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8. Solar System Origins

8. Solar System Origins. Chemical composition of the galaxy The solar nebula Planetary accretion Extrasolar planets. Our Galaxy’s Chemical Composition. Basic physical processes “ Big Bang ” produced hydrogen & helium Stellar processes produce heavier elements Observed abundances

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8. Solar System Origins

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  1. 8. Solar System Origins • Chemical composition of the galaxy • The solar nebula • Planetary accretion • Extrasolar planets

  2. Our Galaxy’s Chemical Composition • Basic physical processes • “Big Bang” produced hydrogen & helium • Stellar processes produce heavier elements • Observed abundances • Hydrogen ~71% the mass of the Milky Way • Helium ~27% the mass of the Milky Way • Others ~ 2% the mass of the Milky Way • Elementsas heavy asiron form in stellar interiors • Elements heavier than iron form in stellar deaths • Implications • A supernova “seeded” Solar System development • It provided abundant high-mass elements • It provided a strong compression mechanism

  3. Solar System Chemical Composition

  4. Coalescence of Planetesimals

  5. Abundance of the Lighter Elements Note: The Y-axis uses a logarithmic scale

  6. The Solar Nebula • Basic observation • All planets orbit the Sun in the same direction • Extremely unlikely by pure chance • Basic implication • A slowly-rotating nebula became the Solar System • Its rate of rotation increased as its diameter decreased • Basic physical process • Kelvin-Helmholtz contraction Gravity  Pressure • As a nebula contracts, it rotates faster • Conservation of angular momentum Spinning skater • Kinetic energy is converted into heat energy • Accretion of mass increases pressure • Temperature & pressure enough to initiate nuclear fusion

  7. Conservation of Angular Momentum

  8. Formation of Any Solar System • Presence of a nebula (gas & dust cloud) • Typically ~ 1.0 light year in diameter • Typically ~ 99% gas & ~1% dust • Typically ~ 10 kelvins temperature • A compression mechanism begins contraction • Solar wind from a nearby OB star association • Shock wave from a nearby supernova • Three prominent forces • Gravity Inversely proportional to d2 • Tends to make the nebula contract & form a star • Pressure Directly proportional to TK • Tends to make the nebula expand & not form a star • Magnetism Briefly prominent in earliest stages • Tends to make the nebula expand & not form a star

  9. More Solar System Formation Stages • Central protostar forms first, then the planets • H begins fusing into He => Solar wind gets strong • This quickly blows remaining gas & dust away • Circumstellar disks • Many are observed in our part of the Milky Way • Overwhelming emphasis on stars like our Sun • Many appear as new stars with disks of gas & dust • Potentially dominant planets • Jupiter >2.5 the mass of all other planets combined • Many exoplanets are more massive than Jupiter • Knowledge is limited by present state of technology

  10. The Birth of a Solar System

  11. Formation of Planetary Systems

  12. Planetary Accretion • Basic physical process • Countless tiny particles in nearly identical orbits • Extremely high probability of collisions • High energy impacts: Particles move farther apart • Lowenergy impacts:Particles stay gravitationally bound • Smaller particles become bigger particles • ~109asteroid-size planetesimals form by accretion • ~102 Moon-size protoplanets form by accretion • ~101 planet-size objects form by accretion • Critical factor • Impacts of larger objects generate more heat • Terrestrial protoplanets are [almost] completely molten • “Chemical” differentiation occurs • Lowest density materials rise to the surface Crust • Highest density materials sink to the center Core

  13. Microscopic Electrostatic Accretion

  14. Condensation Temperature • Basic physical process • Point source radiant energy flux from varies µ1/D2 • Ten times the distance One percent the energy flux • Any distant star is essentially a point source • The concept applies to all forming & existing stars • At some distance, it is cold enough for solids to form • This distance is relatively close for rocks • Much closer to the Sun than the planet Mercury • This distance is relatively far for ices • Slightly closer to the Sun than the planet Jupiter • This produces two types of planets • High densitysolidplanetsTerrestrial planets • Low density gaseous planets Jovian planets

  15. Two Different Formation Processes

  16. Condensation In the Solar System

  17. The Center of the Orion Nebula

  18. Mass Loss By a Young Star In Vela

  19. http://www.rssd.esa.int/SA-general/Projects/Staff/perryman/planet-figure.pdfhttp://www.rssd.esa.int/SA-general/Projects/Staff/perryman/planet-figure.pdf Exoplanet Detection Methods

  20. Extrasolar Planets: 13 Sept. 2002 • Basic facts • No clear consensus regarding a definition • Usually only objects <13 MassJup & orbiting stars • Objects > 13 MassJup are considered “brown dwarfs” • Objects < 13 MassJup are considered anomalies • Orbiting a massive object fusing H into He • A star in its “normal lifetime” • Summary facts • 88 extrasolar planetary systems • 101 extrasolar planets • 11 multiple–planet systems • Unusual twist • A few “planetary systems” may be “star spots” • Magnetic storms comparable to sunspots on our Sun

  21. Exoplanets Confirmed by 2007 • 18 July 2003 • 117 extrasolar planets • 102 extrasolar planetary systems • 13 extrasolar multiple–planet systems • 4 July 2005 • 161 extrasolar planets • 137 extrasolar planetary systems • 18 extrasolar multiple–planet systems • 19 September 2007 • 252 extrasolar planets • 145 extrasolar planetary systems • 26 extrasolar multiple–planet systems

  22. Extrasolar Planets Encyclopaedia 27 January 2010 429 planets 363 planetary systems 45 multiple planet systems

  23. MassJup Extrasolar Planets: Size Distribution

  24. Most Recent Confirmed Exoplanets • 29 January 2013 • 863 extrasolar planets • 678 extrasolar planetary systems • 129 extrasolar multiple–planet systems • 2,233 unconfirmed Kepler candidates

  25. Exoplanets: 17 September 2013 http://exoplanets.org/

  26. http://exoplanets.org/multi_panel.gif Exoplanets: Orbital Distribution

  27. http://exoplanets.org/fe_bargraph_public.jpg Exoplanets: Star Iron Content

  28. Star Gliese 86: Radial Velocity Data • Doppler shift data reveal an extrasolar planet • An orbital period of ~ 15.8 days • A mass of ~ 5 . MJupiter

  29. http://www.gemini.edu/images/stories/press_release/pr2008-6/fig1.jpghttp://www.gemini.edu/images/stories/press_release/pr2008-6/fig1.jpg Possible First Exoplanet Photo

  30. Galactic chemical composition ~98% hydrogen + helium ~ 2% all other elements Solar System formation Solar nebula Compression mechanism Gravity, pressure & magnetism Protostar with circumstellar disk Planetary accretion Concept of condensation temperature Rock & ices can form Extrasolar planets 863 confirmed 2,233 Kepler candidates Important Concepts

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