The Ghost NebulaCourse AnnouncementsAssignmentsOrigins of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonOrigin of the MoonEvolution of the MoonEvolution of the MoonEvolution of the MoonEvolution of the MoonNear-side, Far-side Dichotomy/ Formation of MariaEvolution of the MoonMERCURY: First from the SunMercury vs. EarthMercury Data Sheet IMercury Data Sheet IIMercury’s appearance in the skyMercury’s appearance in the skyMercury’s Orbit and RotationMercury’s Orbit and RotationMercury’s Orbit and RotationMercury’s Orbit and RotationMercury’s Orbit and RotationMercury’s Orbit and RotationMercury’s Orbit and RotationMercury’s Orbit and RotationThe Ghost NebulaCredit: Adam Block/Mount Lemmon SkyCenter/U. ArizonaCourse Announcements•Thanksgiving Week planningNo classes Wednesday, 23 Nov.•Exam 2 grading underway–Expected return date: Friday, 4 Nov.AssignmentsReading Assignments•No new readingParallel Lectures•CC Astronomy – Episode 13: Mercury [Watch for Wed., 2 Nov.]Mastering Astronomy•Chapter 8 Homework[Due Wed. 2 Nov. at 11:59 PM EDT]Origins of the MoonEvidence to help us discriminate between hypotheses•The overall composition of the Moon is very similar to the composition of Earth’s mantle (and crust)–Similar rocky material and metal content•Unlike the Earth, the Moon lacks a significant iron core–Overall deficiency of amount of iron compared with Earth.•Relative to the size of the planet it orbits, the Moon is very large (largest relative-to-planet size in the Solar System)–Angular momentum of the the Earth-Moon system must be accounted for –Given a formation hypothesis, does the physics work? •Finer detail: Oxygen isotopes, volatile content, etc.(Interested in these details. See these “Science” articles 1 & 2)Origin of the MoonOld Ideas•Coformation (Sister) Hypothesis: Earth and Moon separately, but at the same time, and out of the same disk material.–Explains chemical similarity between the Moon and Earth’s crust and mantle, but if true, the Moon should have a roughly equivalent amount of iron as the Earth.Need an explanation that accounts for chemical similarity to Earth’s mantle and overall iron deficiency… Composition and density…Origin of the MoonOld Ideas•Coformation (Sister) Hypothesis: Earth and Moon separately, but at the same time, and out of the same disk material.–Explains chemical similarity between the Moon and Earth’s crust and mantle, but if true, the Moon should have a roughly equivalent amount of iron as the Earth.Need an explanation that accounts for chemical similarity to Earth’s mantle and overall iron deficiency… Composition and density…Nope!Origin of the MoonOld Ideas•Capture Theory: Earth and Moon formed separately in different locations in the disk, and then the Moon was captured–Explains overall composition and density dissimilarities, BUT if we consider the physics involved for Earth to capture such a large object is it possible?•Very Very Difficult to nearly impossibleNeed an explanation that accounts for chemical similarity to Earth’s mantle and overall iron deficiency… Composition and density…Origin of the MoonOld Ideas•Capture Theory: Earth and Moon formed separately in different locations in the disk, and then the Moon was captured–Explains overall composition and density dissimilarities, BUT if we consider the physics involved for Earth to capture such a large object is it possible?•Very Very Difficult to nearly impossible…Need an explanation that accounts for chemical similarity to Earth’s mantle and overall iron deficiency… Composition and density…Nope!Origin of the MoonOld Ideas•Fission (Daughter) Hypothesis: Earth and Moon formed as a single object, and due to a very high rotation rate, the Earth spun off (rotational fission) the Moon–Explains composition similarity between Earth’s mantle and the Moon. But can this really happen based on physics?•NOPE: No reason for Earth to spin that fast, and even if it did, the spun off object wouldn’t have a stable orbitNeed an explanation that accounts for chemical similarity to Earth’s mantle and overall iron deficiency… Composition and density…Origin of the MoonOld Ideas•Fission (Daughter) Hypothesis: Earth and Moon formed as a single object, and due to a very high rotation rate, the Earth spun off (rotational fission) the Moon–Explains composition similarity between Earth’s mantle and the Moon. But can this really happen based on physics?•NOPE: No reason for Earth to spin that fast, and even if it did, the spun off object wouldn’t have a stable orbitNeed an explanation that accounts for chemical similarity to Earth’s mantle and overall iron deficiency… Composition and density…Wise et al. (1963)Origin of the MoonOld Ideas•Fission (Daugher) Hypothesis: Earth and Moon formed as a single object, and due to a very high rotation rate, the Earth spun off (rotational fission) the Moon–Explains composition similarity between Earth’s mantle and the Moon. But can this really happen based on physics?•NOPE: No reason for Earth to spin that fast, and even if it did, the spun off object wouldn’t have a stable orbitNeed an explanation that accounts for chemical similarity to Earth’s mantle and overall iron deficiency… Composition and density…Nope!Origin of the MoonCurrent Idea•Giant Impact Hypothesis: When the Earth was still young and molten, it experienced a grazing impact with a Mars-sized protoplanet (dubbed Theia). The result was the current Earth and a Moon composed almost entirely of Earth and Theia mantle material–Explains composition similarity between Earth’s mantle and the Moon… also can really happen based on physics!Need an explanation that accounts for chemical similarity to Earth’s mantle and overall iron deficiency… Composition and density…Origin of the MoonGiant Impact HypothesisSnap shots of a Giant Impact Hypothesis simulation.Colors indicate composition.Blue – Silicates (Rock)Red – IronEnd of simulation is disk rock-rich, iron-poor disk of material (3x mass of Moon in this sim.) out of which the Moon will formCool Video of a sim. -1SwRI Simulation - 2From Canup et al., 2012, ScienceOrigin of the MoonGiant Impact HypothesisSimulation of Proto-Earth and Theia, a Mars-sized
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