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A1 12 Rings


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Miller's Astronomy 1 lecture notes on Gas Giant Rings

Miller's Astronomy 1 lecture notes on Gas Giant Rings

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  • 1. Rings of the Gas Giants LACC §11.1, 11.4 • Understand what conditions and processes shaped the gas giant planets’ ring systems: Roche limit, shepherding moons • Know the following ring systems in some detail: Jupiter (dust from moons?), Saturn (recent break up of icy object?), Uranus (break up of a moon?), Neptune (unknown) • Bright = icy and young, Dark = dusty and old An attempt to answer the “big questions”: what is out there? Are we alone?
  • 2. Ring Systems
  • 3. Ring Systems
  • 4. Ring Systems Moons of Saturn: Moons of Jupiter: 1.Atlas 1.Metis 2.1980S27 2.Adrastea 3.1980S26 3.Amalthea 4.Janus 4.Thebe 5.Epimetheus 5.Io 6.Mimas 6.Europa 7.Enceladus 7.Ganymede 8.Telesto 8.Callisto 9.Tethys 9.Leda 10.Calypso 10.Himalia 11.Dione 11.Lysithea 12.1980S6 12.Elara 13.Rhea 13.Ananke 14.Titan 14.Carme 15.Hyperion 15.Pasiphae 16.Iapetus 16.Sinope 17.Phoebe
  • 5. Jupiter’s Ring Jupiter's intricate, swirling ring system is formed by dust kicked up as interplanetary meteoroids smash into the giant planet's four small inner moons, according to... NASA's Galileo spacecraft. status980915.html
  • 6. Saturn’s Rings Most of the rings are only a few tens of meters thick with a total mass equivalent to a medium sized moon. The rings are made out of particles ranging from microscopic dust to barnyard sized boulders with perhaps a few kilometer-sized objects as well. ...the rings are composed mostly of ice crystals with some impurities. Scientists once thought that the rings were formed at the same time, as the planets when they coalescing out of swirling clouds of interstellar gas 4.8 billion years ago. Under this model, remnants of material within the Roche limit could not condense and would become rings. However, in recent years this idea seems to be flawed. The rings appear to be young, perhaps only hundreds of millions of years old. One of the clues to this theory is that the rings are bright. As Saturn travels though space, the rings accumulate dust particles that have been darkened from solar radiation. If the rings were old, they should appear dark. Another theory suggests that perhaps a comet few too close to Saturn and tidal forces broke it into pieces.... Perhaps one of Saturn's moons was struck by an asteroid smashing it into the bits and pieces that form the rings. saturnrings.htm
  • 7. Saturn’s Rings
  • 8. Saturn’s Rings This image shows Saturn's rings and the shadow of nearby Mimas. They are now nearly edge-on toward the Sun, and long moon shadows drape across them. Scientists are now studying the clumpy, disturbed ring material, stretching up to two miles above the ring plane - contrasted with an estimated normal ring thickness of only six feet close-Sensational-cosmic-images-bring-ringed-planet-life.html
  • 9. Saturn’s Rings: Shepherd Moons This composite of two images shows Pan, left, and Prometheus, right, in nearby rings. Pan is trailed by a series of edge waves in the outer boundary of the gap. Prometheus just touches the inner edge of Saturn's F ring, and is followed by a series of dark channels close-Sensational-cosmic-images-bring-ringed-planet-life.html
  • 10. Uranus’s Ring(s) Radio measurements showed the outermost ring, the epsilon, to be composed mostly of ice boulders several feet across. However, a very tenuous distribution of fine dust also seems to be spread throughout the ring system. The particles that make up the rings may be remnants of a moon that was broken by a high- velocity impact or torn up by gravitational effects.
  • 11. Shepherd Moons Shepherd moons work in pairs on the inner and outer edge of rings to gravitational push and pull (accelerate and de-accelerate) ring particles. The result is to confine the ring particles to within the shepherd moons orbits.
  • 12. Neptune’s (Rings) None of Neptune’s rings were detected from scattering effects on Voyager’s radio signal propagating through the rings, which indicates that they are nearly devoid of particles in the centimetre size range or larger. The fact that the rings were most visible in Voyager images when backlit by sunlight implies that they are largely populated by dust-sized particles, which scatter light forward much better than back toward the Sun and Earth.Their chemical makeup is not known, but, like the rings of Uranus, the surfaces of Neptune’s ring particles (and possibly the particles in their entirety) may be composed of radiation-darkened methane ices. The present rings are narrow, and scientists have found it difficult to explain how the orbits of the known moons can effectively confine the natural radial spreading of the rings. This has led many to speculate that Neptune’s present rings may be much younger than the planet itself, perhaps substantially less than a million years. The present ring system may be markedly different from any that existed a million years ago. It is even possible that the next spacecraft to visit Neptune’s rings will find a system greatly evolved from the one Voyager 2 imaged in 1989.
  • 13. Rhea’s (Rings!? 6 March ‘08)
  • 14. Ring Systems They are not stable; they evolve and change over time. Unless something replenishes them or keeps them from dissipating, they will not last longer than a few 100 millions years; one of Neptune’s might not last a century. They generally form inside a planet’s Roche limit. Object’s that come closer than this distance to a planet tend to be ripped apart by tidal forces. Since the gas giants have strong gravitational fields, they have strong tidal forces. Shepherding moons are moons that keep a ring system nice an tidy, by not letting material drift out of a ring and/ or into gaps.
  • 15. HW Ch 11: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch 11, pp. 263-264: 9. • Ch 13: Image Analysis Quiz accessible from: fid=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of next class period. Be working your Solar System project.