1. Nebular Theory 9/4/2015

2. © 2005 Pearson Education Inc., publishing as Addison-Wesley Nebular Theory of the Solar System 1.Large bodies in the Solar System have orderly motions. 2.There are three types of planets. –small, rocky terrestrial planets –large, hydrogen-rich Jovian planets –tiny, rocky/icy Dwarf planets (tends to be irregular) 3.Asteroids & comets exist in certain regions of the Solar System

3. © 2005 Pearson Education Inc., publishing as Addison-Wesley The Solar Nebula The nebular theory holds that our Solar System formed out of a nebula (name given to the cloud of gas from where our Solar System formed) which collapsed under its own gravity. Evidence: – We can observe stars forming in interstellar clouds of gas. – The Orion Nebula shown has newborn solar systems in it!

4. The Nebular Theory of Solar System Solar NebulaProtoplanetary DiskProtosun Gravitational Collapse Terrestrial Planets Accretion Jovian Planets Asteroids Comets Leftover Materials Metal, Rocks Condensing Phase Sun Gases, Ice Heating &  Fusion Gravity Leftover Materials

5. © 2005 Pearson Education Inc., publishing as Addison-Wesley Gravitational Collapse The early stages of our solar nebula: – very cold – somewhat spherical – few lights years in diameter – rotating slightly It was given a “push” by an event. https://www.youtube.com/watch?v=RgfbjHz_UTo https://www.youtube.com/watch?v=RgfbjHz_UTo – perhaps the shock wave from a nearby supernova

6. © 2005 Pearson Education Inc., publishing as Addison-Wesley As the nebula shrank due to instability, gravity increased, causing collapse. As the nebula “falls” inward, gravitational energy is converted to heat. As the nebula’s radius decreases, it rotates faster Conservation of Angular Momentum Conservation of Angular Momentum Gravitational Collapse

7. © 2005 Pearson Education Inc., publishing as Addison-Wesley Flattening of the Solar Nebula As the nebula collapses, clumps of gas collide & merge. The spinning nebula assumes the shape of a disk.

8. © 2005 Pearson Education Inc., publishing as Addison-Wesley Why does the cloud spin? It’s part of a spinning galaxy—lots of angular momentum available Particles closer to the center of galaxy move more rapidly than particles farther away… speed decreases with distance. As a shock wave and then gravity compress the cloud, some of the momentum from the galactic disc creates an interstellar cloud This is similar to the formation of cyclones and hurricanes in our atmosphere.

9. © 2005 Pearson Education Inc., publishing as Addison-Wesley Rotating disk with collapsing cloud Particles orbit center of cloud because of gravity while the center is rotating. The cloud and the particles around it are also rotating. Particles on outside rotate more slowly than material on inside. Disk begins to swirl.

10. © 2005 Pearson Education Inc., publishing as Addison-Wesley Collapse of the Solar Nebula http://hubblesite.org/hubble_discoveries/discovering_pla nets_beyond/how-do-planets-form

11. © 2005 Pearson Education Inc., publishing as Addison-Wesley Orderly Motions in the Solar System The Sun formed in the very center of the nebula. – temperature & density were high enough for nuclear fusion reactions to begin The planets formed in the rest of the disk.

12. © 2005 Pearson Education Inc., publishing as Addison-Wesley More Support for the Nebular Theory We have observed disks around other stars. These could be new planetary systems in formation. Proto-Solar systems in the Orion Nebula!