mean synodic period*

378.10 Earth days

mean orbital velocity

9.7 km/sec

equatorial radius**

60,268 km

polar radius**

54,364 km


5.685 * 1026 kg

mean density

0.69 g/cm3

equatorial gravity**

896 cm/sec2

polar gravity**

1,214 cm/sec2

equatorial escape velocity**

35.5 km/sec

polar escape velocity**

37.4 km/sec

rotation period (magnetic field)

10 hr 39 min 24 sec (Voyager era); about 10 hr 46 min (Cassini-Huygens mission)

inclination of equator to orbit


magnetic field strength at equator

0.21 gauss

number of known moons

at least 47

planetary ring system

3 major rings comprising myriad component ringlets; several less-dense rings

*Time required for the planet to return to the same position in the sky relative to the Sun as seen from Earth.

**Calculated for the altitude at which 1 bar of atmospheric pressure is exerted.

A quarter century later, however, some measurements made by Cassini indicated that the field was rotating with a period 6-7 minutes longer. It is believed that the solar wind is responsible for some of the difference between the two measurements of the rotational period. The time differences between the rotation periods of Saturn's clouds and of its interior have been used to estimate wind velocities. Other radio bursts with periods of about 10 hours 10 minutes originate with lightning in Saturn's atmosphere.

Because the four giant planets have no solid surface in their outer layers, by convention the values for the radius and gravity of these planets are calculated at the level at which one bar of atmospheric pressure is exerted. By this measure, Saturn's equatorial diameter is 120,536 km (74,898 miles). In comparison, its polar diameter is only 108,728 km (67,560 miles), or 10 percent smaller, which makes Saturn the most oblate (flattened at the poles) of all the planets in the solar system. Its oblate shape is apparent even in a small telescope. Even though Saturn rotates slightly slower than Jupiter, it is more oblate because its rotational acceleration cancels a larger fraction of the planet's gravity at the equator. The equatorial gravity of the planet, 896 cm (29.4 feet) per second per second, is only 74 percent of its polar gravity. Saturn is 95 times as massive as Earth but occupies a volume 766 times greater. Its mean density of 0.69 g/cm3 (0.4 oz/in3) is thus only some 12 percent of Earth's. Saturn's equatorial escape velocity—the velocity needed for an object, which includes individual atoms and molecules, to escape the planet's gravitational attraction at the equator without having to be further accelerated—is nearly 36 km per second (80,000 miles per hour) at the one-bar level, compared with 11.2 km per second (25,000 miles per hour) for Earth. This high value indicates that there has been no significant loss of atmosphere from Saturn since its formation.

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