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The Planets
Ali Nork
Planetary Revolution
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Planets revolve counterclockwise
around Sun
Planets revolve on a common
plane called the ecliptic
• Pluto’s orbit is tipped 17.2°
• Other planets tipped no more than
3.4°
Planetary Rotation
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Almost all planet rotate
counterclockwise, but
• Venus rotates backwards
(retrograde)
• Uranus and Pluto rotate on sides
w/ equator perpendicular to orbit
Inner Planets
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Terrestrial, or “earthlike”
Mercury, Venus, Earth, Mars
Closer to sun
Small diameter/mass
Density greater than water (35g/cm3)
Rocky crust, dense mantle
Very dense core w/ Fe and Ni
Inner planets cont’d….
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Impact craters
Few moons (actually- Mercury and
Venus have no moons)
Less atmosphere
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Animation here
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Outer Planets
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Jovian planets- Jupiter-like
Gas giants- Jupiter, Saturn, Uranus,
Neptune
Huge compared to Earth
Large mass, low density
(<1.75g/cm3)
Mostly gaseous (H and He)
Outer Planets cont’d….
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Have rings
Have many moons- Jupiter (63),
Saturn (62), Uranus (27), Neptune
(13)
Separated from terrestrial planets by
the Asteroid Belt
What’s Up With Pluto?
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Was considered a planet for 76 years
2006- reclassified as a dwarf planet
Mostly ice
Very small (1/20 the mass of
Mercury)
Has 3 moons (Charon, Nix and
Hydra)
Highly eccentric (elliptical) orbit
which crosses Neptune’s
http://en.wikipedia.org/wiki/Image:TheKuiperBelt_Orbits_Pluto_Eclipti
c.svg
Origin of the Solar System
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Solar nebula model- ss formed out of
an eastward rotation interstellar
cloud 5 billion years ago
• Dust and gas cloud (mostly H and
He)
Cloud condensed due to gravity;
speed of rotation increased; became
flattened
Densest area in middle became the
sun
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Disk eventually cooled; different
elements and compounds condensed
depending on distance from sun
Tiny grains of condensing material
accumulated and collided; eventually
formed planetismals (“baby planets”)
Jupiter was the first large planet to
form in outer ss; probably prevented
other outer planets from growing larger
Asteroid belt (interplanetary debris
between Mars and Jupiter) remains b/c
Jupiter’s gravity prevented it from
creating a planet
Planetary Formation
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Terrestrial planets formed where
temps were very high and metals
and silicates could form solids
Jovian planets formed at lower
temps where gas became ice
No planets in asteroid belt b/c Jupiter
is so massive and its gravity
disturbed planet formation
Larger mass enables planets to hang
onto particles in rings; less impacted
by solar wind (far away from sun)
Planetary Satellites
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Moons are natural planetary
satellites that revolve around a
planet
Some cool moon facts:
• Jupiter’s moon Ganymede is the largest
one in our solar system
• Saturn’s moon Titan has a mostly
nitrogen atmosphere and has liquid
hydrocarbon lakes; also has water ice
• Mars has 2 tiny moons (Phobos and
Deimos) which may be captured
asteroids
Ganymede
Titan
Phobos and Deimos
Voyager I “family portrait”
-Taken in
1990 after
Voyager I
and II left
Pluto’s
probit
Asteroids
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Rocky masses that revolve around
Sun; usually between Mars and
Jupiter
Debris left over by a planet that
failed to from (about 2.8 AU from
Sun)
Need a telescope to view them
Largest is Ceres (578 mi wide)
Comets
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Nucleus of ice and debris; coma is
gas surrounded by nucleus
Comets cont’d…
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Tail points away from sun and is
caused by solar wind
Long, eccentric orbit which goes
outside the 9 (or 8) planets
Orbital periods can be long or short
Comet Shoemaker-Levy 9 slammed
into Jupiter’s atmosphere in 1994
Kuiper Belt
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Located beyond planet Neptune
Home to over 700,000 icy, small
objects (Pluto, Quaoar)
Sometimes objects are redirected
towards the sun (disturbed by
gravity of one of the gas giants)
Oort Cloud
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Home to many comets
Located 50,000 AU from the sun
Outer edge defines the boundary of
our solar system
Members include Sedna and various
comets
Meteoroids
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Rocky, icy fragment in space
Range in size from small sand
particles to boulders
Meteor (shooting star) is light
produced when enters Earth’s
atmosphere due to friction
Meteorite is meteoroid that has
struck Earth’s surface
• May produce impact craters
Meteoroids cont’d…
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Meteoroids can’t be seen, but
meteors can b/c of light produced
Maybe formed from impacts between
asteroids
Micrometeoroids- tiny fragments that
often hit Earth
• Can travel at high speeds and damage
spacecraft