Saturn

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth.[22][23] It only has one-eighth the average density of Earth; however, with its larger volume, Saturn is over 95 times more massive.[24][25][26] Saturn is named after the Roman god of wealth and agriculture; its astronomical symbol (♄) represents the god's sickle. The Romans named the seventh day of the week Saturday, Sāturni diēs ("Saturn's Day") for the planet Saturn.[27]

Saturn
Pictured in natural color approaching equinox, photographed by Cassini in July 2008; the dot in the bottom left corner is Titan
Designations
Pronunciation/ˈsætərn/ (listen)[1]
Named after
Saturn
AdjectivesSaturnian /səˈtɜːrniən/,[2] Cronian[3] / Kronian[4] /ˈkrniən/[5]
Orbital characteristics[6]
Epoch J2000.0
Aphelion1,514.50 million km (10.1238 AU)
Perihelion1,352.55 million km (9.0412 AU)
1,433.53 million km (9.5826 AU)
Eccentricity0.0565
378.09 days
9.68 km/s (6.01 mi/s)
317.020°[8]
Inclination
113.665°
2032-Nov-29[10]
339.392°[8]
Known satellites82 with formal designations; innumerable additional moonlets.[6]
Physical characteristics[6]
Mean radius
58,232 km (36,184 mi)[lower-alpha 1]
Equatorial radius
Polar radius
Flattening0.09796
Circumference
Volume
Mass
  • 5.6834×1026 kg
  • 95.159 Earths
Mean density
0.687 g/cm3 (0.0248 lb/cu in)[lower-alpha 2] (less than water)
0.22[13]
35.5 km/s (22.1 mi/s)[lower-alpha 1]
10 h 32 m 36 s
(synodic; solar day)[7]
10h 33m 38s + 1m 52s
1m 19s
[14][15]
Equatorial rotation velocity
9.87 km/s (6.13 mi/s; 35,500 km/h)[lower-alpha 1]
26.73° (to orbit)
North pole right ascension
40.589°; 2h 42m 21s
North pole declination
83.537°
Albedo
Surface temp. min mean max
1 bar 134 K
0.1 bar 88 K[18] 97 K[19] 151 K[18]
−0.55[20] to +1.17[20]
14.5″ to 20.1″ (excludes rings)
Atmosphere[6]
Surface pressure
140 kPa[21]
59.5 km (37.0 mi)
Composition by volume
96.3%±2.4%hydrogen (H
2
)
3.25%±2.4%helium (He)
0.45%±0.2%methane (CH
4
)
0.0125%±0.0075%ammonia (NH
3
)
0.0110%±0.0058%hydrogen deuteride (HD)
0.0007%±0.00015%ethane (C
2
H
6
)
Ices:

    Saturn's interior is most likely composed of a core of iron–nickel and rock (silicon and oxygen compounds). Its core is surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and finally a gaseous outer layer. Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. An electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than the Earth's, but which has a magnetic moment 580 times that of Earth due to Saturn's larger size. Saturn's magnetic field strength is around one-twentieth of Jupiter's.[28] The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h (1,100 mph; 500 m/s), higher than on Jupiter but not as high as on Neptune.[29]

    The planet's most famous feature is its prominent ring system, which is composed mostly of ice particles, with a smaller amount of rocky debris and dust. At least 82 moons[30] are known to orbit Saturn, of which 53 are officially named; this does not include the hundreds of moonlets in its rings. Titan, Saturn's largest moon and the second largest in the Solar System, is larger than the planet Mercury, although less massive, and is the only moon in the Solar System to have a substantial atmosphere.[31]