as101 lesson 8
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30 Terms
Sources of universe’s first elements
Big Bang produced mostly hydrogen, helium, and a little lithium
Sources of heavier elements
Made in stars and spread when stars die
Galactic recycling
Old stars eject heavy elements that become part of new stars and planets
Trigger for solar system formation
Probably shock wave from nearby nova or supernova
Solar nebular theory
Solar system formed from collapsing cloud of gas and dust
Three main nebular processes
Heating, spinning faster, flattening into disk
Why nebula heated up
Infalling material gained kinetic energy as it collapsed
Why nebula spun faster
Conservation of angular momentum
Why nebula flattened into disk
Natural result of rotation during collapse
Nebular theory explains
Planets orbit in same direction, same plane, and mostly circular orbits
Temperature gradient
Inner nebula hotter, outer nebula cooler
Why inner planets became terrestrial
Only rock and metal could condense close to Sun
Why outer planets became jovian
Beyond frost line ices could condense and build massive cores
Frost line (ice line)
Distance from Sun beyond which water and other volatiles could freeze
Planetesimal
Kilometre-sized building block of planets
How planetesimals formed
Condensation + accretion of small particles
Condensation
Atoms/molecules added to growing grains
Accretion
Small solid particles stuck together to make larger bodies
Inner planetesimals composition
Mostly rock and metal
Outer planetesimals composition
Rock, metal, and lots of ice
Asteroids
Rocky/metallic leftover planetesimals
Comets
Icy leftover planetesimals with dust and rock
Solar wind
Stream of charged particles from young Sun
Effect of solar wind
Blew out leftover gas and dust from solar system
Why jovian planets grew larger
Ice-rich cores formed beyond frost line and captured lots of gas
Why terrestrial planets stayed smaller
Only rock/metal available in hot inner solar system
Heavy bombardment
Leftover debris kept striking planets early in solar system history
Kuiper Belt
Region beyond Neptune holding many icy bodies/comets
Oort Cloud
Distant spherical reservoir of comets
Nebular theory best fits solar system because
Explains major solar system features better than rival ide