Download Goal: To understand how Saturn formed and what its core is like

Goal: To understand how our
solar system formed and what it
like today
Objectives:
1) Formation of stars
2) Solar Nebula
3) Terrestrial Planets
4) Gas Giants
5) Other debris
6) Orbital motions
In the beginning
• All you have is a large cloud of dust and
gas.
• This cloud is very large and very cold.
• They are called Giant Molecular Clouds.
• Somehow the cloud
collapses.
The initial cloud
• Is made of mostly
Hydrogen (~90% by weight).
• Most of the rest is Helium (9%)
• 1-2% are everything else (in Astronomy
we call the everything else “metals” including Oxygen).
• The cloud has some spin. What will that
do?
Spin city
• The small amount of spin
acts like a merry-go-round.
• Much like on a merry-go-round, this
spinning motion pushes things outward.
• However, nothing stops the collapse in the
vertical direction, so the cloud collapses to
a disk.
• The gas in the disk is literally in orbit
around the center of the gas cloud.
Disc
• The cloud which will form the sun quickly
collapses to a spinning disc.
• The particles that can get into orbit around
the forming star in the middle (called a
protostar) survive.
• The rest get
gobbled up when
they fall to the
center.
Waves
• Density waves form in the cloud.
• These waves will lead to the formation of
the planets.
Terrestrial Planets
• The inner part of the disk is hot.
• The only materials that can be solid in this
heat are rocky materials such as iron and
silicon.
Tar Line
• At some distance carbon compounds can
become solid and form tarry substances.
• This distance is called the tar line.
• There is a lot more carbon than there is iron and
silicon in the cloud forming the sun.
• So, even though there is less material overall to
form a planet at this distance a much larger
percentage of it becomes solid.
• This allows you to build much larger planets!
Ice Line
• Similar to the tar line but is the point where
materials such as water, ammonia, and
methane can freeze.
• Since there is a lot more of this than
carbon even it allows you to build large
planets.
Gas Giants – rocky stage
• During this stage you start out with small
“dirty snowballs”.
• These snowballs are half rock and half ice.
• In time they fuse with other snowballs to
make larger snowballs.
• In a few million years they will form the
core of a gas giant which is about the size
of the earth but ten times the mass of the
earth.
Run Away Accretion
• Once the core of a gas giant becomes 10
earth masses it can capture and hold onto
gas.
• Most of the gas is Hydrogen and Helium,
so this is pretty tough to do.
• There is a LOT of gas.
• There is far more gas than everything
else.
• So, at this point it grows very quickly.
And they are off to the races!
• Since Jupiter was outside the tar line
(carbon line) but inside the water line at
this time Saturn might have hit the
runaway phase first.
• Once it did, it was a race against time to
gobble up material before the sun is
officially born and blasts all the remaining
gas out of the solar system.
Formation of Major Moons
• While gas giants are in their runaway
accretion phase they form an accretion
disk of dust and gas and ice (similar to the
accretion disk around the sun).
• Much like planets form around the sun so
too would the major moons form around
gas giants.
Minor Moons
• The minor moons would have been
captured either during this earliest era
where there was a lot of debris and
Neptune and Jupiter tossing stuff around.
• Others could have been captured comets
later.
• All orbit the planet backwards (retrograde).
Additional debris - asteroids
• There are regions of space that do not
form planets.
• One is our asteroid belt.
• In this region gravity from Jupiter would
have made rocks that hit each other break
each other apart instead of make bigger
rocks.
Additional debris - TNOs
• In the outer solar system just beyond the
orbit of Neptune there are objects known
as Trans-Neptunian Objects (TNOs).
• These did not have enough time to form
into a planet.
Additional debris – Oort Cloud
• Some objects were tossed into
enormously large orbits by the gas giants
(cough – Jupiter – cough).
• These orbits can go out as far as a light
year.
• This is the source of long period comets.
Orbits of Planets
• In our solar system all of the planets orbit
in the same direction and in the same
plane.
• The planets are held into place by gravity.
Gravity
• As you move further from an object the
gravity it exerts on you decreases by the
distance to its center squared.
• So, planets that orbit further from the sun
have less gravity exerted on them (in
terms of acceleration)
Conclusion
• We have explored the formation of our
solar system and how that affects the
composition and distribution of its planets.
• We have also explored the basics of our
solar system.