Origin of the Solar System

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1 Solar nebula Formation of planetismals Formation of terrestrial planets Origin of the Solar System

2 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 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!

The number of protons in an atom determines the element; however, the number of neutrons can vary Isotope Radioactivity Some elements are stable (never changing)

4 The number of protons in an atom determines the element; however, the number of neutrons can vary Isotope Radioactivity 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 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 Some Naturally Occurring Radioactive Isotopes and their half-lives Radioactive Isotope (parent) Uranium-238 Potassium-40 Uranium-235 Carbon-14 Product (Daughter) Lead-216 Argon-40 Lead-207 Nitrogen-14 Half Life (years) 4.5 Billion 1.26 Billion 0.7 Billion 5,715

7 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!

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!

8 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 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? The Big Bang

10 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

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

11 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 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 The Solar Nebula Elements that make up the solar nebula Hydrogen and Helium are most abundant, Oxygen is thirdmost abundant, C, N, Ne, Mg, Si, S, Fe, Ni are also fairly common

The Formation of the Protoplanetary disk As the original gas cloud (which rotates slowly about a common axis) collapses, it begins to rotate faster conservations angular momentum As the

14 The Formation of the Protoplanetary disk 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 PTYS/ASTR as 206 a protoplanetary Origin disk of the Solar System

15 Concept of Angular Momentum

16 Hubble Spce Telescope Images of protoplanetary disks (or proplyds) in the Orion nebula

17 The sequence of solar-system formation and how long it takes

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

18 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 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 Small dust particles accreted to make planetesimals Planetesimals accreted (and collided with other planetesimals) to form protoplanets Formation of terrestrial planets The protoplanets were at least partially molten denser iron-rich material fell to the center, bringing heavier metals with it, making an ironrich core (differentiation) PTYS/ASTR A terrestrial 206 planet!

material provided the core Once large enough, they could attract H and He Disk

21 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 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 Finding Extrasolar Planets 1

24 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 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 Format: First Exam 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 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 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 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 Earthcentered system, elliptical orbits, Kepler s laws, Newton s laws, gravity

30 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, lightgathering ability, resolution, CCDs, adaptive optics

31 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

Comparative Planetology II: The Origin of Our Solar System. Chapter Eight

Comparative Planetology II: The Origin of Our Solar System Chapter Eight ASTR 111 003 Fall 2007 Lecture 07 Oct. 15, 2007 Introduction To Modern Astronomy I: Solar System Introducing Astronomy (chap. 1-6)