Look at slides summary of parts 1 3 why are there two

Look at slides; summary of parts 1-3
 Why are there two major types of planets? Need to understand heating of the solar nebula
o As the nebula contracts, gravitational potential energy is converted into kinetic
energy (conservation of energy)
 The motion of atoms is accelerated by gravity as its atoms fall in is
randomized via collisions, increasing thermal energy (becomes hotter) at
expense of gravitational potential energy
 Another way to look at it is that gravity is compressing the nebula, and
when you compress a gas it heats up
o The sun is formed at the center of the disk, since gas contracts toward the center
and density builds up there
o Nebula became hottest in the center, where the sun is formed, because most
gravitational potential energy is released at smallest distances, due to gravitational
force increasing as inverse square of distance
o Since the heating source (the sun) was in the center, the nebular disk was hotter in
the center and cooler in the outer parts far from the sun
 Main ingredients (composition of nebular also called interstellar) gas
o Hydrogen and helium gas, hydrogen compounds, rock, and metal
o Condensation temperature and abundance are both relevant
 Why are there two major types of planets? (The Frost Line)

 How did the terrestrial planets form?
 Accretion of Planetesimals
 Why did the Jovian planets get so big?
 How did the Jovian moons form?
 Asteroids and comets: leftovers from accretion
o Rocky planetesimals formed inside frost line
 Most collected into terrestrial planets
 But closer to Jupiter, Jupiter’s gravity stirs things up, keeping
planetesimals from collecting into a planet
 These are the asteroids, mostly found in the asteroid belt
 Icy planetesimals from outside frost line
 Most accreted and became Jovian planets
 But some were scattered into the inner solar system, colliding with
sun or terrestrial planets
 And some were ejected into the Oort Cloud (comets)
 Details: Heavy bombardment
o Leftover planetesimals (asteroids and comets) bombarded planets in the late
stages of solar system formation, with many consequences
 Details: Origin of Earth’s water
o Water probably came to Earth after its formation by way of icy planetesimals
(comets) during bombardment period
 Captured moons
o Lecture slides

2/27: The Age of the Solar System
 Elements
o