The Planets

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The Planets!

• There is so much information! What do we really
  need to know?!

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Planets

• Terrestrial (Earth-like)
• Smaller, made of rock, closer to the Sun
• Mercury, Venus, Earth, Mars
• Gas Giants
• Large, made of dense gases
• Jupiter, Saturn, Uranus, Neptune
• Far from the Sun
• Pluto doesnt fit into either group (and YES,
  still a planet!)

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Relative Size of Objects in our Solar System
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Average TemperaturesMeasured in Kelvin
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Relative DiametersCompared to Earth
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Relative Densities of the PlanetsWater has a
density of 1g/cubic cm
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Inner Planets Close to the Sun, solar heat
vaporized ices and prevented lightweight
elements, like hydrogen and helium, from
condensing. Outer Planets In the solar
system's outer region, though, it was chilly
enough for ices to remain intact. They, too,
merged into planetessimals, which in turn came
together to form the cores of the giant planets
Plenty of hydrogen and helium remained in this
region far from the Sun. As the giant planets
grew, their gravity swept up much of these
leftovers, so they grew larger still..
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But why, WHY?
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Think About It!

• Why are all orbits in the same direction ?
• Why are most orbits in the same plane ?
• Why do we have terrestrial and gas giant groups
  of planets ?

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All stars form from cloudsof gas and dust which
roam our galaxy.

• Eventually, gravity causes the cloud to collapse
  since the cloud is spinning, material falls in
  along the "poles" faster than it does near the
  "equator". This flattening results in a disk-like
  object.

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Gravity slowly pulls material from the cloud into
the center of this disk, forming a new star.

• While the star continues to grow, lumps form in
  the disk which will ultimately become planets.

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Formation of Protoplanets

• The disk eventually thins as more material falls
  onto the star and the protoplanets.
• A hole in the disk near the star forms as
  material is completely incorporated into the star
  and planets.

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Inner Planets Formation

• Now fully formed planets exist within the hole,
  even as new planets are still under construction
  in the outer parts of the disk.

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When the Dust Clears

• It leaves a fully formed solar system like our own

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Atoms and molecules within the nebula combined to
form larger particles and eventually planets.
The Sun determined what kinds of particles
could exist.
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The Sun, our nearest star

• A massive ball of hot gas situated at the center
  of our solar system.  

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The Terrestrial Planets
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Terrestrial Characteristics

• Smaller
• Closer to the sun, warm
• Higher densities
• Slower rotations
• Solid Surfaces
• Evidence of plate tectonics
• No or Fewer Moons

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The Terrestrial Planets

• Planets forming close to Sun
• warmer
• strong gravitational forces from Sun
• hard for light elements to condense from gas to
  solid (no water condensed)
• hard for solids to collect together
• planets made of heavy elements only tend to be
  smaller
• fewer moons because
• small mass of planets weaker gravity
• close to Sun competition with Sun's gravity

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Mercury

• It is difficult to observe Mercury from
  ground-based telescopes because it never strays
  far from the Sun.
• It has an elliptical orbit which, although not as
  elliptical as Pluto's, is worth noting since it
  means the closest it gets to the Sun is 46
  million km while the furthest it ever gets is 70
  million km.  

The Planet with the most Elliptical Orbit that
is an Official Planet!
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Venus - the hell planet

• Venus is our closest neighbor in the solar
  system. 
• Often and on a clear night, it can be seen in
  the  sky just after dawn or in the early evening.
• The pale yellow clouds in it's thick atmosphere
  of Carbon Dioxide reflect light from the Sun very
  effectively
• This reflectivity and it's relative closeness
  enables us to see it with the naked eye.

Backwards rotation Most circular orbit
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Earth and Moon

• Only planet with a hydrosphere
• Experiences seasons due to its axial tilt
• Thin atmosphere of nitrogen and oxygen
• Life, only planet with it?

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Mars- the red planet

• Full-globe picture taken from the Hubble space
  telescope.
• Mars surface contains
• craters
• volcanoes
• polar ice caps
• fleecy white clouds in the thin Martian
  atmosphere
• Mars is tilted like the Earth and experiences
  seasons like the Earth
• Mars also has a similar day length to the Earth

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The Jovian PlanetsGas Giants
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Gas Giant Characteristics

• Larger
• Mostly Hydrogen and Helium
• Jupiter and Saturn contain the most.
• Uranus and Neptune contain larger fractions of
  water, ammonia, methane, and carbon monoxide.
• Low densities
• Rapid Rotations
• Thick Atmospheres
• All have Rings possibly formed when a moon was
  destroyed by a collision or ripped apart by the
  Giants gravity
• Many Moons found farther out than the Rings

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The Jovian PlanetsGas Giants

• Planets farther from Sun
• colder
• less effects of Sun's gravity
• light and heavy elements included in planet (also
  water and ice) - mainly hydrogen
• by trapping all elements, planets become large
  and attract even more gas
• more moons because
• large mass of planets strong gravity
• far from Sun little competition with Sun

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Jupiter- the giant planet

• Largest Planet
• 11X the diameter of the Earth
• Much less dense than the Earth
• Composed of mainly Hydrogen and Helium
• No solid surface
• 39 Moons
• 1 Ring

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Saturn The Ringed Planet

• A common feature of the gas giants  is the
  existence of rings around them.
• Although Saturn's rings are easily the most
  obvious and spectacular, Jupiter, Neptune and
  Uranus all have ring systems.
• Saturn is the least dense of all of the planets
• Second largest planet
• 30 moons

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Uranus-the tilted planet

• Uranus is around the same distance from Saturn as
  Saturn is from the Sun. 
• The discovery of Uranus effectively doubled the
  size of the known Universe. 
• It was the first planet to be discovered with a
  telescope. 
• The methane in its atmosphere reflects blue
  light
• 21 Moons

Rotates backwards and has a rotation tilted at 98
degrees from its orbital plane
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Neptune- the blue giant

• Now we are nearing the outer edges of our solar
  system. 
• Neptune is 4500 million km from the Sun
• The Sun would appear  to be little more than a
  bright star way way off.
• Little was known about Neptune until the Voyager
  2 space probe passed right by in
  1982..........wonder how long that took to get
  there?
• 8 Moons

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Pluto- Planet?

• Pluto is at the outer most edge of our solar
  system and it is the smallest planet of all. 
• It has an elliptical orbit that sometimes brings
  it is closer to the Sun than Neptune.
• One of its moons, Charon, is half the size of
  Pluto.

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2006 Definition of a Planet

• The 2006 definition of "planet" by the
  International Astronomical Union (IAU) states
  that, in the solar system, a planet is a
  celestial body that
• Is in orbit around the Sun,
• Has sufficient mass so that it assumes a
  hydrostatic equilibrium (nearly round) shape, and
  
• Has cleared the neighborhood" around its orbit.
• A body that meets only the first two is
  classified as a dwarf planet
• A body that meets only the first is a small
  solar system body

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Pluto- Planet? Dwarf Planet? Escaped Moon of
Neptune?Kuiper Belt Object?

• A probe was just launched on January 19, 2006 to
  explore Pluto. It should arrive in June 2015.
• New Horizons will slingshot around Jupiter at
  about 0543 GMT (1243 a.m. EST) Wednesday,
  February 27, 2007 (Today!)

New Horizons Space Probe
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New Horizons

• New Horizons is on the fastest spacecraft trip
  ever to the outer Solar System. It reached the
  orbit of Earth's Moon in fewer than 9 hours, then
  hustled off toward Jupiter. It will be passing by
  Jupiter from February 25 and March 2, 2007.
• The interplanetary cruise then will extend
  through June 2015 when New Horizons will arrive
  at the Pluto system for a five-month-long
  reconnaissance flyby of the planet, its moon
  Charon and two other unnamed moons just
  discovered in 2005