Sky and Solar System - Moons, Tides and Planetary Rings - Slides | ASTRO 120, Exams of Astronomy

Download Sky and Solar System - Moons, Tides and Planetary Rings - Slides | ASTRO 120 and more Exams Astronomy in PDF only on Docsity! Astro 120 Fall 2003: Lecture 20 page 1 • Saturn’s Large Satellites, and Titan • Moons of Uranus and Neptune • Tidal Forces = differential gravitational force (stretch) • Effects of Tidal Forces • Deformation, Spin synchronization, Orbital changes • The Roche Distance: Tidal Breakup • Planetary Rings • What are they? Why so flat? • Structure within the rings • gaps, resonances, and shepherding moon(lets) • Ring Systems • Saturn, Uranus, Jupiter, Neptune Reading: Chapter 13, Sect. 13.1-13.3, 13.6 and Chapter 9, Sect. 9.4 Exam 2 - Thursday evening, November 13 MOVIE- Deep Impact - ISU Geology Club, 7PM tonight Brief review of last time: Moons, Tides, & Planetary Rings Astro 120 Fall 2003: Lecture 20 page 2 • Meteorite • tiny body (< 1cm to ~10 m) entering atmosphere • nearly all burn up completely - comet dust? • fragment(s) that survive to ground • Meteor - a “shooting star” • flash of light as meteoroid burns up • 80-90 km high at brightest • average meteor rate - about 7/hr (in a dark sky) • BUT: METEOR SHOWERS: • occur when Earth passes through orbit of a comet • annual events - up to 60 or more per hour • mostly small particles, but still bright meteors • appear to radiate from a point in sky: “radiant” Meteors and Meteorites LEONIDS - Nov 17 Astro 120 Fall 2003: Lecture 20 page 3 Leonid meteor shower - 1998 Leonids- 2001 Astro 120 Fall 2003: Lecture 20 page 4 • Stony meteorites (94% of all falls) • ordinary chondrites (~80%) • chondrules - silicate balls • other inclusions - Al, Mg, S • achondrites (~10%) • stones with no inclusions • carbonaceous chondrites (~ 4 %) • carbon-rich inclusions • complex organic molecules (amino acids) • water-rich chondrules - never melted! • Iron meteorites (5% of all falls) • nearly pure iron/nickel alloy • large crystals - very slow cooling • Stony- Iron meteorites (1% of all falls) • mixture of iron and slicates Types of Meteorites primitive or processed, they are all older than dirt Astro 120 Fall 2003: Lecture 20 page 5 • Irons: • ages of 4.6 Gyr - among oldest objects known • clear evidence of melting, and slow cooling • remnant of a differentiated protoplanetary core • size of body > 100 km • Ordinary chondites: • also 4.6 Gyr old • matrix and chondrules - once molten • possible crust/mantle of parent body • others maybe from never-differentiated bodies • Carbonaceous chondites: • some inclusions possibly older than 4.6 Gyr • water-rich minerals, fragile carbon compounds never melted! • pristine material out of which planets formed? History of Meteorites many meteorites are left-overs from the formation of the planets Astro 120 Fall 2003: Lecture 20 page 6 Origin of Meteorites - parent body(s)? # x 0.3 + 0.4 = Pred Planet actual 0 x 0.3 + 0.4 = 0.4 Mercury 0.39 1 x 0.3 + 0.4 = 0.7 Venus 0.72 2 x 0.3 + 0.4 = 1.0 Earth 1.0 4 x 0.3 + 0.4 = 1.6 Mars 1.5 8 x 0.3 + 0.4 = 2.8 ???? ? (1801) 16 x 0.3 + 0.4 = 5.2 Jupiter 5.2 32 x 0.3 + 0.4 = 10.0 Saturn 9.5 64 x 0.3 + 0.4 = 19.6 Uranus 19.2 1781 Neptune 30.1 1844 128 x 0.3 + 0.4 = 38.8 Pluto 39.5 1930 The case of the missing planet... Bode’s law (1772) “predicts” semimajor axes Astro 120 Fall 2003: Lecture 20 page 7 Asteroids • Numbers • over 4,500 orbits known • brightest still invisible to unaided eye • largest = Ceres: 1000km diameter • a few dozen bigger than 100 km • common size: 10-20 km • countless more of smaller size • The Main “Asteroid Belt” • semi-major axes between 2.1 and 3.3 a.u. • average = 2.81 - very close to Bode prediction! • total mass << Mass of our Moon swarm of small bodies orbiting (mostly) between Mars & Jupiter Astro 120 Fall 2003: Lecture 20 page 8 Other Asteroid Groups: Trojans @ “Lagrangian Points” Hidalgo - beyond Jupiter; Chiron - beyond Saturn!