12. Jovian Planet Systems

1. 12. Jovian Planet Systems Do there exist many worlds, or is there but a single world? This is one of the most noble and exalted questions in the study of Nature. St. Albertus Magnus (1206 – 1280) scholar and patron saint of scientists © 2004 Pearson Education Inc., publishing as Addison-Wesley

2. 12.1 The Jovian Worlds: A Different Kind of Planet Our goals for learning: • Briefly describe the major features of the Jovian planets. • Why are Jovian planets so different from terrestrial planets? © 2004 Pearson Education Inc., publishing as Addison-Wesley

3. Jovian Planet Properties © 2004 Pearson Education Inc., publishing as Addison-Wesley

4. Jovian Planet Properties • Compared to the terrestrial planets, the Jovians: • are much larger & more massive • are composed mostly of Hydrogen, Helium, & Hydrogen compounds • have no solid surfaces • rotate more quickly • have slightly “squashed” shapes • have many moons • have ring systems © 2004 Pearson Education Inc., publishing as Addison-Wesley

5. Why are the Jovian Planets so Different? • They formed beyond the frost line to form large, icy planetesimals which were massive enough to… • Capture H/He far from Sun to form gaseous planets. • Each Jovian planet formed its own “miniature” solar nebula. • Moons formed out of these disks. © 2004 Pearson Education Inc., publishing as Addison-Wesley

6. 12.2 Jovian Planet Interiors Our goals for learning: • Briefly describe the interior structure of Jupiter. • Why is Saturn almost as big in radius as Jupiter? • How do the Jovian planet interiors differ, and why? © 2004 Pearson Education Inc., publishing as Addison-Wesley

7. Inside Jupiter Although Jupiter has no solid surface and consists mostly of H & He, it does have distinct interior layers, defined by phase. • Moving from the surface to the core: • temperature increases • pressure & density increases • The core of Jupiter is slightly larger than Earth. • But it is 5 times as dense! • thank to tremendous weight from above • So Jupiter's core has 10 times the mass of Earth. © 2004 Pearson Education Inc., publishing as Addison-Wesley

8. Inside Jupiter • Jupiter emits almost twice as much energy as it absorbs from the Sun. • accretion, differentiation, radioactivity can not account for it • Jupiter must still be contracting • Jupiter has 3 x more mass than Saturn, but is not much larger! • the added weight of H & He compresses the core to a higher density • just like stacking pillows • Add even more mass, and Jupiter would get smaller. • Jupiter is about as large as a planet can get. • Uranus & Neptune have less mass than Saturn, yet • they have higher densities • they must be made of denser material © 2004 Pearson Education Inc., publishing as Addison-Wesley

9. Inside the Jovian Planets • All Jovian cores appear to be similar. • made of rock, metal, and Hydrogen compounds • 10 x the mass of Earth • Uranus & Neptune captured less gas from the Solar nebula. • accretion of planetesimals took longer • not much time for gas capture before nebula was cleared out by Solar wind • Only Jupiter and Saturn have high enough pressure for H & He to exist in liquid and metallic states. © 2004 Pearson Education Inc., publishing as Addison-Wesley

10. 12.3 Jovian Planet Atmospheres Our goals for learning: • How is Jupiter’s atmospheric structure similar to Earth’s? • Why does Jupiter have three distinct cloud layers? • What is the Great Red Spot? • How do other Jovian atmospheres compare to Jupiter’s? © 2004 Pearson Education Inc., publishing as Addison-Wesley

11. Jupiter’s Atmosphere • In 1995, the Galileo space probe plunged into the planet Jupiter! • It measured the atmospheric structure of Jupiter • thermosphere {absorbs Solar X-rays} • stratosphere {absorbs Solar UV} • troposphere {greenhouse gases trap heat from both Jupiter and the Sun} • Sound Familiar? • These are the same structures found in Earth’s atmosphere. • Atmospheres are governed by interactions between sunlight and gases. © 2004 Pearson Education Inc., publishing as Addison-Wesley

12. Jupiter’s Cloud Layers • Convection in the troposphere causes Jovian weather. • Warm gas rises to cooler altitudes, where it condenses to form clouds. • Three gases condense in the Jovian atmosphere: • ammonia (NH3) • ammonium hydrosulfide (NH4SH) • water (H2O) • They condense at different temperatures, so their clouds form at different altitudes. © 2004 Pearson Education Inc., publishing as Addison-Wesley

13. Jupiter’s Cloud Layers • Like Earth, Jupiter has circulation cells in its atmosphere. • Jupiter is much larger & rotates much faster. • Coriolis effect is much stronger on Jupiter • circulation cells are split into many bands of rising and falling air • these are the colored “stripes” which we see • The so-called: • zones (rising air) • belts (falling air) © 2004 Pearson Education Inc., publishing as Addison-Wesley

14. Jovian Storms • We also see high pressure storms • analogous to hurricanes, but they rotate in the opposite direction • Jupiter • the Great Red Spot • we are not sure why it is red • Neptune • the Great Dark Spot © 2004 Pearson Education Inc., publishing as Addison-Wesley

15. The Jovian Atmospheres • The temperature profile of each planet determines the color of its appearance. • Cloud layers form where a particular gas condenses. • Saturn has the same cloud layers as Jupiter. • they form deeper since Saturn is colder overall • they are spread farther apart since Saturn has lower gravity • Uranus & Neptune • cold enough to form methane clouds © 2004 Pearson Education Inc., publishing as Addison-Wesley

16. Why Uranus & Neptune are Blue • They have a higher fraction of methane gas. • Methane absorbs red sunlight. • Only blue light is reflected back into space by the clouds. • Uranus is “tipped” on its side. • It should experience the most extreme seasonal changes. • no clouds or banded structure seen in 1986 when N pole facing Sun • no weather, no internal heat? • HST saw storms in 1998, perhaps b/c the S hemisphere is warming now • long seasons cause more haze so that Uranus is a paler blue than Neptune 1986 - Visual 1998 - IR © 2004 Pearson Education Inc., publishing as Addison-Wesley

17. 12.4 Jovian Planet Magnetospheres Our goals for learning: • Contrast Jupiter’s magnetosphere with Earth’s. • How does Jupiter’s magnetosphere interact with Io? • How do other Jovian magnetospheres compare to Jupiter’s? © 2004 Pearson Education Inc., publishing as Addison-Wesley

18. Jupiter’s Magnetosphere • Its general properties are very similar to Earth’s, except • it is about 20,000 times stronger • it extends 3,000,000 km beyond Jupiter • Charged particles from the Solar wind (& Io) cause auroras. © 2004 Pearson Education Inc., publishing as Addison-Wesley

19. The Io Torus • The moon Io loses volcanic gases into space. • gases are ions on Sulfur, Oxygen, Sodium • they form a donut-shaped belt of charged particles, called the Io torus • they follow Io’s orbit & are a source of charged particles for the auroras • they alter the surfaces of other moons & form bombardment atmospheres © 2004 Pearson Education Inc., publishing as Addison-Wesley

20. Jovian Magnetospheres • Saturn, Uranus, & Neptune have smaller & weaker magnetospheres. • fraction of electrically conducting material in interiors is smaller • Solar wind is weaker farther out, or else their magnetospheres would be even smaller • we can not explain the magnetic field tilts of Uranus & Neptune. © 2004 Pearson Education Inc., publishing as Addison-Wesley

21. 12.5 A Wealth of Worlds: Satellites of Ice and Rock Our goals for learning: • Why can active geology occur on much smaller worlds when they are made of ice rather than rock? • What makes Io so volcanically active? • Why do we suspect a subsurface ocean on Europa? • Briefly describe key features of the moons Ganymede, Callisto, Titan, & Triton. © 2004 Pearson Education Inc., publishing as Addison-Wesley

22. medium moons 300 to 1,500 km in diameter large moons greater than 1,500 km in diameter both groups formed like planets out of the “mini-Solar nebulae” surrounding the Jovian planets small moons less than 300 km across they are not spherical probably captured asteroids Jovian Planets have Numerous Moons We can divide them into three groups: © 2004 Pearson Education Inc., publishing as Addison-Wesley

23. You might think these moons are too small for active geology to occur. • You would be wrong! • terrestrial planets are made mostly of rock • Jovian moons are made mostly of ice • Ices melt at lower temperatures than rock. • less heating is required to have molten cores • volcanism and tectonics can occur • There is another heat source. • tidal heating plays a more important role • There is very little erosion due to lack of substantial atmospheres with the exception of Titan. © 2004 Pearson Education Inc., publishing as Addison-Wesley

24. The Large Jovian Moons sulfur volcanoes • Jupiter • Io • Europa • Ganymede • Callisto • Saturn • Titan • Neptune • Triton world of water ice (and liquid?) active ice world dead & dirty ice world has a thick atmosphere (N2 & CH4) nitrogen volcanoes, retrograde orbit © 2004 Pearson Education Inc., publishing as Addison-Wesley

25. The Jovian Moons • The moons of Jupiter become less dense as you get farther from Jupiter • “mini Solar System” • Gravitational tidal heating keeps the interiors of the inner moons hot. © 2004 Pearson Education Inc., publishing as Addison-Wesley

26. Io • Jupiter’s tidal forces flex Io like a ball of silly putty. • friction generates heat • interior of Io is molten • Volcanoes erupt frequently. • sulfur in the lava accounts for yellow color • surface ice vaporizes and jets away • Evidence of tectonics & impact cratering is covered. © 2004 Pearson Education Inc., publishing as Addison-Wesley

27. Europa • metallic core, rocky mantle, and a crust made of H2O ice • Its fractured surface tells a tale of tectonics. • few impact craters seen • double-ridged cracks • jumbled icebergs • These provide photographic evidence of a subsurface ocean. • Europa has a magnetic field. • implies liquid salt water beneath the icy crust • Where liquid water exists, there could be life! © 2004 Pearson Education Inc., publishing as Addison-Wesley

28. Ganymede • largest moon in the Solar System • Its surface has 2 types of terrain: • heavily cratered, implies old • long grooves, few craters, implies young like Europa • It also has a magnetic field. • Could it have subsurface ocean? • case not as strong as Europa’s • tidal heating would be weaker • would need additional heating from radioactive decay © 2004 Pearson Education Inc., publishing as Addison-Wesley

29. Callisto • It has an old surface. • heavily cratered, dirty ice • cratering reveals clean, white ice • no evidence of tectonics • Its interior did not differentiate. • rock mixed with ice • It does not experience tidal heating. • Yet it has a magnetic field. • Could it have a subsurface ocean anyway? © 2004 Pearson Education Inc., publishing as Addison-Wesley

30. Titan • largest of Saturn’s moons • It has a thick atmosphere. • Nitrogen (90%), Argon, methane, ethane • N comes from dissociated NH3 • methane, ethane are greenhouse gases: surface is warmer than it should be • ethane may condense to form clouds and rain • The atmosphere blocks our view of Titan’s surface. • it may have oceans of ethane • erosion may be important © 2004 Pearson Education Inc., publishing as Addison-Wesley

31. Triton • It orbits in the opposite direction of Neptune's rotation in a highly inclined orbit. • this implies that it was probably captured by Neptune • It has a thin Nitrogen atmosphere, sublimed from the surface. • Some sort if volcanic activity occurs. © 2004 Pearson Education Inc., publishing as Addison-Wesley

32. 12.6 Jovian Planet Rings Our goals for learning: • What do Saturn's rings look like? • How do other ring systems compare to Saturn’s? • What is the origin of planetary rings? © 2004 Pearson Education Inc., publishing as Addison-Wesley

33. The Rings of Saturn • From Earth, they look solid. • concentric rings separated by the Cassini division • From spacecraft flybys, we see thousands of individual rings. • separated by narrow gaps • they differ in brightness & transparency • From within the rings, we would see many individual particles • size ranges from boulders to dust • made of reflective H2O ice (snowballs) • many collisions keep ring thin © 2004 Pearson Education Inc., publishing as Addison-Wesley

34. Gravitational interaction with moons inside the rings push particles into specific orbits. clear gaps Interaction with larger, distant moons can clear gaps and form ripples. Dark patches called spokes appear and disappear. They are still a mystery. Perhaps they might be particles of dust drawn out by Saturn’s magnetic field. Rings, Ripples, and Spokes © 2004 Pearson Education Inc., publishing as Addison-Wesley

35. Comparing Jovian Ring Systems • Compared to Saturn, the other ring systems: • have fewer particles • are smaller in extent • have darker particles • Why this is so, we are not sure. • Other unsolved mysteries: • Uranus’ rings are eccentric and slightly tilted from its equatorial plane. • Neptune has partial rings. © 2004 Pearson Education Inc., publishing as Addison-Wesley

36. Origin of Planetary Rings • Within 2 or 3 planetary radii of a planet, its tidal forces will be greater than the gravity holding a moon together. • a moon which wanders too close will be torn apart • matter from the mini-nebula at this distance will not form moon • Rings can not last the age of the Solar System. • particles will be ground to dust by micrometeorite collisions • atmospheric drag will cause ring particles to fall into planet • There must be a source to replenish ring particles. • the gradual dismantling of small moons, which formed from the mini-nebula, by collisions, tidal forces, etc. • The appearance of ring systems must change dramatically over millions or billions of years. © 2004 Pearson Education Inc., publishing as Addison-Wesley

37. What have we learned? • Briefly describe the major features of the Jovian planets. • Largely composed of hydrogen, helium, & hydrogen compounds. No solid surfaces. Fast rotation. Slightly “squashed” shapes. Many moons. Ring systems. • Why are Jovian planets so different from terrestrial planets? • Formed in cold, outer Solar System at the centers of “miniature Solar nebulas.” • Briefly describe the interior structure of Jupiter. • Central core of H compounds, rocks, & metals. Next layer up contains metallic H, followed by a layer of liquid H, followed by the gaseous atmosphere. Pressure, density, & temperature all increase with depth. © 2004 Pearson Education Inc., publishing as Addison-Wesley

38. What have we learned? • Why is Saturn almost as big in radius as Jupiter? • Adding mass to a Jovian planet does not necessarily increase its size, because the stronger gravity compresses the mass to greater density. Jupiter is near the maximum possible size for a Jovian planet. • How do the Jovian planet interiors differ, and why? • All have cores of about the same mass, but differ in the amount of surrounding H and He. Accretion took longer in the more spread out regions of the outer Solar System, so the more distant planets captured less gas from the Solar nebula before it was blown away by the Solar wind. © 2004 Pearson Education Inc., publishing as Addison-Wesley

39. What have we learned? • How is Jupiter’s atmospheric structure similar to Earth’s? • Troposphere, stratosphere, and thermosphere created by similar interactions of gas and sunlight. • Why does Jupiter have three distinct cloud layers? • Different gases condense at different temperatures. Jupiter has three cloud layers, each at the altitude where a particular gas can condense. • What is the Great Red Spot? • A giant, high-pressure storm. © 2004 Pearson Education Inc., publishing as Addison-Wesley

40. What have we learned? • How do other Jovian atmospheres compare to Jupiter’s? • Atmospheric structures all similar, but each is progressively colder with distance from the Sun. Saturn is the most similar to Jupiter. Uranus and Neptune are cold enough to have a methane cloud layer, which leads to their blue colors. Seasons play a major role on Uranus. • Contrast Jupiter’s magnetosphere with Earth’s. • Similar general properties, but far larger with a magnetic field 20,000 times stronger. © 2004 Pearson Education Inc., publishing as Addison-Wesley

41. What have we learned? • How does Jupiter’s magnetosphere interact with Io? • The magnetosphere contains charged particles coming from Io, which create the Io torus. The particles, in turn, bombard the surface of Io, creating a thin bombardment atmosphere. • How do other Jovian magnetospheres compare to Jupiter’s? • Smaller, with weaker magnetic fields. • What makes Io so volcanically active? • Tidal heating, caused by the title force of Jupiter as Io moves through its elliptical orbit, which in turn is caused by orbital resonances with Europa & Ganymede. © 2004 Pearson Education Inc., publishing as Addison-Wesley

42. What have we learned? • Why can active geology occur on much smaller worlds when they are made of ice rather than rock? • Ices soften and melt at much lower temperatures than rock, allowing icy volcanism and tectonics at surprisingly low temperatures. • Why do we suspect a subsurface ocean on Europa? • Photos show evidence of water flows on the surface, magnetic field measurements support the presence of a salty ocean, and there is enough tidal heating to melt a thick layer of ice beneath the surface. © 2004 Pearson Education Inc., publishing as Addison-Wesley

43. What have we learned? • Briefly describe key features of the moons Ganymede, Callisto, Titan, & Triton. • Ganymede: largest moon in Solar System; might have subsurface ocean. Callisto: ancient cratered surface, but still could have subsurface ocean Titan: only moon with a thick atmosphere. Triton: probably a captured moon, despite its large size. • What do Saturn’s rings look like? • From a distance they look fairly solid, but we see thousands of individual rings and gaps up close. Within them are countless individual particles. © 2004 Pearson Education Inc., publishing as Addison-Wesley

44. What have we learned? • How do other ring systems compare to Saturn’s? • The other Jovian rings contain fewer particles, are smaller in extent, and darker in color. • What is the origin of planetary rings? • Ring particles are constantly destroyed through impacts or other processes. Thus, the rings must be replenished with new particles over time, or else disappear. Ring particles probably come from the dismantling of many small moons formed in the “miniature Solar nebulas” that produced the Jovian planets billions of years ago. © 2004 Pearson Education Inc., publishing as Addison-Wesley