10 Chapter 10 – How did the planets form?
OpenStax Astronomy Chapter 7 & Chapter 14
Disks and Angular Momentum
I. Disks
A. Protostars are surrounded by orbiting in a flat, rotating
1. Disk is formed at protostellar core collapses
B . in the disk:
1. Falls on the , making it bigger
2. Forms other bodies in the (planets, comets, etc.)
3. Gets back into interstellar
C. This disk for the formation of planets with of the Solar System
1. Planets orbit in a , so material they formed from was in a disk
2. All planets in same , so original material must have orbited in direction
3. Meteorites made of pieces, suggests formed out of small pieces too
II. How disks
A. protostellar core due to
1. for particles along the of spin (top/bottom) to toward the center
2. for particles to fall in from
What happens to the gravitational energy of gas as it falls toward and eventually hits the disk surrounding a protostar?
A. It is converted into thermal energy, heating the disk.
B. It is converted into light energy, giving off a flash of light upon impact.
C. It is converted into potential energy as the gas plows through the disk and comes out the other side.
D. It simply dissipates.
B. : Flat , a shrinking sphere
1. Example:
C. Disk and out because of the of angular momentum
III. Aside: What is ? (Section 3.2)
A. Momentum of something or in orbit
B. on:
1. How it is rotating (velocity)
2. of object
3. How object is (radius)
4. Angular Momentum = mass × velocity × radius (L = mvr)
C. of Angular Momentum
1. of angular momentum
2. doesn’t disappear, must somewhere
3. For an object (mass doesn’t change), when (spreads out) and vice versa
4. Example:
Planet Formation
IV.
A. In disk, particles of dust and gas will collide slowly and together
1. Due to
2. Works for particles from dust grain up to size
B. of particles (bigger than boulders) smaller ones when they collide
1. Sometimes again, so not always uniform growth
C. Get even larger objects, more than 1 mile across, called (tiny planets)
1. pulls smaller particles of its path it
2. just chance collisions in direct path like with smaller particles
D. If planetesimals consume to clear their orbit, grow into
E. If some material in orbit, leftover planetesimals are called depending on size and location
Which of the following statements is FALSE?
The Protoplanetary Disk
Why are there rocky planets and gas planets in our Solar System?
V. Disk
A. Two parts: disk
B. are different
C. Disk is
1. Heated by
2. Heated by conversion of to thermal energy
D. Inner disk has only materials
1. Do at temperatures
2. materials, like Iron, Silicates, and Carbon
E. Disk is
1. Too from star to get much
F. Outer Disk contains and materials
1. melt or evaporate at temperatures
2. (water, ammonia, and methane) and light (Hydrogen and Helium)
VI.
A. Orbits a , Mass than 13 Jupiter masses, its orbit of debris
B. of the dust and of determines what planets are made of
C. planets are , made of materials
1. Planets: Mercury, Venus, Earth, Mars
D. planets have materials and like gas and ice
1. Giants: Jupiter, Saturn, Uranus, Neptune
E. Composition tells us where planet
1. But, planets can from where formed due to gravity of other planets
2. Example: , gas giants that orbit very close to their star
The difference in composition between the gas giant planets and the terrestrial planets is most likely caused by the fact that:
A. The giant planets are much larger
B. The terrestrial planets are magnetic
C. The terrestrial planets are closer to the Sun
D. The giant planets started out hotter
Tutorial Activity – Solar System Formation
(near/far from the sun or both).
2. What are Jovian (Giant) planets? List the Jovian planets and where they are located in the solar system.
3. Compare the terrestrial to Jovian planets (i.e. big/small in size, high/low density)
| Characteristic | Terrestrial Planets | Jovian Planets |
| Size and mass | ||
| Average density | ||
| Solid surface? | ||
| Temperature |
4. Consider some general characteristics of the orbits of the planets in the solar system.
(a) Do the planets orbit in random directions?
(b) Are the orbits highly elliptical or almost circular?
(a) Orderly motion of the planets and moons
(b) Why are there 2 types of planet (terrestrial and Jovian)? Let’s answer this in several parts:
i. What is the frost line and where do you think it is located?
ii. What did the terrestrial planets form from and why were they small?
iii. What did the Jovian planets form from and why were they large?
7. Suppose we find different planetary systems with the properties described. (These are not real
discoveries.) Decide whether the discovery should be considered reasonable or surprising in the context
of the disk theory. Explain your reasoning.
(a) System A has three large Jovian planets in its inner solar system and six small terrestrial planets
in its outer solar system.
(b) System B has six terrestrial planets in its inner solar system and four Jovian planets in its outer
solar system.
(c) System C has eight planets that all orbit in random directions and in different planes.
