ASTR 151 Chapter 6 Part 2
ASTR 151 Chapter 6 Part 2 ASTR 151 001
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This 3 page Class Notes was uploaded by Wesley Fowler on Friday March 25, 2016. The Class Notes belongs to ASTR 151 001 at a university taught by Dr. Sean Lindsay in Spring 2016. Since its upload, it has received 20 views.
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Date Created: 03/25/16
Wesley Fowler ASTR Chapter 6 Nebular Theory The nebular theory claims that the existing solar system was formed by the collapse of a giant cloud of interstellar gas and dust. 1. A cloud of gas and dust (nebula) exists 2. The nebula is compressed (by gravity, shockwave?) 3. Conservation of angular momentum causes nebula to rotate faster 4. The rotation speed causes the nebula to flatten into a disc called the Solar Nebula. It has a large central mass called the protosun 5. The dense materials (dust) in the Solar Nebula accrete together into planets and other solar system bodies Nebular theory is well supported by visual observation! Condensation Theory Condensation refers to the changing of phases, typically from gas to liquid. However, when dealing with the solar system, it’s from gas to solid. The planets and objects farther away from the sun are composed of more materials than the ones closer to the sun - This is called the compositional gradient of the solar system The planets and objects farther away from the sun have lower temperatures than the ones closer to the sun - This is called the temperature gradient of the solar system The temperature gradient of the early Solar Nebula explains why rocky planets formed close to the sun, while planets farther away remained gaseous. - Solid materials require higher temperatures to condense - Solid materials have higher densities than gaseous ones Hot: 1200-1500 K Warm: Around 500 K Cool: 200-300 K Cold: Around 50 K Ice Line: (T = 273 K) - Boundary in which icy grains can form Planet Building 1. Condensation of solids (Condensation Theory): Two grains of ice for each grain of rock - Inner SS: Rock and Metal grains available - Middle SS: Metal, Rock, and High T ices (e.g., water) - Outer SS: Metal, Rock , High and Low T ices 2. Accretion of solids: Grains clump together in the protostellar cloud - More material is available farther from the sun due to lower density, thus larger planets 3. Collection of solid grains into planetesimals: Grow from cm to km - Gravitational attraction begins when planetesimals reach 10-100km in size - Leftovers of these are asteroids! 4. Formation of protoplanets out of planetesimals: Begin to have strong gravitational force - 100 – 1000+ KM in size 5. Combination of protoplanets via collision - How we think the moon was formed, why Venus rotates “backwards” This process explains how terrestrial planets, rocky cores of gaseous planets, and other SS objects are formed. The sequence takes about 100 million years. Core-Accretion Theory Much larger protoplanets form beyond the ice line due to the abundance of materials that have not condensed. - Gas giant planets have solid cores that have an immense gravitational force. These cores attract huge amount of gas from the nebula itself, and thus become massive. The core-accretion theory is disapproved of by many scientists, as the time required for the exceeds beyond the lifetime of solar nebula Gravitational Instability Theory The giant gaseous planets formed in a very similar way that the Solar nebula did, with gases from the original nebula condensing into planets The gravitational instability theory is disapproved of by many scientists because there is simply not enough mass in the solar disc to cause this type of gravitational collapse. The core-accretion theory is currently better supported than the gravitation instability theory. Clearing the Disk Strong solar winds blow interstellar dust, gas, and leftover planetesimals out of the solar system. This isolates and defines the specific planets and interstellar objects