1. PTYS/ASTR 206Origin of the Solar System 2/13/07 Origin of the Solar System Solar nebula Formation of planetismals Formation of terrestrial planets

2. PTYS/ASTR 206Origin of the Solar System 2/13/07 Announcements There will be another preceptor-led study group Wednesday at 10:30AM in room 330 of Kuiper Be sure to pick up all assignments in the box – it will be completely cleared out by Thursday PM. Exam on Thursday (2/15) –Closed book, closed note, no electronic devices –Brief review today Reading for next class (next Tuesday) –7-6, 7-7 (review), 9-2, 9-3

3. PTYS/ASTR 206Origin of the Solar System 2/13/07 How Old is the Solar System ? How can we determine this ? –Radioactive dating –Need to find the right material to date ! –Because of plate tectonics and geological activity, Earth rocks are not a good indicator of the age of the Solar System –Meteorites!

4. PTYS/ASTR 206Origin of the Solar System 2/13/07 Radioactivity The number of protons in an atom determines the element; however, the number of neutrons can vary –Isotope Some elements are stable (never changing) Others are unstable, and “disintegrate” into a more-stable isotope of the same element This “decay” of the unstable isotope happens spontaneously and the element is radioactive

5. PTYS/ASTR 206Origin of the Solar System 2/13/07 Radioactive Dating Each type of radioactive nucleus decays at its own characteristic rate, called its half-life, which can be measured in the laboratory This is the key to a technique called radioactive age dating, which is used to determine the ages of rocks

6. PTYS/ASTR 206Origin of the Solar System 2/13/07 Some Naturally Occurring Radioactive Isotopes and their half-lives Radioactive Isotope (parent) Product (Daughter) Half Life (years) Uranium-238Lead-2164.5 Billion Potassium-40Argon-401.26 Billion Uranium-235Lead-2070.7 Billion Carbon-14Nitrogen-145,715

7. PTYS/ASTR 206Origin of the Solar System 2/13/07 How Old is the Solar System? The oldest rocks found anywhere in the solar system are meteorites, the bits of meteoroids that survive passing through the Earth’s atmosphere and land on our planet’s surface Radioactive age-dating of meteorites, reveals that they are all nearly the same age, about 4.56 billion years old (4.56 Gy) –Oldest Earth rocks – about Gy –Zircons (ancient sand grains) – over 4 Gy –Moon rocks – oldest are about 4.3 Gy ANSWER: 4.56 Billion Years !

8. PTYS/ASTR 206Origin of the Solar System 2/13/07 How did the Solar System Form? What we know: –The planets have orbits that are in a plane (the ecliptic plane) –The planets orbit the Sun in the same direction! –Terrestrial planets: small, rocky bodies made of heavy elements Close to the Sun –Jovian planets: large bodies made of light elements (H, He) Far from the Sun –The Sun – primarily H, He ?

9. PTYS/ASTR 206Origin of the Solar System 2/13/07 The Big Bang The theory of the origin of the Universe Only Hydrogen and Helium (perhaps small amounts of Li and Be) would survive the enormous temperatures of the Big Bang Where did all the heavy elements (like Iron, Oxygen, etc.) come from?

10. PTYS/ASTR 206Origin of the Solar System 2/13/07 The formation of Stars Hydrogen and Helium gas clouds are formed due to mutual gravitational effects The gas cloud begins to collapse -- Jeans instability Kelvin-Helmholtz contraction –Gravitational energy  thermal energy –As the gas/dust cloud contracts, it heats up The birth of a “protostar”

11. PTYS/ASTR 206Origin of the Solar System 2/13/07 The protostar As the protostar continues to “accrete” material, its center is under extreme pressure As the core is put under more pressure and gets hotter and hotter, thermonuclear fusion starts to occur –It is now a full-fledged star Formation of different atomic elements –These are released as the star evolves and eventually dies (either gradually, or by supernova)

12. PTYS/ASTR 206Origin of the Solar System 2/13/07 We are made out of “star dust” ! Space has mostly H and He, but heavier elements also exist (resulting from nuclear reactions that occurred in now-dead stars) The material from which our solar system formed is called the Solar Nebula

13. PTYS/ASTR 206Origin of the Solar System 2/13/07 The Solar Nebula Elements that make up the solar nebula Hydrogen and Helium are most abundant, Oxygen is third- most abundant, C, N, Ne, Mg, Si, S, Fe, Ni are also fairly common

14. PTYS/ASTR 206Origin of the Solar System 2/13/07 As the original gas cloud (which rotates slowly about a common axis) collapses, it begins to rotate faster –conservations angular momentum As the cloud shrinks, it also flattens The flattened, rotating disk of gas and dust from which our solar system is made of is known as a protoplanetary disk The Formation of the Protoplanetary disk

15. PTYS/ASTR 206Origin of the Solar System 2/13/07 Concept of Angular Momentum

16. PTYS/ASTR 206Origin of the Solar System 2/13/07 Hubble Spce Telescope Images of protoplanetary disks (or proplyds) in the Orion nebula

17. PTYS/ASTR 206Origin of the Solar System 2/13/07 The sequence of solar-system formation and how long it takes

18. PTYS/ASTR 206Origin of the Solar System 2/13/07 Condensation Dust in the early solar nebula acted as condensation nuclei (nuclei upon which other elements attach to) If an element has a temperature above the condensation temperature – it will be a gas It the temperature is below the condensation temperature – it is solid (or liquid) –Iron, nickel have high condensation temperatures –Hydrogen and Helium have very low condensation temperatures

19. PTYS/ASTR 206Origin of the Solar System 2/13/07 The composition of the solar system was arranged largely by how far it was from the protostar Elements with high condensation temps. (iron, nickel, rocky material, etc.) in the inner solar system –Terrestrial planets! methane, ammonia, etc. remained as ice in the outer solar system

20. PTYS/ASTR 206Origin of the Solar System 2/13/07 Formation of terrestrial planets Small dust particles accreted to make “planetesimals” Planetesimals accreted (and collided with other planetesimals) to form protoplanets The protoplanets were at least partially molten –denser iron-rich material fell to the center, bringing heavier metals with it, making an iron- rich core (differentiation) –A terrestrial planet!

21. PTYS/ASTR 206Origin of the Solar System 2/13/07 There are currently two theories for the formation of Gas Giants Core accretion model –Bottom up model –Started with a core, then accreted H and He –Ices and rocky material provided the core –Once large enough, they could attract H and He Disk instability model –“top down” model –Formed directly from the protoplanetary disk as a “clump” of H and He

22. PTYS/ASTR 206Origin of the Solar System 2/13/07 Extrasolar Planets About 10 years ago, astronomers began finding extrasolar planets, or planets orbiting other stars –More than 100 have been detected –Can be detected by amateurs They are not actually seen, instead, their effects on their parent star are observed

23. PTYS/ASTR 206Origin of the Solar System 2/13/07 Finding Extrasolar Planets 1

24. PTYS/ASTR 206Origin of the Solar System 2/13/07 Finding Extrasolar Planets 2 The planets themselves are not visible; their presence is detected by the “wobble” of the stars around which they orbit

25. PTYS/ASTR 206Origin of the Solar System 2/13/07 Extrasolar Planets Most of the extrasolar planets discovered to date are quite massive and have orbits that are very different from planets in our solar system

26. PTYS/ASTR 206Origin of the Solar System 2/13/07 First Exam Format: –5 short-answer questions –30 multiple choice questions To be answered on the scantron sheets BRING A #2 PENCIL ! –Closed book, closed notes, no electronic devices (including calculators!) –The allotted time will be ~72 minutes

27. PTYS/ASTR 206Origin of the Solar System 2/13/07 First Exam What will it cover? –Mostly material discussed in the lectures –Reading – Chapters 1-8 –Note: some lecture topics are discussed more in the textbook –The exam is usually balanced by lecture material (~4 questions per lecture, typically) How much does it count towards the final grade? –Either 20% or 10% of your overall grade depending on how you do on the second exam (the best score of the 2 is 20%, the worst is 10%).

28. PTYS/ASTR 206Origin of the Solar System 2/13/07 First Exam What should you study? –Go over lecture slides –Textbook Go over guiding questions at the beginning of each chapter Go over key ideas and review questions at the end of each chapter –Review in-class activities, homework, and quizzes All solutions are posted on the website –Go over the practice exam –Note that to ensure the maximum possibility of success, you should do all of the above and not just the practice exam! What should you ignore when studying? –There won’t questions like the quantitative problems found on the homework –Do NOT bring a calculator!

29. PTYS/ASTR 206Origin of the Solar System 2/13/07 First exam: A brief review Chapter 1 –powers-of-ten notation Chapter 2 –The sky, diurnal motion, celestial sphere, reason for the seasons, equinoxes Chapter 3 –Reason for lunar phases, when they rise/set, lunar eclipses, solar eclipses Chapter 4 –Copernicus heliocentric system vs. Ptolemaic Earth- centered system, elliptical orbits, Kepler’s laws, Newton’s laws, gravity

30. PTYS/ASTR 206Origin of the Solar System 2/13/07 First Exam: A brief review Chapter 5 –radiation and spectroscopy, Kirchoff’s laws, Wien’s law, Stefan-Boltzman law Basic properties of waves Electromagnetic spectrum Blackbody radiation Absorption and Emission lines Doppler effect Chapter 6 –Telescopes (how they work), magnification, light- gathering ability, resolution, CCDs, adaptive optics

31. PTYS/ASTR 206Origin of the Solar System 2/13/07 First exam: A brief review Chapter 7 –Layout of the solar system, properties of the planets, average density, kinetic energy, escape speed, spectroscopy Chapter 8 –Origin of the solar system, the nebular hypothesis, extrasolar planets, radioactive dating