INTERSTELLAR CLOUDSStars and planets form from interstellar clouds
Interstellar clouds contain Hydrogen and Helium gas with small amounts of other elements and dust
Orion Nebula
COLLAPSING CLOUDAt first density of interstellar gas is low
Gravity draws matter together until it is concentrated enough to form stars and planets
COLLAPSE ACCELERATESRotation causes cloud to spin faster and collapse to gradually accelerate - due to centripetal force
Rotation slows collapse in equatorial plane - flattened
Becomes rotating disk with dense [matter] at center - protostar
SUN IS FORMEDSun formed when dense [gas and dust] at center of rotating disk reached a temperature and pressure high enough to fuse Hydrogen into Helium
Rotating disk surrounding our young Sun became solar system
TEMP GRADIENTArea closest to center was warm, outer edge was cold
Results in different elements and compounds condensing at varying distances from sun - affects planet composition
PLANET COMPOSITIONInner planets rich in higher melting point elements
Outer planets composed of lighter, more volatile elements
Temp gradient is reason outer planets and their moons are mostly gases and ices, and inner planets are rocky and dense
PLANETS ARE FORMED
Tiny grains accumulate and merge to form large particles
Particles grow as grains collide - form planetesimals hundreds of km’s in diameter
Growth continues as planetesimals collide and merge to form planets
Called Nebular Theory
DEBRISDebris - material that remained after planets and satellites formed
Debris that didn’t crash into planets or get ejected from solar system became comets or asteroids
Most asteroids found b/w Jupiter and Mars in asteroid belt - held there by Jupiter’s gravitational force