1Jupiter and Saturn:Lords of the PlanetsChapter Fourteen2Guiding Questions1. Why is the best month to see Jupiter different from one year to the next?2. Why are there important differences between the atmospheres of Jupiter and Saturn?3. What is going on in Jupiter’s Great Red Spot?4. What is the nature of the multicolored clouds of Jupiter and Saturn?5. What does the chemical composition of Jupiter’s atmosphere implyabout the planet’s origin?6. How do astronomers know about the deep interiors of Jupiter and Saturn?7. How do Jupiter and Saturn generate their intense magnetic fields?8. Why would it be dangerous for humans to visit certain parts of the space around Jupiter?9. How was it discovered that Saturn has rings?10.Are Saturn’s rings actually solid bands that encircle the planet?11.How uniform and smooth are Saturn’s rings?12.How do Saturn’s satellites affect the character of its rings?Jupiter and Saturn are the most massive planetsin the solar system• Jupiter and Saturn are both much larger than Earth• Each is composed of 71% hydrogen, 24% helium, and 5% all other elements by mass• Both planets have a higher percentage of heavy elements than does the Sun• Jupiter and Saturn both rotate so rapidly that the planets are noticeably flattenedLong orbital periods of Jupiter and Saturn cause favorable viewing times to shift3Unlike the terrestrial planets, Jupiter and Saturnexhibit differential rotationAtmospheres• The visible “surfaces” of Jupiter and Saturn are actually the tops of their clouds• The rapid rotation of the planets twists the clouds into dark belts and light zones that run parallel to the equator• The outer layers of both planets’ atmospheres show differential rotation– The equatorial regions rotate slightly faster than the polar regions• For both Jupiter and Saturn, the polar rotation rate is nearly the same as the internal rotation rateSpacecraft images show remarkable activityin the clouds of Jupiter and Saturn4Storms• Both Jupiter and Saturn emit more energy than they receive from the Sun• Presumably both planets are still cooling • The colored ovals visible in the Jovian atmosphere represent gigantic storms• Some, such as the Great Red Spot, are quite stable and persist for many years Storms in Saturn’s atmosphere seem to be shorter-lived5The internal heat of Jupiter and Saturn has a major effect on the planets’ atmospheresA space probe has explored Jupiter’s deepatmosphere• There are presumed to be three cloud layers in the atmospheres of Jupiter and Saturn• The reasons for the distinctive colors of these different layers are not yet known• The cloud layers in Saturn’s atmosphere are spread out over a greater range of altitude than those of Jupiter, giving Saturn a more washed-out appearance• Saturn’s atmosphere contains less helium than Jupiter’s atmosphere• This lower abundance may be the result of helium raining downward into the planet• Helium “rainfall” may also account for Saturn’s surprisingly strong heat output6The oblateness of Jupiter and Saturn reveals their rocky cores• Jupiter probably has a rocky core several times more massive than the Earth• The core is surrounded by a layer of liquid “ices” (water, ammonia, methane, and associated compounds)• On top of this is a layer of helium and liquid metallic hydrogen and an outermost layer composed primarily of ordinary hydrogen and helium• Saturn’s internal structure is similar to that of Jupiter, but its core makes up a larger fraction of its volume and its liquid metallic hydrogen mantle is shallower than that of JupiterMetallic hydrogen inside Jupiter and Saturn endows the planets with strong magnetic fields• Jupiter and Saturn have strong magnetic fields created by currents in the metallic hydrogen layer• Jupiter’s huge magnetosphere contains a vast current sheet of electrically charged particles• Saturn’s magnetic field and magnetosphere are much less extensive than Jupiter’sJupiter and Saturn have extensive magnetospheres• The Jovian magnetosphere encloses a low-density plasma of charged particles• The magnetosphere exists in a delicate balance between pressures from the plasma and from the solar wind• When this balance is disturbed, the size of the magnetosphere fluctuates drastically7Synchrotron RadiationCharged particles in the densest portions of Jupiter’s magnetosphere emit synchrotron radiation at radio wavelengthsEarth-based observations reveal three broad ringsencircling Saturn• Saturn is circled by a system of thin, broad rings lying in the plane of the planet’s equator• This system is tilted away from the plane of Saturn’s orbit, which causes the rings to be seen at various angles by an Earth-based observer over the course of a Saturnian year8Saturn’s rings are composed of numerous icyfragments, while Jupiter’s rings are made of smallrocky particles• The principal rings of Saturn are composed of numerous particles of ice and ice-coated rock ranging in size from a few micrometers to about 10 m• Jupiter’s faint rings are composed of a relatively small amount of small, dark, rocky particles that reflect very little light • Most of its rings exist inside the Roche limit of Saturn, where disruptive tidal forces are stronger than the gravitational forces attracting the ring particles to each other• Each of Saturn’s major rings is composed of a great many narrow ringlets9The faint F ring, which is just outside the A ring, is kept narrow by the gravitational pull of shepherd satellitesSaturn’s rings consist of thousands of narrow,closely spaced ringlets10Saturn’s inner satellites affect the appearanceand structure of its rings11Key Words•A ring•B ring• belts• brown oval•C ring• Cassini division• current sheet•D ring• decametric radiation• decimetric radiation• differential rotation•E ring• Encke gap•F ring•G ring• Great Red Spot• hot spot• internal rotation period• light scattering• liquid metallic hydrogen• noble gases• nonthermal radiation,• oblate, oblateness•plasma• ring particles• ringlets• Roche limit• shepherd satellite• synchrotron radiation• thermal radiation• tidal force• white oval• zonal winds•