The Origin of the Solar System

1. 0 The Origin of the Solar System Please swipe your ID for attendance tracking and take your assigned transmitter. Movie: The History of the Solar System

2. :10 0 of 5 How old is the Solar System? • 1.3 million years • 350 million years • 1.7 billion years • 4.5 billion years • 13 billion years

3. 0 The Formation of Stars:Giant Molecular Clouds Barnard 68 Visible Star formation← collapse of the cores ofgiant molecular clouds:Dark, cold, dense cloudsobscuring the light of stars behind them.

4. :10 0 of 5 Which wavelength range is adjacent to the visible spectrum and has longer wavelengths than visible light? • X-rays • Gamma-Rays • Stingrays • Infrared light • Ultraviolet light

5. 0 The Formation of Stars:Giant Molecular Clouds Barnard 68 Infrared Visible Star formation← collapse of the cores ofgiant molecular clouds:Dark, cold, dense cloudsobscuring the light of stars behind them. (More transparent in infrared light.)

6. 0 Parameters of Giant Molecular Clouds Size: r ~ 50 pc Mass: > 100,000 Msun Temp.: a few 0K Dense cores: R ~ 0.1 pc M ~ 1 Msun

7. 0 (Bok) Globules Compact, dense pockets of gas which may contract to form stars. ~ 10 – 1000 solar masses; Contracting to form protostars

8. 0 Protostars Protostars = pre-birth state of stars: Hydrogen to Helium fusion not yet ignited Still enshrouded in opaque “cocoons” of dust => barely visible in the optical, but bright in the infrared.

9. :10 0 of 5 Do you expect stars to form isolated? • Yes. • No, they should form in groups of a few (2 – 5) • No, they should form in large groups (several 100s or 1000s) • No, actually all stars in a galaxy (several billions) should form at the same time.

10. 0 Open Clusters of Stars Large masses of Giant Molecular Clouds => Stars do not form isolated, but in large groups, calledOpen Clusters of Stars. Open Cluster M7

11. :10 0 of 5 What happens to a spinning object if it contracts? • It stops rotating. • Its rotation slows down. • Its rate of rotation remains unchanged. • Its rotation speeds up.

12. 0 Protostellar Disks Conservation of angular momentum leads to the formation of protostellar disks → birth place of planets and moons

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14. 0 The Solar Nebula Hypothesis Planets form at the same time from the same cloud as the star. Planet formation sites observed today as dust disks of T Tauri stars. Sun and our Solar system formed ~ 4.6 billion years ago.

15. :10 0 of 116 Would you expect that other stars have planetary systems too? • Yes. • No.

16. 0 Extrasolar Planets All stars have gone through basically the same formation process as the sun. → Many stars should have planets! → planets orbiting around other stars = “Extrasolar planets” Extrasolar planets can not be imaged directly. Detection using the “wobbling” technique: Look for “wobbling” motion of the star due to the gravitational pull of the planet on the star.

17. :10 0 of 116 Would you expect that there are still new solar systems being formed at this time? • Yes. • No.

18. 0 Evidence for Ongoing Planet Formation Many young stars in the Orion Nebula are surrounded by dust disks: Probably sites of planet formation right now!

19. 0 Dust Disks around Forming Stars Dust disks around some T Tauri stars can be imaged directly (HST).

20. :10 0 of 116 What is radioactivity? • The decay of atomic nuclei, resulting in the emission of radio waves. • The decay of atomic nuclei, resulting in the emission of gamma-rays. • The fusion of atomic nuclei, resulting in the emission of radio waves. • The fusion of atomic nuclei, resulting in the emission of gamma-rays. • The emission of radio waves by stars like our sun.

21. The Age of the Solar System Sun and planets should have about the same age. Ages of rocks can be measured through radioactive dating: Measure abundance of a radioactively decaying element to find the time since formation of the rock Dating of rocks on Earth, on the Moon, and meteorites all give ages of ~ 4.6 billion years.

22. :10 0 of 116 If you start out with 1 kg of a radioactive substance with a half-life of 150 years, how long does it take until there is nothing left? • 150 years. • 300 years. • 1,500 years. • An infinite amount of time (in principle). • Impossible to tell with the given information.

23. :10 0 of 116 What is “condensation”? • The melting of a substance. • The transition of a substance from the liquid to the gas phase. • The transition of a substance from the gas to the liquid phase. • The transition of a substance from the liquid to the solid phase.

24. 0 Condensation in the Early Solar System Only condensed materials could stick together to form planets Temperature in the protostellar cloud decreases outward. Further out → Protostellar cloud cooler → metals with lower melting point condensed → change of chemical composition throughout solar system Lighter substances condense at lower temperatures. → Average density of planets decreases outwards!

25. Formation and Growth of Planetesimals Planet formation starts with clumping together of grains of solid matter: Planetesimals Planetesimals (few cm to km in size) collide to form planets. Planetesimals grow through condensationand accretion.

26. :10 0 of 116 What happens if you try to mix oil and water? • They will mix to a uniform solution. • The oil will sink to the bottom, the water will “swim” on top of it. • The water will sink to the bottom, the oil will “swim” on top of it.

27. 0 The Growth of Protoplanets As rocks melted, heavier elements sink to the center →differentiation →Terrestrial planets have heavy-metal (iron) cores and mantles of lighter substances

28. The Story of Planet Building Planets formed from the same protostellar material as the sun. Rocky planet material formed from clumping together of dust grains in the protostellar cloud. Mass of more than ~ 15 Earth masses: Mass of less than ~ 15 Earth masses: Planets can grow by gravitationally attracting material from the protostellar cloud Planets can not grow by gravitational collapse Earthlike planets Jovian planets (gas giants)

29. :10 0 of 116 Which features on the surface of the moon tell us that there were many small bodies (rocks) remaining in the solar system after it formed? • A dense atmosphere. • The large, uncratered maria. • Lots of impact craters in the lunar highlands. • High mountains.

30. 0 Clearing the Nebula Remains of the protostellar nebula were cleared away by: • Sweeping-up of space debris by planets • Ejection by close encounters with planets Surfaces of the Moon and Mercury show evidence for heavy bombardment by asteroids.

31. 0 Ejection of small bodies by massive planets

32. 0 Clearing the Nebula Remains of the protostellar nebula were cleared away by: • Sweeping-up of space debris by planets • Solar wind • Ejection by close encounters with planets • Radiation pressure of the sun Surfaces of the Moon and Mercury show evidence for heavy bombardment by asteroids.

33. 0 Final overview movie