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Solar nebula Formation of planetismals Origin of the Solar System Formation of terrestrial planets PTYS/ASTR 206 Origin 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 PTYS/ASTR 206 Origin 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! PTYS/ASTR 206 Origin of the Solar System 2/13/07 • 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 PTYS/ASTR 206 Origin 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 PTYS/ASTR 206 Origin 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-238 Lead-216 4.5 Billion Potassium-40 Argon-40 1.26 Billion Uranium-235 Lead-207 0.7 Billion Carbon-14 Nitrogen-14 5,715 PTYS/ASTR 206 Origin 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 PTYS/ASTR 206 ANSWER: 4.56 Billion Years ! Origin 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 Solar System – The Sun – primarilyOrigin H, ofHe 2/13/07 PTYS/ASTR 206 ? 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? PTYS/ASTR 206 Origin 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” PTYS/ASTR 206 Origin 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) PTYS/ASTR 206 Origin 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 PTYS/ASTR 206 Origin 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 thirdmost abundant, C, N, Ne, Mg, Si, S, Fe, Ni are also fairly common PTYS/ASTR 206 Origin of the Solar System 2/13/07 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 PTYS/ASTRas 206 a protoplanetary Origin disk of the Solar System known 2/13/07 Concept of Angular Momentum PTYS/ASTR 206 Origin of the Solar System 2/13/07 Hubble Spce Telescope Images of protoplanetary disks (or proplyds) in the Orion nebula PTYS/ASTR 206 Origin of the Solar System 2/13/07 The sequence of solar-system formation and how long it takes PTYS/ASTR 206 Origin 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 PTYS/ASTR 206 Origin 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 PTYS/ASTR 206 system Origin 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 ironrich core (differentiation) – A terrestrial planet!Origin of the Solar System PTYS/ASTR 206 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” PTYS/ASTR Origin of the Solar System of H206and He 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 PTYS/ASTR 206 Origin of the Solar System 2/13/07 Finding Extrasolar Planets 1 PTYS/ASTR 206 Origin 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 theyOrigin orbit PTYS/ASTR 206 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 PTYS/ASTR 206 Origin 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 PTYS/ASTR 206 Origin 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%). PTYS/ASTR 206 Origin 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! PTYS/ASTR 206 Origin 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 Earthcentered system, elliptical orbits, Kepler’s laws, Newton’s laws, gravity PTYS/ASTR 206 Origin 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, lightgathering ability, resolution, CCDs, adaptive optics PTYS/ASTR 206 Origin 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 PTYS/ASTR 206 Origin of the Solar System 2/13/07