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Unit 7: The Outer Planets Mr. Ross Brown Brooklyn School for Law and Technology In this unit we will learn about: • Characteristics of the outer planets, how they compare to each other & to the inner planets • The internal sources of heat of these planets • Jupiter’s Great Red Spot • Why Uranus and Neptune appear blue • The moons of the gas giants • Why some of these moons appear geologically active • The rings around the gas giants Why name it after Jupiter? • 11 January 2016 • Do now: How do Jupiter’s mass, diameter, and density compare to the Earth’s? Why name it after Jupiter? • Jupiter, king of the gods • Largest planet in our Solar System, mass and diameter • Mass > all other planets combined • 10x Earth’s diameter, >300x mass Why name it after Jupiter? • Atmosphere: mostly Hydrogen, Helium, and hydrogen-rich Methane (CH4,) Ammonia (NH3,) and Water (H2O) • Clouds of H2O ice and NH3 • Clouds spin over planet faster than on Earth • Jupiter rotates once every 10 hours, equator bulges Jupiter’s Interior • All based on theory • Mass calculated by observing gravitational attraction on moons • Once we calculate radius we can obtain volume, and thus density • Jupiter’s is 1.3 g/cm3) (Water is 1, Earth is 5.5) • Composed of light elements (H2) Jupiter’s Interior • Tremendous gravity holds it all together • Deep inside compressed to 3x density of iron Jupiter’s Interior Jupiter’s atmosphere • Jupiter’s heat radiates up to space, cools and drops in convection currents. • Jupiter’s speedy rotation produces a strong Coriolis effect • Strong winds, > 300 kpm (200 mph) Coriolis Effect Coriolis Effect on Jupiter Coriolis Effect on Jupiter • Conflicting currents create vortices • Great Red Spot, first identified in 1600s Jupiter’s Magnetic Field • Convection of metallic liquid hydrogen core magnetic field much stronger than Earth’s Jupiter’s Magnetic Field • Aurora Jupiter’s Rings • Very thin, hard to see • Tiny particles of rock dust held by gravity Jupiter’s Moons • Galilean moons (Io, Europa, Ganymede, Callisto) are very large – All but Europa are larger than our Moon – Ganymede is largest moon in our Solar System – Amalthea, 5th largest, is much smaller Io • Closest to Jupiter • Between Jupiter and Europa, tremendous tidal forces generate heatvolcanoes (sulfurs) Europa • Smallest Galilean moon • Crust of ice, cracked, with frozen mineral-rich water seeping through cracks Ganymede and Callisto • Appear like our Moon but surface is mostly ice • Callisto may have water like Europa Galilean Moon Densities are Highest Jupiter’s Other Moons • Much smaller, most likely captured asteroids • Tilted orbits Homework #12 • 12 January 2016 • If Jupiter were moved closer to the Sun, what do you think would happen to it? Why name it after Saturn? • 19 January 2016 • Do now: How do Saturn’s mass, diameter, and density compare to Earth’s? Why name it after Saturn? How does Saturn differ from Earth? • 2nd largest in solar system, twice as far from Sun as Jupiter (10 AU) • Diameter 9.5x Earth, mass 95x Earth, but density is only 0.7 g/cm3 • Largely hydrogen & hydrogen-rich compounds About those rings…. • Very wide, very thin – From 30,000 km above atmosphere to 136,000 km – Only a few hundred meters thick – And very small (centimeters) particles About those rings…. About those rings…. • Gaps – Caused by gravity of tiny moons orbiting Saturn – Shepherding satellites: two moons in a close, common orbit Homework #13 • 19 January 2016 • What are the rings of Saturn made of? How do astronomers know this? Where do planetary rings come from? • 20 January 2016 • Do now: Where indeed do planetary rings come from? Where do planetary rings come from? • Not just Saturn – Easier to see from side of planet away from Sun • How old are they? – From planet’s origin or trapped particles? – Why not clump and form a moon? Why didn’t Saturn’s rings become a moon? • The Roche Limit – If a moon gets too close to a planet, gravity could rip it apart – The point where this occurs is 2.44 planetary radii, called the Roche Limit Saturn’s Moons • One very large and 61 smaller Saturn’s Moons Saturn's Moons • Less dense than Galilean moons – Ice interior? • Most are heavily cratered meaning……? • 21 January 2016 • Do now: What have we learned about the Outer, or Jovian, or Gas Giant planets? What’s so special about Uranus? • 22 January 2016 • Do now: Why does Uranus appear blue? What’s so special about Uranus? • Diameter 4x Earth, mass 15x • 19 AU from Sun • 1781, first observed by Herschel – First thought it was a comet What’s so special about Uranus? • Of course, rich in hydrogen – Water, ammonia, methane – Methane gas absorbs red light, thus Uranus appears blue • Density 1.27 g/cm3 – Compare to Jupiter and Saturn What’s so special about Uranus? • That tilt, tho! – Equator almost perpendicular to orbit Uranus’ Tilt Uranus’ Moons • 5 large moons and about 20 smaller What does our study of the other planets tell us about Neptune? • 25 January 2016 • Do now: What are the principal components of Neptune’s atmosphere? And what can you predict about its inner structure? What does our study of the other planets tell us about Neptune? • Similar to Uranus in size – Diameter 3.9x Earth, mass 17x – Blue – 30 AU from Sun, so hard to study • Voyager 2 mission 1989 – Encircled by bands – Large dark blue spot • Perhaps no longer there today What does our study of the other planets tell us about Neptune? What does our study of the other planets tell us about Neptune? • Discovered from predictions – Separately by English & French astronomers 1840s – Saw that Uranus didn’t follow a predicted orbit, so they knew something was there What does our study of the other planets tell us about Neptune? • Structure similar to Uranus – Planet is a hot mixture of ammonia, water, & methane – Atmosphere is hydrogen/ hydrogen compounds – Density 1.67 – Light atoms but as core of silicon and iron What does our study of the other planets tell us about Neptune? • Atmosphere – Blue, so methane atmosphere – Cloud bands • Coriolis effect, rotates every 16 hours – Winds over 2200 km/ hour at equator • Radiates energy, perhaps from its creation, creating convection Neptune’s Moons • 6 small moons in close, circular orbit, and 7 much further away • Triton, as big as Jupiter’s Europa, orbits backwards (clockwise) – From Kuiper Belt? • So massive it has its own atmosphere! Triton Streaks from geysers Comparison of Solar System Objects