Chapter 11 11.1 A Different Kind of Planet Jovian Planet Systems • Our goals for learning • Are jovian planets all alike? • What are jovian planets like on the inside? • What is the weather like on jovian planets? • Do jovian planets have magnetospheres like Earth’s? Jovian Planet Composition Are jovian planets all alike? • Jupiter and Saturn – Mostly H and He gas • Uranus and Neptune – Mostly hydrogen compounds: water (H 2 O), methane (CH 4 ), ammonia (NH 3 ) – Some H, He, and rock Density Differences Density Differences 2 2 Density (g/cc) Density (g/cc) • But that explanation 1.5 1.5 doesn’t work for • Uranus and Neptune 1 1 Jupiter…. are denser than Saturn 0.5 because they have less 0.5 H/He, proportionately 0 0 r n s e r n s e e u n e u n r r t t u n u n i u i u p t p t a t a t a a u r p u r p S S U e U e J J N N 1
Sizes of Jovian Planets Sizes of Jovian Planets • Greater compression • Adding mass to a is why Jupiter is not jovian planet much larger than compresses the Saturn even though it underlying gas is three times more layers massive • Jovian planets with even more mass can be smaller than Jupiter What are jovian planets like on Rotation and Shape the inside? • Jovian planets are not quite spherical because of their rapid rotation Inside Jupiter Interiors of Jovian Planets • High pressures • No solid surface. inside Jupiter cause phase of hydrogen • Layers under high pressure and to change with depth temperatures. • Cores (~10 Earth masses) made of hydrogen • Hydrogen acts like a compounds, metals & rock metal at great depths • The layers are different for the different because its electrons planets. WHY? move freely 2
Comparing Jovian Interiors Inside Jupiter • Core is thought to be made of rock, metals, and hydrogen compounds • Models suggest cores of jovian planets have similar • Core is about same composition size as Earth but 10 • Lower pressures inside Uranus and Neptune mean no times as massive metallic hydrogen Jupiter’s Internal Heat Internal Heat of Other Planets • Jupiter radiates • Saturn also radiates twice as much energy it twice as much energy it receives receives from Sun from Sun • Energy probably comes from differentiation (helium rain) • Energy probably • Neptune emits nearly twice as much energy comes from slow as it recieves, but the source of that energy contraction of remains mysterious interior (releasing potential energy) What is the weather like on Jupiter’s Atmosphere jovian planets? • Hydrogen compounds in Jupiter form clouds • Different cloud layers correspond to NH 3 freezing points of NH 4 SH different hydrogen H 2 O compounds 3
Jupiter’s Jovian Planet Atmospheres colors • Other jovian planets have cloud layers similar to Jupiter’s • Different compounds make clouds of different colors • Ammonium sulfide clouds (NH 4 SH) reflect red/brown. • Ammonia, the highest, coldest layer, reflects white. Saturn’s Methane on Uranus and Neptune colors • Methane gas of Neptune and Uranus absorb red light but transmit blue light • Blue light reflects off methane clouds, making those planes look blue • Saturn’s layers are similar, but deeper in and farther from the Sun --- more subdued. Jupiter’s Bands Jupiter’s White ammonia Great clouds form Coriolis effect where air rises Red changes N-S flow to E-W Between white Spot winds clouds we see deeper reddish clouds of NH 4 SH Warmer red bands are brighter in IR • A storm twice as wide as Earth • Has existed for at least 3 centuries 4
Do jovian planets have Weather on Jovian Planets magnetospheres like Earth’s? • All the jovian planets have strong winds and storms Jupiter’s Magnetosphere Other Magnetospheres • All the jovian planets have substantial magnetospheres, but Jupiter’s is largest by far Aurora on Jupiter • Jupiter’s strong magnetic field gives it an enormous magnetosphere • Gases escaping Io feed the donut-shaped Io torus What have we learned? What have we learned? • Are jovian planets all alike? • What is the weather like on jovian planets? – Jupiter and Saturn are mostly H and He gas – Multiple cloud layers determine colors of jovian planets – Uranus and Nepture are mostly H compounds – All have strong storms and winds • What are jovian planets like on the inside? • Do jovian planets have magnetospheres – Layered interiors with very high pressure and like Earth’s? cores made of rock, metals, and hydrogen compounds – All have substantial magnetospheres – Very high pressure in Jupiter and Saturn can – Jupiter’s is largest by far produce metallic hydrogen 5
What kinds of moons orbit the 11.2 A Wealth of Worlds: Satellites of Ice and Rock jovian planets? • Our goals for learning • What kinds of moons orbit jovian planets? • Why are Jupiter’s Galilean moons so geologically active? • What is special about Titan and other major moons of the solar system? • Why are small icy moons more geologically active than small rocky planets? Medium & Sizes of Moons Large Moons • Small moons (< 300 km) • Enough self-gravity to be spherical – No geological activity • Have substantial • Medium-sized moons (300-1,500 km) amounts of ice. – Geological activity in past • Formed in orbit • Large moons (> 1,500 km) around jovian planets. – Ongoing geological activity • Circular orbits in same direction as planet rotation. Small Small Moons Moons • Far more numerous than the medium and large • Captured asteroids or comets, so orbits do moons. not follow usual patterns. • Not enough gravity to be spherical: “potato- shaped” 6
Why are Jupiter’s Galilean Io’s Volcanic Activity moons so geologically active? • Io is the most volcanically active body in the solar system, but why? Tidal Heating Io’s Volcanoes Io is squished and stretched as it orbits But why is its Jupiter • Volcanic eruptions continue to change Io’s surface orbit so elliptical? Orbital The tugs add up over time, making all 3 Resonances Europa’s Ocean: Waterworld? orbits elliptical. Every 7 days, these 3 moons line up. 7
Tidal stresses crack Europa’s Europa’s interior also warmed by tidal heating surface ice. Ganymede Callisto • “Classic” cratered • Largest moon in the iceball. solar system • No tidal heating, • Clear evidence of no orbital geological activity resonances. • Tidal heating plus • But it has heat from radio- magnetic field !? active decay? What is special about Titan and Titan’s Atmosphere other major moons of the outer solar system? • Titan is the only moon in the solar system to have a thick atmosphere • It consists mostly of nitrogen with some argon, methane, and ethane 8
Titan’s Surface Medium Moons of Saturn • Huygens probe provided first look at Titan’s surface in early 2005 • Almost all show evidence of past volcanism • Liquid methane, “rocks” made of ice and/or tectonics Medium Moons of Uranus Neptune’s Moon Triton • Varying amounts of • Similar to Pluto, but geological activity larger • Moon Miranda has • Evidence for past large tectonic geological activity features and few craters (episode of tidal heating in past?) Why are small icy moons more Rocky Planets vs. Icy Moons geologically active than small rocky planets? • Rock melts at higher • Ice melts at lower temperatures temperatures • Only large rocky • Tidal heating can planets have enough melt internal ice, heat for activity driving activity 9
What have we learned? What have we learned? • What kinds of moons orbit jovian planets? • What is special about Titan and other major moons of the solar system? – Moons of many sizes – Titan is only moon with thick atmosphere – Level of geological activity depends on size – Many other major moons show signs of geological • Why are Jupiter’s Galilean moons so activity geologically active? • Why are small icy moons more geologically – Tidal heating drives activity, leading to Io’s active than small rocky planets? volcanoes and ice geology on other moons – Ice melts and deforms at lower temperatures enabling tidal heating to drive activity 11.3 Jovian Planet Rings What are Saturn’s rings like? • Our goals for learning • What are Saturn’s rings like? • How do other jovian ring systems compare to Saturn’s? • Why do the jovian planets have rings? What are Saturn’s rings like? Earth-based view • They are made up of numerous, tiny individual particles • They orbit over Saturn’s equator • They are very thin 10
Spacecraft view of ring gaps Artist’s conception of close-up Gap Moons Shepherd Moons • Some small moons create gaps within rings • Pair of small moons can force particles into a narrow ring How do other jovian ring systems Resonance Gaps compare to Saturn’s? • Orbital resonance with a larger moon can also produce a gap 11
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