A Guide to what you need to know EXAM 3 EXPECTATIONS Exam 3 Content What and how much of what Exam 3 will cover Chapter 8 Moon Formation Evolution Mercury Chapter 9 Venus Chapter 10 Mars Chapter 11 Jupiter Chapter 12 Saturn up to Friday 18 Nov Lecture Exam 3 structure 105 Points on Exam Top score 105 Multiple choice Fill in the Blank Concept Questions Short Answer There will be bonus questions worth 5 pts total Max score possible 105 5 110 Must Knows Chapter 8 Moon Formation part Know the Four Moon formation hypotheses and why Giant Impact is favored 1 Coformation Sister Theory Moon and Earth formed together FAILS because in this case the Moon should have a similar composition to Earth e g The Moon should have a significant iron core 2 Fission Daughter Theory While molten the Earth spun really fast and spun off the Moon Explains composition similar to Earth s Mantle but FAILS because why would the Earth be spinning that fast Must Knows Chapter 8 Moon formation part Know the Four Moon formation hypotheses and why Giant Impact is favored 3 Capture Theory Moon and Earth formed separately in different parts of the disk hence different composition and the Earth captured the Moon FAILS because nearly impossible for the Earth to capture a moon sized object 4 Giant Impact Theory favored theory The early already differentiated Earth experience a giant impact with a Mars sized protoplanet named Theia at a glancing blow that stripped off mantle material that became the Moon THE PHYSICS ALLOWS THIS Must Knows Chapter 8 Moon Evolution Part Know that planetary scientists think that the original surface of the Moon was a global lunar magma ocean that was melted via repeated impacts Formation of the Maria Crust formed and later during the Late Heavy Bombardment the very large impact basins very big craters were filled with the magma underneath the thin near side crust forming large roughly circular smooth areas that were enriched in iron hence darker in color These lava filled basins became the maria Maria are these very large ancient magma flooded impact basins Maria appear on the Lunar Near side because crust is thinner than it is on the Lunar Far side Giving rise to the Near side Far side dichotomy i e the face we see nearly all the maria on the near side while the far side is almost entirely cratered highland terrain Must Knows Chapter 8 Mercury 1st Planet from the Sun Due to it s proximity to the Sun and having an orbit interior to Earth s Mercury always appears close to the Sun Maximum angular distance 28o This occurs when Mercury is at greatest elongation largest angle you can draw between Earth Sun line and Mercury or Venus if you are considering that planet Mercury has a 3 2 spin orbit resonance Know what a spin orbit resonance is That is if I give you that Planet Memptine has a 7 5 spin orbit resonance you can tell me that Planet Memptine rotates about its axis SEVEN times for every FIVE times it orbits its star Must Knows Chapter 8 Mercury Know that Mercury has no permanent atmosphere Know that Mercury does have a global magnetic field that is likely created by the dynamo effect but is 1 that of Earth s How Mercury is able to generate a mag field having such a slow rotation rate is a current area of research helping us understand how planetary dynamos actually operate Likely the slow rotation is compensated for by the absolutely enormous 85 of the radius iron core Know that water ice has been found surprisingly on both the Moon and Mercury in the dark depths of the permanently shadowed craters at the poles Permanently shadowed because of almost no axial tilt Know that Mercury has the largest iron core of the terrestrial planets relative to planet size 85 of its radius Must Knows Chapter 8 Mercury Know the major surface features of Mercury Large scale topography Covered with impact craters with smooth intercrater plains between the craters Major surface feature Caloris Basin a very large 1400 km ancient impact basin that has an associated weird terrain on the direct opposite side antipodal just a cool word of Mercury Unique to Mercury Mercury is the only planet to have step walled pits called hollows that are found exclusively on crater floors and crater rims Mercury has several 100 km long tall few km cliffs called scarps and given names of Something Rupes that formed as a result of Mercury significantly cooling in its interior due to small size and shrinking The shrinking squeezed the crust resulting in the scarps We see scarps on the Moon as well that are formed by the same process However the Moon s scarps however are much smaller and indicate a smaller amount of shrinkage Must Knows General Comparative Planetology Mars s relative small size small baked potato compared to Earth implies that it has cooled to the point where it can no longer support a planetary dynamo and generate a mag field Venus s similar size to Earth indicates that it should have an internal structure similar to Earth molten metallic core convective mantle but no plate tectonics However very slow rotation rate of 243 days retrograde rotation backwards compared to the other planets and expectation based on nebular theory is too slow to support a planetary dynamo and hence no magnetic field for Venus Must Knows General Comparative Planetology Know how we use Real vs Expected Temperatures for terrestrial planets and gas giant planets to infer different information Terrestrial planets Real Temp Expected temp implies the greenhouse effect caused by greenhouse gases and therefore has an atmosphere Exam 2 material Gas giant planets Real Temp Expected Temp implies that the planet is radiating away more energy than it is receiving from the Sun and therefore must have an internal heat source Exam 3 Material Expected temperature determined by the planet s distance from Sun and its albedo how reflective Must Knows General Vocabulary related to Comparative Planetology Albedo describes the amount of light reflected by an object in our cases planets It is a number between 0 and 1 such that an albedo of 0 3 Earth s albedo indicates 30 of incident sunlight reflected back out to space An object with an albedo of 0 would be a perfect blackbody An object with an albedo of 1 would perfectly reflect all incoming radiation Courtesy of U of Washington Must Knows General Vocabulary related to Comparative Planetology Opposition is the the point in time when the Sun Earth Planet form a straight line with the Earth in the middle That is
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