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Accretion Theory = Clumping of gas/dust caused by gravity forms planets and stars (our sun) Nebula =A cloud of gas & dust particles light years across 1st Generation nebula-formed right after the big bang & made of only Hydrogen & Helium gas 2nd Generation nebula-from exploded star matter with heavier elements Gravity Causes Accretion Small masses randomly collide into bigger particles Increasing particle sizes have more mass & more gravity Skater video Collapsing causes a spin (angular momentum) Spinning results in flattening (disc shape) Sun-formed from majority of the mass in the middle Remaining mass flattens into an Accretion disc Planetisimals = 100’s of moon size pieces that clump to become the planets Carina Nebula 7,500ly away. Collapsing nebula w/ new star formation (see dust jets) Hubble Telescope Fusion Begins! When central mass has enough mass, atoms begin to merge under gravity & fusion begins Fusion explosion blows out un-clumped dust and gas off inner planets toward outer ones Young star jetting out material in an accretion disc news.nationalgeographic.com Solar System Formation-short Accretion-long Spinning out planetisimals NOVA-Earth Formation 3.5min Review: Steps of Accretion 1. Nebula condenses under gravity 2. Spins w/ angular momentum 3. Flattening into a disc (frisbee) shape 4. Fusion cleans out inner planets of unaccreted gasses/dust 5. Gas planets form as they collect gases ejected from inner planets 6. Planetisimals accrete into planets Inner Terrestrial Planets Closer to the sun Rocky (heavier elements) & small Little or no atmospheres No to few moons (very little gas stuck b/c hotter, closer to sun) Outer Gas Giants (Jovian) Planets Farther from sun Mostly Gas (light elements) Thick atmospheres Liquid cores w/ ices Many moons w/ high ice content (colder so the gas stuck & became liquid or even frozen solid) Volatile gases cooled farther from sun Outside 3-4 AU ice grains condensed (the “snow line”) to produce gas giants planets enough to condense (solid) Too to snow Interior layers, atmosphere & ocean form Heat from collisions & radioactive material caused melting Dense material sank = core & Light floated up = crust Volcanoes & Comets produced atmosphere & oceans Evidence –Accretion Craters! Earth’s craters have eroded Moon-no erosion b/c no water cycle or atmosphere Meteor Crater, Arizona Meteor Impact Manicouagan impact crater in Quebec, Canada Evidence-Planet Size & Density Differences Inner & outer planet groups shows some accretion occurred before fusion Planets may move after formation (some Hot Jupiters) Pluto? Teacher “planet” giving an acceleration boost using gravity to a “satellite” student Evidence- Composition of NonPlanetary Rock Asteroids, Meteorites & Comets unchanged from nebula-minerals & gases in ratios expected High water & gas content of comets = ocean & atmosphere material Evidence –Flat Spinning Disc All Planets orbit CCW (& most revolve CCW) – nebula spun as it condensed giving accreted material forward (tangential) momentum Spinning caused centripetal force to flatten into disc Asteroid Belt remnants of Planetisimals Jupiter pulled planetisimals out of orbit & pulverized into small particles. Evidence-Multiple Massive extinctions Accretion of asteroids caused planet wide climate change & extinction events K-T extinction 65mya 50% of all species gone Iridium element found in asteroids in planet wide rock layer Evidence-Age of Solar System Rocks Planets & Sun accreted together so all same age 4.6 billion yrs old (meteorites) 4.3 byo Earth rocks (older rocks eroded) Age of sun 4.6 byo Age of Moon Atmosphere & Oceans evolved after cooling 1st atmosphere-blown off by tifhiggins.blogspot.com alienatmosphere.volcano.jpg sun’s 1st fusion 2nd Atmosphere –gases from comet collisions & volcanic gases Free Oxygen (O2) added 2.5bya by cyanobacteria (blue-green algae)-caused mass extinction Ozone (O3) formed after and buffered planet from sun radiation Ocean water condensed from comets/volcanoes Ocean formation Other planetary systems beyond our solar system First 55 Extra-Solar Planets Discovered Approximate masses in terms of the mass of Jupiter Closer than the Earth-Sun distance Most of the mass of the solar system is contained in the Sun; the planets contribute only 0.2 percent. b. All the planet’s orbits lie roughly in a single plane. c. The Sun’s rotational equator lies nearly in this plane. d. The planets and the Sun all orbit in the same west-toeast direction. e. Planetary orbits are nearly circular f. Planets differ in composition g. The composition of the planets varies roughly with distance from the Sun. dense, metal-rich planets lie in the inner system. h. Outer planets are more massive than inner planets, and most of the mass of outer planets is composed of hydrogen and helium.