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Grades will be posted in MyUCFGrades Quiz for Ch. 6 has been posted and is due next Mon. night (as usual) Outline Ch.6 Solar System (Different from Book’s outline) I. Overall Properties of Solar System and its Formation II. Extrasolar Planets Outline Ch.6: Solar System (Different from Book’s outline) I. Overall Properties of Solar System: 1. 2. 3. 4. Nearly co-planar orbits (disk-shaped) All planets orbit Sun in same direction as Sun’s rotation MOST (but not all) planets rotate in same direction as their obits around Sun Planets: Small dense terrestrial planets in inner SS Large, low density, Jovian planets in outer SS Pluto is exception (Cont.) Outline Ch.6 (Cont.) I. Overall Properties (cont): 5. 6. 7. In general: closer to Sun, higher density Hot near Sun cold far away Composition of Solar Nebula The planets are tiny compared to the distances between them (a million times smaller than shown here), but they exhibit clear patterns of composition and motion. The patterns are more important than numbers, names, and other details What have we learned? • What does the solar system look like? Our solar system consists of the Sun, nine eight planets -----and their moons, and vast numbers of asteroids and comets. Each world has its own unique character, but there are many clear patterns among the worlds. Clues to the Formation of Our Solar System Our Goals for Learning • What features of our solar system provide clues to how it formed? • What theory best explains the features of our solar system? What have we learned? • What features of our solar system provide clues to how it formed? Four major features provide clues: (1) Planets all orbit the Sun in same direction as Sun’s rotation (counterclockwise when seen from North), most planets rotate in same direction as their orbit. (2) The eight oficial Planets divide clearly into two groups: terrestrial and jovian (Jupiter-like). (3) The solar system contains large numbers of asteroids and comets. (4) There are some notable exceptions to these general patterns. What have we learned? • What theory best explains the features of our solar system? The nebular theory, which holds that the solar system formed from the gravitational collapse of a great cloud of gas. Slowly rotating interstellar cloud of gas and dust collapses to form the Solar Nebula Solar Nebula: rotating, disk-shaped cloud out of which Sun and planets formed I. Overall Properties (cont): 7. Composition of Solar Nebula: 98% Hydrogen & Helium, 2% all other elements Condensation of solids from nebula: Inner part is hot, only high density materials (metals and silicates) can condense Outer regions cooler, can condense lower density materials like water ice and other ices Condensation of Solids from Solar Nebula (not exactly like the book) HOT COLD Asteroids and comets accreted at different distances from the Sun, resulting in different ice contents: comets have more ice What have we learned? • Where did the solar system come from? The cloud of gas that gave birth to our solar system was the product of recycling of gas through many generations of stars within our galaxy. This gas consisted of 98% hydrogen and helium and 2% everything else combined. What have we learned? • What caused the orderly patterns of motion in our solar system? A collapsing gas cloud naturally tends to heat up, spin faster, and flatten out as it shrinks in size. Thus, our solar system began as a spinning disk of gas. The orderly motions we observe today all came from the orderly motion of this spinning disk of gas. Question 1 What factors do you think might have contributed to the difference between Terrestrial and Jovian Planets: a) Temperature (hotter near Sun and colder far from Sun) b) Size of Orbits (larger orbits can “sweep” more material) c) The composition of the Solar Nebula Question 1 What factors do you think might have contributed to the difference between Terrestrial and Jovian Planets: a) Temperature (hotter near Sun and colder far from Sun) b) Size of Orbits (larger orbits can “sweep” more material) c) The composition of the Solar Nebula d) All of the above Question 2 How did the composition of the Solar Nebula affect the composition of the planets? 1. Metals and Silicates can condense at higher temperatures than water and other gases 2. Hydrogen, helium, and oxygen were more abundant than metals and silicates 3. The higher the mass a planet has, the larger the atmosphere it can retain. The correct answer is A. 1 and 2 C. 3 only B. 1 only D. 1, 2 and 3 Question 2 How did the composition of the Solar Nebula affect the composition of the planets? 1. Metals and Silicates can condense at higher temperatures than water and other gases 2. Hydrogen, helium, and oxygen were more abundant than metals and silicates 3. The higher the mass a planet has, the larger the atmosphere it can retain. The correct answer is A. 1 and 2 C. 3 only B. 1 only D. 1, 2 and 3 I. Overall Properties (cont): 7. Composition of Solar Nebula: 98% Hydrogen & Helium, 2% other elements Condensation of solids from nebula: Inner part is hot, only high density materials (metals and silicates) can condense Outer regions cooler, can condense lower density materials like water ice and other ices Near Sun: terrestrial planets Far from: Sun Jovian planets Question 3 If I tell you a planet has many moons is it likely to be a) b) c) d) Terrestrial Jovian Pluto an asteroid Question 3 If I tell you a planet has many moons is it likely to be a) b) c) d) Terrestrial Jovian Pluto an asteroid What have we learned? • Why are there two types of planets? Inner solar system: high temperatures, only metal and rock could condense. Outer solar system: cold temperatures, more abundant ices condense along with metal and rock. What have we learned? • How do we explain the • Where did asteroids existence of our Moon and other and comets come “exceptions to the rules”? from? •Most of the exceptions Asteroids are the probably arose from collisions rocky leftover or close encounters with planetesimals of leftover planetesimals, the inner solar especially during the heavy system, and comets are the icy bombardment that occurred early in the solar system’s leftover history. Our Moon is probably planetesimals of the result of a giant impact the outer solar between a Mars-size system. planetesimal and the young Earth. What have we learned? • When did the planets form? The planets began to accrete in the solar nebula about 4.6 billion years ago, a fact we determine from radioactive dating of the oldest meteorites. 6.5 Other Planetary Systems Our Goals for Learning • How do we detect planets around other stars? • What have other planetary systems taught us about our own? Outline Ch.6 (Cont.) (Different from Book’s outline) II. Extrasolar Planets Are there planets around other stars? Have we “seen” them? Outline Ch.6 (Cont.) II. Extrasolar Planets Are there planets around other stars? YES, more than 400! Have we “seen” them? Outline Ch.6 (Cont.) II. Extrasolar Planets Are there planets around other stars? YES more than 400! Have we “seen” them? We have not seen most of them (not directly), we have “seen” only a few so far Outline Ch.6 (Cont.) II. Extrasolar Planets About 430 detected so far We have not “seen” most of them yet, they are detected indirectly using radial velocity and transits in front of stars Types of planets: all strange (because those are the only ones we can detect) No Earth-sized extraterrestrial planet yet More than 450 known extrasolar planets as of Sept. 2010 •Most are more massive than Jupiter and closer to their star than Earth is to Sun! •Are revisions to the nebular theory are necessary? •Planets can apparently migrate inward from their birthplaces. Orbits of 3 planets around star Upsilon Andromeda Is Earth Unusual? No Earth-like planets found yet. Observations are not good enough to tell if they are common or rare Available methods can only detect BIG planets so far. What have we learned? • How do we detect planets around other stars? So far, we are able to detect most extrasolar planets indirectly by observing the planet’s effects on the star it orbits. Most discoveries to date have been made with the Doppler technique, in which Doppler shifts reveal the gravitational tug of a planet (or more than one planet) on a star. A few planets have been observed to “transit” in front of their star (wee see a decrease in the light from the star). A few planets have been observed directly, i.e., photons emitted by them have been detected What have we learned? • What have other planetary systems taught us about our own? Planetary systems exhibit a surprising range of layouts, suggesting that jovian (Jupiter-like) planets sometimes migrate inward from where they are born. What have we learned? • What have other planetary systems taught us about our own? Planetary systems exhibit a surprising range of layouts, suggesting that jovian (Jupiter-like) planets sometimes migrate inward from where they are born. This lesson has taught us that despite the successes of the nebular theory, it needs some refinement.