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The Jovian Planets Chapter 7 Topics • • • • • Jupter, Saturn, Uranus, Neptune How do we know? Why do we care? What is common about the outer planets? What is peculiar to each of these planets? Jovian planets (Jupiter-like) Size radius is about 1/10 of the radius of the Sun Terrestrial Distance from the Sun Jovian Terrestrial Jovian small--1/100 radius large --1/10 radius of the Sun of the Sun orbit at 0.4 to 1.5 orbit at 5 to 30 AU AU few none rocks and metals many (# growing) all have rings gasses and ice Composition 0.71 to 1.67 g/cm3 So what are they made of? mostly gasses (hydrogen, helium) and ice Jupiter • largest planet • Great Red Spot • studied by Pioneer, Voyager 1 & 2, Galileo spacecraft • liquid interior (very high pressure and temperature) • 16 moons (4 largest are the Galilean moons) Io • Active volcanoes Europa • subsurface ocean • cracked ice Ganymeade • lots of faults • strong magnetic field Callisto • old surface (meaning that it’s not undergoing lots of change except for impact craters) Saturn • Large, thin rings • Rings are held together by the gravitational attraction of “shepharding” satellites • Major Gaps: The Cassini and Enke divisions Titan • larger than Mercury • has an atmosphere • probably has oceans of methane Uranus • discovered in 1781 • shows no cloud banding • axis of rotation is only tilted 8 degrees from the ecliptic • 84 year orbital period • rings originally discovered during occultation of a star • young rings (what’s the source of dust?) Neptune • noted by Galileo • the exact path of Uranus could not be explained by the gravitational pulls of the Sun, and the other planets. What does this mean? • discovered in 1846 • 164 year orbital period • strong magnetic field Triton • density 2.1 g/cm3 • atmosphere (nitrogen) • impact craters due to comets • ice made of water • active ice volcanoes • retrograde orbit (it’s going the wrong way) • probably captured by Neptune Extrasolar planets • How many planets have we discovered besides those in our solar system? • I’m starting to lose count, but it’s now over 100. • Planets are even found in binary star systems. • We analyze the wobble in a star by studying the Doppler shift in its spectrum and determine the approximate masses and distances of the orbiting planets. How do we know? • How do we know that the outer planets are mostly gas and mostly made up of hydrogen and helium? • How do we know that the atmosphere of a planet has methane? • How do we know the period of rotation of the outer planets? (Note: we use a different technique of measuring rotational period of the terrestrial planets.) • How do we know that a moon’s surface is ice? • How do we know the size of matter within the rings? • How do we know that a moon has an “old” surface and that the moon has little geologic activity?