Download Collapse of the Solar Nebula - Indiana University Astronomy

Exam #2
Wednesday, March 31
Review session Monday, March 29
7:30 –9:30 pm
Morrison Hall 007
Terrestrial
Jovian
Two “flavors” of planets
Terrestrial Planets
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Jovian Planets
Size:
small
large
Location:
closer to Sun
distant
Composition: rocky/metallic
gaseous/icy
Temperature: hotter
cold
Rings:
none
ubiquitous
Rotation rate: slow
rapid
Surface:
solid
not solid
Atmosphere:
minimal
substantial
Moons:
few to none
many
So how do we account for what we
see in the solar system?
The Nebular
Theory
The Solar system
was formed from
a giant, swirling
interstellar cloud
of gas and dust
(the solar nebula)
The Nebular Theory
 Start with a giant, swirling interstellar cloud of
gas and dust (the solar nebula)
Recipe for solar system formation
 Start with a giant, swirling interstellar cloud of
gas and dust (nebula)
 Perturb cloud to begin its collapse
 Sit back and let physics take over
Important physics in forming stars
stars & planets

Gravity

Gas pressure

Conservation of Angular Momentum

Conservation of Energy

Phases of matter
The struggle to form
stellar/planetary systems
Gravity vs Gas Pressure
Protosolar
nebula
Slowly rotating
System initially in pressure balance – no collapse
Gravity seeks to collapse cloud
System initially in pressure balance – no collapse
Gas
pressure
expand
cloud
System
initially in seeks
pressure to
balance
– no collapse
gas pressure
gravity
System initially in balance – no collapse
gas pressure
gravity
Now, whack
the cloud
(don't use an
actual
hammer)
Perturbation triggers collapse – gravity is winning
As collapse proceeds, rotation rate increases
As collapse continues, the rotation rate
increases while nebula flattens
Building the Planets. I
COLLAPSE OF PROTOSTELLAR CLOUD INTO A
ROTATING DISK
Composition of disk:
 98% hydrogen and helium
 2% heavier elements (carbon,
nitrogen, oxygen, silicon, iron,
etc.).
Most of this was in gaseous
form!
Collapse of the Solar Nebula
As the solar nebula collapsed to a diameter of
200 A.U. (1 LY = 63, 240 AU), the following happened:


The temperature increased as it collapsed
(conservation of energy; gravitational potential energy
becomes thermal energy)
The rotation rate increased (conservation of angular
momentum)

The nebula flattened into a disk (protoplanetary disk)

Motions of material in the disk became circularized
Material in the newly formed proto-planetary disk is:
Orbiting in approximately the same
plane
Orbiting in approximately circular orbits
This is the situation with the orbits of planets, so now
we have the material in the proper location and
moving in the proper manner.
Examples of protoplanetary disks
According to our theory of solar system formation, what
three major changes occurred in the solar nebula as it
shrank in size?
(blue) It got hotter, its rate of rotation increased, and it
flattened into a disk.
(red) It gained energy, it gained angular momentum, and
it flattened into a disk.
(yellow) Its mass, temperature, and density all increased.
(green) I have no idea
According to our theory of solar system formation, what
three major changes occurred in the solar nebula as it
shrank in size?
(blue) It got hotter, its rate of rotation increased, and it
flattened into a disk.
(red) It gained energy, it gained angular momentum, and
it flattened into a disk.
(yellow) Its mass, temperature, and density all increased.
(green) I have no idea
Which law best explains why the solar
nebula spun faster as it shrank in size?
(blue) Law of universal gravitation.
(red) Einstein's law that E = mc2.
(yellow) Conservation of angular
momentum.
(green) Conservation of energy.
Which law best explains why the solar
nebula spun faster as it shrank in size?
(blue) Law of universal gravitation.
(red) Einstein's law that E = mc2.
(yellow) Conservation of angular
momentum.
(green) Conservation of energy.
Why did the solar nebula end up with a disk shape
as it collapsed?
(blue) The force of gravity pulled the material
downward into a flat disk.
(red) It flattened as a natural consequence of
collisions between particles in the nebula, changing
random motions into more orderly ones.
(yellow) The law of conservation of energy.
(green) It was fairly flat to begin with, and retained
this flat shape as it collapsed.
Why did the solar nebula ended up with a disk shape
as it collapsed?
(blue) The force of gravity pulled the material
downward into a flat disk.
(red) It flattened as a natural consequence of
collisions between particles in the nebula, changing
random motions into more orderly ones.
(yellow) The law of conservation of energy.
(green) It was fairly flat to begin with, and retained
this flat shape as it collapsed.
Which law best explains why the central
regions of the solar nebula got hotter as
the nebula shrank in size?
(blue) Newton's third law.
(red) Law of conservation of energy.
(yellow) Law of conservation of angular
momentum
(green) The two laws of thermal radiation.
Which law best explains why the central
regions of the solar nebula got hotter as
the nebula shrank in size?
(blue) Newton's third law.
(red) Law of conservation of energy.
(yellow) Law of conservation of angular
momentum
(green) The two laws of thermal radiation.
Building the Planets. II
There was a range of
temperatures in the
proto-solar disk,
decreasing outwards
Condensation: the formation of solid or liquid particles
from a cloud of gas (from gas to solid or liquid phase)
Different kinds of planets and satellites were formed out of
different condensates
Ingredients of the Solar Nebula
Metals : Condense into solid form at 1000 – 1600 K
iron, nickel, aluminum, etc. ; 0.2% of the solar nebula’s
mass
Rocks : Condense at 500 – 1300 K
primarily silicon-based minerals; 0.4% of the mass
Hydrogen compounds : condense into ices below ~ 150 K
water (H2O), methane (CH4), ammonia (NH3), along with
carbon dioxide (CO2), 1.4% of the mass
Light gases (H & He): Never condense in solar nebula
hydrogen and helium.; 98% of the mass
The "Frost Line” - Situated near Jupiter
Rock & Metals can form anywhere it is cooler than about 1300 K.
Carbon grains & ices can only form where the gas is cooler than
300 K.
Inner Solar System:
* Too hot for ices & carbon grains.
Outer Solar System:
* Carbon grains & ices form beyond the "frost line".
Building the Planets. III
Accretion
Accretion is growing by colliding and sticking
The growing objects formed by accretion –
planetesimals (“pieces of planets”)
Small planetesimals came in a
variety of shapes, reflected in many
small asteroids
Large planetesimals (>100 km
across) became spherical due to the
force of gravity
In the inner solar system (interior to
the frost line), planetesimals grew by
accretion into the Terrestrial planets.
In the outer solar system (exterior to
the frost line), accretion was not the
final mechanism for planet building –
nebular capture followed once
accretion of planetesimals built a
sufficiently massive protoplanet.
Building the Planets. IV. Nebular Capture
Nebular capture – growth of icy
planetesimals by capturing
larger amounts of hydrogen and
helium. Led to the formation of
the Jovian planets
Numerous moons were formed by the same processes
that formed the proto-planetary disk
Condensation and accretion created “mini-solar systems”
around each Jovian planet
What do we mean by the frost line when we discuss the
formation of planets in the solar nebula?
(blue) It is another way of stating the temperature at
which water freezes into ice.
(red) It is the altitude in a planet's atmosphere at which
snow can form.
(yellow) It marks the special distance from the Sun at
which hydrogen compounds become abundant;
closer to the Sun, there are no hydrogen
compounds.
(green) It is the distance from the Sun, beyond which
the temperature was low enough for ices to
What do we mean by the frost line when we discuss the
formation of planets in the solar nebula?
(blue) It is another way of stating the temperature at
which water freezes into ice.
(red) It is the altitude in a planet's atmosphere at which
snow can form.
(yellow) It marks the special distance from the Sun at
which hydrogen compounds become abundant;
closer to the Sun, there are no hydrogen
compounds.
(green) It is the distance from the Sun, beyond which
Which of the following types of
material can condense into what we
call ice at low temperatures?
(blue) hydrogen and helium
(red) metal
(yellow) hydrogen compounds
(green) rock
Which of the following types of
material can condense into what we
call ice at low temperatures?
(blue) hydrogen and helium
(red) metal
(yellow) hydrogen compounds
Examples: water (H2O), Methane (CH3), Ammonia (NH4)
Building the Planets. V.
Expulsion of remaining gas
The Solar wind is a flow of charged particles
ejected by the Sun in all directions. It was
stronger when the Sun was young. The wind
swept out a lot of the remaining gas
Building the Planets. VI.
Period of Massive Bombardment
Planetesimals remaining after the clearing of the solar
nebula became comets and asteroids
Rocky leftovers became asteroids
Icy leftovers became comets
Many of them impacted on objects within the solar
system during first few 100 million years (period of
massive bombardment - creation of ubiquitous craters).
Brief
Summary