Lec26-Apr23 - 4/23/10 Discussion QuesGon Which of the...

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Unformatted text preview: 4/23/10 Discussion QuesGon Which of the following statements about planetary ring systems is false? Astro 109 Lecture 26: Rings April 23 A.  B.  C.  D.  E.  Rings lie in the equatorial plane of the planet. Rings are composed of small parGcles. Rings are generally found in a planet’s Roche zone. Not all Jovian planets (in our solar system) have rings. Orbital moGon of ring material is governed by Newton’s laws. Apr. 23 Key Concepts Saturn •  ring structure and dynamics •  Gdal disrupGon, Roche limit / Roche zone •  interacGons with moons Apr. 23 Apr. 23 Apr. 23 Apr. 23 http://mydarksky.org/2008/12/30/ringless-saturn/" 1 4/23/10 RotaGon Discussion QuesGon Saturn’s rings are A.  B.  C.  D.  •  1895: James Keeler used the Doppler effect to study how the rings rotate •  discovered they are a swarm of individual parGcles solid enough to stand on. a collecGon of solid parGcles. a collecGon of liquid drops. thin streams of gas. Apr. 23 Apr. 23 http://www.sunflower-astronomy.com/KCKCC_Docs/Saturns_Rings.pdf" 7 Discussion QuesGon Inside the rings Saturn’s rings are flat and circular because A.  B.  C.  D.  E.  of resonances with Saturn’s moons. collisions eliminate crossing orbits. they were created that way. they are made of liquid water. they rotate in the opposite direcGon to Saturn’s spin. 8 ArGst’s concepGon, based on inferred distribuGon of parGcle sizes Apr. 23 Apr. 23 cf. Lec 25 Roche limit, or Roche zone Tidal disrupGon Gdal forces are stronger closer to the planet too close, and the moon can be ripped apart! Apr. 23 Apr. 23 http://www.astro.washington.edu/users/smith/Astro150/Tutorials/TidalHeat/" 2 4/23/10 Apr. 23 Apr. 23 Discussion QuesGon The Cassini division is caused by A.  B.  C.  D.  E.  collisions between ring parGcles. bending waves in the ring plane. spiral density waves in the ring plane. resonance with Saturn’s moon Mimas. shepherd moons. What causes the Cassini division? a = 117580 km •  Inner radius of Cassini division: P2 •  Orbital period: Moon Orbital period (d) Mimas 0.942 Enceladus 1.37 Tethys 1.89 Dione 2.74 Rhea 79.33 Apr. 23 Apr. 23 15.95 Iapetus Gravity from Mimas tends to “kick” parGcles out of this region. 4.52 Titan Apr. 23 ⇒P a3 M = 0.476 d ∝ Apr. 23 3 4/23/10 False color to illustrate variaGons Natural color Apr. 23 http://apod.nasa.gov/apod/ap040723.html" Apr. 23 Apr. 23 Apr. 23 Discussion QuesGon Shepherd moons Narrow rings keep their shape because A.  B.  C.  D.  E.  Apr. 23 http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=2048" the parGcles want to bunch together. they are held together by electrical forces. they are held together by the planet’s magneGc field. there has not been enough Gme for them to spread out. small shepherd moons prevent them from spreading. Apr. 23 4 4/23/10 Apr. 23 http://photojournal.jpl.nasa.gov/animation/PIA07712" Apr. 23 Discussion QuesGon Jupiter’s ring Why are Jupiter’s rings so much harder to see than Saturn’s? A.  There is less material in Jupiter’s rings than in Saturn’s. B.  The parGcles in Jupiter’s rings are mostly small and rocky. C.  The parGcles in Jupiter’s rings are mostly ice, so the rings are transparent. D.  Both A and B. E.  Both A and C. Apr. 23 http://photojournal.jpl.nasa.gov/catalog/PIA01529" Apr. 23 Uranus’s rings: occultaGon Apr. 23 Apr. 23 5 4/23/10 Apr. 23 Apr. 23 Neptune’s rings HW quesGons 26. What observaGons of Saturn’s rings proved that they are not solid? 32. During the planning stages for the Pioneer 11 mission, when relaGvely lihle was known about Saturn’s rings, it was proposed to have the spacecrai fly through the Cassini division. Why would this have been a bad idea? 33. What is the relaGonship between Saturn’s satellite Mimas and the Cassini division? 34. Why is the term “shepherd satellite” appropriate for the objects so named? Explain how a shepherd satellite operates. Apr. 23 Apr. 23 6 ...
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This note was uploaded on 09/15/2011 for the course PHYS 109 taught by Professor Pryor during the Spring '09 term at Rutgers.

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