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Chapter 6b Clues to the Origin of the Solar System The Birth of the Solar System 1. The Solar Nebula Motions Clues for the Model ! Planets revolve about Sun in same direction. ! Planets revolve about Sun in a common plane. ! Sun also rotates in the same direction. Summary of steps Composition 2. The collapse Start of Collapse Stages of Collapse Angular momentum 3. Proto Stars Proto Stars Stellar Disk T-Tauri Winds Inner Planets variable star LL Orionis Nebular theory Early attempt: A cloud of gas broke into rings and condensed to form planets. There were doubts about the stability of such rings! Observations suggest that the Sun and planets formed together from a spinning cloud of dust and gas---The Solar Nebula. Composition ! Sun, Jupiter, and Saturn have same hydrogen dominated composition implying they formed from the same materials. ! Terrestrial planets and satellites are deficient in light gases and ices. Formed too close to Sun for gases/ices to remain, leaving heavier rock and metal. Sec 1 Outer Planets General steps BIRTH PLACE OF STARS Orion Nebula M42 Giant molecular clouds The Orion Nebula is at the edge of an immense interstellar molecular cloud only 1,500 light-years away--the nearest large star-forming region. Catastrophic theories Scientists then considered accidental or unlikely celestial events such as close encounter of the sun with a star? Such encounters are quite rare and the hot gases would dissipate rather than condense to planets The cloud is roughly Condensation theory 90 % hydrogen, Added effects of interstellar dust to the nebular theory. The dust help cool the nebula and acts to allow the condensation of particles 9 % helium with of else small Composition amounts of everything (like iron, carbon, oxygen, inter stellar gas...).and Sec 1 dust Sec 1 Supernova Supernova creates a shock wave that pushes on nearby nebula The initial collapse takes less than 100,000 years. shock wave Cloud of gas and dust contracts due to gravity; Conservation of angular momentum This large swirling cloud that formed the Solar System is referred to as the Solar Nebula . As the cloud collapses, it heats up and compresses in the center. Collapsing gas and dust heats through collisions to around 3000 K so everything in gaseous form ProtoStars The cloud flattens to a disk due to rotation The Eagle Nebula ProtoStars The protostar is likely to be surrounded by a remnant of the cloud from which it formed. -- ultimately creating the comet-shaped clouds of glowing gas Proto star (T Tauri Phase) The star is bursting out of its dusty shell driven by the central heat and strong T Tauri Winds. protostars. Gas molecules and dust grains in circular orbits --those on noncircular orbits collide with particles and eventually dampen noncircular motion. Ultraviolet radiation from the star and nearby hot stars rapidly destroys the cloud Eventually the star completes its contraction, where it begins to burn hydrogen Formation of Terrestrial and Jovian Small dust grains in the disk collide and coalesce. This process continues until the clumps are a few hundred kilometers across. At this time the objects are referred to as planetesimals. ! outer gas cooler than the inner gas !metal stuff can condense (freeze) at high temperatures while volatile stuff condenses at lower temps !at Jupiter temperature cool enough to freeze water further out ammonia and methane freezing out Asteroid belt: remains of rocky planetesimals. There could have been a planet but it never formed due to the effect of Jupiter The gravity of the planetesimals is large enough to start attracting other planetesimals and so form larger bodies. Kuiper Belt 3 2 Jupiter can capture comets or eject comets from the solar system. Oort Cloud 4 1 5 6 Ejections of Comets End of Chapter 6b The Solar System Go to Chapter 7a