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Structure & Formation of the Solar System

• What is the Solar System? – The Sun and

everything gravitationally bound to it.

• There is a certain order to the Solar System.

• This gives us information on its formation.

The planets to scale with a portion of the Sun visible in the background.

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Part 1: Structure of the Solar System• All the planets orbit the

Sun in the same direction.

• All the planets orbit within nearly the same plane. Like a disk.

• Two type of planets– Solid, rocky, small

planets close to the Sun (like Earth)

– Gaseous, large planets far from the Sun (like Jupiter)

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The Sun• The Sun is a star.• It is completely gaseous.• It emits light and heat through

nuclear fusion in its core.• It is by far the largest object in

the Solar System. 700 times more massive than all of the other objects in the Solar System put together.

• It is composed mostly of Hydrogen and Helium gas and traces of many other elements.

• The Sun spins on its axis counter-clockwise.

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The PlanetsIn order of

increasing distance from the Sun:

– Mercury– Venus– Earth– Mars

– Jupiter– Saturn

– Uranus– Neptune

– Pluto

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The Planets• All the planets

orbit in the same direction counter-clockwise as seen from above Earth’s North Pole.

• All the planets spin counter-clockwise too except for Venus, Uranus and Pluto.

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The Inner or Terrestrial Planets• Mercury, Venus,

Earth and Mars share certain characteristics:– All are rocky bodies.– All have solid

surfaces.– Except for Mercury

all have at least a thin atmosphere

• They are called Terrestrial planets because of their resemblance to Earth.

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The Outer or Jovian Planets• Jupiter, Saturn,

Uranus and Neptune share certain characteristics:– All are large,

gaseous bodies.– All have very thick

atmospheres, with possibly liquid interiors and solid cores

– All have rings

• They are called Jovian planets because of their resemblance to Jupiter.

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Pluto

• Pluto is unlike any of the terrestrial or jovian planets.– much farther from the Sun

than the terrestrial planets.– much smaller than any

jovian planet.– composition is thought to

be a mixture of ice and rock

• It is similar to some of the satellites of the jovian planets and similar to some asteroids.

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Satellites (Moons)

Ganymede, Callisto, Io, and Europa.Four of Jupiter’s largest satellites.These were discovered by GalileoGalilei and together are called theGalilean satellites of Jupiter.

• Most of the planets have satellites.

• Most of the satellites orbit in the equatorial plane of the planet.

• Most satellites orbit counter-clockwise.

• The jovian planets have more than a dozen satellites each.

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Comets and Asteroids

• The Solar System is filled with millions of smaller bodies.

• Comets - composed of ice and rock

• Asteroids - composed of rock and/or metal

• There is also dust in space which can be seen in meteor showers

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Part 2: Solar System Formation• Our Milky Way Galaxy is

filled with cold, dark clouds of gas and dust.

• These clouds are mostly hydrogen and helium with dust containing mostly iron, rock, and ice.

• The Solar System is thought to have formed from a huge, slowly rotating cloud about 4.5 billion years ago

• A nearby passing star or stellar explosion may have caused the cloud to collapse

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Collapsing Gas Clouds• As the cloud collapsed the

original slow spin began to speed up. This caused the cloud to flatten into a disk shape.

• The gravitational pull of the cloud caused it to shrink further and caused most of the material to fall towards the core forming a large bulge.

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Collapsing Gas Clouds?• In the Great Nebula of

the constellation Orion are huge clouds of gas and dust.

• Among these clouds the Hubble Space Telescope observed lumps and knots that appear to be new stars and planets being formed.

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Planets in Formation?• Around the star Beta

Pictoris a large disk of dust and gas has been observed.

• The light from the star is much brighter than the disk so it had to be blocked for the disk to appear clearly.

• Disks have been seen around other stars too including Vega.

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Birth of the Sun• As material falls into

towards the disk it collides with other material and heats up and melts.

• The increasing mass of the core also increases the gravitational pull and causes more material to be pulled in.

• When the mass is large enough and temperatures high enough nuclear fusion reactions begin in the core and a star is born!

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Heating and Condensation of the Solar Nebula

• The heat from the Sun prevents ices from reforming on the dust grains in the region near the Sun.

• Ices condensed only in the outer parts of the Solar nebula.

• In the inner portion of the disk only materials like iron and silicates (rock) can condense into solids. Slowly they form clumps of material.

• In the outer portion of the disk much more material can condense as solids including ice. This extra material allows clumps to grow larger and faster.

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Gravity does the job• Within the disk, material is

constantly colliding with one another. If the collisions are not too violent material may stick together.

• In the outer parts of the Solar Nebula the planets become large enough to have a significant gravitational pull and collect gas around them.

• Planets in the inner nebula can not grow enough to collect much gas.

• Eventually most but not all of the material was swept up by the planets.

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The Last of the Planetesimals

The remaining material exists today as– comets which were flung

out to a region far beyond Pluto called the Oort cloud and

– asteroids mostly between Mars and Jupiter (the Asteroid Belt) and beyond Pluto (the Kuiper Belt)