- 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.
- always points away from the sun
