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| synodic_period = 378.09 days〔 | avg_speed = 9.69 km/s〔 | inclination = | asc_node = | arg_peri = | mean_anomaly = | satellites = 62 with formal designations; innumerable additional moonlets.〔 | maximum distance from sun = 1.5 billion km (938 million miles) | minimum distance from sun = 1.35 billion km (840 million miles) | physical_characteristics = yes | flattening = | equatorial_radius = | polar_radius = | mean_radius = 〔〔 | surface_area = | volume = | mass = | density = 〔〔 (less than water) | surface_grav = | escape_velocity = 35.5 km/s〔〔 | sidereal_day = 10.55 hours〔 (10 hr 33 min) | rot_velocity = | axial_tilt = 26.73° (to orbit)〔 | right_asc_north_pole = | declination = 83.537°〔 | albedo = | magnitude = +1.47 to −0.24〔 | angular_size = 14.5″ to 20.1″〔 (excludes rings) | temperatures = yes | temp_name1 = 1 bar level | min_temp_1 = | mean_temp_1 = 134 K (−139°C)〔 | max_temp_1 = | temp_name2 = 0.1 bar | min_temp_2 = | mean_temp_2 = 84 K〔 | max_temp = | pronounced = 〔 | adjectives = Saturnian, Cronian | atmosphere = yes | atmosphere_ref =〔 | scale_height = 59.5 km | atmosphere_composition = by volume: Ices: * ammonia (NH3) * water (H2O) * ammonium hydrosulfide (NH4SH) }} 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 about nine times that of Earth. Although only one-eighth the average density of Earth, with its larger volume Saturn is just over 95 times more massive.〔 Saturn is named after the Roman god of agriculture; its astronomical symbol ((unicode:♄)) represents the god's sickle. Saturn's interior is probably composed of a core of iron–nickel and rock (silicon and oxygen compounds). This core is surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and finally outside the Frenkel line a gaseous outer layer. Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. Electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than Earth's, but 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.〔 The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach , higher than on Jupiter, but not as high as those on Neptune. Saturn has a prominent ring system that consists of nine continuous main rings and three discontinuous arcs and that is composed mostly of ice particles with a smaller amount of rocky debris and dust. Sixty-two〔 〕 moons are known to orbit Saturn, of which fifty-three are officially named. This does not include the hundreds of moonlets comprising the 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. == Physical characteristics == Saturn is a gas giant because it is predominantly composed of hydrogen and helium ('gas'). It lacks a definite surface, though it may have a solid core.〔 Saturn's rotation causes it to have the shape of an oblate spheroid; that is, it is flattened at the poles and bulges at its equator. Its equatorial and polar radii differ by almost 10%: 60,268 km versus 54,364 km, respectively.〔 Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. Saturn is the only planet of the Solar System that is less dense than water—about 30% less.〔 Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm3 due to the atmosphere. Jupiter has 318 times the Earth's mass,〔 while Saturn is 95 times the mass of the Earth,〔 Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System.〔 On 8 January 2015, NASA reported determining the center of the planet Saturn and its family of moons to within . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Saturn」の詳細全文を読む スポンサード リンク
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