Solar system


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Solar system

  1. 1. Making a Solar System
  2. 2. Learning Objectives What are the features of our Solar System? Where are asteroids, comets and each planet? Where is most of the mass? In what direction do planets orbit and rotate? How does the Nebular Theory explain our Solar System? If the Solar System forms from a ball (sphere) of gas, why do the planets orbit in a flat plane (the ecliptic)? What is the source of energy of the protosun? What key factor guides the types of planets that form at each distance from the Sun? What is the Frost Line? How do planets form from planetesimals? How do planetesimals relate to the Kuiper and Asteroid Belts? The Oort Cloud? The Period of Heavy Bombardment?
  3. 3. What is the Age of the Solar System? Earth: oldest rocks are 4.4 billion years Moon: oldest rocks are 4.5 billion years Mars: oldest rocks are 4.5 billion years Meteorites: oldest are 4.6 billion years Sun: fusion models based on energy output and how much of the Sunʼs hydrogen has been fused so far estimate an age of 4.5 billion years (next lecture) Age of Solar System is around 4.6 billion years old
  4. 4. Solar Nebula Theory Proposed by the German philosopher Immanuel Kant The Solar System formed from a spinning cloud of gas, dust, and ice  Mostly hydrogen and helium  4.6 billion years ago
  5. 5. Solar Nebula Theory In these clouds are small clumps that become gravitationally unstable The gas and dust has mass (thus gravity) Gravitational attraction between all particles pull them toward the center of the cloud, and the cloud contracts
  6. 6. But.. Not all the mass falls in directly. Why? The gas cloud (which is three-dimensional, of course so think of it as a ball) is spinning slightly. This causes the formation of a flattened structure as it collapses Forms a pancake-like disk, concentrated at the center, with a rotation in the original direction of spin
  7. 7. At the center of this mess… …the Sun begins to form As gas and dust fall towards the middle of the cloud of dust, their gravitational potential energy is turned into heat The stuff nearest the center starts to give off light and heat. This is the protosun Protosun forms in first 2-3 slides
  8. 8. But weʼre not finished yet… Because this is not yet the Sun as we know it. Its energy is still coming entirely from gravitational contraction Eventually, it becomes so hot and dense, fusion begins (hydrogen converts to helium, and energy is released) Initial contraction to hydrogen ignition takes about 100 million years Protosun forms in first 2-3 slides
  9. 9. Planet Formation in the Disk Heavy elements clump  Form dust grains Dust grains collide, stick together  Form planetesimals  Like asteroids & comets Big planetesimals attract small ones  Collisionsbuild up inner planets, outer planet cores
  10. 10. Why are the Planets Different? Temperature (and thus distance from the center of the cloud) is the key factor!
  11. 11. Why are the Planets Different?  Temperature is the key factor  Inner Solar System: Hot  Light elements (H, He) and “ices” vaporized  Blown out of the inner Solar System by the solar wind  Only heavy elements (iron etc.) left  Outer Solar System: Cold  Too cold to evaporate ices to space  Rock & ice “seeds” grew large enough to pull gasses (H, He) onto themselves
  12. 12. Formation of the Inner Planets The inner Solar System was too hot for ices and light gases to exist. Thus, planetesimals consisted entirely of heavy elements (they were just rocks) Planetesimals run into each other, then coalesce to form protoplanets Protoplanets accrete (attract) more planetesimals until almost all matter in inner Solar System is swept up
  13. 13. Formation of the Inner Planets Computer models show it takes a few hundred million years to form four inner planets The Sun would have begun fusion by then
  14. 14. Formation of the Outer Planets The process is initially very similar to the formation of the inner planets Since it is colder at this distance, ices can exist, and planetesimals consist of rock and ices. This leads to larger protoplanets, which ultimately become the rocky, icy cores of the outer planets Finally, because hydrogen and helium havenʼt been cleared from the area, the outer planets gravitationally attract huge amounts of these gases. Planets become much bigger than inner planets
  15. 15. Heavy Bombardment There were billions of planetesimals in the early Solar System Many collided with the young planets  Look at the Moon & Mercury  Period of heavy bombardment  Lasted for about the first 800 million years of the Solar System (after which most of the planetesimals had hit something or gone into stable orbits)
  16. 16. Fates of the Planetesimals Between Mars and Jupiter  Remain as the asteroids Near Jupiter & Saturn  Ejected from the Solar System Near Uranus & Neptune  Ejected to the Oort Cloud Beyond Neptune  Remain in the Kuiper Belt
  17. 17. Results Most stuff goes into the planets Asteroids and comets are left-over planetesimals  “Fossils” of Solar System birth The Solar System continues to evolve, but slower  Outer planets still contracting  Earth and Venus are still volcanically active  Impacts from left-over planetesimals continue
  18. 18. The TheConstellation Orion Orion Nebula
  19. 19. Disks around Young Stars are Common
  20. 20. Next TimeOur Beacon: The Sun