The Planets: Formation of the Solar System

• 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)
• 2^nd 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

• 2^nd 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

• 4^th 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
• 5^th 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 2^nd 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

• 2^nd 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
    • 2^nd largest moon in the solar system
    • Has an atmosphere (mostly made of methane)
  • Shepard Moons
  • help maintain Saturn’s rings

Uranus

• 7^th planet (19.2 AU)
• 1^st 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.