Astr Sol SysCoReq ASTR 1211S
Astr Sol SysCoReq ASTR 1211S ASTR 1010
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This 15 page Class Notes was uploaded by Adelia Adams on Monday October 12, 2015. The Class Notes belongs to ASTR 1010 at Georgia Southern University taught by James Higdon in Fall. Since its upload, it has received 24 views. For similar materials see /class/222010/astr-1010-georgia-southern-university in Astronomy at Georgia Southern University.
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Date Created: 10/12/15
Lecture 14 The Planet Saturn Outline 0rbital and Physical Properties Saturn s Atmosph ere Saturn s Interior amp M agnetasphere Saturn s Spectacular Ring System Jupiter the Comet E ater The Moons afSamrn Saturn s Orbit Saturn 395 orbit is elliptical closest 90 AU furthest 101 AU Saturn s orbital period 294 years Saturn39s orbit Saturn s spin axis is tilted 267 degrees Saturn has Seasons rings look different at different parts of its orbit Earth vs Saturn Saturn s Atmosphere Composition Saturn s Atmosphere Structure 200 1 00 Stratosphere 100 200 Water ice 300 l l 0 100 200 Temperature K 300 sajequoune uuea emssazd Saturn s Atmosphere Winds Wind patterns on Saturn are similar to those on Jupiter but faster North pole Nonhpom gm South gate 1 000 1 500 Eastward wind speed kmh Saturn s Atmosphere Storms Jupiterstyle spots rare on Saturn don t form often and quickly dissipate if they do Giant Storm at South Pole Infrared image of Saturn shows that the South pole is warmest point in atmosphere South pole in middle ofits NZ 0year summer Hovering over S Pole is a giant hurricanelike storm with Eye Why the S Pole is so warm is unknown Saturn s Internal Structure We expect Saturn s interior to be similar to Jupiter s Molecular hydrogen 6 Pressure 5 x 106 atm x Radius 30000 km Temperature 8000 K Pressure 3 x 106 atm i J Radius 60000 km f i 1 Pressure 10 atm l Temperature 250 K 390 rock core Metallic y y hydrogen Saturn s Magnetic Field Saturn also has a strong magnetic eld but only 120th as strong as Jupiter s Creates aurora The Rings of Saturn Ring features visible from Earth s surface C ring B ring Cassini Division A ring Encke gap The gaps or divisions are due to the gravitational in uence of Saturn s moons 13 The First Views of Rings Galileo s rst report in 1610 called them handles When he looked again in I 612 Galileo was astonished to nd that the rings had vanished ll Galileo s 2 report 1616 Huygens 1655 suggested that the ring was a solid disk 14 The Rings of Saturn What are they I it Saturn s Spectacular Ring System Voyager I amp 1 1980s showed Saturn s ring system to be far richer and much more complicated than imagined The A B C amp D rings are actually composed of gt1 000 ringlets each only 2 km wide each composed of streams of orbiting particles V K Gaps and major I divisions in the rings are 1 formed by the gravity of l quot moons embedded in the rings themselves or a few of the larger moons outside the rings The Rings are amazingly thin I 0 m Cassini 2005 Saturn s Spectacular Ring System The spokes appear to be microscopic dust particles suspended above the rings by electrostatic forces Their motions are not governed by gravity like the rest1qgf the ring but seem to be synchronized with Saturn s magnetosphere instead Saturn s Spectacular Ring System Another view of the rings showing the Cassini division to be not empty Saturn s Spectacular Ring System Perhaps the strangest ring is the outermost F ring It appears to be composed of a small number of braided or intertwined ringlets Kinks are also visible What is responsible for this extremely narrow ring 10 Shepherd Moons in Action This movie om Cassini in 2005 two Shepherd Prometheus inner amp they are tidally like Earth 5 moon Composition of the Rings Additional Rings Visible During Eclipse of the Sun by Saturn On 15 Sept 2006 Cassini witnessed a total eclipse of the Sun by Saturn Faint outer rings can be seen by the sunlight they scatter Unlike rings A B C D amp F the Ering is composed of microscopic d10396 m dust grains that are coated with waterammonia ice 23 Saturn s Gigantic T ilted Phoebe Ring In October the discovery of a much larger ring just overlapping the orbit of the moon Phoebe was announced This ring was found by its IR emission samm This feature is tilted by 2 7 relative to Saturn s equator like Phoebe It extends from 128 207 RSam and is very thick maybe 20x Saturn s diameter The ring appears to be made of dust particles chipped o ofPhoebe by meteor impacts 24 Saturn39s Largest Ring 12 Origin of the Phoebe ring The Phoebe ring appears to be largely made up of microscopic dust grains with little if any ice Since it shares Phoebe s orbit it s origin is no doubt tied to Phoebe Closeup images of Phoebe left by Cassini show an extremely cratered moon one seemingly almost battered to bits It s easy to imagine that the material in the Phoebe ring was chipped o ofPhoebe by a large number of meteorite impacts 25 The Phoebe Ring was Discovered by its IR Emission Saturn Dust Ring 13 The Origin of Saturn s Rings iiiquotw Problems for old ring idea The rings appear to be too dynamic to have lasted gt4billi0n years The high re ectivity of the ring implies pure ice If the rings are old the gradual accumulation of dust on the ring particles would greatly reduce their re ectivity this suggests an age lt ZOOmillion years Problems with collisional idea Moonmoon collisions would be extremely rare Comets capable of destroying a moon are rare and likely 4billi0n years ago7 Did the Rings form from a shredded moon A Tidal Force is the di erence in the force of gravity on the two sides of a moon If the di erence exceeds the moon s ability to hold itself together the moon is broken up Destroyed Q Ji Roche iimit Satellite Egg 14 The Roche Limit on other Planets i 1 MT 1 H Roche limit approximate vGassini division B ring Planet radius Planet surface Jupiter Saturn Uranus Neptune This Doesn t Really Solve the Riddle Moons exist within the rings e g Pandora amp Prometheus in Fring so the idea that one of Saturn s moons could wander inside the Roche Limit and get smashed up to form the rings doesn t hold water A comet would be smashed to smithereens if it entered the Roche Limit But it would have to be a remarkably gigantic comet d 400 km to provide the material for Saturn s rings r quot717 Uni 1 iii ti 5 I f I 39i LJliquotii ilAi I1ii i i ii iiiiig i iiiii i j i mi 30 15
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