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Lec25-Apr21 - Key Concepts • ;dal forces,...

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Unformatted text preview: 4/21/10 Key Concepts •  ;dal forces, resonances Astro 109 Lecture 25: Moons •  ice geology •  each moon has a unique story April 21 Apr. 21 Jupiter’s Galilean Satellites Apr. 21 Apr. 21 Io has volcanoes! Discussion Ques;on Among the Galilean moons of Jupiter, the inner moons have younger surfaces than the outer moons. How do we know? A.  The inner moons were not formed un;l recently. B.  The inner moons have few impact craters while the outer moons have many. C.  The inner moons are more colorful than the outer moons. D.  The inner moons have shorter orbital periods. E.  From radioac;ve da;ng of rocks retrieved from each of the moons. Apr. 21 Apr. 21 1 4/21/10 Visible light Apr. 21 Apr. 21 Apr. 21 Thermal emission (false color) From Galileo Apr. 21 Tidal hea;ng Discussion Ques;on The source of energy for Io’s volcanoes is A.  B.  C.  D.  E.  heat from the Sun. heat within Io leZ over from its forma;on. radioac;ve decay of elements, which keeps Io hot. ;dal hea;ng from Jupiter. Jupiter’s magne;c field. elongated orbit around Jupiter  ­ ­> ;dal forces vary in strength Io “flexes” ever 1.8 d period (effects exaggerated here) Apr. 21 Apr. 21 http://www.astro.washington.edu/users/smith/Astro150/Tutorials/TidalHeat/" 2 4/21/10 Discussion Ques;on Orbital resonance Why is the orbit of Io around Jupiter not circular? •  Io goes around twice while Europa goes around once A.  B.  C.  D.  Jupiter’s ;dal forces make the orbit elongated. Jupiter’s magne;c field makes the orbit elongated. The force from Io’s volcanic erup;ons affects the orbit. A resonance with Europa and Ganymede keeps Io’s orbit from becoming circular. E.  None of the above; Io’s orbit is circular. Apr. 21 •  call this a 2:1 orbit resonance •  every 3.6 days they “meet up” •  each ;me, Europa’s gravity gives Io a “kick” that keeps Io’s orbit elongated Apr. 21 http://www.astro.washington.edu/users/smith/Astro150/Tutorials/TidalHeat/" Europa Apr. 21 Apr. 21 Discussion Ques;on Lineae Europa shows few signs of cratering because A.  B.  C.  D.  E.  Jupiter’s gravity deflects asteroids away from it. Jupiter’s magne;c field deflects asteroids away from it. its interior is warm, so water can fill any craters that form. it is a small moon, so few meteors hit it. lava flows cover any craters that form. (approx. true color) Apr. 21 Apr. 21 3 4/21/10 Model for Europa (enhanced color) http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=5543" Apr. 21 Apr. 21 Ganymede Apr. 21 Apr. 21 Callisto Apr. 21 Saturn’s moon Titan Apr. 21 4 4/21/10 Apr. 21 mosaic of images from Cassini Apr. 21 from the Huygens lander “rocks” of water ice Apr. 21 from the Huygens lander Apr. 21 Discussion Ques;on The chemical methane plays a role on Saturn’s moon Titan analogous to that of water on Earth because A.  methane and water have similar mel;ng and boiling temperatures. B.  methane can exist as a solid, liquid, and vapor on Titan. C.  methane is the most abundant gas in Titan’s atmosphere. D.  methane escapes easily from the upper atmosphere. E.  residents of Titan use it to wash their clothes. Radar map  ­ ­> dark places don’t reflect radio waves Apr. 21 Apr. 21 5 4/21/10 Apr. 21 Apr. 21 Apr. 21 Apr. 21 Apr. 21 Apr. 21 6 4/21/10 Apr. 21 Apr. 21 Uranus’s moon Miranda Apr. 21 Apr. 21 Neptune’s moon Triton HW ques;ons 9. What is the source of energy that powers Io’s volcanoes? How is it related to the orbits of Io and the other Galilean satellites? 18. What surface features on Europa provide evidence for geological ac;vity? 26. Why are numerous impact craters found on Ganymede and Callisto but not on Io or Europa? 32. In what way do hydrocarbons on Titan behave like water on Earth? Apr. 21 Apr. 21 7 ...
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