• A great cloud of gas and dust (called a nebula) begins to collapse and spin
  • Nebula begins to flatten into a spinning pancake shape with a bulge at the center
  • This is due to forces of gravity and rotation
  • Further collapse causes certain regions to condense into the sun, planets, and moons
  • In the center is the sun
  • Inner planets are small, dense, & rocky
  • Outer planets are large, less dense, and made of gas

**In order to be classified as a planet, an object in space must meet 3 criterion; It must:

  • orbit the sun.
  • maintain a roughly circular shape.
  • be large enough to clear it’s orbital path of other debris/objects.

The Planets

  • Closest to the Sun (0.4 AU)
  • 2nd smallest planet
  • Shortest orbit (1 year = 88 days)
  • 1 Mercury Day = 59 days
  • Temperature = from -180°C to 425°C
  • Many impact craters, basins, and rilles
  • Most of these were created from meteor bombardment during the formation of the solar system

Venus

  • 2nd from the sun (0.7AU)
  • Orbit (1 Venus year) = 225 days
  • Retrograde Rotation
  • spins the opposite direction
    • 1 Venus day = 243 Earth days
    • Nearly the same size as Earth
    • Extremely weak magnetic field
    • Always covered by thick clouds
    • Impossible to see the surface!
      • Little water vapor in clouds
    • Mostly CO2 and sulfuric acid!
      • RUNAWAY Greenhouse Effect!
    • Making it the hottest planet! (475 °C)
      • Mountains & Canyons
      • Volcanoes (recent activity?)

Mars

  • 4th planet (last terrestrial planet)
  • Rotation (1 day) = 24 hours 37 minutes
  • Orbit (1 year)= 687 days
  • Approximately 1/3 the size of Earth
  • Has 2 moons = Phobos & Deimos
  • Not spherical (Large asteroids?)
    • Has a reddish-brown color
    • Due to blowing dust & rocks
      • Has an atmosphere with clouds – Mainly CO2 w/ N and Ar
      • Has polar ice capse w/seasons
      • Made of CO2 & frozen water
      • Many mountains & canyons
    • Valles Marineris
      • Home of the biggest volcano in the solar system!
    • Olympus Mons
      • HOWEVER, NO plate tectonic activity has been noted.

Jupiter

  • Largest Planet
  • 318 x’s  mass of Earth
  • 2 ½ x’s more massive than all other planets combined
  • 5th Planet (5.2 AU)
  • Rotation (1 day) = 9 hours 55 minutes
  • Orbit (1 year) = 11.9 years
  • Massive magnetic field
  • Atmosphere = mostly H & He
  • Gives off more heat than it receives from the Sun
  • 16 moons & one faint ring
  • May have been a 2nd sun if it had been larger!
  • Complex Atmosphere
  • Colorful bands, high winds
  • Light colored bands = zones
  • Dark colored bands = belts
    • Many storms
    • The Great Red Spot
    • Driven by Jupiter’s internal energy
    • Existed for at least 400 years!
      • 16 Moons à 4 largest = Jovian Moons
      • Io = The Volcanic Moon
    • Many active Volcanoes
      • Europa = The Ice Moon
    • Thick layers of ice covering more ocean water than on Earth!
      • Ganymede = The Largest Moon
      • Callisto = The Cratered Moon

Saturn

  • 2nd most massive planet
  • Rotation (1 day) = 10-11 hours
  • Orbit (1 year) = 29 years 6 months
  • Lowest density of any planet
  • It would float in water!
    • Elaborate Ring System – chunks of ice and rock
    • Atmosphere of H & He gas
    • Gives off more heat than it receives
    • Very large magnetic field, but weaker than Jupiter’s
    • Storms & high-velocity winds
    • Complex Ring System
    • made up of mostly ice & rock
    • only 10 km thick
    • Rings are NOT uniform
    • Spokes” have been found
      • 19 known moons
    • Titan = Saturn’s largest moon
      • 2nd largest moon in the solar system
      • Has an atmosphere (mostly made of methane)
    • Shepard Moons
    • help maintain Saturn’s rings

Uranus

  • 7th planet (19.2 AU)
  • 1st planet discovered in “modern times” (1781)
  • Spins through space on it’s side!
  • Rotation (1 day) = 17 hours
  • Orbit (1 year) = 84 years
  • Rings and 21 Moons
  • Atmosphere mostly of H & He
  • Generally featureless
  • Blue color from methane gas
  • Magnetic field is NOT on the same axis as its poles!

Neptune

  • Highly elliptical orbit (30 AU at max!)
  • At times our most distant planet
  • Rotation (1 day)  = 16 hours
  • Orbit (1 year) = 165 years
  • Atmosphere =             H, He, and methane
  • Methane give it the bluish color
  • Storms = Wind speeds of 730 mph
  • The Great Dark Spot (similar to Jupiter’s)
    • Faint ring system
    • 8 Moons (2 large & 6 smaller)
    • Triton = similar in size to our moon
      • Orbits Neptune in a retrograde motion
      • Degrading orbit = it will eventually crash!

**Pluto

  • Dwarf planet
  • 2/3 the size of the Moon
  • Rotation (1 day) = 6 ½ days
  • Orbit (1 year)= 165 years & highly elliptical
  • Little atmosphere & very cold temperatures
  • 1 Moon = Charon
  • Nearly the same size as Pluto!

Other Objects

  • Comets
  • small bodies of dust & ice (“dirty snowballs”) composed of water, CO2, ammonia, & methane ices
  • Tail” is from ions being blown off from the solar wind
    • always points away from the sun
      • Asteriods
    • Rocky and metallic objects too small to be considered planets
    • Highest concentration = belt between Mars and Jupiter
      • Meteors, Meteroids, & Meteorites
    • Small pieces of space debris on a collision course with the Earth are called meteoroids
    • When meteoroids enter the Earth’s atmosphere they are called meteors
    • Most burn up before they hit the Earth.
      • Shooting Stars!
    • Some large ones have caused major damage!
    • A meteorite is a part of a large meteoroid that survives it’s trip through the atmosphere and strikes Earth’s surface.
      • Most are found in Antarctica.

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