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November 10.docx

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Wilfrid Laurier University
Shohini Ghose

November 10, 2011 Formation of the Solar System:  The nebular theory states that our solar system formed from the gravitational collapse of a giant interstellar gas cloud—the solar nebula  Kant and Laplace proposed the nebular hypothesis over two centuries ago  A large amount of evidence now supports this idea  Predictions of this theory have been accurate The Birth of the Solar System:  Solar nebula was initially a cold low density cloud of gas of diameter 100-200 AU  Collapse of the gas may have been triggered by a cosmic event such as the shock wave of a nebula Spinning Cloud:  Initial slow rotation speed of the cloud increased as the cloud contracted (ice skater)  The cloud heated up as it contracted  The sun formed at the center where temperatures and densities were highest Disks around other stars:  Observation of disks around other stars support the nebular hypothesis Motion in the Solar System:  The spinning disk explains the uniform motion observed in the solar system today planets all orbit the same direction of the spin of the disk they were formed from  Planets orbit in the same plane because of the flattening of the disk they were formed from Why are the two types of planets?  Inner part of disks are hotter than outer parts  Rock can be solid at much higher temperatures than ice  Inside the ice line (frost line): too hot for hydrogen compounds to form ices. Only rocks and metals can be solid  Out the ice line: cold enough for ices to form How did terrestrial planets form?  Small particles of rock and metal (seeds) were present inside the ice line  Planetesimals of rock and metal built up as these particles collided. This process is called accretion o Many smaller objects collected into just a few large ones o Computer simulations support this process o Meteorites provide evidence of early condensation  Gravity eventually assembled these planetesimals into terrestrial planets over a few million years  Heat cause melting and differentiation inside the planets How did Jovian planets form?  Ice could also form planetesimals outside the frost line  Larger planets may have been able to form from H and He gases by direct gravitational collapse without an accretion phase  Planets were large enough to draw in surrounding gas to form moons and rings What ended the era of planet formation?  Outflowing matter from the Sun – the solar wind – blew away the leftover gases Where did asteroids and planets come from?  Leftovers from the accretion process  Rocky asteroids inside frost line  Icy comets outside frost line beyond orbit of Pluto Asteroid Orbits:  Most asteroids orbit in a belt between Mars and Jupiter  Trojan asteroids follow Jupiter’s orbit  Rocky planetesimals between Mars and Jupiter did not accrete into a planet  Jupiter’s gravity stirred up asteroid orbits and prevented their accretion into a planet Origin of Meteorites:  Primitive: o About 4.6 billion years old o Accreted in the Solar nebula
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