Chapter 11 Jupiter Chapter 11 opener. Jupiter is certainly one of the most fascina6ng objects in the solar system. This is a true color mosaic, constructed from two dozen images taken by a camera onboard the Cassini spacecra@ during its closest approach in 2001. It is the most detailed portrait of Jupiter ever produced, resolving features to as small as 60 kilometers. Note the Great Red Spot a storm that has been under way for several hundred years. Everything seen here is a cloud, from the equatorial regions that show alterna6ng light and dark belts, to high- la6tude areas that appear more monled. All these varying structures display differing cloud heights, thickness, and chemical composi6ons. (JPL)
Units of Chapter 11 11.1 Orbital and Physical Properties 11.2 The Atmosphere of Jupiter A Cometary Impact 11.3 Internal Structure Almost a Star? 11.4 Jupiter s Magnetosphere 11.5 The Moons of Jupiter 11.6 Jupiter s Ring
11.1 Orbital and Physical Properties This figure shows the solar system from a vantage point that emphasizes the relationship of the jovian planets to the rest of the system Figure 11-1. Solar System Perspec/ve This is a varia6on on Figure 6.5 neither an overhead view or an edge- on view of our solar system, but an oblique view from a distant perspec6ve illustra6ng the jovian planets rela6ve to their terrestrial cousins. Jupiter orbits at a distance of 5.2 AU from the Sun, outside the asteroid belt but well inside the Kuiper belt.
11.1 Orbital and Physical Properties Three views of Jupiter: From a small telescope on Earth; from the Hubble Space Telescope; and from the Cassini spacecraft Figure 11-2. Jupiter (a) Photograph of Jupiter made through a ground- based telescope, showing the planet and several of its Galilean moons. (b) A Hubble Space Telescope image of Jupiter, in true color. Features as small as a few hundred kilometers across are resolved. (c) A Cassini spacecra@ image of Jupiter, taken while the vehicle was on its way to Saturn, shows intricate clouds of different heights, thicknesses, and chemical composi6on. (NASA; AURA)
11.1 Orbital and Physical Properties Mass: 1.9 10 27 kg (twice as much as all other planets put together) Radius: 71,500 km (11.2 times Earth s) Density: 1300 kg/m 3 cannot be rocky or metallic as inner planets are Rotation rate: Problematic, as Jupiter has no solid surface; different parts of atmosphere rotate at different rates From magnetic field, rotation period is 9 hr, 55 min
11.2 The Atmosphere of Major visible features: Jupiter Bands of clouds; Great Red Spot Figure 11-4. Jupiter s Red Spot Voyager 1 took this photograph of Jupiter s Great Red Spot (upper right) from a distance of about 100,000 km. Resolu6on is about 100 km. Note the complex turbulence to the le@ of both the Red Spot and the smaller white oval below it. (For scale, planet Earth has been superposed.) (NASA)
11.2 The Atmosphere of Jupiter Atmosphere has bright zones and dark belts Zones are cooler, and are higher than belts Stable flow, called zonal flow, underlies zones and bands Simplified model Figure 11-5. Jupiter s Convec/on The colored bands in Jupiter s atmosphere are associated with ver6cal convec6ve mo6on. Upwelling warm gas results in zones of lighter color; the darker bands overlie regions of lower pressure where cooler gas sinks back down into the atmosphere. As on Earth, surface winds tend to blow from high- to low- pressure regions. Jupiter s rapid rota6on channels those winds into an east west flow panern, as indicated by the three yellow- red arrows drawn atop the belts and zones. The inset is a Voyager photo of part of Jupiter s cloud layer, as seen from above, showing the planet s actual banded structure. (NASA)
11.2 The Atmosphere of Real picture is much more complicated Jupiter Here: Wind speed with respect to internal rotation rate Figure 11-6. Zonal Flow The wind speed in Jupiter s atmosphere, measured rela6ve to the planet s internal rota6on rate. Alterna6ons in wind direc6on are associated with the atmospheric band structure.
11.2 The Atmosphere of Jupiter Composition of atmosphere: mostly molecular hydrogen and helium; small amounts of methane, ammonia, and water vapor These cannot account for color; probably due to complex chemical interactions
11.2 The Atmosphere of Jupiter No solid surface; take top of troposphere to be at 0 km Lowest cloud layer cannot be seen by optical telescopes Measurements by Galileo probe show high wind speeds even at great depth probably due to heating from planet, not from Sun Figure 11-7. Jupiter s Atmosphere Models of the ver6cal structure of Jupiter s atmosphere suggest that the planet s clouds are arranged in three main layers, each with quite different colors and chemistry. The colors we see in photographs of the planet depend on the cloud cover. The white regions are the tops of the upper ammonia clouds. The yellows, reds, and browns are associated with the second cloud layer, which is composed of ammonium hydrosulfide ice. The lowest (bluish) cloud layer is water ice; however, the overlying layers are sufficiently thick that this level is not seen in visible light. The blue curve shows how Jupiter s atmospheric temperature depends on al6tude. (For comparison with Earth, see Figure 7.2.)
11.2 The Atmosphere of Jupiter Great Red Spot has existed for at least 300 years, possibly much longer Color and energy source still not understood Figure 11-9. Red Spot Details These Voyager 2 close- up views of the Great Red Spot, taken 4 hours apart, show clearly the turbulent flow around its edges. The general direc6on of mo6on of the gas north of (above) the spot is westward (to the le@), whereas gas south of the spot flows east. The spot itself rotates counterclockwise, sugges6ng that it is being rolled between the two oppositely directed flows. The colors have been exaggerated somewhat to enhance the contrast. (NASA)
11.2 The Atmosphere of Jupiter Lightning-like flashes have been seen; also shorterlived rotating storms One example: Brown Oval, really a large gap in clouds Figure 11-10. Brown Oval This brown oval in Jupiter s northern hemisphere is actually a break in the upper cloud layer, allowing us to see deeper into the atmosphere, where the clouds are brown. The oval s length is approximately equal to Earth s diameter. (NASA)
11.2 The Atmosphere of Jupiter Recently, three white storms were observed to merge into a single storm, which then turned red. This may provide some clues to the dynamics behind Jupiter s cloud movements. Figure 11-11. Red Spot Junior (a) Between 1997 and 2000, astronomers watched as three white ovals in Jupiter s southern hemisphere merged to form a single large storm. Each oval, captured here by the Cassini spacecra@ cameras, is about half the size of Earth. (b) In early 2006 the white oval turned red, producing a second red spot! The color change may indicate that the storm is intensifying. (c) In mid- 2008, the Hubble telescope recorded this sequence of images at monthly intervals (le@ to right), showing a baby red spot (arrows) approaching the Great Red Spot and being destroyed by it.(nasa)
Discovery 11-1: A Cometary Impact July 1994: Comet Shoemaker-Levy 9, in fragments, struck Jupiter, providing valuable information about cometary impacts
11.3 Internal Structure Find that Jupiter radiates more energy than it receives from the Sun: Core is still cooling off from heating during gravitational compression Could Jupiter have been a star? No; it is far too cool and too small for that. It would need to be about 80 times more massive to be even a very faint star.
11.3 Internal Structure No direct information is available about Jupiter s interior, but its main components, hydrogen and helium, are quite well understood. The central portion is a rocky core. Figure 11-12. Jupiter s Interior Jupiter s internal structure, as deduced from Voyager measurements and theore6cal modeling. The outer radius represents the top of the cloud layers, some 70,000 km from the planet s center. The density and temperature increase with depth, and the atmosphere gradually liquefies at a depth of a few thousand kilometers. Below a depth of 20,000 km, the hydrogen behaves like a liquid metal. At the center of the planet lies a large rocky core, somewhat terrestrial in composi6on, but much larger than any of the inner planets. Although the values are uncertain, the temperature and pressure at the center are probably about 25,000 K and 60 million (Earth) atmospheres, respec6vely.
Discovery 11-2: Almost a Star? Jupiter is much too small to have become a star needs 80 times more mass! But its energy output was larger in the past; could have been 100 times brighter than the Moon as seen from Earth Dwarf star in Jupiter s place probably would have made stable planetary orbits impossible Jupiter played invaluable role in sweeping solar system clear of debris before too much reached Earth otherwise life on Earth might not have been possible
11.4 Jupiter s Magnetosphere Jupiter is surrounded by belts of charged particles, much like the Van Allen belts but vastly larger Magnetosphere is 30 million km across Figure 11-15. Jupiter s Magnetosphere Jupiter s inner magnetosphere is characterized by a flat current sheet consis6ng of charged par6cles squeezed into the magne6c equatorial plane by the planet s rapid rota6on. The plasma torus, a ring of charged par6cles associated with the moon Io, is discussed in Sec6on 11.5.
11.4 Jupiter s Magnetosphere Intrinsic field strength is 20,000 times that of Earth Magnetosphere can extend beyond the orbit of Saturn Figure 11-13. Pioneer 10 Mission The Pioneer 10 spacecra@ (a forerunner of the Voyager missions) did not detect any solar par6cles while moving far behind Jupiter in 1976. Accordingly, as sketched here, Jupiter s magnetosphere apparently extends beyond the orbit of Saturn.
11.5 The Moons of Jupiter 63 moons have now been found orbiting Jupiter, but most are very small The four largest are the Galilean moons, so called because they were first observed by Galileo: Io, Europa, Ganymede, Callisto Galilean moons have similarities to terrestrial planets: orbits have low eccentricity, largest is somewhat larger than Mercury, and density decreases as distance from Jupiter increases
11.5 The Moons of Jupiter Jupiter with Io and Europa. Note the relative sizes! Figure 11-17. Jupiter, Up Close Voyager 1 took this photo of Jupiter with ruddy Io on the le@ and pearllike Europa toward the right. Note the scale of objects here: Both Io and Europa are comparable in size to our Moon, and the Red Spot is roughly twice as big as Earth. (NASA)
11.5 The Moons of Jupiter Interiors of the Galilean moons Figure 11-18. Galilean Moon Interiors Cutaway diagrams showing the interior structure of the four Galilean satellites. Moving outward from Io to Callisto, we see that the moons densi6es steadily decrease as the composi6on shi@s from rocky mantles and metallic cores in Io and Europa, to a thick icy crust and smaller core in Ganymede, to an almost uniform rock and ice mix in Callisto. Both Ganymede and Europa are thought to have layers of liquid water beneath their icy surfaces.
11.5 The Moons of Jupiter Io is the densest of Jupiter s moons, and the most geologically active object in the solar system: Many active volcanoes, some quite large Can change surface features in a few weeks No craters; they fill in too fast Io has the youngest surface of any solar system object
11.5 The Moons of Jupiter Orange color is probably from sulfur compounds in the ejecta Figure 11-19. Io Jupiter s innermost moon, Io, is quite different in character from the other three Galilean satellites. Its surface is kept smooth and brightly colored by the moon s constant volcanism. The resolu6on of the Galileo photograph in (a) is about 7 km. In the more detailed Voyager image (b), features as small as 2 km across can be seen. (NASA)
11.5 The Moons of Jupiter Cause of volcanism: Gravity! Io is very close to Jupiter and also experiences gravitational forces from Europa. The tidal forces are huge and provide the energy for the volcanoes. Figure 11-20. Volcanoes on Io The main image shows a Galileo view of Io with a resolu6on of about 6 km. The dark, circular features are volcanoes. The le@ inset shows an umbrella- like erup6on of one of Io s volcanoes, captured as Galileo flew past this fascina6ng moon in 1997; the plume measures about 150 km high and 300 km across. The right inset shows another volcano, this one face- on, where surface features here are resolved to just a few kilometers. (NASA)
11.5 The Moons of Jupiter Volcanic eruptions also eject charged particles; these interact with Jupiter s magnetosphere and form a plasma torus
11.5 The Moons of Jupiter Europa has no craters; surface is water ice, possibly with liquid water below Tidal forces stress and crack ice; water flows, keeping surface relatively flat Figure 11-22. Europa (a) Voyager 1 mosaic of Europa. Resolu6on is about 5 km. (b) Europa s icy surface is only lightly cratered, indica6ng that some ongoing process must be oblitera6ng impact craters soon a@er they form. The origin of the cracks crisscrossing the surface is uncertain. (c) At 5- m resolu6on, this image from the Galileo spacecra@ shows a smooth yet tangled surface resembling the huge ice floes that cover Earth s polar regions. This region is called Conamara Chaos. (d) This detailed Galileo image shows pulled apart terrain that suggests liquid water upwelling from the interior and freezing, filling in the gaps between separa6ng surface ice sheets. (NASA)
11.5 The Moons of Jupiter Ganymede is the largest moon in the solar system larger than Pluto and Mercury History similar to Earth s Moon, but water ice instead of lunar rock Figure 11-23. Ganymede (a) and (b) Voyager 2 images of Ganymede. The dark regions are the oldest parts of the moon s surface and probably represent its original icy crust. The largest dark region visible here, called Galileo Regio, spans some 3200 km. The lighter, younger regions are the result of flooding and freezing that occurred within a billion years or so of Ganymede s forma6on. The light- colored spots are recent impact craters. (c) Grooved terrain on Ganymede may have been caused by a process similar to plate tectonics on Earth. The area shown in this Galileo image spans about 50 km and reveals a mul6tude of ever- smaller ridges, valleys, and craters, right down to the resolu6on limit of the spacecra@ s camera (about 300 m, three 6mes the length of a football field). The image suggests erosion of some sort, possibly even caused by water. (NASA)
11.5 The Moons of Jupiter Callisto is similar to Ganymede; no evidence of plate activity Figure 11-24. Callisto (a) Callisto, the outermost Galilean moon of Jupiter, is similar to Ganymede in overall composi6on, but is more heavily cratered. The large series of concentric ridges visible at le@ is known as Valhalla. Extending nearly 1500 km from the basin center, the ridges formed when ripples from a large meteori6c impact froze before they could disperse completely. Resolu6on in this Voyager 2 image is about 10 km. (b) This higher- resolu6on Galileo image of Callisto s equatorial region, about 300 200 km in area, displays more clearly its heavy cratering. (NASA)
11.6 Jupiter s Ring Jupiter has been found to have a small, thin ring Figure 11-25. Jupiter s Ring Jupiter s faint ring, as photographed (nearly edge- on) by Voyager 2. Made of dark fragments of rock and dust possibly chipped off the innermost moons by meteorites, the ring was unknown before the two Voyager spacecra@ arrived at the planet. It lies in Jupiter s equatorial plane, only 50,000 km above the cloud tops. (NASA)
Summary of Chapter 11 Jupiter is the largest planet in the solar system Rotates rapidly Cloud cover has three main layers, forms zone and band pattern Great Red Spot is a very stable storm Pressure and density of atmosphere increase with depth; atmosphere becomes liquid and then metallic
Summary of Chapter 11 (cont.) Relatively small rocky core (but still about 10x size of Earth) Still radiating energy from original formation 63 moons, four very large Io: active volcanoes, due to tidal forces Europa: cracked, icy surface; may be liquid water underneath Ganymede and Callisto: similar; rock and ice