Nobody knows exactly how long a day lasts on Saturn
Saturn has no solid surface to track, and its clouds spin at different speeds depending on latitude. Voyager's radio readings suggested a day of about 10 hours 39 minutes, but when Cassini arrived in 2004 the radio signal had slowed by several minutes. The true length of its day remains elusive.
Astronomers juggle several rotation systems. The equatorial belts circle in about 10 hours 14 minutes, while most other latitudes take roughly 10 hours 38 minutes. Measurements from Cassini, Voyager and Pioneer combined give about 10 hours 32 minutes for the planet as a whole, and studies of the C Ring point to a similar figure. In 2007 researchers found that the planet's radio pulses did not track its spin at all, possibly because water vapour vented by geysers on the moon Enceladus becomes charged and drags on Saturn's magnetic field.
The second-largest planet is also the only one in the Solar System less dense than water, averaging 0.69 grams per cubic centimetre. About nine times Earth's radius, it carries 95 Earth masses, less than a third of Jupiter's, yet the two giants together hold 92 percent of all planetary mass around the Sun. Ammonia crystals high in its atmosphere give it a pale yellow tint, and winds reach 1,800 kilometres per hour.
Despite being made mostly of hydrogen and helium, nearly all its mass is not gas: under crushing pressure the hydrogen turns liquid and, deeper down, metallic. Electric currents in that metallic layer probably generate its magnetic field. Ring measurements suggest a diffuse core of roughly 17 Earth masses spreading across about 60 percent of the planet's radius. The core reaches about 11,700 degrees Celsius, and Saturn radiates 2.5 times as much energy as it receives from the Sun. Part of that heat may come from helium droplets raining down through the lighter hydrogen, releasing energy by friction.
At least 293 moons orbit Saturn, and Titan, larger than Mercury, is the only moon anywhere with a thick atmosphere. The planet takes its name from the Roman god of agriculture and wealth, father of Jupiter, and Saturday was named for it.
Source: Saturn
