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Solar System Formation

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Your Parents’ Solar System

21st Century Solar System

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Sun

Terrestrial Planets

Asteroid Belt

Jovian Planets

Kuiper Belt

Oort Cloud

The 21st Century Solar System

The Solar System: List of Ingredients

Ingredient Sun Jupiter Other planets Everything else

Percent of total mass

99.8% 0.1%

0.05% 0.05%

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The Sun •  A middle-aged, average star:

– Mostly Hydrogen & Helium – 99.8% of the Solar System – ~4.6 billion years old

•  Shines because it is hot: – Surface Temp ~6000 C – Mostly Visible, UV & IR light

•  Kept hot by nuclear fusion in its core:

– Builds Helium from Hydrogen fusion.

– Will shine for ~12 billion years

The Sun dominates the Solar System

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Terrestrial Planets •  Mercury, Venus, Earth & Mars

–  “Earth-Like” Rocky Planets – Largest is Earth – Only in the inner solar system (0.4 to 1.5 AU)

•  Rocky Planets: – Solid Surfaces – Mostly Silicates and Iron – High Density: (rock & metal) – Earth, Venus, & Mars have atmospheres

The Terrestrial Planets

Earth (1 M⊕)

Mars (0.11 M⊕)

Venus (0.82 M⊕)

Mercury (0.055 M⊕)

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The Jovian Planets •  Jupiter, Saturn, Uranus & Neptune

– Largest Planets: at least 15 times mass of Earth. – Only in the outer solar system (5 to 30 AU) – No solid surfaces (mostly atmosphere) – Low density

•  Gas Giants: (Jupiter & Saturn) – Thick H/He atmosphere, liquid hydrogen mantle, ice core

•  Ice Giants: (Uranus & Neptune) –  Ice/rock core & mantle, thin H/He atmosphere

The Jovian Planets

Jupiter (318 M⊕)

Uranus (15 M⊕)

Saturn (95 M⊕)

Neptune (17 M⊕)

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Dwarf Planets

•  Defined by the IAU (International Astronomical Union) in 2006

•  Dwarf Planets: –  Ceres: first of the Asteroids, discovered in 1801 –  Pluto: trans-Neptunian object discovered in

1930 –  Eris: trans-Neptunian object discovered in 2005 –  Haumea (trans-Neptunian, suspected) –  Makemake (trans-Neptunian, suspected)

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Dwarf Planets

The Giant Moons

•  Moon: any natural satellite orbiting a planet or dwarf planet

•  Giant Moons: – Earth: The Moon (Luna) –  Jupiter: Io, Europa, Ganymede, & Callisto – Saturn: Titan – Neptune: Triton

•  Many smaller moons, both rocky & icy. •  Only Mercury & Venus have no moons.

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The Giant Moons

Pluto

Triton Titan

Callisto

Ganymede

Moon

Io

Europa

Mercury

Rhea

Iapetus

Titania

Oberon

Pallas

Vesta

Hygeia

Mimas

Enceladus

Miranda Proteus

Ceres

Tethys Dione

Ariel Umbriel

Charon

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Kuiper Belt

•  Class of icy bodies orbiting beyond Neptune. – Found only in the outer Solar System (>30AU) – Densities of 1.2 to 2 g/cc (mostly ices)

•  Examples: – Pluto & Eris (icy dwarf planets) – Kuiper Belt Objects (30-50AU) – Charon, Pluto’s large moon – Sedna & Quaor: distant large icy bodies

Kuiper Belt

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Oort Cloud

•  Spherical cloud of comets. – Extends out to almost 50,000 AU (1 light-year) – May contain trillions of comets – The outer edge is the farthest reach of the Sun’s

gravitational pull. – There are no confirmed observations – its

existence is theoretical only.

Oort Cloud

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The Leftovers (small bodies) •  Asteroids:

– Made of rock & metal (density 2-3 g/cc) – Sizes: Few 100km to large boulders – Most are found in the Main Belt (2.1-3.2 AU)

•  Meteoroids: – Bits of rock and metal – Sizes: grains of sand to boulders

•  Comets: – Composite rock & ice “dirty snowballs” – Longs tails of gas & dust are swept off them when

they pass near the Sun.

Differences

•  Meteoroid – A PARTICLE from an asteroid or comet orbiting the sun

•  Meteor – Observed as it burns up in Earth’s atmosphere: Called a shooting star

•  Meteorite: Survives its passage through the Earth’s atmosphere and impacts Earth’s surface

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More Differences

•  Asteroid – Rocky body orbiting the sun •  Comet – Ice & dust hear the sun, a tail of

gas and particles pointing away from the sun

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Asteroids

253 Mathilde 951 Gaspra 243 Ida

Meteor burning up in the atmosphere.

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Comet P/Halley Comet P/Wilt

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Comparing Sizes of Stars & Planets

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Is Pluto a Planet?

What to consider? • Size? • Shape? • Orbit? • What is it made

of?

IAU Definition of a Planet In 2006, the International Astronomical Union

(IAU) came up with the following definition of a planet: §  orbits the Sun §  has sufficient mass for its self-gravity to overcome

rigid body forces so that it assumes a hydrostatic equilibrium shape (i.e., it is spherical),

§  has cleared the neighborhood around its orbit, §  is not a satellite

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IAU Definition of a Dwarf Planet In 2006, the International Astronomical Union

(IAU) came up with the following definition of a dwarf planet: §  orbits the Sun §  has sufficient mass for its self-gravity to overcome

rigid body forces so that it assumes a hydrostatic equilibrium shape (i.e., it is spherical),

§  has not cleared the neighborhood around its orbit, §  is not a satellite