The formation of the solar system began from a large cloud of gas and dust called the solar nebula. As the nebula collapsed due to gravity, it formed a disc with the sun at the center. Planetesimals within the disc collided and accreted to form the planets. The nebular theory explained many characteristics of the solar system but did not account for all observations. The modern condensation theory expanded on this model and better explained features such as the asteroid belt and comets through processes like condensation and fractionation within the early solar system.

1. Formation of the Solar System
1) The Nebular Theory: The theory that our solar
system formed from a swirling mass of gas and dust.
a. Nebula: Any large cloud of interstellar gas and dust.
b. The Nebular theory was one of the first heliocentric
theories for the formation of the solar system.
c. In Nebular Theory, a nebula (called the solar nebula),
collapsed in on its own gravity, forming a disc. Over time
the disc developed Protoplanets in rings around a Protosun,
a hot ball of gas well on its way to becoming the sun.
d. Over time the material clumped together further to form the
planets and eventually the sun.

2. e. What this Explained
- Almost all objects formed in the same disc they all
now revolve in the plane of the ecliptic
- Almost objects rotate the same direction (except
Venus) as the sun rotates on its axis.
- Almost all objects revolve around the sun in the
same direction the sun rotates
f. What this didn't explain
- Why the solar system is highly differentiated
- The existence of the Asteroid Belt.
- The existence of Comets

3. 2. Condensation Theory: The modern version of the
Nebular Theory.
A. The solar system formed from a large
spinning cloud of gas and dust, called the
solar nebula.
B. Once gravity pulled it to a diameter of less
then 100au, the solar nebula had become a
wide rotating disc.

4. C. Planet Formation
1) Accretion: The process by which dust particles
stick together to form larger partials, called
planetesimals about the size of small moons.
Imagine a snowball thrown through a blizzard.
Getting larger as it hits other snowflakes
2) Planetesimals collided and formed larger
bodies called protoplanets.
3) The four largest protoplanets became the Jovian
planets and the four smallest the Terrestrial Planets.

5. D. Differentiation of the Solar System:
1) As the cloud of gas and dust colapsed into a disc,
it heated up.
Hottest near the protosun
Cooler as you move away from the protosun

6. Graph of Temperature vs. Distance from the sun.

7. 2) Condensation: The process of going from a
gas to a solid or liquid. This temperature is
different for different materials!!
- In general, denser materials can condense at higher
temperatures.
Metals
Rocky materials
Water Ice Ammonia
(Frost Line)

8. 3) The order in which materials condensed in the
early solar system is called the Condensation
Sequence.
4) This determined what the solid portion of
planetesimals (and later planets) were composed
of.
Metals
Rocky materials
Water Ice Ammonia
(Frost Line)

9. D. Differentiation of the Solar System (continued)
5) Formation of Asteroids
- When planetesimals collide with high relative
velocity (very fast head-on collisions) they broke
apart rather then coalesced.
- This process is called Fractionation
- The material between Jupiter and mars is given
high relative velocities by the pull of Jupiter's
gravity.
6) Formation of Comets
- Comets form beyond the frost-line in the same way
as asteroids.
- The combined gravity of all the Jovian planets
causes the Fractionation

10. 7) Location of Comets
a. The majority of comets are found in the Oort
Cloud.
b. The Oort Cloud is tens of thousands of AU across
& and comets in this region have a period of no less
then 200 years.
c. Beyond the orbit of Neptune is the Kuiper Belt
which contains many of the shorter period comets.
8) the Role of Comets in planet formation
a. During accretion there were thousands of times
more comets that had not been swept up by the
protoplanets.
b. remember that water could not condense out in for
the terrestrial planets. Impacts from Comets helps
account for this irregularity.

11. E. Formation of Moons
1) Captured Moons
a. When asteroids or comets pass too close to
a planet they get captured by that planets
gravitational pull.
b. Often these are temporary moons and
escape after thousands or millions of years.
c. Include the two moons of Mars (Phobos and
Deimos) and the majority of outer planet
moons.

12. 2. Naturally Forming Jovian Moons
a. Beyond the frost line there was much more
material to form large bodies.
b. Each of the Jovian planets formed a mini-accretion
disc in a plane perpendicular to their axis of rotation.
c. In this disc moons formed in a process very similar
to the formation of the planets.
d. These systems of moons even underwent a small
scale version of differentiation around their parent
planets.

13. 3. Formation of Earth's Moon (Giant Impact Hypothesis)
a. Planets located inside of the Frost-Line did not
have enough material to form their own accretion
discs.
b. About 4 billion years ago, an object roughly the
size of mars colided with the Proto-Earth.
c. A great deal of material was flung off into space
around the earth which formed an accretion disc.
d. The moon formed as these materials coalesced.

17. E. Survey of The Solar Systems Moons
1. The Galilean Moons (Jupiter's first four)
a. Io
- The most volcanically active body in the solar system.
- Heat is generated by the tidal forces between Jupiter and Io
b. Europa
- Has massive amounts of water in the form of ice covering the
surface.
- Some scientists have speculated that tidal forces may heat the
interior to the point of having a liquid ocean.
c. Ganymede
- Largest moon in the solar system (slightly larger then Mercury)
- Composed mostly of water and ammonia ices with a small rocky
core.
d. Callisto
- Similar in composition to Ganymede
- Most striking feature is a large crater surrounded by concentric
circles.

18. 2) Moons of Saturn & Neptune
a. Titan (Saturn)
- The largest of Saturn's moons
- Similar in composition to Ganymede & Callisto
- Has a thick Nitrogen-Argon atmosphere with traces of
Methane.
- Retains its atmosphere because of its low temperature
b. Triton (Neptune)
- Smallest of the 6 largest moons
- Orbits retrograde around Neptune
- Retrograde orbit may be the result of a large impact or
Triton may be a captured moon.

19. 2) Moons of Mars
a. Deimos (Panic) & Phobos (Fear)
- Deimos is about 28km long and 20km wide
- Phobos is about 16km long and 10km wide
- Named after the horses that pulled the chariot of the
Roman god of war (Mars).
- Very different in composition to Mars indicating that they
did not form with the planet.
- Most likely were asteroids that were slowed by the early
Martian atmosphere and were captured.

20. F. Lunar History (Four Stages)
1) Differentiation
a. As the moon accreted it increased in
temperature.
b. The newborn moon was entirely liquid. This
was supported by examining rocks brought
back from the Apollo landings.
c. Because it was liquid denser materials sank
to the core lighter materials to the surface
forming a crust.
d. Unlike the earth, the moon has very little
Iron in its core and has no magnetic field.

21. 2. Lunar Cateclysm
a. When the crust has solidified, it immediately
became cratered by materials left over at the end
of planet building.
b. The crust was shattered to a depth of 10km which
produced many deep, multi-ringed, craters.
c. This period of heavy impacts took place over the
course of 500 million years.

22. 3. Flooding of the Maria
a. During the Lunar Cateclysm, the interior of the
moon was similar in temperature to that of the earth.
b. When the impacts shattered the crust, magma from
the mantle filled in the low lying areas to create the
maria.
c. Because of the tidal forces between the earth and
moon, the crust of the moon is slightly thinner on the
earth side. Thus there are many more maria on the
side facing the earth and almost none on the opposite
side.

23. 3. Slow Surface Evolution
a. Over time micro-meteorite impacts work to slightly
erode some of the oldest features.
b. Overall the surface features of the moon are fixed.
c. There is no longer any internal heat, nor any
atmosphere to shape the landscape.
d. The only large scale changes take place when
there is the occasional impact on the surface. None
have been witnessed in human history.

24. G. Earth's History (Four Stages)
1) Differentiation
a. As the moon accreted it increased in
temperature.
b. Unlike the moon, the earth also received
interior heat from the breakdown of
radioactive metals.
c. Because it was liquid denser materials sank
to the core lighter materials to the surface
forming a crust.
d. This allowed the earth to separate into the
current Crust, Mantle & Core.

25. 2. Cratering
a. When the moon went through the Lunar Cataclysm,
the Earth also underwent a period of heavy
cratering.
b. The Crust of the earth was pulverized by the left
over rocky and icy materials from planet formation.
c. It was during this period that many comets hit the
earth giving it a large portion of the water we enjoy
today.

26. 3. Flooding
a. Radioactive heating warmed and softened the
crust.
b. During cratering the crust easily cracked down to
the mantle magma to rise up and fill the craters.
c. Additionally as the surface and atmosphere cooled,
water began to precipitate out of the air. Water then
filled the lowest basins creating the first oceans.
d. Note that flooding on Earth involved both lava and
water.

27. 4. Slow Surface Evolution
a. Over time heat from the Earth's interior has caused
the crust to break into plates that slide on top of
the mantle.
- This results in Mountain Building, and Plate
Destruction when one plate moves beneath
another.
b. Wind and water also act to erode surface features.
c. The Earth's atmosphere prevents most small
meteorites from having any effect on the surface.
d. For the most part the first billion years of Earth's
history has been destroyed by these processes.

28. H. (mostly) Unique Features of the Earth
1. Earth's Active Crust
- Activity in the crust (volcanoes, earthquakes, etc) is
driven by internal heat.
- The interior of the other terrestrial planets have long since
cooled to the point where they can no longer drive motion
in the crust.

29. H. (mostly) Unique Features of the Earth
2. Earth's Magnetic Field
- Heat from the Earth's interior causes the molten metal
core to convect and mix while the earth rotates on its
axis.
- This combination of hot spinning metal produces the
earth's magnetic field.
- Gives us the north and south poles
- Deflects the Sun's solar wind around the
Earth, protecting us from the radiation.
- When solar wind particles get trapped in
the magnetic field at the poles they
produce the Northern & Southern Lights.

30. H. (mostly) Unique Features of the Earth
3. Earth's Atmosphere
- Earth is the only known atmosphere that contains
significant amounts of oxygen gas (21%)
- The majority of the atmosphere is Nitrogen Gas (70%).
This is because Nitrogen gas is very nonreactive and
does not break down easily.
- The atmosphere includes Carbon Dioxide
gas which plays an important role in
regulating the temperature of the planet.
- In the upper atmosphere there is a layer of
Ozone which helps protect living things
from UV radiation from the sun.

31. H. (mostly) Unique Features of the Earth
1. Life
- The only known planet to have living things.
- On the whole, life works against the several accepted
laws of the universe including the tendency towards
entropy (disorder) and movement of matter to the lowest
energy state.
- Living things are responsible for the
high concentration of very reactive
oxygen gas in the atmosphere.
- The Earth is located in what is called
the habitable zone. An area around the
sun with relatively small temperature
extremes and where liquid water can
exist.