Our Solar System and Its Origin

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Oort Cloud

Long Period Comets (period > 200 years) seems to come mostly from a spherical region at about 50,000 AU from the Sun.

NASA Figure

Slide 10

Common Characteristics and Exceptions of the Solar System

We need to be able to explain all these!

Slide 11

Common Characteristics and Exceptions

Slide 12

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…

Slide 13

The Nebular Theory* of Solar System Formation

Interstellar Cloud (Nebula)

*It is also called the ‘Protoplanet Theory’.

Slide 14

A Pictorial History

Gravitational Collapse

Accretion

Nabular Capture

Interplanetary Cloud

Condensation

Slide 15

The Interstellar Clouds

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)

Slide 16

Collapse of the Solar Nebula

Gravitational Collapse

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