MASON ASTR 111 - Comparative Planetology II: The Origin of Our Solar System

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Comparative Planetology II: The Origin of Our Solar SystemIntroduction To Modern Astronomy I: Solar SystemConstrains on ModelsOrigin of Chemical ElementsOrigin of Chemical ElementsIntroduction To Modern Astronomy I: Solar SystemThe age of Solar SystemThe age of Solar SystemSolar Nebula HypothesisSolar Nebula HypothesisSolar Nebula HypothesisSolar Nebula HypothesisFormation of PlanetsFormation of PlanetsFormation of Terrestrial PlanetsFormation of Terrestrial PlanetsFormation of Jovian Planets Extrasolar PlanetsExtrasolar Planets Final Notes on Chap. 8Advanced Question Chap. 8, Q31 in P206Comparative Comparative PlanetologyPlanetologyII:II:The Origin of Our Solar SystemThe Origin of Our Solar SystemChapter EightASTR 111 – 003 Fall 2007Lecture 07 Oct. 15, 2007Introducing Astronomy (chap. 1-6)Introduction To Modern Astronomy I:Solar SystemPlanets and Moons (chap. 7-15)Chap. 16:Chap. 28:Ch7: Comparative Planetology ICh8: Comparative Planetology II:The Origin of Our Solar SystemCh9: The Living EarthCh10: Our Barren MoonCh11: Earthlike PlanetsCh12: Jupiter and SaturnCh13: Satellites of Jupiter & SaturnCh14: Uranus, Neptune and BeyondCh15: Vagabonds of Solar SystemConstrains on Models• Any theoretical models must be able to explain the observed properties of the present-day planets1. The terrestrial planets, which are composed primarily of rocky substances, are relatively small, while the Jovianplanets, which are composed primarily of hydrogen and helium, are relatively large2. All of the planets orbit the Sun in the same direction, and all of their orbits are in nearly the same plane3. The terrestrial planets orbit close to the Sun, while the Jovian planets orbit far from the SunOrigin of Chemical Elements• Composition of the solar system (by mass)– Dominated by hydrogen (H, 71%) and helium (He, 27%)– All other chemical elements, combined, make up the remaining 2%, e.g., oxygen (O), carbon (C), nitrogen (N), Iron (Fe), silicon (Si).– For each 1012H atoms, 1011He, 8.5X108O, 6 gold atomAbundances in the Solar System (by number)• Hydrogen and helium atoms were produced in the Big Bang that happened 13.7 billion years ago.• All heavier elements were manufactured by stars later.– Thermal-nuclear fusion reaction in the interior of stars– Supernova explosions. • As it dies, a star ejects a large amount of material containing heavy elements into the interstellar medium• New stars form from the enriched interstellar medium, and have the similar abundance as the interstellar medium.• Solar system contains “recycled” heavy elements from stars that died long ago.Origin of Chemical ElementsASTR 111 – 003 Fall 2007Lecture 08 Oct. 22, 2007Introducing Astronomy (chap. 1-6)Introduction To Modern Astronomy I:Solar SystemPlanets and Moons (chap. 7-15)Chap. 16:Chap. 28:Ch7: Comparative Planetology ICh8: Comparative Planetology II:The Origin of Our Solar SystemCh9: The Living EarthCh10: Our Barren MoonCh11: Earthlike PlanetsCh12: Jupiter and SaturnCh13: Satellites of Jupiter & SaturnCh14: Uranus, Neptune and BeyondCh15: Vagabonds of Solar SystemThe age of Solar System• The solar system is believed to be about 4.56 billion years old• Radioactive dating is used to determine the ages of rocks– Radioactive elements decay into other elements or isotopes– The decay rate, measured in half life, is constant for radioactive element. • e.g., Carbon 14 (-> Nitrogen 14): 5730 years; • e.g., Uranimum 238 (-> Lead 206): 4.5 billion year– By measuring the numbers of the radioactive elements and the newly-created elements by the decay, one can calculate the age• All Meteorites show nearly the same age, about 4.56 billion years.– Meteorites are the oldest rocks found anywhere in the solar system– They are the bits of meteoroids that survive passing through the Earth’s atmosphere and land on our planet’s surface• On the Earth, most rocks are only hundreds of millions of years old.• Moon rocks are also about 4.5 billion years oldThe age of Solar SystemSolar Nebula Hypothesis• Hypothesis: the Sun and planets formed from a common solar nebula.• Solar nebula is a vast, rotating cloud of gas and dustin the interstellar space• It is so far the most successful model of the origin of the solar system.A common rotating cloud explains why all planets orbit the Sun in the same direction.0803002.movFLASH• The nebula began to contract about 4.5 billion years ago, under its own gravity• Protosun: as it contracted, the greatest concentration occurred at the center of the nebula, forming a relatively dense region called the protosun• The protosun’ temperature continued to climb, because of the conversion of gravitational energy into thermal energy• Eventually (~10 million years), the center temperature reached ~ 2 million Kelvin, and nuclear reaction ignited, and contraction stopped.• Nuclear reactions continue to the present day in the interior of the Sun.Solar Nebula Hypothesis• Protoplanetary disk: At it contracted, the cloud flattened and spun more rapidly around its rotation axis, forming a disk surrounding the protosun.• It spun faster because of the conservation of angular momentumSolar Nebula Hypothesis• The flattened disk is also an effect of the rotation of the nebula. Solar Nebula Hypothesis• The centrifugal force of the rotation slows down the material on the plane perpendicular to the rotational axis fall toward the center• But the centrifugal force has no effect on the contraction along the rotational axisProto-stars and Proto-planetary disks in Orion Nebula• A substance is in the sate of either solid or gas, but not in liquid, if the pressure is low, such as in the atmosphere• Condensation temperature determines whether a certain substance is a solid or a gas. – Above the condensation temperature, gas state– Below the condensation temperature, solid sate• Hydrogen and Helium: always in gas state, because concentration temperatures close to absolute zero• Substances such as water (H2O), methane (CH4) and ammonia (NH3) have low concentration temperature, ranging from 100 K to 300 K– In solid state, they form ice particles• Rock-forming substances have concentration temperatures from 1300 K to 1600 K– Through collision and merge, they form dust grainFormation of Planets• In the nebula, temperature decreases with increasing distance from the center of the nebula• In the


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MASON ASTR 111 - Comparative Planetology II: The Origin of Our Solar System

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