PPlalanneett FFoorrmmaattioionn DDavidavid SpergelSpergel AASSTT 220055 AsAstrtroonnoommyy NeNewsws FFlalasshh ßß Biggest solar flare ever recorded went off today ßß Sun is in the midst of a period of very intense solar activity ßß Coronal mass ejection is not aimed at Earth (unlike last week’s much weak flare) BasicBasic ParadigmParadigm ß Laplace introduced in the 1700’s: the key elements of the theory ß A slowly spinning cloud collapses and cool to form the Sun and a rotating disk. This rotating disk fragments to form the planets ß Key element: Angular momentum conservation Laplace(1749-1827) KeKeyy SSolaolarr SSyysstetemm ObservationalObservational FactsFacts II ßß Solar system planets are all nearly coplanar and orbit the Sun in a prograde direction. ßß Planets occupy most of the stable orbits ßß Small planets, composed mainly of rocky material lie closest to the Sun. Mercury has the highest density ßß Gas planets (Jupiter has 90% H and HE, Saturn ~80%; Neptune and Uranus contain 5-20% H and He) ßß Asteroids occupy region between Mars and Jupiter. Collisionally evolved population KeKeyy SSolaolarr SSyysstetemm ObservationalObservational FactsFacts IIII ßß Comets: swarms of ice-rich solid bodies (1012- 1013 1 km size objects isotropically distributed at ~104 AU) ßß Satellite systems: mini-solar systems around Jupiter and Saturn ßß Uniform isotopic composition ßß Differentiating and melting: all the major planets, moons and many asteroids ßß Impact craters seen on most satellites. Current impact rates can not explain number of craters. ßß Angular Momentum Distribution SStatarr FormFormaationtion ßß MolecMolecularular ccloudslouds:: ssitesites ofof sstartar formationformation ß Clouds compressed by spiral arms or by shocks from supernova ß Cloud cores collapse ß Initially cores can cool but eventually become too dense to cool ß Angular momentum conservation limits collapse ß Fragmentation into binaries (most stars in binaries) ß Central core reaches temperatures greater than million degrees and begin to burn Deuterium ß Wind from young star may end collapse phase PPrere-Ma-Mainin SSeeqquueennccee SStatarsrs ß Stars that are still collapsing ß After ~million years, PMS enter T Tauri phase ß Broad spectral energy distribution (disk?) ß X-ray emission; large sunspots; rapid rotation ß Strong bipolar outflows seen in many PMS PProto-sroto-stetellallarr disdiskkss PrimPrimitiveitive SolarSolar NebulaNebula ßß Based on converting observed solar system into gas disk (0.02 solar mass disk) ßß Infall stage ßß Disk stage ß Evolution governed by angular momentum transport ß Role of magnetic fields ß Gravitational torques ß Dust grains condense in cooling disk ß After 106 -107 years, T Tauri winds clear gas DustDust DisksDisks ß Dust disks seen in infrared: excess above stellar blackbody ß Coronagraphs have detected dust disks around nearby stars. ß Some stars have much more dust than our Sun ß Variations in dust properties FFoorrmmaatiotionn ooff SSoolidlid BBooddieiess ß Grain condensation and growth ß Grains slowly separate from gas in disk ß Growth from 1 cm - 1 km is not understood ß Drag problem: 1 m size objects spiral inwards within 100 yr ß Agglomeration growth: grains collide and stick ß Alternative approach: quiescent disk: dust cools and coagulates to form planet ß Planetesimals to Planet Embryos ß Gravitational focusing is now important ß Evolution sensitive to velocities of planetesimals in disk ß Runaway growth starts once gravitational focusing is important. Embryo growth stops when the planet has accumulated nearly all of the nearby mass. Needs new material scattered into its accretion zone (other embryos? Drag?) FormFormationation ofof TTeerrerresstiatiall PPlalanenetsts ß Self-limiting nature of growth may lead to regularly spaced embryos ß Bombardment phase and planetary differentiation ß Accumulation and loss of volatiles FormFormationation ofof JovianJovian PlanetsPlanets ßß Large amounts of H and He suggest that Jupiter and Saturn formed within 107 yr ßß Gas Instability hypothesis ß Massive disks are unstable to clumping ß Problems: Uranus and Neptune; Differentiation seen in outer planets; asteroids, etc ßß Core Instability hypothesis ß First accrete planetesimals ß Planetesimal accrete an atmosphere from the surrounding gas nebula. Accretion rate is rapid once mass exceeds 10-20 Earth Masses ßß Theory predicts gas giants should only form in outer regions of solar system. PPlalanneettaarryy MMigigrraattioionn ß Planets interact with accretion disk. They excite waves in the disk and transfer energy and angular momentum to the disk ß This drag force pulls planet inwards. Rapid process: Earth in a gaseous disk is dragged inwards in 105 years ß Does this process destroy all planets? Multiple generations of planets? Pan in Saturn’s ring SmSmallall BodiesBodies ßß Fossils from solar system formation ßß Asteroid belt: Jupiter strong gravitational pull prevented the formation of a planet. Heated up orbits so collisions are too violent ßß Comets: Formed among outer planets gravitationally ejected outward ß Kuiper Belt ß Oort Cloud OOriginrigin ofof PPlalanenetataryry SSaatetellitellitess ß Jovian moons ß Martian moons (captured planetesimals) ß Earth/Moon system: giant impact model ß Mars size object collides with Earth after it has differentiated ß Ring of material around Earth coagulates to form Moon ß Explains similarities between Earth’s crust and moon AreAre EarthsEarths ComCommmon?on? ßß WWee dondon’’tt knowknow howhow toto formform planetsplanets soso hardhard toto tell.tell. ßß HHowow imimportantportant isis mmigration?igration? WWherehere therethere sseevveerarall ggeenneerarattioionnss ooff JupitersJupiters?? ßß DDidid thethe SunSun formform inin anan unusualunusual environmenvironment?ent? AlAl26 suggestssuggests thethe presencepresence ofof nearbynearby dyingdying ststarar...