Named after the Roman king of the gods, Jupiter, at an average distance of 778,547,200 kilometers or 5.2 AU, is the fifth planet from the Sun and with a diameter of 142,984 kilometers is by far the largest planet in the Solar System one thousand times the size of Earth in volume.

Jupiter like Saturn is a true gas giant with an extremely deep atmospheric blanket as befits a planet with more matter than all the other planets combined. In the southern hemisphere a large reddish oval called the "Great Red Spot" located high in the atmosphere's outer layer moves majestically westward through clouds that have a mean temperature of -121 C and are composed of ammonia, hydrogen sulphide and water. The atmosphere is mainly hydrogen and helium, a downward direction producing a steady increase in pressure along with a corresponding increase in temperature untill it begins to resemble molten metal: at present Jupiter's internal structure is thought to consist of a layer of gaseous hydrogen, overlaying a layer of liquid hydrogen, overlaying a layer of liquid metalic hydrogen with some helium, surrounding a small rocky core with a mass of 12 Earths or more. Though much is still hypothetical the darkness is slowly being peeled away, the blanks filled in.

Although the likelihood of life on Jupiter is highly improbable, an interesting hypothesis was advanced some years ago by the late American astronomer, author and popularizer of science Carl Sagan concerning the possibility of ammonia based life existing in Jupiter’s upper atmosphere.

A Jovian ecology was envisioned based loosely on that of Earth’s oceans. The principal life forms were labeled “sinkers", "floaters" and "hunters.” The “sinkers” were short lived plankton type organisms, “floaters“ giant sentient gas bags and “hunters” gas propelled squid like predators that attacked and fed on the "floaters."

So far there has been no evidence from the many probes that have explored the Jovian system that Sagan’s hypothesis has any substance, though in all fairness Galileo is the only spacecraft to have actually orbited the giant planet long term (to date) [1] witnessing the impact of Comet Shoemaker-Levy 9 upon approach in 1994 and parachuting an atmospheric probe deep into its atmosphere in 1995.

Juno, the second mission in NASA's New Frontiers Program is currently orbiting Jupiter its JunoCam camera operational the first images awe-inspiring.
Launched on August 5, 2011, it completed a five year voyage of more than 2.8 billion kilometers (1.74 billion miles) before assuming a polar orbit on July 4, 2016. The spacecraft will measure thermal radiation emanating from deep within the atmosphere, the observations complementing earlier studies by assessing the abundance and distribution of water and therefore oxygen, the overall goal to provide a broader insight into the planets composition (does it have a rocky core) and origin.

Jupiter has a faint ring system [2] composed of three main segments: innermost a halo ring which is actually a 10,000 km thick torus of dust and debris, then a main ring and then a gossamer ring itself divided into inner and outer bands. In addition a very faint and tenuous outer ring circles at great distance from and in an opposite direction to the other rings. The main ring is composed of material from the moons Adrastea and Metis. The inner and outer gossamer rings are composed of material from the shepherd moons Thebe and Amalthea. [3] The origin of the faint and tenuous outer ring is unknown.

To date Jupiter has 79 known moons: Metis, Adrastea, Amalthea, Thebe, Io, Europa, Ganymede, Callisto, Themisto, Leda, Himalia, Lysithia, Elara, Dia, Carpo, Euporie, Thelxinoe, Euanthe, Helike, Orthosie, Iocaste, Praxidike, Harpalyke, Mneme, Hermippe, Thyone, Ananke, Herse, Aitne, Kale, Taygete, Chaldene, Erinome, Aoede, Kallichore, Kalyke, Carme, Callirrhoe, Eurydome, Pasithee, Kore, Cyllene, Eukelade, Pasiphae, Hegemone, Arche, Isonoe, Sinope, Sponde, Autonoe, Megaclite, and as yet unnamed S/2018 J 1, S/2017 J 4, S/2003 J 12, (
Valetudo proposed for S/2016 J 2), S/2003 J 3, S/2011 J 1, S/2003 J 18, S/2010 J 2, S/2017 J 7, S/2016 J 1, S/2017 J 3, S/2003 J 16, S/2017 J 9, S/2017 J 6, S/2003 J 19, S/2003 J 15, S/2003 J 10, S/2003 J 23, S/2017 J 5, S/2017 J 8, S/2017 J 2, S/2010 J 1, S/2011 J 2, S/2017 J 1, S/2003 J 4, S/2003 J 9, S/2003 J 5, S/2003 J 2.

[1] During the latter days of 2000 early days of 2001, in what can only be called a unique occurrence, the Cassini-Huygens spacecraft en route to Saturn temporarily joined Galileo in its flyby of Jupiter.

[2] A planetary ring is a flat disk shaped band composed of rock or ice dust, larger rocks, boulders and ice chunks which circle in a planet's equatorial plane.

[3] “Shepherd” moons are small satellites orbiting within gaps or at the periphery of planetary rings their gravitational presence producing a distinct edge to the matter comprising the ring.

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