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-Melissa Greenberg, Arielle Hoffman,
Zachary Feldmann, Ryan Pozin,
Elizabeth Weeks, Christopher Pesota,
& Sara Pilcher
Formation Overview
 All explanations as to how the solar system was formed
are only theories and may change/evolve as scientists
and astronomers continue to learn more
 The formation of the solar system that we know today
occurred 4.6 billion years ago when a giant dense cloud
of gas and dust known as a molecular cloud collapsed
upon itself.
 There was most likely a disturbance caused by a
supernova (an exploding star), and the resulting waves
compressed the cloud causing gravity to pull the gas and
dust together, thus forming a solar nebula.
 This caused the entire cloud to start spinning: the center
having the highest angular velocity became extremely
hot and dense comparatively, with a ring of gas and dust
surrounding it, forming a proto star.
Overview Continued…
 Of all the matter that composed the molecular cloud, the
majority of the collapsing mass assembled in the center,
forming what would later be the sun, while the rest
flattened out into a “protoplanetary disc” with a
diameter of 200 au, which would latter form the planets,
moons and asteroids.
 The protoplanetary disc became thinner and thinner as
the proto star pulled in more matter. Eventually particles
in this disc began clumping. These clumps continued to
add mass as they accumulated more particles- these
“clumps” would eventually form the planets and moons
in our solar system.
Overview Continued…
 After more than 50 million years of spinning and gaining heat
and density, the hydrogen in the center of the protostar was
under enough pressure to begin “thermonuclear fusion”.
 The new star continued to grow in size, temperature, mass and
density until it reached a state of hydrostatic equilibrium- at
this point it became a main sequence star and the sun we
know today.
 Close to the growing star only rocky materials could stand the
growing intense heat. Therefore, most of the rocky material
settled close to the sun, which is the reason that the planets of
the inner solar system are composed of rock.
 The lighter and less dense material such as gas and ice
settled in the outer part of the disc the reason for the gas
giants of the outer solar system.
A Closer Look: Video Clip
http://www.youtube.com/watch?v=-ht2yzscaDc
Mercury
 Formed from a condensed nebula
 Created a dense metallic core with a
thin silicate crust
 Asteroids bombarded the surface,
internal lava flowed out and formed a
new crust
 When the planet cooled and shrank,
another wave of lava covered the old
crust
 Mercury will remain unchanged for
centuries!
Planetary Motion
 Stars and planets are formed when clouds of
interstellar gas and dust collapse.
 Both the clouds and the material in these
clouds are in constant motion. Thus, planets
are formed in this state of motion.
 The rotation in these clouds is called
“angular momentum”; it is conserved (“The
Law of Conservation of Momentum”) in our
universe and it can be transferred but not
created or destroyed.
Law of Conservation of
Momentum
 For example, an
http://www.youtube.com/watch?v=V3UsrfHa4MQ
Why do some planets rotate
differently?
 Almost all planets rotate in the same
direction (counter-clockwise) and on the
same plane.
 They spin in a “direct sense” – that is, they
spin in the same direction as they orbit the
sun. (The gravity of the sun keeps the planets
in their orbits)
 The two exceptions are Venus and Uranus.
 These differences are believed to stem from
collisions early in their formation.
Venus
 Venus rotates backwards (clockwise) compared to
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the other planets.
Why? Cratering evidence suggests that early in
formation there were still many “mini-planets”
orbiting the sun.
It is thought that Venus encountered one of these
planets and absorbed it into its own body.
This body would have contributed angular
momentum (along with kinetic energy and mass.)
So, new spin and mass seriously altered the original
spin of Venus, which was most likely similar to that
of the other planets.
Earth
 Formed 4.5 billion years ago
 Travels in an elliptical orbit around the sun
 Has a velocity in a direction that is perpendicular to the force
of the sun’s pull (would travel in a straight line if the sun
wasn’t present)
 Kepler’s Laws of Planetary Motion: 1st law states that each
planet travels along an ellipse, with the sun at one focus
 All planets rotate around themselves, BUT orbit around the sun!
A Theory on the Formation of the
Moon
 A small planetary body hit the Earth late in its
growth process, blowing out rocky debris
 A fraction of that debris went into orbit around the
Earth
 It became the moon– VOILA!!
 This is a good hypothesis because:
 The Earth has a large iron core, while the moon does not
 Earth’s mean density of 5.5 grams/cubic cm, while the
moon’s mean density is 3.3 grams/cubic cm– This correlates
with moon’s lack of iron
 The moon has exactly the same oxygen isotope
composition as the Earth
Mars
 Direct accretion from grain particles in the
protosolar nebula led to the creation of Mars,
similar to planetary compositions like Earth
and Mercury
 Formed after the formation of Jupiter
 Formed from a large planetesimal that
separated from the asteroid belt
The Asteroid Belt
 Separates the first 4 terrestrial planets from the 4
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outer gas-giant planets
Between 2 and 4 astronomical units (avg. distance
between the Earth and the Sun)
Initially, the matter in the asteroid belt was
enough to form 2-3 Earth-like planets
As the planets migrated, the gravitational pulls
created by Jupiter and Saturn excited the region,
increasing the velocities relative to each other
Currently has a total mass equivalent to about
1/2000 of the Earth’s mass
The Asteroid Belt
 There was a lot of debris left over from this
Continued…
formation. Some of the rocky material rotates
around the sun in the asteroid belt, never fully
coming together separating the gas planets from
the rocky ones. Another asteroid belt that lies
beyond Neptune is called the Kuiper belt. Most
of the left over rocky debris formed the Oort
cloud a giant spherical cloud of rock nearly a light
year away from the sun. The remaining gas and
small particles left over from the molecular cloud
was blown away by the solar wind in the early
years of the suns life.
Jupiter
 began with the build up of ice covered dust in the outer, cold
solar nebula
 Small particles of ice and dust came together, forming larger and
larger objects.
 Once it gathered together enough mass, its gravity attracted more
dust, as well as hydrogen and helium.
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The heaviest elements sunk into the core of the planet, surrounded
by the lighter hydrogen and helium in its atmosphere.
 2.5 times bigger than any other planet in solar system
 Considered Failed Star, in that was once very hot and on the verge of
stellar fusion but it cooled.
 Because of its immense gravity, scientists theorize that Jupiter was
influential in the formation of other planets (like earth!).
Saturn
Formed from a solar nebula about 4.6 Billion years ago
a vast cloud of cold gas and dust which was disturbed somehow perhaps by colliding with another cloud, or the shock wave from a
supernova.
cloud compressed down, forming a protostar in the center,
surround by a flattened disk of material.
Inner part of disc had heavier elements and created planets and
other planetesimals.
Outer disc made of ice.
Rings created by deteriorating planet?
Uranus
 Uranus rotates “on its side”, 90 degrees
relative to its original orbit.
 It too was likely hit by an early planetoid,
causing it to have a skewed axial tilt.
 “It has been described as having an axial tilt
of 82° and a negative rotation of −17 hours,
or, equivalently, of having an axis tilted at 98°
and a positive rotation.”
Neptune
Much controversy as to how and especially where Neptune was formed.
Solid, heavy matter core surrounded by gasses, ice and dust.
Too far out for such matter to accumulate.
Scientists suggest “Migration Theory”
Theorized that the solid core came from remnants of the Kuiper Belt.
The Former Planet- Pluto
 Now considered the largest member of the
distinct population called the Kuiper belt
(composed of rock & ice, and is relatively
small)
 Pluto doesn’t orbit the sun in the same
direction as the other planets do
 It’s inclined at 18 degrees, which makes it
more elliptic compared to the existing
planets
 For a period of time it is closer to the sun than
Neptune is, due to its eccentricity
Conclusion: The Future of
the Solar System
In an estimated 5.4 billion years thermonuclear fusion will no longer
take place at the core of the sun. The entire supply of hydrogen will
have been turned to helium. Once this happens, the sun will go from
being a main sequence star to a red giant. The diameter of a red
giant is typically 260 times larger than that of a main sequence star.
The sun will decrease in temperature and over time the layers of the
red giant will shed and leave in its place a white dwarf. Said white
dwarfs would be incredibly dense, containing half the mass of the
original star while having the same diameter as Earth.