Long Period Comets (period > 200 years) seems to come mostly from a spherical region at about 50,000 AU from the Sun.
Common Characteristics and Exceptions of the Solar System
We need to be able to explain all these!
Planetary Nebula or Close Encounter?
Historically, two hypothesis were put forward to explain the formation of the solar system….
Gravitational Collapse of Planetary Nebula (Latin for “cloud”)
Solar system formed form gravitational collapse of an interstellar cloud or gas
Close Encounter (of the Sun with another star)
Planets are formed from debris pulled out of the Sun during a close encounter with another star. But, it cannot account for
The angular momentum distribution in the solar system,
Probability for such encounter is small in our neighborhood…
The Nebular Theory* of Solar System Formation
Interstellar Cloud (Nebula)
*It is also called the ‘Protoplanet Theory’.
A Pictorial History
The primordial gas after the Big Bang has very low heavy metal content (Chapter 17)…
The interstellar clouds that the solar system was built from gas that has gone through several star-gas-star cycles. (Chapter 12)
Heating Prototsun Sun
In-falling materials loses gravitational potential energy, which were converted into kinetic energy. The dense materials collides with each other, causing the gas to heat up. Once the temperature and density gets high enough for nuclear fusion to start, a star is born.
Spinning Smoothing of the random motions
Conservation of angular momentum causes the in-falling material to spin faster and faster as they get closer to the center of the collapsing cloud. demonstration
Flattening Protoplanetary disk. Check out the animation in the e-book!
The solar nebular flattened into a flat disk. Collision between clumps of material turns the random, chaotic motion into a orderly rotating disk.
This process explains the orderly motion of