Gas in the solar nebula was mostly hydrogen and helium, but there were trace amounts of hydrogen compounds, rock, and metals
Inner parts of disk are “hotter” than outer parts
Rocks can be solid at much higher temperatures than ice
Inside the “frost line” too hot for hydrogen compounds to form
Outside the “frost line ” cold enough for gases and ices to condense
.2% 1,000 – 1,600 K Iron (Fe), Nickel (Ni), Aluminum (Al) Metals .4% 500 – 1300 K Various Rock 1.4% < 150 K Water (H20), Methane (CH4), Ammonia (NH3) Hydrogen Compounds 98% Do not condense in nebula Hydrogen (H), Helium (He) Hydrogen and Helium Gas Relative Abundance in Solar System Condensation Temperature Examples
Terrestrial planets (Mercury, Venus, Earth, and Mars) all formed 0.3 AU from the sun.
Rock could condense beyond this distance
Jovian planets (Jupiter, Saturn, Uranus, and Neptune) all formed beyond the frost line (3.5 AU)
Hydrogen compounds formed the cores of these planets
Continues to support nebular theory
What about planet orbits?
But more questions remain
Earth formation Nebula forms out of H, He clouds and fusion products from now dead stars. Gravity pulls gas and dust inward, and rotation makes a accretionary disk. The proto-sun is at the center and fusion begins when it is hot enough. Heavier elements concentrate in the inner rings. Collisions and gravitational attraction leads to the formation of planetesimals. Gravity reshapes the proto-Earth into a sphere Soon after Earth formed, a Mars-size planet collided with Earth, blasting debris into space that will form our Moon. Volcanic gases form the atmosphere, and as Earth cools, moisture condenses and rains into oceans. Some gases may have come from passing comets.