Transcript Origin of Our Solar System

Origin and History of Our
Solar System
TEK Objective 5: Earth in space and time.
The student understands the solar nebular
accretionary disk model. The student is
expected to:
a) analyze how gravitational condensation of solar
nebular gas and dust can lead to the accretion of
planetesimals and protoplanets;
b) investigate thermal energy sources, including
kinetic heat of impact accretion, gravitational
compression, and radioactive decay, which are
thought to allow protoplanet differentiation into
layers;
Where did Earth come from?
The origin of the planets
in our Solar System has
been debated since 1755
when Immanuel Kant
proposed the first
theory
During the 1900s, many
believed Earth was not a
unique occurrence because
of the recent discovery of
other planetary systems
around other stars
Scientists
debated whether
the origin of our
Solar System was
usual, or a
common
consequence of
star formation
Two Main Theories
The Nebular
Hypothesis
The
Protoplanet
Hypothesis
Most generally accepted
evolutionary model for the origins
of solar systems
The current working model for the formation of the
Solar System, it incorporates many of the
components of the nebular hypothesis, but adds
some new aspects.
Sun-like stars usually take around 100 million years to form.
Nebula are star “nurseries”, where stars are born. This
nebular photograph was taken by the Hubble Space
Telescope
A nebula is the product of a
supernova event. The death of
one system, may well be the birth
of another!
The Nebular Hypothesis
Kant believed a nebula
began to collapse due
to gravity, and slowly
began to rotate. The
rotation turned the
nebula into a flattened
disk of debris. At the
center, the Sun
formed as all the
densest materials fell
in, and over time, it
heated up and ignited.
This ignition blew the
debris into rings
orbiting the star.
Laplace stated that
these rings coalesced
into planets.
https://youtu.be/PL3YNQK9
60Y
These are
protoplanetary discs
imaged by the Hubble
Space Telescope,
from the Orion
Nebula.
Scientists suspect
these are the early
stages of planetary
systems forming, some
1,500 light years away!
28.5 x 1015 km
Nebular Hypothesis:
How
Does
Accretion – gradual growth of planets by the
accumulation ofHeavy
other smaller
bodies
bombardment
Accretion
Occur?
period on Mercury (4.1
3.8 bya)
Protostar forms with opaque
core

Energy is given off by protostar causing a cooling




Cooling causes gas to condense into tiny specs of
metal, rock, & ice “Stellar Debris”
Stellar Debris begins to stick together to form
Planetesimals
Accrection of Planetesimals forms Protoplanets
Some Planetsimals will form into asteroids,
comets, and moons
1. What are the two main theories about the origins of our solar
system?
2. What is a nebula?
3. How do nebulas form?
4. Describe Kant’s Nebular Hypothesis in a nutshell.
5. Describe how planetesimals and protoplanets are different.
6. Describe the process of accretion, and how it allows planets to
grow larger.
7. Describe what the “heavy bombardment” stage of solar
system development was, and when it happened.
The Protoplanet Hypothesis
Because
During the mid 1900s,
scientists weren’t astronomers called
completely happy their new version of
with the nebular nebular hypothesis the
Protoplanet
hypothesis, other
Hypothesis
explanations of
planet formation
were sought.
The
The solar system begins to
form as a rotating cloud, or
Protoplanet
Hypothesis
nebulae, collapses
Instabilities in the nebulae cause
dust particles to stick together
and accrete into billions of
planetesimals with diameters of
about 10 meters. The
planetesimals then collide and
form protoplanets.
Meanwhile, the protosun in the
center of the nebular disk
becomes massive and hot enough
to "turn on" by fusing hydrogen.
https://youtu.be/Uhy1fucSRQI
The Sun begins to radiate energy
and vaporize dust in the inner part
of the Solar System. The remaining
gas is blown away by solar winds (or
T Tauri winds), to join the outer
planetary gas giants.
The main difference between nebular theory, and protoplanet theory is that in
the nebular theory, the Sun forms before the planets, and in the protoplanet
theory, the Sun forms concurrently with the planets, and right alongside them.
The planets continue building, accreting debris and increasing their mass and
gravitation. Then, the Sun ignites, and blows away all the rest of the dust.
The forces operating
during the formation
of the Solar System
were responsible for
the diversity of
matter in the Solar
System and also
responsible for
diversity of
planetary internalstructures.
As the nebula cools
1) The inner zone stays warm (>100 ° C) and only high temperature condensates
form - giving the terrestrial planets high density.
Five major elements; Fe, Mg, Si, O, and S; comprise at least 95% of the mass of each
of the terrestrial planets. These elements are high temperature condensates.
2) Outer zone cools more, so low-T materials condense into the outer - low
density planets with lots of, ice, and frozen gases like CH4, CO2 etc...
8. What is the main difference between Nebular
Hypothesis of solar system formation, and Protoplanet
Hypothesis?
9. What version of solar system origins is accepted today?
10. What are the five major high temperature condensates
that compose the terrestrial planets?
11. Describe briefly why planets in our solar system formed
where they did.
This model shows planetesimal
accretion in our solar system. The
total time frame for the process is
about 441 million years.
There were as many as 11 inner
planetesimals after 79 million years,
and six after 151 million years.
Suggestions are that the Earth
accreted in about 100 million years.
The terrestrial planets (inner rocky
planets) formed close to the sun,
because nothing else would accrete
there. The gases all vaporized
because of the temperature.
Gases have the chance to freeze past
the frost line (between Mars and
Jupiter), and the outer planets are
composed largely of frozen gases as a
result.
Planets can differentiate by mass and
density, the same way that solar systems do.
As you might remember:
Potential energy is stored, while kinetic
energy is possessed by objects in motion.
Early differentiation of the Earth involved the
separation of Fe-Ni rich (heavy) from silicate
material (light) to form the core and mantle.
High temperatures were necessary and
differentiation likely occurred in response to
large-scale melting, induced by high-energy
impacts. (kinetic heat of impact accretion)
Kinetic energy from these impacts caused the
melting.
"Earth's accretion history was dominated by
multiple high-energy collisions with Moon- to
Mars-sized bodies
Over time, differentiation
occurred based on temperature
and density.
Silicates include minerals that
contain both oxygen and
silicon, and compose the vast
majority of the Earth’s crust.
High-density materials tend to sink through lighter materials. Iron, the most
common element to form a very dense molten metal phase, tends to congregate
towards planetary interiors.
The main zones in the solid Earth are the very dense iron-rich metallic core, the
less dense magnesium-silicate-rich mantle and the relatively thin, light crust
composed mainly of silicates of aluminum, sodium, calcium and potassium.
Even lighter still are the
watery liquid hydrosphere
and the gaseous, nitrogenrich atmosphere.
low-density silicate rocks,
such as granite, are well
known and abundant in the
Earth's upper crust.
Temperature within the Earth increases with depth.
The Earth's internal heat comes from a combination of
residual heat from planetary accretion (about 20%) and heat
produced through radioactive decay (80%).
The major heat-producing
isotopes in the Earth are
potassium-40, uranium-238,
uranium-235, and thorium232. At the center of the
planet, the temperature may
be up to 7,000 K
(Water freezes at 273
Kelvins)
12. Explain how kinetic heat of impact accretion is how early Earth
began differentiating.
13. Why does it make sense that Earth’s hydrosphere and atmosphere
formed where they did?
14. How does the thermal structure of the Earth change from crust to
core?
15. Other than impact accretion, what other force accounts for the
internal temperature of the Earth?
16. What are the major heat-producing isotopes in the Earth?