giant impact ○ 12:3:2 ratio ○ Nix, Charon, Kerberos, Hydra, Styx ■ Styx: mythological river underworld Pluto’s size: ○ 50 km larger than Eris and largest known KBO ○ Diameter 19% of Earth’s Pluto’s Density: ○ Icy and less rocky ○ Thin crust (mantle) of ice and rock surrounding a shell of liquid water surrounding a rocky core Pluto’s Atmosphere: ○ Extensive ○ 1700 km above its surface ○ Surface pressure is quite small Surface features: ○ Heart-shaped mostly flat ○ Tombaugh Regio

Ceres ● Only dwarf planet not found in Kuiper Belt

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Largest asteroid Giuseppe Piazzi discovered January 1st, 1801 Icy mantle, surrounding rocky core Waver vapour

Other Dwarf Planets ● Eris, Haumea, Makemake ● Other candidates: (sedna, Quaoar, orcus)

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Mike Brown ○ Discovered Eris ○ “10th planet” ○ Eccentric ○ One moon: Dysnomia Haumea & Makemake ○ Similar orbital characteristics ○ Giant collision with trans-Neptunian object ○ Haumea largest remaining object along with its two captured moons ○ Makemake is spherical with no moons

Lesson 12 Self-Test 1. What do small moons in the solar system have in common? a. They are usually non-spherical in shape 2. Which planet do the Galilean moons orbit? a. Jupiter 3. This satellite’s interior has probably warmed enough by tidal stressing to have a liquid water ocean below an icy crust a. Europa

4. Which of the following describes Jupiter’s moon Io? a. It has no impact craters 5. What role do Europa and Ganymede play in helping to make Io geologically active? a. They help keep Io’s orbit eccentric by periodically pulling on it together 6. Which of the following most closely matches the average thickness of Saturn’s rings? a. A ten-story apartment building 7. Which of the following is not a likely source of the rings around the Jovian planets? a. As a leftover unaccreted material from the same time that the planets themselves formed 8. What role does Mimas play in helping to form the Cassini division in Saturn’s rings? a. It periodically tugs on any particles that appear in the division, making their orbits elliptical 9. What did the Huygens probe discover about Saturn’s moon Titan? a. Methane rains onto the surface, evaporates, and rains again cyclically 10. What do the moons Ariel, Titania, Umbriel, and Miranda have in common? a. They are moons of Uranus, and names characters in Shakespeare’s plays 11. Why is Triton referred to as Neptune’s “backward” moon? a. It orbits in the opposite direction of its revolution 12. How massive is Pluto’s moon Charon, compared to Pluto? a. One tenth as massive 13. Why do the majority of confirmed dwarf planets in the solar system reside? a. The Kuiper Belt 14. What do the orbits of the confirmed dwarf planets have in common? a. They are more eccentric than the planet’s orbits 15. Pluto does not gravitationally dominate its neighbourhood and cleared it of debris a. True...