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Formation of the solar system. Origin of basic properties. Descartes, Kant, Laplace. Basic Objectives. 1. To find clues on the planet formation mechanisms & time scales To identify signatures of planet-bearing stars. Central Issues. How do planets form so prolifically?
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Basic Objectives • 1. To find clues on the planet formation mechanisms & time scales • To identify signatures of planet-bearing stars Central Issues • How do planets form so prolifically? • How do we characterize the essential properties of planets? • Is the solar system architecture a rule or an exception? Methodology & approach • Spectroscopic and photometric observations • Outer solar system exploration • Meteoritic analysis • Fractionation of heavy elements through dust evolution • Core accretion model of planet formation • Planetary orbital migration • Long term planetary dynamical evolution
Angular momentum Angular momentum = mass x speed x radius
Contraction & spin up Angular momentum = speed x radius Shrinking radius => spin up
HST images give size & S(r) O’Dell & Wen 1992, Ap.J., 387, 229. Section of the Orion Nebula 218-354 183-405 100 AU radius 206-446 114-426 2000 AU 400 AU McCaughrean & O’Dell 1996, AJ, 108, 1382.
Solar Nebula Disks can build planets Limit Beckwith & Sargent 14 Taurus Ophiuchus 12 Andre & Montemerle 10 8 6 4 2 0 1 0.0001 0.001 0.01 0.1 Mdisk (M¤) assumes gas/dust = 100
Economic analogy Conclusion: rental houses are mostly owned by the top 10%
Observations: young stars • Continuum radiation: dust mass distribution (MMSN x 3) • Sizes and surface density distribution (100 AU, S~r-1) • Gas accretion rate (10-8 M yr-1) • Grain phases and size evolution (growth and sedimentation) • Coexistence of hydrogen gas and dust grains (gas depletion) • Disk frequency evolution time scale in clusters (10 Myr) • Debris disk structures (embedded companions?)
Inner disks disappear ~ 10 Myr Hillenbrand & Meyer 2000, in preparation 1.0 r Oph CrA N2024 0.8 N1333 Mon R2 Trap Taurus 0.6 LHa101 N7128 L1641y Fraction of disks L1641b ONC 0.4 Lupus IC 348 N2264 Cha 0.2 TW Hyd Pleiades Hyades 0.0 a Per Ursa Major 10 100 1 Gyr 1 0.1 Age (Myr)
Time scale determination from age distribution Conclusion: 1) college students are mostly young adults, 2) bachelor’s degree takes 4-5 years on average
Disk heating Internal dissipation stellar irradiation
Elemental abundance in meteorites Similar to the Sun
Nuclear chronology Half life
Range of half life U 238: 4.47*109 yearsTh 234: 24.1 daysHe 4: StablePa 234: 6.7 hoursC 11: 20.3 minutesB 11: stableU 235m: 26 minutesU 235: 7.04*108yearsFm 256: 2.62 hoursXe 140: 13.6 secondsPd 112: 21 hoursPo 212: 299 nanosecondsSe 82: 1.3*1020 years Solar system: 4.6 Gyr old
Chondritic meteorites • Limited size range, sm-cm, • Glass texture, flash heating, • Age difference with CAI’s, • Matrix glue & abundance, • Weak tensile strength. • Formation timescale 2-3 Myr
Supernova precursor Injection of radioactive Al26
Collisions: piles of loose fragmentation Weak sticking strength Shared orbits and repeated encounters Piles of loose gravel (coagulation vs collapse)
Preferred cradles of gas giants: snow line Limited by: Isolation slow growth
Iron fingers & double diffusive instability Heat transport bottleneck Many channels to bypass the heat barrier and shorten the growth time scale
Disk clearing Stellar magnetosphere Photo-evaporation Stellar wind
Scattering & Ejection Thommes