Saturn and its rings

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Saturn and its rings moons
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• Fast Facts on Saturn
• average distance from Sun 9.5 AU
• 10 AU (maximum) and 9 AU (minimum)
• eccentricity 0.05 (5x Earth like Mars)
• orbital period 29.3 years (30 yrs)
• mass 5.7 x 1026 kg 95x Earths mass
• Gravity on Saturn 0.92 times Earths!
• diameter 120,536 km (9.5 Earth equator)
• and 108,728 km (8.5x Earth poles)
• average density 687 kg/m3
• rotation period (poles) 10 h 39.5 min
• rotation period (equator) 10 h 14 min
• average T of cloud tops in atmosphere
• 93 K -180 C -292 F
• albedo 0.46 albedo of rings 0. 80
• tilt of planets orbital plane relative

Voyager image of Saturn can just make out 2 of
Saturns small moons Tethys and Dione two of 31
total moons!
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Observing Saturn from Earth

• Saturn is the most distant planet that we
• can see with the naked eye looks like a
• bright star in the night sky
• Historical observations quickly revealed
• the system of rings around the planet
• Saturn is rising in the sky around midnight
• - transits overhead around 5 am
• Saturn is observed during oppositions
• - nearly yearly
• - next one 31st December 2003
• - disk of Saturn is 21 (size of Mars)

Galileo 1610

• Huygens 1655 rings/disk

Cassini - 1675 gap in rings
Commons - 1883 photograph
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Saturns 27 degree tilt on its axis relative to
orbit plane produces different views - Rings
seen edge on, underside, and top views -
Seasons on Saturn are much longer (7-8
years) - last edge on view in 1995-96 next one
2008-9 - currently high ring inclination angle
22 degrees!
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• Saturn Ring Plane
• Crossings
• occur when Earth passes into the
• same plane as rings directly
• edge-on view of planet
• - opportunity to learn more about rings,
• determine thickness of rings and discover
• new satellites
• - occur on 13-16 year intervals
• - some are more favorable than others
• - last one 1995-1996 very favorable
• - next favorable one 2038
• now until 2008, well see underside

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Saturns Rings Most unusual, striking feature of
the planet Saturn
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Composition of Saturns Rings

• If rings were solid, gravitational forces would
  tear rings apart
• an indefinite number of unconnected particles
  J.C. Maxwell
• 1895 rings confirmed not to be solid by James
  Keeler
• - using Doppler shift, inner rings moving more
  quickly than outer rings
• - if made of solid rings, would expect solid
  body rotation signature
• - rings of Saturn made of moonlets, small
  ring particles