Nebular
Theory:
Summary
Origin of the Asteroids
•The Solar wind cleared the leftover gas, but not the leftover
planetesimals.
•Those leftover rocky planetesimals which did not accrete onto a
planet are the present-day asteroids.
•Most inhabit the asteroid belt between Mars & Jupiter.
–Jupiter’s gravity prevented a planet from forming there.
Origin of the Comets
•The leftover icy
planetesimals are the
present-day comets.
•Those which were
located between the
Jovian planets, if not
captured, were
gravitationally flung in
all directions into the
Oort cloud.
•Those beyond
Neptune’s orbit
remained in the ecliptic
plane in what we call
the Kuiper belt.
The nebular theory predicted the existence
of the Kuiper belt 40 years before it was
discovered!
Exceptions to the Rules
•There were many more leftover planetesimals than we
see today.
• Most of them collided with the newly-formed planets
& moons during the first few 108 years of the Solar
System.
• We call this the heavy bombardment period.
So how does the nebular theory deal with exceptions,
i.e. data which do not fit the model’s predictions?
