Transcript Origin of Our Solar System

Origin 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;
Where did Earth come from?
Two Main Theories
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
In 1755 Immanuel Kant proposed that a
solar nebulae was pulled together by
gravity so that it collapsed into a flat,
rotating disk that eventually coalesced
into the Sun and planets
Remember…solar
nebulae are huge
clouds of dust
and gas
The Nebular Hypothesis
Laplace stated that after
the matter split off, it
coalesced into a planet. The
process repeated itself,
resulting in a planet each
time. The matter left over
was the Sun.
Much like a figure
skater. You may have
noticed that skaters can
spin much faster if they
pull their arms closer to
their bodies. The more
concentrated their body
masses are, the faster
they'll be able to rotate.
Problems With the Nebular Hypothesis
Used a flat, rotating nebula as the Solar
System's origin to explain why all the planets
orbit in nearly the same plane and in the
same direction
All planets revolve around the Sun in a counterclockwise direction within a 7°
band of the equatorial region of the Sun, and nearly all of them also turn on
their individual axes in a counterclockwise direction as well.
Contradicted the observation that the Sun
contains most (99%) of the Solar System's
mass but only a small fraction of its angular
momentum (rotates slowly)
Remember, angular momentum is the measure of the tendency of a rotating
body to remain rotating
Also…
If rings of matter were split off,
as Laplace stated, they
wouldn't be pulled together to
form planets but would
disperse into space.
Accretion – gradual growth of planets by the
How Does
Accretion
Occur?
accumulation ofHeavy
other smaller
bodies
bombardment
period on Mercury

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
The Protoplanet Hypothesis
Because of faults
in the nebular
hypothesis, other After many failures,
explanations of such as the encounter
hypothesis,
planet formation
astronomers returned
were sought.
to the nebular
hypothesis to find
improvements during
the mid 1900s.
What’s
wrong
that?
Rogue star
passes with
close to
the
Sun.
Hot gases expand, not
Gas
is “tidally” removed
condense…so
hot gasfrom
would
both rogue star and Sun
not form clumps and planets.
Rogue star material is less dense
Also…star
are
and becomesencounters
outer Solar System
extremely
rare, so rare in fact
planets
that it should not happen in
Inner
Solar System
material
is
the lifetime
of the
Universe!
more dense and becomes
terrestrial planets
Improvement to Solar Nebular
Theory: The Protoplanet Hypothesis
Formed
independently
by
Carl von
Weizsacker
Gerard Kuiper
The
The solar system begins to
Protoplanet
form as aHypothesis
rotating cloud, or
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.
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.