8. Solar System Origins

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Patience Barker
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1 8. Solar System Origins Chemical composition of the galaxy The solar nebula Planetary accretion Extrasolar planets Our Galaxy s Chemical Composition es Big Bang produced hydrogen & helium Stellar processes produce heavier elements Observed abundances Hydrogen Helium Others ~71% the mass of the Milky Way ~27% the mass of the Milky Way ~ 2% the mass of the Milky Way Elements as heavy as iron 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 Solar System Chemical Composition Coalescence of Planetesimals Abundance of the Lighter Elements 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 Note: The Y-axis uses a logarithmic scale 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

2 Conservation of Angular Momentum 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 d 2 Tends to make the nebula contract & form a star Pressure Directly proportional to T K 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 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 The Birth of a Solar System Formation of Planetary Systems Planetary Accretion Countless tiny particles in nearly identical orbits Extremely high probability of collisions High energy impacts: Particles move farther apart Low energy impacts: Particles stay gravitationally bound Smaller particles become bigger particles ~10 9 asteroid-size planetesimals form by accretion ~10 2 Moon-size protoplanets form by accretion ~10 1 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

3 Microscopic Electrostatic Accretion Condensation Temperature Point source radiant energy flux from varies 1/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 density solid planets Low density gaseous planets Terrestrial planets Jovian planets Two Different Formation Processes Condensation In the Solar System The Center of the Orion Nebula Mass Loss By a Young Star In Vela

Exoplanet Detection Methods http://www.rssd.esa.int/sa-general/projects/staff/perryman/planet-figure.pdf Extrasolar Planets: 13 Sept.

4 Exoplanet Detection Methods Extrasolar Planets: 13 Sept Basic facts No clear consensus regarding a definition Usually only objects <13 Mass Jup & orbiting stars Objects > 13 Mass Jup are considered brown dwarfs Objects < 13 Mass Jup 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 Exoplanets Confirmed by July extrasolar planets 102 extrasolar planetary systems 13 extrasolar multiple planet systems 4 July extrasolar planets 137 extrasolar planetary systems 18 extrasolar multiple planet systems 19 September extrasolar planets 145 extrasolar planetary systems 26 extrasolar multiple planet systems Extrasolar Planets Encyclopaedia 27 January planets 363 planetary systems 45 multiple planet systems Extrasolar Planets: Size Distribution Most Recent Confirmed Exoplanets 29 January extrasolar planets 678 extrasolar planetary systems 129 extrasolar multiple planet systems 2,233 unconfirmed Kepler candidates Mass Jup

5 Exoplanets: 17 September 2013 Exoplanets: Orbital Distribution Exoplanets: Star Iron Content Star Gliese 86: Radial Velocity Data Doppler shift data reveal an extrasolar planet An orbital period of ~ 15.8 days A mass of ~ 5. M Jupiter Possible First Exoplanet Photo Important Concepts 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

Formation of the Solar System Chapter 8

Formation of the Solar System Chapter 8 To understand the formation of the solar system one has to apply concepts such as: Conservation of angular momentum Conservation of energy The theory of the formation