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General Physical Science Chapter 16 The Solar System The Solar System: An Overview The solar system is a complex system of moving masses held together by gravitational forces. 8 major planets • Wanderers 3 dwarf planets More than160 moons Asteroids, comets meteoroids Solar wind • Charged particles, gases, interstellar dust The Solar System: An Overview Geocentric Model Everything rotates around the earth • Pushed by the Catholic Church • Very difficult to explain some observed motions Heliocentric Model Copernicus Revolves around the sun 1 The Solar System: An Overview Tycho Brahe Known for accurate measurement of the positions of stars and planets • Unaided eye! Data analyzed by Kepler Kepler then used this data to devise his Laws of Planetary Motion. Laws of Planetary Motion First Law (Law of Elliptical Motion) All planets move in elliptical paths around the Sun with the Sun as one focus of the ellipse Major axis Semi--major axis Semi • For Earth, semi major axis = 1 AU Laws of Planetary Motion Second Law (Law of Equal Areas) An imaginary line joining the planet and the sun sweeps an equal area in an equal period of time. Perihelion Aphelion • Point that planet is closest to the sun (Jan. 4) • Point that planet is farthest from the Sun (July 5) 2 Laws of Planetary Motion Laws of Planetary Motion Third Law (Harmonic Law) The square of the sidereal period of a planet is proportional to it’s semisemi-major axis. Sidereal • Time for one revolution around the Sun • 1 year for earth T2 = kR3 • R = length of semisemi-major axis • T = time • When T in years, R in AU, then k = 1 year2 / AU3 Example Calculate the period of a planet whose orbit has a semisemi-major axis of 1.52 AU T2 = kR3 R = 1.52 AU k = 1 y2 / AU3 T2 = (1) (1.52)3 (y2 AU3 / AU3) T2 = 3.51 y2 T = 1.87 y 3 The Solar System and Planetary Motion Learning Goals Name some early astronomers and outline some theories concerning the historical development of astronomy as it relates to the solar system. State and explain Kepler’s laws of planetary motion. Questions: 1–4 Exercises: 1 – 11 odd Major Planet Classifications and Orbits Galileo Galilei First to observe the Moon through a telescope Observed 4 moons around Jupiter • First to prove Earth not the only center of motion in the universe. universe. • Showed that Venus had phases similar to the Moon. Major Planet Classifications and Orbits Issac Newton Incorporated work of Copernicus, Kepler, Kepler, and Galileo to formulate gravitational theory Invented calculus • Used to explain Kepler’s First Law • Used Conservation of Angular Momentum to explain Kepler’s 2nd Law Mass of the Solar System 99.87% of the mass is the Sun • More than ½ of remaining mass is Jupiter 4 Major Planet Classification Inferior planets Planets with their orbit inside that of Earth. Mercury, Venus Superior planets Planets with their orbit outside that of Earth. Mars, Jupiter, Saturn, Uranus, Neptune, Pluto Terrestrial Jovian (Earth-like) planets (Earth- Mercury, Venus, Earth, Mars (Jupiter-like) planets (Jupiter- Jupiter, Saturn, Uranus, Neptune Planetary Motion Prograde motion Counter clockwise as viewed from the North Pole All planetary orbits Most planetary rotation Retrograde motion Clockwise as viewed from the North Pole Venus, Uranus rotation Relative Size of the Planets and the Sun 5 Major Planet Classifications and Orbits Sidereal Period Time for one orbit relative to a distant star Conjunction 2 planets lined up with Sun Inferior planets • Same side – inferior conjunction • Opposite Side – superior conjunction Superior Planets • Same side – conjunction • Opposite sides – opposition Conjunction and Opposition The Solar System: An Overview Learning Goals Describe the composition, structure, and motions of the planets. Questions: 5–7 6 The Planet Earth Unique Large amounts of surface water • NOT only body with water Atmosphere contains oxygen Temperate climate Living organisms • As far as we know Earth Oblate spheroid Slightly larger diameter at the equator than from pole to pole (43 km) due to Earth’s rotation one part in 300 (1 inch in 25 ft) Albedo 0.33 2 separate motions rotation revolution Earth Tilted 23.5O from orbital plane tilt plus revolution leads to seasons Focault Pendulum Proved rotation of the Earth • • • • • Released with no lateral motion Direction of pendulum swing appears to change Apparent change due to Earth’s rotation. At the North pole rotation is 90O in 6 hours Direction is constant relative to external reference 7 Focault’s Pendulum Earth Parallax Apparent shift in position of closer stars against background of farther stars Simulate with finger lined up with more distant object Use to determine distance from stars Earth Parsec Distance to a star when it exhibits a parallax of 1 second (angular measurement 1/3600 degree) Aberration of starlight Apparent change in direction of light from star Snowflakes in snowstorm Raindrops in moving car 8 Facts and Figures Earth Learning Goals Identify some chemical and physical properties of the Earth Define and explain Earth’s two major motions. Questions: 8 – 10 The Terrestrial Planets Relatively small Made up primarily of rocks and metals High density (5 g/cm3) Solid Surface Magnetic fields Relatively close to the Sun No ring systems Earth, Mars have moons 9 Mercury Shortest revolution (88 days) Only visible at sunrise or sunset Surface similar to the Moon absence of significant atmosphere • Surface temperature varies from - 180OC to 430OC evidence that once had thin atmosphere Mercury – Facts and Figures Venus Closest to Earth Third brightest object in the sky Very similar to Earth Atmosphere 96% CO2 Surface temp 480OC • Greenhouse Effect Surface pressure 90 atm 10 Venus Surrounded by clouds Albedo 0.78 Mostly H2SO4 / H2O Sulfur dust gives yellow color Atmosphere rotational period 4 days (Retrograde) Planetary rotation 243 days (retrograde) Surface mapped by radar May have been struck during formation Many surface features Evidence of former volcanic activity Most features about 400 million years old Venus – Facts and Figures Mars 1.5 x as far from the Sun as Earth Tilted 24O Rotation 24.5 hours 687 day synodic period 2 small moons Phobos (fear) Deimois (panic) 11 Mars Moons are tidetide-locked Rotational period equals synodic period Same as Earth’s Moon = 3.9 g / cm3 Cratered Density ‘Canals’ Polar caps Summer - H2O Winter - H2O and CO2 Mars Volcanic activity Olympus Mons • 24 km high Crater is 80 km and base is 600 km • Largest known volcano in the Solar System • Earth - Mauna Loa about 9 km Martian Exploration From 1976 – present! Mars Valles Marineris 400 km long 6 km deep Thought to be stress fracture Unmanned exploration Viking I (1976) Pathfinder (1997) • Sojourner 12 Mars Evidence of fluid flow at one time! Supported by findings of Mars Global Surveyor (2000) The Terrestrial Planets Origins thought to be similar to Jovian Planets Predominant elements were H and He Solar heat provided enough energy for these gases to escape Left behind the highhigh-density rocky core Mars – Facts and Figures 13 The Terrestrial Planets Learning Goals List and compare the physical characteristics of the terrestrial planets. Questions: 11 – 13 The Jovian Planets Gas giants No solid surface Low density (average 1.2 g/cm3) Inner rock core • About the density of water Lower temperatures did not allow H and He to escape Significant Differences between Terrestrial and Jovian Planets 14 Jupiter Largest Planet d = 1.3 g/cm3 Liquid metallic hydrogen with a rocky core Atmosphere ‘Bands’ on surface H2, He, CH4, NH3 Mean temp –148OC Great Red Spot Perpetual storm Jupiter Shoemaker – Levy 9 Comet fragments smashed into Jupiter’s atmosphere Visible from Earth Dark spots approx. size of the Earth! Jupiter also has a ring system Not visible from Earth Jupiter’s Rings 15 Moons of Jupiter 16 or more observed Difference is line between small moon and big rock Four moons observed by Galileo in 1610 Io Europa Ganymede (largest moon in Solar System) Callisto Jupiter – Facts and Figures Saturn Most prominent feature is the ring system 3 ring systems A, B, and C Rings formed by tidal forces 16 Saturn’s Rings Many individual ringlets Color is computer enhancement of chemical composition. Does have moons Largest is Titan Titan Only satellite known with a hazy atmosphere N2 (about 90%) Ar (less than 10%) Methane and other hydrocarbons Saturn – Facts and Figures 17 Uranus Discovered Very in 1781 Internal structure different than Jupiter and Saturn Less massive Larger rocky core thin ring system Larger particles Not much reflection Uranus Ring System True Color Representation Uranus – Facts and Figures 18 Neptune Twin of Uranus Found in part by mathematical calculations based on disturbances in orbit of Uranus Dark spot similar to Great Red Spot on Jupiter Rings of Neptune Were predicted by blocking of starlight Observations were questionable. Ring system confirmed with Voyager 2 Neptune – Facts and Figures 19 The Jovian Planets Learning Goals: List and compare the properties of the Jovian planets. Identify the major differences between the terrestrial and Jovian planets Questions: 14 – 17 The Dwarf Planets Category added in 2006 by International Astronomical Union Plutoids Must orbit sun Nearly round from selfself-gravity Dominant body in it’s orbit Ceres Between Mars and Jupiter Discovered in 1801 Formerly classified as an asteroid Smallest of the dwarf planets 20 Ceres – Facts and Figures Pluto Most distant from the Sun Discovered in 1930 by observers in AZ Some similarities to Uranus/Neptune Not enough to classify as ‘Jovian” At times Pluto closer than Neptune! Charon Satellite of Pluto Largest satellite relative to planet size Discovered in 1978 ½ size of Pluto 21 Orbital Plane Pluto – Facts and Figures Eris Furthest from the Sun Discovered in 2003 Slightly larger than Pluto Very elliptical orbit 22 Eris – Facts and Figures …and beyond? Kuiper Most Belt From Neptune to Eris Home for comets and cometary material Exploration slated for 2015 distant object is Sedna 90 AU / 75 AU axes Termination shock Edge of solar system Solar wind meets interstellar material The Dwarf Planets Learning Goals: List and compare the properties of the Dwarf planets.. planets List the physical properties of Pluto Questions: 18, 19 23 Origin of the Solar System Solar Nebula About 4.5 billion years ago Began to condense under influence of it’s own gravity Condensation nucleus now part of the Sun Conservation of angular momentum began to cause nebula to spin Caused flattening • Pizza dough Origin of the Solar System Kepler’s Third Law stated that outer material would rotate slower Created ‘shear forces’ This matter began to condense into the planets. planets. Origin of the Solar System Formed Space ‘protoplanets’’ ‘protoplanets Protoearth probably 1000 x more massive than the Earth today Similar in composition to the Jovian planets Heating of the terrestrial planets drove off the gases was ‘thicker’ with dust Shielded planets initially from solar energy Became clear from planetary accumulation and solar wind transport. 24 Origin of the Solar System Learning Goal: Describe the theory for the origin of the solar system that is most widely accepted by astronomers. Questions: 20 – 21 Other Planetary Systems Difficult to detect visually Reflected light washed out by light from star Observe other effects Gravitational • ‘Wobble’ • Doppler effect Over 200 other planets have been detected indirectly! Spectroscopically determined water on one exoplanet 25 Other Planetary Systems Learning Goal Describe the methods used to discover planets around other stars Questions: 22 – 23 Terms; Matching, Multiple Choice, and FillFill-in in--the the--Blank Questions; Visual Connection and Applying your Knowledge Key General Physical Science Chapter 16 The Solar System 26