Planetary Systems ASTR Formation of the Solar System

Transcription

1 Planetary Systems ASTR Formation of the Solar System

2 Topic titles 1. Overview of the Solar System 2. Dynamics 3. Energy 4. Planetary Atmospheres 5. Planetary Surfaces 6. Planetary Interiors 7. Magnetospheres and Interplanetary Medium 8. Meteorites 9. Asteroids 10. Comets 11. Rings 12. Planet formation 13. Extrasolar planets

3 Topics Overview Angular momentum problem Nucleosynthesis Star formation The protoplanetary disk Condensation and growth of solid objects Formation of terrestrial planets Formation of giant planets Planetary migration Asteroids, meteorites and comets Planetary rotation Origin of planetary satellites Confronting theory and observation

4 Observational constraints star formation

5 Nucleosynthesis

6 Nucleosynthesis

7 Nucleosynthesis Primordial n p + + e - + ν n + p + H + 2H + He + Stellar p-p: 2H + He 2+ CNO cycle: 2H + CNO He 2+ Triple α: 3 He 2+ C 6+ α capture: C + He O O + He Ne etc. n capture: x E + n x+1 E slow fast n p + + e - + ν

8 Overview 1. The "solar nebula" is disturbed and collapses under its own gravity. 2. The initial collapse in less than 100,000 years. 3. Protostar at center, gas orbits/flows around it. Most adds to the mass of the forming star, but centrifugal force creates "accretion disk" that radiates energy and cools. 4. First brake point. Accretion disk unstable and forms second star. OR 5. Accretion disk forms metal, rock and ice. 6. Dust particles form boulders and eventually asteroids. 7. Run away growth to large asteroid or lunar size (inner solar system) and 1-5 M E (outer solar system). Discontinuity Mars/Jupiter (snowline). A few hundred thousand to about twenty million years, with the outermost taking the longest to form. 8. At 1 million years, strong solar wind sweep away protoplanetary nebula. Some protoplanets accrete to become gas giant, others become rocky or icy bodies. Accretionary growth of "planetesimals" million years, present solar system but few big collisions produce Mercury and the Moon). 10. Explains our system very well but not extrasolar planets. Observational bias or problems with the theory?

9 Formation of terrestrial planets Dynamics of final stage of planetesimal accretion

10 Molecular clouds Eagle Nebula (M16)

11 Orion Nebula (M42)

12 Overview

13 Collapse of molecular clouds year Gravitational energy Kinetic energy + Heat

14 Observational constraints circumstellar disks HST near-infrared image of HH 30. FOV 20"x20", 2800 A.U. x 2800 A.U. (35 times the solar system) at the distance of Taurus. HST near-infrared image of IRAS FOV 10"x10", which corresponds to 1400 A.U. x 1400 A.U. (17 times the solar system) at the distance of Taurus.

15 Overview

16 The Angular Momentum Problem Body Mass Orbit Period Rotation Angular radius rate momentum Sun ~20 Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Total angular momentum, ω(total) = ω(orbit) + ω(rotation)

17 Dynamic evolution Magnetic torques Gravitational torques Viscous torques

18 Possible Models for Primordial Solar Grains a. SiO 2 by oxidation of silicates in H 2 + O 2 flame b. Gold colloidal aggregates

19 Possible Models for Primordial Solar Grains c. Soot aggregates by acetylene combustion d. Numerical simulations of ballistic cluster-cluster accretion

20 Possible Models for Primordial Solar Grains e. An IDP collected in the stratosphere by U2

21 Chemistry

22 Chemistry

23 -2 H 2 O Chemistry Log (abundance wrt H 2 ) -4-6 CO CO 2 CH 4 N2 NH Heliocentric distance (AU)

24 Condensation and growth of solid objects Timescales Planetesimals Planetary embryos Velocities Collisions Runaway growth

25 Runaway growth

26 Formation of terrestrial planets Dynamics of final stage of planetesimal accretion

27 Formation of giant planets

28 Formation of giant planets Core instability hypothesis

29 Formation of the Moon 1.The Fission Theory: The Moon was once part of the Earth and somehow separated from the Earth early in the history of the Solar System. The present Pacific Ocean basin is the most popular site for the part of the Earth from which the Moon came. 2.The Capture Theory: The Moon was formed somewhere else, and was later captured by the gravitational field of the Earth. 3.The Condensation Theory: The Moon and the Earth condensed together from the original nebula that formed the Solar System. 4.The Colliding Planetesimals Theory: The interaction of earth-orbiting and Sun-orbiting planetesimals (very large chunks of rocks like asteroids) early in the history of the Solar System led to their breakup. The Moon condensed from this debris. 5.The Ejected Ring Theory: A planetesimal the size of Mars struck the earth, ejecting large volumes of matter. A disk of orbiting material was formed, and this matter eventually condensed to form the Moon in orbit around the Earth.

30 Formation of the Moon

31 Formation of the Moon

32 Formation of Other Satellites