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12b. Saturn• Saturn data• Saturn seen from the Earth• Saturn rotation & structure• Saturn clouds• Saturn atmospheric motions• Saturn rocky cores• Saturn magnetic fields• Discovering Saturn’s rings• Structure of Saturn’s rings• Rings & shepherd satellites
Saturn Data: Special Features• Saturn is the 2nd Jovian planet from the Sun• Saturn is the 2nd largest Jovian planet• Saturn is dominated by a bright ring system• Saturn has no solid surface
– ~ 85% Jupiter’s diameter but ~ 30% Jupiter’s mass• Saturn has a bland yet dynamic atmosphere
– Great White Spot, belts & zones…• Saturn interior consists of three layers
• Extremely high wind speeds– ~ 500 m . sec–1 near the equator– ~ 67% the speed of sound in Saturn’s atmosphere
Saturn’s True Colors Seen By HST
1994
Cloud Layers of Jupiter & Saturn
Saturn’s Interior is Like Jupiter’s• Saturn is the most oblate of all the planets
– ~ 9.8% shorter polar than equatorial diameter– Greater if Jupiter & Saturn had same structures
• Jupiter has ~ 2.6% of its mass in a rocky core• Saturn has ~ 10% of its mass in a rocky core
• Saturn has relatively little liquid metallic H2
– Too little mass to compress very much hydrogen
• Saturn’s magnetosphere is relatively weak– Not enough liquid metallic hydrogen– Saturn has no volcanic satellite
• Few sulfur ions in Saturn’s magnetosphere
The Interiors of Jupiter & Saturn
Auroral Rings on Saturn From HST
Saturn Generates Its Own Energy• Two observations
– Saturn emits more energy than it gets from the Sun• ~ 25% more per kg than Jupiter
– Saturn’s atmosphere is distinctly deficient in helium• 13.6% for Jupiter but only 3.3% for Saturn
• One possible process– Helium is cold enough the condense in Saturn’s air
• Helium precipitation falls to lower levers– Gravitational energy is converted into heat energy– Helium permanently removed from Saturn’s upper atmosphere
– Energy conversion equals Saturn’s excess heat
Saturn’s Moon Titan’s Atmosphere• Titan data
– Second largest Solar System satellite
5,150 km– Only satellite with a substantial atmosphere
• Gerard Kuiper detects CH4 absorption spectrum
1944• Overall composition is ~ 98.4% N2
• ~ 1.5 x Earth’s pressure with ~ 10 x Earth’s gas– Weaker gravity does not compress gas as much
– Titan is perpetually cloud covered• Titan’s surface comparable to full moonlight on Earth
• Some implications– Hydrocarbon fog & rain obscure surface visibility– Surface may be covered with hydrocarbon “goo”– Surface has liquid hydrocarbon oceans
• InfraRed radiation penetrates clouds to “see” surface
Saturn & Titan’s Atmosphere
Hydrocarbon Seas on Titan
Saturn’s Six Icy-Surfaced Satellites• Mimas & Enceladus
– Small
• Tethys & Dione– Medium
• Rhea & Iapetus– Large
Cassini/Huygens on Earth
Cassini/Huygens at Saturn
Cassini & Huygens Explore Saturn• The overall mission
– Launched 15 Oct. 1997 by a Titan IVB/Centaur• Largest, heaviest, most complex interplanetary spacecraft