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A Guide to the Solar System

Earth, as viewed by the

Voyager spacecraft

Solar System

on a shoe string budget

Reading: Chapter 12

Relative Sizes of the Sun and

Planets

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• Radius: 108 x radius of Earth

• Mass: 333,000 x mass of Earth

• Over 99.9% of solar system’s mass

• Surface temperature 5800 K

The Sun

• Composition: 98% hydrogen and helium, 2% other

elements

• In 1 second the Sun produces a million times the total

energy used in the US in 1 year !

The Sun

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• Made of metal and rock; large iron core, no atmosphere

• Desolate, cratered

• Very hot and very cold: 425°C (day), –170°C (night)

• Rotates 3 times in every 2 orbits around the Sun

Mercury

0.4 AU from sun

0.38 x radius of Earth

0.055 x mass of Earth

• Extreme greenhouse effect: Hotter than Mercury: 470°C,

day and night

• Atmospheric pressure like 1km underwater!

• No oxygen or water

Venus

0.7 AU from sun

0.95 x radius of Earth

0.82 x mass of Earth

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• An oasis of life

• The only surface liquid water in the solar system

• A surprisingly large moon

Earth

• Looks almost Earth-like, but don’t go without a spacesuit!

• Giant volcanoes, a huge canyon, polar caps, more…

• Water flowed in the distant past; could there have been life?

• Dramatic Mars movies and simulations:

maasdigital.com/gallery.html

esa.int/SPECIALS/Mars_Express/SEMINCO7BTE_0.html

Mars

1.5 AU from sun

0.53 x radius of Earth

0.11 x mass of Earth

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• Much farther from

Sun than inner

planets

• Mostly H/He; no

solid surface

• 300 times more

massive than

Earth

• Many moons,

rings …

Jupiter

5.2 AU from sun

11.2 x radius of Earth

318 x mass of Earth

Jupiter’s moons

can be as

interesting as

planets

themselves,

especially

Jupiter’s four

Galilean moons

• Io: Active volcanoes all over

• Europa: Possible subsurface ocean

• Ganymede: Largest moon in solar system

• Callisto: A large, cratered “ice ball”

Jupiter

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Jupiter's Ring System

Jupiter's Ring System

Jupiter

Saturn

• Giant and gaseous like Jupiter

• Spectacular rings made of ices and rocks

• Many moons, including cloudy Titan• Cassini spacecraft currently studying it

9.5 AU from sun

9.4 x radius of Earth

95.2 x mass of Earth

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Saturn

Cassini’s view of Saturn with the Sun behind it

Can you spot Earth ?

Saturn

Cassini’s view of Saturn with the Sun behind it

Now can you spot Earth ?

Check out saturn.jpl.nasa.gov/home/index.cfm for more

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• Smaller than

Jupiter/Saturn;

much larger than

Earth

• Made of H/He gas

& hydrogen

compounds

(H2O, NH3, CH4)

• Extreme axis tilt

• Moons & rings

Uranus

19.2 AU from sun

4 x radius of Earth

14.5 x mass of Earth

• Similar to

Uranus (except

for axis tilt)

• Many moons

(including

Triton)

• Has rings

Neptune

30.1 AU from sun

3.9 x radius of Earth

17.1 x mass of Earth

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Pluto: A Dwarf Planet

• Much smaller than other planets: Dwarf planet

• Icy, comet-like composition

• Its moon Charon is similar in size

• The plane of its orbit is tilted

• Other dwarf planets: Eris, Ceres

39.5 AU from sun

0.18 x radius of Earth

0.0022 x mass of Earth

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Motion of Planets

• All planets in

the solar system

orbit in the

same direction

and in nearly

the same plane

• Most also rotate

in that direction

Two Main Planet Types

• Terrestrial planets

are rocky,

relatively small,

and close to the

Sun

• Jovian planets are

gaseous, larger,

have rings and are

farther from Sun

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Notable Exceptions

• Several

exceptions to

the normal

patterns need to

be explained

Small Bodies in the Solar System

• Small bodies, the leftover “scraps” from the formation of the

Solar System, fall into three distinct groups:

1 asteroids

• rocky or metallic in composition

• most are located between the orbits of Mars and Jupiter

http://www.nasa.gov/mission_pages/WISE/multimedia/pia12469.html

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2 Kuiper belt comets

• made mostly of ice

• orbit the Sun beyond

Neptune

• orbit in same

direction and plane as

the planets

3 Oort cloud comets

• made mostly of ice

• orbit at the outer

fringe of the Solar

System

• spherically distributed

about the Sun

Small Bodies in the Solar System

Properties of Asteroids• They are small in size.

• the largest one, Ceres, (now a dwarf planet) is only 1,000 kmacross

• They are not spherical in shape.

• shaped more like “potatoes”

• gravity not strong enough to compress rocky material

• odd shapes imply that some are fragments from asteroidcollisions

• Small asteroids are morecommon than large asteroids.

• All the asteroids in the solarsystem wouldn’t add up toeven a small terrestrial planet.

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Rocks Falling from the Sky

• meteor – a trail of light caused by a particle which enters

Earth’s atmosphere.

• most of these particles are the size of a pea

• they completely burn up in Earth’s atmosphere

• meteorite – a rock which is large enough to have survived its

fall to Earth

• they caused a brighter meteor…sometimes called a fireball

• How can you tell that you have a meteorite?

– they have a higher metal content than terrestrial rocks

– they contain Iridium and other isotopes not found in

terrestrial rocks

Comets

• Comets are icycounterparts to asteroids.

• Unlike planets, they arenot confined to the eclipticand disappear after severalweeks

• Most comets remainperpetually frozen in theouter solar system.

• Only comets that enter theinner solar system growtails.

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Composition and Structure of Comets

• Comets are “dirty snowballs”…ice mixed with rock and dust.

• ices are H2O, CO2, CO, NH3, CH4

• nucleus

• the “dirty snowball”

• how the comet appears farfrom the Sun

• coma

• surrounds nucleus when nearthe Sun

• sublimated gas & dust

• plasma tail

• ionized gas swept back bySolar wind

• dust tail

• dust particles swept backmore slowly by radiation

A Comet’s Journey

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Meteor Showers

• Earth is impacted by an estimated 25 million small particles

each day which cause meteors.

• When the Earth passes through the trail of a comet, the

number of particles impacting the Earth’s atmosphere

increases. We call this a meteor shower.

Perseid meteor

shower against the

backdrop of an

aurora, (2000).

Meteor Showers

• Showers occur on the same dates each year, corresponding to

when the Earth crosses a given comet’s orbit.

• The meteors appear to emanate from one point in the sky.