Week 9: Saturn

Saturn Facts

• 6th planet from the sun

• jovian planet

  • shares similarities with Jupiter

    • but Jupiter is bigger than Saturn

• distance from the sun = 900 million miles or about 10 AU

  • saturn is almost twice as far from the sun as Jupiter

• diameter = 72,000 miles or about 9 Earth diameters

• volume = more than 750 Earths

  • more volume than Earth

  • less volume than Jupiter

• mass = 95 Earth masses

  • more mass than Earth

  • less mass than Jupiter

• Density = 0.69 g/cm³

  • very low density!

    • lowest of any known object in the solar system

    • less dense than water!

      • Saturn would float in large body of water

• Surface gravity = 1.16 g (earth’s gravitational pull )

• temperature at cloud tops = -290 degrees F

• composition = mostly Hydrogen and He, some other gasses

• satellites = 146

  • has more satellites than any other planet in our solar system

    

Saturn in Mythology

• Saturn was Jupiter’s father - god of time

  • also father to Pluto and Neptune

    • Oracle told him he would be overthrown by one of his sons

      • so to solve that problem, he ate his sons when they were born

        • his wife and sister hid Jupiter from him

          • Jupiter came back and overthrew him

Jupiter’s Rotation and Revolution

• period of rotation: 10 hours and 14 minutes

  • fast but not as fast as Jupiter

  • Saturn exibits differential rotation

• period of revolution: 29.5 years (amount of time it takes to go around the sun)

• axial tilt: 27 degrees F

  • has seasons!

Tidal Force

• Tide (Tidal Force): a stretching force due to gravity pulling on one side of a body more strongly than the other side

  • remember, gravity gets exponentially weaker with distance

Roche limit

• Roche limit: the distance from a body at which another body will be broken up due to tidal forces

  • this is what happened to Shoemaker-Levy 9 comet for Jupiter

    

History of observations of Saturn

• first telescopically observed in 1610 by Galileo

  • thought the rings were two smaller bodies fixed near Saturn

    • thought they looked like Saturn’s “ears”

      

Saturn’s rings (observations)

• 1657: Christiaan Huygen hypothesized that these “ears” were actually rings

  • Huygen also discovered titan (Saturn’s satellite")

• 1675: Giovanni Cassini discovered the “Cassini Division”

  • “Cassini Division” : a gap in the rings

    • the rings are a bunch of tiny little bodies (boulders, ice chunks)

      • rings are thin (3 story building)

Orientation of rings

• Orientation of rings changes with Saturn’s cycle

•     29.5 year cycle

  

• saturn’s rings are objects getting pulled towards Saturn’s center

  • objects on top move down ward rotation

  • objects on bottom move upward rotation

    • hit each other in center and straighten out

      

What are the rings made of?

• rings system is made up of chunks of ice and rocks

• size ranges from a small as grains of sand to as big as a house

  

Shepard Moons

• help keep rings stable / in place

  • any objects within inner/outer ring is pulled towards center of rings

    

Shepard Moons: Janus and Epimetheus

• have co-orbital motion

  • Epimetheus orbits closer to Saturn, so has shorter orbital period and eventually approaches Janus from behind

    • as they get closer, they tug on each other gravitationally

      • when near each other, they pull on each other and trade orbits

        • tugging by epimetheus slows down janus, which makes it fall towards saturn in its orbit

          • janus speeds. up eipmetheus which makes it rise

            • janus has 4x the mass of epimetheus so it moves inward and epimetheus moves outward

              • closer to saturn, Janus speeds up in its orbit

                • farther from saturn, epimetheus slows down

                  • janus will slowly creed ahead of epimetheus

                    • four years later they do the same dance in reverse

Layers of Saturn

• very similar to Jupiter

• again, layers aren’t this distinct

  • gradual transition

    

Saturn also has belts and zones

• similar to jupiter

  • belts = darker regions

  • zones = lighter regions

    

Storms on Saturn

• storms have large storms

  • can wrap around entire planet

    

Saturn’s Hexagon

• storms within Saturn

  

Saturn’s Auroras

• Saturn has strong magnetic field that causes auoras when wind crashes into them

  

Cassini Spacecraft

• launched in 1997

• arrived at saturn in 2004

  • mission ended 2017

• dropped the Huygens probe onto Titan

  

• took photos of shadows on saturn’s rings

  • structures cast shadows on the main rings, shown in photo below

    

Huygens Probe

• part of Cassini spacecraft, released onto titan

  • one of Saturn’s satellites

Saturn’s Satellites

Titan

• Saturn’s largest satellite

• thick atmosphere (mostly nitrogen)

  • 1.5x thicker than Earth’s atmosphere

    • contains organic molecules!

      • Methane

        • clouds of methane

        • surface has methane lakes

        • methane snow

        • possible methane drainage channels that may have formed from the evaporation or movement of methane

          

          
          

What Huygens Saw on Titan

Enceladus

• diameter = 318 miles (1/6th moon’s diameter)

• albedo: 97%

  • albedo: how reflective a body is

• surface is made of water ice

  • has water ice geysers

    • water geysers: water volcanos

  • thought that there are water streams under frozen ice surface

    

• Crater counting: how we can determine planet age by surface of the body

  • by counting craters (little holes/dots on planets)

    

Saturn’s E rings

• created by Enceladus’s water ice geysers

  • Enceladus’s shoots out ice geyers, making saturn’s ring (labelled E ring)

Other Moon/satellites of Saturn

• Mimas

  • looks like death star

    

• Phoebe

  • orbits saturn backwards / in opposite direction of other moons

    

• Hyperion

  

• Rhea

  • Rhea has its own ring of pebbles and boulders