Chapter 11 & Chapter 12 Jupiter & Saturn © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 11.1 Orbital and Physical Properties • Mass: 1.9 × 1027 kg (twice as much as all other planets put together) • Radius: 71,500 km (11.2 times Earth’s) • Density: 1300 kg/m3—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 – Equator spins faster • From magnetic field, rotation period is 9 hr, 55 min (9h 50min at equator) © 2011 Pearson Education, Inc. 11.2 The Atmosphere of Jupiter Major visible features: Bands of clouds; Great Red Spot © 2011 Pearson Education, Inc. 11.2 The Atmosphere of Jupiter • Atmosphere has bright zones and dark belts • Zones are warmer, and are higher than belts • Stable flow, called zonal flow, underlies zones and bands • Simplified model © 2011 Pearson Education, Inc. 11.2 The Atmosphere of Jupiter Real picture is much more complicated Here: Wind speed with respect to internal rotation rate © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 11.2 The Atmosphere of Jupiter Lightning-like flashes have been seen; also shorter- lived rotating storms One example: Brown Oval, really a large gap in clouds © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Discovery 11-1: A Cometary Impact July 1994: Comet Shoemaker-Levy 9, in fragments, struck Jupiter, providing valuable information about cometary impacts © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 11.4 Jupiter’s Magnetosphere Intrinsic field strength is 20,000 times that of Earth Magnetosphere can extend beyond the orbit of Saturn © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 11.5 The Moons of Jupiter Jupiter with Io and Europa. Note the relative sizes! © 2011 Pearson Education, Inc. 11.5 The Moons of Jupiter Interiors of the Galilean moons © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 11.5 The Moons of Jupiter Orange color is probably from sulfur compounds in the ejecta © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 11.5 The Moons of Jupiter Volcanic eruptions also eject charged particles; these interact with Jupiter’s magnetosphere and form a plasma torus © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc. 11.5 The Moons of Jupiter Callisto is similar to Ganymede; no evidence of plate activity © 2011 Pearson Education, Inc. 11.6 Jupiter’s Ring Jupiter has been found to have a small, thin ring © 2011 Pearson Education, Inc. Units of Chapter 12 12.1 Orbital and Physical Properties 12.2 Saturn’s Atmosphere 12.3 Saturn’s Interior and Magnetosphere 12.4 Saturn’s Spectacular Ring System 12.5 The Moons of Saturn Dancing Among Saturn’s Moons © 2011 Pearson Education, Inc. 12.1 Orbital and Physical Properties View of rings from Earth changes as Saturn orbits the Sun - Why is Saturn the flattest planet? 10% difference between Equatorial and polar diameters Saturn Orbits Differentially, similar to Jupiter. Equator – 10 hrs 14 min Higher Latitudes – 10 hrs 40 min © 2011 Pearson Education, Inc. 12.2 Saturn’s Atmosphere Saturn’s atmosphere also shows zone and band structure, but coloration is much more subdued than Jupiter’s Mostly molecular hydrogen, helium, methane, and ammonia; helium fraction is much less than on Jupiter © 2011 Pearson Education, Inc. 12.2 Saturn’s Atmosphere This true-color image shows the delicate coloration of the cloud patterns on Saturn © 2011 Pearson Education, Inc. 12.2 Saturn’s Atmosphere Similar to Jupiter’s, except pressure is lower Three cloud layers Cloud layers are thicker than Jupiter’s; see only top layer © 2011 Pearson Education, Inc. 12.2 Saturn’s Atmosphere Structure in Saturn’s clouds can be seen more clearly in this false-color image © 2011 Pearson Education, Inc. 12.2 Saturn’s Atmosphere Wind patterns on Saturn are similar to those on Jupiter, with zonal flow © 2011 Pearson Education, Inc. 12.2 Saturn’s Atmosphere Jupiter-style “spots” rare on Saturn; don’t form often and quickly dissipate if they do © 2011 Pearson Education, Inc. 12.2 Saturn’s Atmosphere This image shows what is thought to be a vast thunderstorm on Saturn, as well as the polar vortex at Saturn’s south pole. © 2011 Pearson Education, Inc. 12.3 Saturn’s Interior and Magnetosphere Interior structure similar to Jupiter’s © 2011 Pearson Education, Inc. 12.3 Saturn’s Interior and Magnetosphere Saturn also radiates more energy than it gets from the Sun, but not because of cooling: • Helium and hydrogen are not well mixed; helium tends to condense into droplets and then fall • Gravitational field compresses helium and heats it up © 2011 Pearson Education, Inc. 12.3 Saturn’s Interior and Magnetosphere Saturn also has a strong magnetic field, but only 5% as strong as Jupiter’s Creates aurorae © 2011 Pearson Education, Inc. 12.4 Saturn’s Spectacular Ring System Saturn has an extraordinarily large and complex ring system, which was visible even to the first telescopes © 2011 Pearson Education, Inc. 12.4 Saturn’s Spectacular Ring System Overview of the ring system A, B, C Rings - B is brightest - C is almost translucent - A is in between in visibility © 2011 Pearson Education, Inc. 12.4 Saturn’s Spectacular Ring System Ring particles range in size from fractions of a millimeter to tens of meters Composition: Water ice—similar to snowballs Why rings? • Too close to planet for moon to form—tidal forces would tear it apart © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc.