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The Solar System 2/21/13 Logistics • Reminder: MRS 1 due tuesday!! • Collect Light & Atoms, Blackbody Radiation and Doppler Shift!! 2 Taking Stock of the Solar System • Sun - a very basic G5 star about 4.5 Gyr old • Have 8 planets – terrestrial planets : mercury, venus, earth, mars – gas giant planets : Jupiter, Saturn – ice giants : Uranus and Neptune • Asteroid Belt - between mars and Jupiter • Kuiper Belt - beyond Neptune The Sun 4 Our Star, the Sun The Sun is the Largest Object in the Solar System • The Sun contains more than 99.85% of the total mass of the solar system • If you put all the planets in the solar system, they would not fill up the volume of the Sun • 110 Earths or 10 Jupiters fit across the diameter of the Sun Eight Comparisons among the nine planets show distinct similarities and significant differences The Four Terrestrial Planets Mercury Distance to Sun = 0.47AU (0.39, e=0.2) Mass = 5.5% Earth Mass Radius = 38.3% Earth Radius Density slightly less than Earth’s Essentially no atmosphere “The Cratered Planet” The Four Terrestrial Planets Venus Distance from Sun = 0.72AU Mass = 82% Earth Radius = 95% Earth Much hotter, 90 x pressure of Earth “Runaway Greenhouse Planet” The Four Terrestrial Planets Earth Earth • Distance from Sun = 1 AU • Mass of Earth = 5.9 x 1027g • Density 5.5 g/cc (water 1 g/cc) The Four Terrestrial Planets Earth • The largest terrestrial planet • Highest density • Only planet with: – – – – Plate tectonics Liquid water on surface Substantial Oxygen in atmosphere Life Earth • Clouds/Atmosphere – Erosion of surface • Albedo = 0.37 • 71% of surface covered in water • Geologically active: – Plate tectonics – Volcanoes The Four Terrestrial Planets Mars Distance from Sun = 1.5 AU Mass = 10% of Earth’s Mass Radius = 50% of Earth’s Radius Density less than Earth’s (4gm/cc) The Gas and Ice Giants JupiterT ext Distance From Sun= 5.2 AU Mass = 318 x Earth’s Mass Radius = 10-11 x of Earth’s Radius Density = 1.3 g/cc (Earth is 5 g/cc, Water is 1 g/cc) The largest planet, known for its great red spot The Gas and Ice Giants Saturn Distance From Sun= 9.6 AU Mass = 95 x Earth’s Mass Radius = 9 x of Earth’s Radius Density = 0.7 g/cc (Earth is 5 g/cc, Water is 1 g/cc) The second largest planet, known for its rings The Gas and Ice Giants Uranus Distance From Sun= 19.2 AU Mass = 15 x Earth’s Mass Radius = 4 x of Earth’s Radius Density = 1.2 g/cc (Earth is 5 g/cc, Water is 1 g/cc) The Gas and Ice Giants Neptune Distance From Sun= 30 AU Mass = 17 x Earth’s Mass Radius = 3.9 x of Earth’s Radius Density = 1.6 g/cc (Earth is 5 g/cc, Water is 1 g/cc) Main Asteroid Belt • Between Orbits of Mars and Jupiter from 2-3.5 AU • 105 objects catalogued, more observed, 49million awaiting classification • Asteroid spacing still millions of miles, but can collide, velocities thousands km/hr • Asteroid “Families” – Asteroids with similar orbits – Originate from the breakup of bigger asteroids http://apod.nasa.gov/apod/ap130218.html 18 Categorization • Planet - (1) orbit around the Sun, (2) enough mass for gravity to make spherical, (3) cleared its orbital neighborhood of debris • Dwarf Planet - satisfies (1) and (2) : Pluto, Ceres, Eris • Small Solar System Bodies - not planets, dwarf planets or moons Dwarf Planets • Pluto – 40 AU, e=0.25 – Largest moon Charon more than half its size – Pluto - 2380km, Charon 1190km • Ceres – 2.76 AU – In Main asteroid belt, first discovered Asteroid 1855 (mistaken for planet) – D~ 940km • Eris – 97 AU from Sun, e=0.44 – Kuiper Belt – D~2400km Inner planets vastly different than outer planets • Inner planets are rocky, like Earth (high density) • Outer planets are gas or ice (low density) 21 Conditions That Theories Should Address • What we know: – planets have orbits nearly in a plane (ecliptic) – planets orbit the sun in the same direction (prograde) – terrestrial planets • small bodies made of heavy elements (C, O, N, Fe, Si) • close to the Sun – jovian planets: • large bodies made of light elements (H, He) • far from the Sun – sun, primarily H, He 22 The solar system formed from a cloud of cold gas and dust called the solar nebula about 4.6 billion years ago Molecular Clouds: Stellar Nurseries • Huge clouds of gas and dust in the galaxy – molecular hydrogen (H2) – many light-years across – contain 10s to 1000s of solar masses of material 24 Molecular Cloud Collapse • Molecular clouds can collapse in onto themselves • Dense clumps of collapsing molecular clouds are regions where stars form 25 Star and Disk Formation • Dense clumps in a collapsing molecular cloud form a disk • Disk is called a “protoplanetary disk” or a proplyd • Protostar is at center of the protoplanetary disk 26 Star Formation • Protostar accretes material from disk – center is under extreme pressure – center gets hotter and hotter – nuclear fusion begins • Now a full-fledged star 27 The Formation of the Protoplanetary disk • As the original gas cloud collapses, it begins to rotate faster – conservation of angular momentum • As the cloud shrinks, it also flattens 28 The Protoplanetary Disk • Hydrogen and Helium are most abundant • O, C, N, Si, Fe also fairly common 29 Condensation in the Protoplanetary Nebula • Chemical composition of solar system arranged by distance from the protosun • Heavy Elements – high condensation temperatures – close to sun • Light Elements – low condensation temperatures – far from sun • Same for molecules 30 Collisions dominated the early solar system • dust collects together into planetesimals • planetesimals collect together into protoplanets • Protoplanets gather up left over debris and became planets Tutorial: Temperature and Formation of Our Solar System – p. 111 • Work with a partner! • Read the instructions and questions carefully. • Discuss the concepts and your answers with one another. Take time to understand it now!!!! • Come to a consensus answer you both agree on and write complete thoughts into your LT. • If you get stuck or are not sure of your answer, ask another group. G. Marcy and P. Butler