Saturn

Saturn  
Saturn imaged by the Cassini Orbiter
Designations
Pronunciation [1]
Adjective Saturnian, Cronian
Epoch J2000.0
Aphelion 1,513,325,783 km
10.115 958 04 AU
Perihelion 1,353,572,956 km
9.048 076 35 AU
Semi-major axis 1,433,449,370 km
9.582 017 20 AU
Eccentricity 0.055 723 219
Orbital period 10,759.22 days
29.4571 yr
24,491.07 Saturn solar days[4]
Synodic period 378.09 days[5]
Average orbital speed 9.69 km/s[5]
Mean anomaly 320.346 750°
Inclination 2.485 240° to Ecliptic
5.51° to Sun’s equator
0.93° to Invariable plane[6]
Longitude of ascending node 113.642 811°
Argument of perihelion 336.013 862°
Satellites ~ 200 observed (61 with secure orbits)
Physical characteristics
Equatorial radius 60,268 ± 4 km[7][8]
9.4492 Earths
Polar radius 54,364 ± 10 km[7][8]
8.5521 Earths
Flattening 0.097 96 ± 0.000 18
Surface area 4.27×10 km²[8][9]
83.703 Earths
Volume 8.2713×10 km³[5][8]
763.59 Earths
Mass 5.6846×10 kg[5]
95.152 Earths
Mean density 0.687 g/cm³[5][8]
(less than water)
Equatorial surface gravity 10.44 m/s²[5][8]
1.065 g
Escape velocity 35.5 km/s[5][8]
Sidereal rotation
period
10.57 hours[10]
(10 hr 34 min)
Equatorial rotation velocity 9.87 km/s[8]
35,500 km/h
Axial tilt 26.73°[5]
North pole right ascension 2 h 42 min 21 s
40.589°[7]
North pole declination 83.537°[7]
Albedo 0.342 (Bond)
0.47 (geom.)[5]
Surface temp.
1 bar level
0.1 bar
min mean max
134 K[5]
84 K[5]
Apparent magnitude +1.47 to −0.24[11]
Angular diameter 14.5" — 20.1"[5]
(excludes rings)
Atmosphere[5]
Scale height 59.5 km
Composition
~96% Hydrogen (H2)
~3% Helium
~0.4% Methane
~0.01% Ammonia
~0.01% Hydrogen deuteride (HD)
0.000 7% Ethane
Ices:
Ammonia
water
ammonium hydrosulfide(NH4SH)
  1. Walter, Elizabeth (April 21, 2003). (Second ed.). Cambridge University Press. . 
  2. Yeomans, Donald K. (2006-07-13). . NASA JPL. http://ssd.jpl.nasa.gov/?horizons. Retrieved 2007-08-08. —At the site, go to the "web interface" then select "Ephemeris Type: ELEMENTS", "Target Body: Saturn Barycenter" and "Center: Sun".
  3. Orbital elements refer to the barycenter of the Saturn system and are the instantaneous osculating values at the precise J2000 epoch. Barycenter quantities are given because, in contrast to the planetary centre, they do not experience appreciable changes on a day-to-day basis from to the motion of the moons.
  4. Seligman, Courtney. . http://cseligman.com/text/sky/rotationvsday.htm. Retrieved 2009-08-13. 
  5. a b c d e f g h i j k l m
  6. . 2009-04-03. http://home.comcast.net/~kpheider/MeanPlane.gif. Retrieved 2009-04-10.  (produced with Solex 10 written by Aldo Vitagliano; see also Invariable plane)
  7. a b c d Seidelmann, P. Kenneth; Archinal, B. A.; A’hearn, M. F.; et al. (2007). . Celestial Mech. Dyn. Astr. 90: 155–180. . http://adsabs.harvard.edu/doi/10.1007/s10569-007-9072-y. 
  8. a b c d e f g h Refers to the level of 1 bar atmospheric pressure
  9. NASA: Solar System Exploration: Planets: Saturn: Facts & Figures
  10. . Astronomy. November 2009. p. 23. 
  11. Schmude, Richard W Junior (2001). . Georgia Journal of Science. http://findarticles.com/p/articles/mi_qa4015/is_200101/ai_n8933308. Retrieved 2007-10-14. 

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus (the Titan father of Zeus), the Babylonian Ninurta and the Hindu Shani. Saturn's symbol represents the Roman god's sickle (Unicode: ).

Saturn, along with Jupiter, Uranus and Neptune, is classified as a gas giant. Together, these four planets are sometimes referred to as the Jovian, meaning "Jupiter-like", planets. Saturn has an average radius about 9 times larger than the Earth's.[12] While only 1/8 the average density of Earth, due to its larger volume, Saturn's mass is just over 95 times greater than Earth's.[13]

Because of Saturn's large mass and resulting gravitation, the conditions produced on Saturn are extreme if compared to Earth. The interior of Saturn is probably composed of a core of iron, nickel, silicon and oxygen compounds, surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium and finally, an outer gaseous layer.[14] Electrical current within the metallic-hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is slightly weaker than Earth's magnetic field and approximately one-twentieth the strength of the field around Jupiter.[15] The outer atmosphere is generally bland in appearance, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h, significantly faster than those on Jupiter.

Saturn has nine rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. Sixty-two[16] known moons orbit the planet; fifty-three are officially named. This is not counting hundreds of "moonlets" within the rings. Titan, Saturn's largest and the Solar System's second largest moon (after Jupiter's Ganymede), is larger than the planet Mercury and is the only moon in the Solar System to possess a significant atmosphere.[17]

Physical characteristics

Due to a combination of its lower density, rapid rotation and fluid state, Saturn is an oblate spheroid; that is, it is flattened at the poles and bulges at the equator. Its equatorial and polar radii differ by almost 10%—60,268 km versus 54,364 km.[5] The other gas planets are also oblate, but to a lesser extent. Saturn is the only planet of the Solar System that is less dense than water. Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm³ due to the gaseous atmosphere. Saturn is only 95 Earth masses,[5] compared to Jupiter, which is 318 times the mass of the Earth[18] but only about 20% larger than Saturn.[19]

Internal structure

Though there is no direct information about Saturn's internal structure, it is thought that its interior is similar to that of Jupiter, having a small rocky core surrounded mostly by hydrogen and helium. The rocky core is similar in composition to the Earth, but more dense. This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid hydrogen/helium layer and a gaseous atmosphere in the outermost 1000 km.[20] Traces of various volatiles are also present. The core region is estimated to be about 9–22 times the mass of the Earth.[21] Saturn has a very hot interior, reaching 11,700 °C at the core and it radiates 2.5 times more energy into space than it receives from the Sun. Most of this extra energy is generated by the Kelvin-Helmholtz mechanism (slow gravitational compression), but this alone may not be sufficient to explain Saturn's heat production. It is proposed that an additional mechanism might be at play whereby Saturn generates some of its heat through the "raining out" of droplets of helium deep in its interior, thus releasing heat by friction as they fall down through the lighter hydrogen.[22]

Atmosphere

The outer atmosphere of Saturn consists of 96.3% molecular hydrogen and 3.25% helium.[23] Trace amounts of ammonia, acetylene, ethane, phosphine and methane have also been detected.[24] The upper clouds on Saturn are composed of ammonia crystals, while the lower level clouds appear to be composed of either ammonium hydrosulfide (NH4SH) or water.[25] The atmosphere of Saturn is significantly deficient in helium relative to the abundance of the elements in the Sun.

The quantity of elements heavier than helium are not known precisely, but the proportions are assumed to match the primordial abundances from the formation of the Solar System. The total mass of these elements is estimated to be 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region.[26]