The Formation of the Solar System
and Extrasolar Planets

As we finish our discussion of the Solar System, there are a few questions that should be addressed

Formation of the Solar System

• Any model of the formation of the Solar System must satisfy at least three facts known from observation.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
• Based on these facts, it is believed that the formation of the solar system was a natural consequence of the formation of the Sun, and passed through three general stages:

 
1. Gas and Dust Stage:

As the solar nebula contracted under its own gravity, the material that did not go into the protosun
 
 
 
 

Material at the inner part of the disk
 
 
 

2. The Middle Stage:

The disk material is composed of
 
 
 
 

This stage must be completed before
 
 
 

3. The Final Stage:

At the end of the Middle Stage, there would be
 
 
 
 

The bodies would
 
 
 
 
 

• How do theoretical computations and observations compare with these ideas?

 

 
 
 
 
 
 
 
 
 

Detection of ExtraSolar Planets

In the last decade, observations seem to indicate that planets around other stars are common.

You might think that to find a planet orbiting another star, all you have to do is look through a big telescope, but it's not so simple. These are perhaps the most difficult observations done in astronomy today.
 

• Why is it so difficult to observe extrasolar planets? Consider an Earth-sized planet orbiting a star just like the Sun 100 light-years away:

 

 
 









1. What is the angular separation between the planet and the star?  . . . group project.

 

 
 
 
 
 
 
 
 
 
 
 

2. If the planet shines by reflected light, how much fainter is it than the star?  . . . another group project.

 

 
 
 
 
 
 
 
 
 
 
 

• So how can we detect extrasolar planets?

 

 
 
 
 
 

When we talked about planetary orbits, we did didn't tell the whole story! When a planet orbits a star:











So when a star has a planet orbiting around it, we should be able to detect
 
 

If this is observed, then we can infer the presence of a planet.
. . . Do you know the difference between deduce and infer?
 
 
 

• What is found?

 

 
 
 
 
 

A summary of possible extra-solar planets (as of October 1998):






• Some Remarks:

 
1. Why do we detect only Jupiter-sized planets close to stars?

 

 
 
 
 
 
 
 
 
 
 

2. Are other explanations of the observations possible?

 

 
 
 
 
 
 
 
 
 
 

3. Can we improve the observations?