Chapter 7 The Outer Planets

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192 Chapter 7 The Outer Planets The Outer Planets: A Comparison Jupiter Saturn Uranus Neptune Pluto Terrestrial core, liquid metallic hydrogen shell, liquid hydrogen mantle Similar to Jupiter, with bigger terrestrial core and less metallic hydrogen Terrestrial core, liquid water shell, liquid hydrogen and helium mantle Similar to Uranus Unknown No solid surface, atmosphere gradually thickens to liquid state, belt and zone structure, hurricanelike features No solid surface, less distinct belt and zone structure than Jupiter No solid surface, weak belt and zone system, hurricanelike features, color from methane absorption of red, orange, yellow Like Uranus Apparently rock and ice Yes Yes Yes Yes No Primarily H, He Primarily H, He Primarily H, He, some CH 4 Primarily H, He, some CH 4 Unknown For detailed numerical comparisons between planets, see Appendix Tables A-1 and A-2. *To see the orientations of these magnetic fields relative to the rotation axes of the planets, see Figure 7-31. 1AU Interior Surface Rings Atmosphere Magnetic Field Saturn Earth Uranus 4.2AU 4.3AU 9.7AU 10.9AU 9.4AU 19,000 × Earth’s total field at its cloud layer, 14 × stronger than Earth’s surface field 570 × Earth’s total field at its cloud layer, 2 ⁄3 × Earth’s surface field 50 × Earth’s total field at its cloud layer, 0.7 × Earth’s surface field 35 × Earth’s total field at its cloud layer, 0.4 × Earth’s surface field Unknown Earth Jupiter Saturn Uranus Neptune Pluto Sun (Stephen P. Meszaros/NASA, M. Buie, K. Horne, and D. Tholen) Neptune Pluto Jupiter
2 193 Chapter 7 The Outer Planets a Voyager 1 view b Voyager 2 view FIGURE 7-4 Jupiter’s Northern and Southern Hemispheres Computer processing shows the entire Jovian atmosphere from (a) Voyager 1 and (b) Voyager 2. A computer was used to “unwrap” the planet’s atmosphere. Notice in both views the dark ovals in the One rust-colored oval feature called the Great Red Spot (Figure 7-5) is so large that it can be seen through a small telescope. It changes dimensions, and at present it is about 25,000 km long by 12,000 km wide, large enough so that two Earths could easily fit side by side inside it. The Great Red Spot was first observed around 1665, either by English scientist Robert Hooke or Italian astronomer Giovanni Cassini. Because earlier telescopes were unlikely to have been able to see it, the Great Red Spot could well have formed long before that time. Heat welling upward from inside Jupiter has maintained this storm for more than three centuries. Consider what life would be like for us if the Earth sustained storms for such long periods. In 1690, Cassini noticed that the speeds of Jupiter’s clouds vary with latitude, an effect called differential rotation. Near the poles, the rotation period of Jupiter’s atmosphere, 9 h 55 min 30 s, is 5 minutes longer than at the equator. Furthermore, clouds at different latitudes circulate in opposite directions—some eastward, some westward. At their boundaries the clouds rub against each other, creating beautiful swirling patterns (see Figure 7-3). The interactions of clouds at different latitudes also help provide stability for storms like the Great Red Spot. Spectra from Earth-based telescopes and from the Galileo probe sent into Jupiter’s upper atmosphere in 1995 give more detail about Jupiter’s atmosphere. More than northern hemisphere and the white ovals in the southern hemisphere. The banded structure is absent near the poles. Notice, too, that the Great Red Spot moved westward while the white ovals moved eastward during the four months between the two Voyager flybys. (NASA) FIGURE 7-5 The Great Red Spot This image of the Great Red Spot, taken by the Galileo spacecraft in 1996, has been color enhanced to show more details of the dynamic activity taking place in and around this giant storm. The counterclockwise circulation of gas in the Great Red Spot takes about six days to make one rotation. The clouds that encounter it are forced to pass around it, and when other oval features are near it, the entire system becomes particularly turbulent, like the batter in a two-bladed blender. (NASA/JPL) WEB LINK 7.4 VIDEO 7.2
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Chapter 7 The Outer Planets

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