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Origin of Our Solar System TEK Objective 5: Earth in space and time. The student understands the solar nebular accretionary disk model. The student is expected to: analyze how gravitational condensation of solar nebular gas and dust can lead to the accretion of planetesimals and protoplanets; Where did we come from? Two Main Theories Sun-like stars usually take around 100 million years to form. Nebula are star “nurseries”, where stars are born. This nebular photograph was taken by the Hubble Space Telescope A nebula is the product of a supernova event. The death of one system, may well be the birth of another! The Nebular Hypothesis In 1755 Immanuel Kant proposed that a solar nebulae was pulled together by gravity so that it collapsed into a flat, rotating disk that eventually coalesced into the Sun and planets Solar nebulae are huge clouds of dust and gas The Nebular Hypothesis Laplace stated that after the matter split off, it coalesced into a planet. The process repeated itself, resulting in a planet each time. The matter left over was the Sun. Much like a figure skater. You may have noticed that skaters can spin much faster if they pull their arms closer to their bodies. The more concentrated their body masses are, the faster they'll be able to rotate. Problems With the Nebular Hypothesis Used a flat, rotating nebula as the Solar System's origin to explain why all the planets orbit in nearly the same plane and in the same direction All planets revolve around the Sun in a counterclockwise direction within a 7° band of the equatorial region of the Sun, and nearly all of them also turn on their individual axes in a counterclockwise direction as well. Contradicted the observation that the Sun contains most of the Solar System's mass but only a small fraction of its angular momentum. Angular momentum is the measure of the tendency of a rotating body to remain rotating Problems With the Nebular Hypothesis If rings of matter were split off, as Laplace stated, they wouldn't be pulled together to form planets but would disperse into space. Process of Nebular Accretion Disk Formation Hypothesis Starts with Solar Nebulae Disturbance (possibly a Supernova) cause gradual collapse of Solar Nebulae Gravity causes cloud to shrink and compress the center which begins to heat up Accretion disk forms as matter spins around the center and forms a flat disk Thermal energy evaporates the disk Process of Nebular Nebular Accretion Disk Formation Hypothesis Protostar forms with opaque core Energy is given off by protostar causing a cooling Cooling causes gas to condense into tiny specs of metal, rock, & ice “Stellar Debris” Stellar Debris begins to stick together Protoplanet – small body to that form Planetesimalscould later form a planet Accrection of Planetesimals forms Protoplanets Accretion – gradual growth of planets by theinto accumulation Some Planetsimals will form asteroids,of other smaller bodies comets, and moons The Protoplanet Hypothesis Because of faults in the nebular hypothesis, other After many failures, such as the explanations of encounter theory, planet formation astronomers were sought. returned to the nebular hypothesis to find improvements during the mid 1900s. The Protoplanet Hypothesis Formed independently by Carl von Weizsacker Gerard Kuiper The The solar system begins to Protoplanet form as aHypothesis rotating cloud, or nebulae, collapses Instabilities in the nebulae cause dust particles to stick together and accrete into billions of planetesimals with diameters of about 10 meters. The planetesimals then collide and form protoplanets. Meanwhile, the protosun in the center of the nebular disk becomes massive and hot enough to "turn on" by fusing hydrogen. The Sun begins to radiate energy and vaporize dust in the inner part of the Solar System. The remaining gas is blown away by solar winds.