Transcript Collapse of the Solar Nebula

Kirkwood Observatory Open House
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for the rest of the
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Homework #7
due Monday, March 29, 2:30 pm
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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Size:
Location:
Composition:
Temperature:
Rings:
Rotation rate:
Surface:
Atmosphere:
Moons:
small
closer to Sun
rocky/metallic
hotter
none
slow
solid
minimal
few to none
Jovian Planets
large
distant
gaseous/icy
cold
ubiquitous
rapid
not solid
substantial
many
Planetary orbits:
1) Prograde
2) approximately coplanar
3) approximately circular
Rotation:
1) Mostly Prograde
2) Includes sun
3) Includes large moons
Surface features of solid objects in
solar system
Craters are
ubiquitous
There are lots of smaller objects in
the Solar System,
some are rocky and some are icy
Asteroids
small
Rocky
Odd-shapes
nearly circular orbits
orbit planes are near Ecliptic Plane
orbits in inner part of solar system
The
“asteroid belt”
Asteroids
Gaspra
Deimos
Mars’ moons and the
asteroid Gaspra
Phobos
Comets
small nucleus
very large tails
“dirty snow ball”
highly eccentric orbits
all orbit inclinations
Comet Wild
Halley’s Comet
Comets are found mainly in two regions of
the solar system
Kuiper Belt Objects
UB313
(1500 miles)
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 Solar nebula may have
been part of a much larger
nebula
Protostellar
nebulae?
Recipe for solar system formation
 Start with a giant, swirling interstellar cloud of
gas and dust (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
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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
Gasinitially
pressure
seeks
to –expand
System
in pressure
balance
no collapse
cloud
gas pressure
gravity
System initially in balance – no collapse
gas pressure
gravity
Now, whack
the cloud
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
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 & ice grains 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
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