1Origin of the Solar SystemLook for General PropertiesDynamical RegularitiesOrbits in plane, nearly circularOrbit sun in same direction (CCW from N.P.)Rotation Axes to orbit plane(Sun & most planets; Uranus exception)Planets contain 98% of angular momentumSpacing and CompositionSpacing increases with distance (roughly logarithmic)Composition varies with distance inner 4: rocky, small, thin atmospheres outer 4: gaseous, large, mostly atmosphereSun contains 99.9% of massd1d212*d2d1~1.5 - 2PlutoMercuryVenus - NeptuneSide View2The Solar SystemDistancefrom Sun.1 1 10 100 AU 1 1 1 1 (Log scale) M V E M J S U N PM (M ) 0.06 1 < .001 95 17 .82 .11 318 15 0.1+ TerrestrialGas GiantsAsteroidsRocky - iron, silicates, …“Icy” - at time of formation (H2O, NH3, CH4, …)Gaseous - H, HeComposition (%)Enhancement to get§ abundanceRocky“Icy”GaseousTerrestrial100<1 0300-500Jupiter6~13~812-40Saturn21~45~3410-60Uranus~28~62~1030 –140Neptune~28~62~1030-115Comets~31~69 ~0Theory of Solar System FormationAll start with rotating diskMinimum mass: 0.01 M§Sum of planets ~ 0.001 M§ but most of H2, He lostNote: Similar to masses of disks around forming starsSome models assume more massive disksTemperature, Density decrease with distance from forming star(Observations suggest slower decrease than models usually assume)DUST PLAYS A KEY ROLE3 No * DustDust CoresIron, Silicon, Oxygen, CarbonTerrestrial PlanetsDust cores and Icy Mantles(H2O, NH3, CH4)Outer Planets4Dust ProcessesDust sinks to midplaneGravitational instability planetesimals (~ 1 km in size)and/orAccretion of dust grains~104yrCollisions between planetesimals rocky planet cores106 - 108 yrproblemGas Processes (Outer Planets)Accretion of gas/gravitational collapse onto rocky coresH, He in atmosphereRings, moons (minature solar system)Planet Forming in a disk5Dust and IceInterstellar dust - core + mantleSilicate (Si + 0 + …)or GraphiteMantle: H2O, NH3, CH4, …?Planet typesInner: Only rocky cores, little or no ice survives rocky planetsOuter: Ice survives comets, icy moons of outer planetsOutgassingPlanet heats internally ice gas thin atmosphere (if pressure, T ok liquid ocean)Conclusions1. Planet formation in a rotating disk with icy dust can explain most of thegeneral facts about our solar system2. Planetary systems are likely to be common since disks with M > Mmin arecommon around forming stars.If we are typical,3. Expect other planetary systems will have ~10 planets, logarithmic spacing,different planet types~6Caveats• Other planetary systems are quite different– Big planets in close– But this is probably due to selection effect• Locations may differ with mass of star– Ices survive closer to lower mass star– May get ice giants in close– Also planets may migrate inwards– May prevent formation of terrestrial planetsFormation of EarthSolid particles fi silicate + ironNo gas collected fi atmosphere outgassedRadioactive heating fi molten core ice gas H2O gas liquid (oceans)CO2 dissolve in oceans carbonate rocksN2 gasEarly Earth AtmosphereN2, CO2 , H2O (CH4, NH3, H2 ?)Reducing (No free O2) Neutral ?Energy Sources7Differentiation of the EarthImpact heating by planetesimals (release of gravitational potential energy)Radioactive nuclei decay (release of nuclear potential energy)unstablenucleusNuclearpotentialenergySmaller nuclei(Fission)Also emit a particles (He)electrons, gamma-rayse.g. 40K Potassium 238U UraniumKinetic energy heatResult: molten EarthIron-Nickel center (core)Silicates float upper levels (mantle)Differentiation released Grav. Potential energy hot coreRadioactive heating continuesResults in layered Earth (like a soft-boiled egg)5 4 3211300240022005000-150Volcanos, etc.1. Inner solid core2. Outer liquid core3. Lower mantle - iron rich silicates, solid4. Asthenosphere (upper mantle) pliable5. Lithosphere - rigid silicates (crust)EggYolkWhiteShellT ~ 4500 K, iron, nickel, …maybe 7200 KLithosphere can “float” on asthenosphere Continental Drift, Earthquakes, Volcanos8Continental Drift Reconstructedhttp://www.odsn.de/odsn/index.htmlShows motion of continental plates over last 150 Myr. Red and green dots show locations of ocean drilling.Formation of Earth and MoonMMoonMEarthLarger than all but PlutoMost terrestrial planets have no moons(Martian moons are captured asteroids)Moon most likely resulted from giant impact0.15 M+EarthM+Moon ( ~0.01 M )+EarthEarth gets more iron r = 5.5 g cm-3Moon mostly silicate rMoon = 3.3 g cm-3+Temperature was very high after impact (10,000 - 60,000 K)Any icy material left?9Origin of AtmosphereCertain “Noble” gases (e.g. Neon) are more rare in Earth atmosphere than in solarnebula. fi Atmosphere not collected from gasReason: Earth is small fi gravity is weakTemperature in solar nebula is high - atoms moving fast, harder to holdOutgassing: “Icy” material vaporized by high temperatures vents, volcanosH2O, NH3, CH4 H2O, N2, CO2Ultraviolet Light Chemical ReactionsRainOceansDissolvedMain constituent ofatmosphereCaCO3sedimentsNo O2 on early Earth; No ozone (O3), so no protection from ultraviolet lightAlternative: Icy materials brought by
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