Saturn

Basic Properties:

  • Mass: 95 M
  • Radius: 9.5 R
  • Density: 0.7 gm/cm3 (12% of Earth’s), less than water
  • "Surface" gravity: 1.1 x Earth’s (at the cloud tops)
  • # of moons: 30+

Orbit and Rotation:

  • Saturn completes 1 orbit around the Sun in ~ 29.5 years. It takes a little of two years to travel through each zodiacal constellation as seen from Earth.
  • Average distance from the Sun = 9.5 AU.
  • Rotates rapidly – 10h 20m, producing a distinct equatorial bulge. Like Jupiter, higher latitudes on Saturn rotate more slowly – which is only possible for a gaseous planet.
  • Rotation axis tilt – 27, quite different from Jupiter’s tilt.

Atmosphere:

  • As with Jupiter, the visible “surface” of Saturn is actually the top of clouds in a bottomless atmosphere.
  • Overall, Saturn displays a more uniform, less colorful appearance than Jupiter. The clouds are less colorful or distinct.
  • Saturn’s weaker gravity produces a thicker cloud layer than on Jupiter, although the composition and layering of the cloud decks are believed similar. The atmosphere extends over a larger distance, compared to Jupiter.
  • The atmosphere is composed of 92% hydrogen, 7% helium, and trace amounts of methane and ammonia. Helium is significantly depleted in Saturn’s atmosphere, compared to Jupiter or the Sun.
  • Bands and occasional “storms” on Saturn are produced by the same processes as on Jupiter, but appear more muted.
  • The zonal wind flows are much stronger on Saturn (compared to Jupiter), reaching 1500 km/hr at the equator.

Interior & Magnetosphere:

  • Saturn radiates 3 times the amount of energy it receives from the Sun.
  • Unlike Jupiter, the source of this “excess” energy is helium precipitation: the slow rain of liquid helium drops in the deep interior.
  • This depletion of helium in Saturn was demonstrated by spectra taken with the Voyager probes, which flew by Saturn in the 1980s. Helium is less abundant, with respect to hydrogen, in Saturn’s atmosphere compared to the Sun or Jupiter.
  • Saturn has cooled off faster than Jupiter, due to its smaller mass, and the heat leftover from formation of the planet contributes much less to the overall energy output.
  • Saturn’s internal structure is believed similar to Jupiter’s, with overall lower temperatures and pressures, and a smaller metallic hydrogen zone.
  • Saturn’s magnetosphere, which is about one-twentieth as strong as Jupiter’s, also emits radio radiation, and is simpler in structure compared to Jupiter’s.

Exploration:

  • Pioneer 11: first spacecraft to Saturn, flyby, Sept 1979.
  • Voyager I & II: flybys, Nov 1980, Aug 1981. Provided first detailed look at the rings and moons of Saturn. Passed through the ring plane, discovered ring “spokes”, the braided F-ring, shepherd satellites.
  • Cassini + Huygens: Launched 1997. First Saturn orbiter. Arrived July 2004. Huygens atmosphere probe descended to the surface of Titan in Jan 2005, and snapped images from the surface, the first time an ice world has been seen close-up.