Jupiter
Jupiter is the fifth planet from the Sun, and the largest in the Solar System. It is a gas giant with a mass nearly 2.5 times that of all the other planets in the Solar System combined and slightly less than one-thousandth the mass of the Sun. Its diameter is 11 times that of Earth and a tenth that of the Sun. Jupiter orbits the Sun at a distance of, with an orbital period of. It is the third-brightest natural object in the Earth's night sky, after the Moon and Venus, and has been observed since prehistoric times. Its name derives from that of Jupiter, the chief deity of ancient Roman religion.
Jupiter was the first of the Sun's planets to form, and its inward migration during the primordial phase of the Solar System affected much of the formation history of the other planets. Jupiter's atmosphere consists of 76% hydrogen and 24% helium by mass, with a denser interior. It contains traces of the elements carbon, oxygen, sulfur, neon, and compounds such as ammonia, water vapour, phosphine, hydrogen sulfide, and hydrocarbons. Jupiter's helium abundance is 80% of the Sun's, similar to Saturn's composition.
The outer atmosphere is divided into a series of latitudinal bands, with turbulence and storms along their interacting boundaries; the most obvious result of this is the Great Red Spot, a giant storm that has been recorded since 1831. Because of its rapid rotation rate, one turn in ten hours, Jupiter is an oblate spheroid; it has a slight but noticeable 6.5% bulge around the equator compared to its poles. Its internal structure is believed to consist of an outer mantle of fluid metallic hydrogen and a diffuse inner core of denser material. The ongoing contraction of Jupiter's interior generates more heat than the planet receives from the Sun. Jupiter's magnetic field is the strongest and second-largest contiguous structure in the Solar System, generated by eddy currents within the fluid, metallic hydrogen core. The solar wind interacts with the magnetosphere, extending it outward and affecting Jupiter's orbit.
At least 97 moons orbit the planet; the four largest moons—Io, Europa, Ganymede, and Callisto—orbit within the magnetosphere and are visible with common binoculars. Ganymede, the largest of the four, is larger than the planet Mercury. Jupiter is surrounded by a faint system of planetary rings. The rings of Jupiter consist mainly of dust and have three main segments: an inner torus of particles known as the halo, a relatively bright main ring, and an outer gossamer ring. The rings have a reddish colour in visible and near-infrared light. The age of the ring system is unknown, possibly dating back to Jupiter's formation. Since 1973, Jupiter has been visited by nine robotic probes: seven flybys and two dedicated orbiters. Jupiter-like exoplanets have also been found in other planetary systems.
Name and symbol
In both the ancient Greek and Roman civilizations, Jupiter was named after the chief god of the divine pantheon: Zeus to the Greeks and Jupiter to the Romans. The International Astronomical Union formally adopted the name Jupiter for the planet in 1976 and has since named its newly discovered satellites for the god's lovers, favourites, and descendants. The planetary symbol for Jupiter,, descends from a Greek zeta with a horizontal stroke,, as an abbreviation for Zeus.In Latin, Iovis is the genitive case of Iuppiter, i.e. Jupiter. It is associated with the etymology of Zeus. The English equivalent, Jove, is known to have come into use as a poetic name for the planet around the 14th century.
Jovian is the adjectival form of Jupiter. The older adjectival form jovial, employed by astrologers in the Middle Ages, has come to mean 'happy' or 'merry', moods ascribed to Jupiter's influence in astrology.
The original Greek deity Zeus supplies the root zeno-, which is used to form some Jupiter-related words, such as zenography.
Formation and migration
Jupiter is believed to be the oldest planet in the Solar System, having formed just one million years after the Sun and roughly 50 million years before Earth. Current models of Solar System formation suggest that Jupiter formed at or beyond the snow line: a distance from the early Sun where the temperature was sufficiently cold for volatiles such as water to condense into solids. First forming a solid core, the planet then accumulated its gaseous atmosphere. Therefore, the planet must have formed before the solar nebula was fully dispersed. During its formation, Jupiter's mass gradually increased until it had 20 times the mass of the Earth, approximately half of which was made up of silicates, ices and other heavy-element constituents. When the proto-Jupiter grew larger than 50 Earth masses it created a gap in the solar nebula. Thereafter, the growing planet reached its final mass in 3–4million years.According to the "grand tack hypothesis", Jupiter began to form at a distance of roughly from the Sun. As the young planet accreted mass, its interaction with the gas disk orbiting the Sun and the orbital resonances from Saturn caused it to migrate inwards. This upset the orbits of several super-Earths orbiting closer to the Sun, causing them to collide destructively. Saturn would later have begun to migrate inwards at a faster rate than Jupiter until the two planets became captured in a 3:2 mean motion resonance at approximately from the Sun. This changed the direction of migration, causing them to migrate away from the Sun and out of the inner system to their current locations. All of this happened over a period of 3–6million years, with the final migration of Jupiter occurring over several hundred thousand years. Jupiter's migration from the inner Solar System eventually allowed the inner planets—including Earth—to form from the rubble.
There are several unresolved issues with the grand tack hypothesis. The resulting formation timescales of terrestrial planets appear to be inconsistent with the measured elemental composition. Jupiter would likely have settled into an orbit much closer to the Sun if it had migrated through the solar nebula. Some competing models of Solar System formation predict the formation of Jupiter with orbital properties that are close to those of the present-day planet. Other models predict Jupiter forming at distances much further out, such as.
According to the Nice model, the infall of proto-Kuiper belt objects over the first 600 million years of Solar System history caused Jupiter and Saturn to migrate from their initial positions into a 1:2 resonance, which caused Saturn to shift into a higher orbit, disrupting the orbits of Uranus and Neptune, depleting the Kuiper belt, and triggering the Late Heavy Bombardment.
According to the Jumping-Jupiter scenario, Jupiter's migration through the early Solar System could have led to the ejection of a fifth gas giant. This hypothesis suggests that during its orbital migration, Jupiter's gravitational influence disrupted the orbits of other gas giants, potentially casting one planet out of the Solar System entirely. The dynamics of such an event would have dramatically altered the formation and configuration of the Solar System, leaving behind only the four gas giants humans observe today.
Based on Jupiter's composition, researchers have made the case for an initial formation outside the molecular nitrogen snow line, which is estimated at from the Sun, and possibly even outside the argon snow line, which may be as far as. Having formed at one of these extreme distances, Jupiter would then have, over a roughly 700,000-year period, migrated inwards to its current location, during an epoch approximately 2–3 million years after the planet began to form. In this model, Saturn, Uranus, and Neptune would have formed even further out than Jupiter, and Saturn would also have migrated inwards.
Physical characteristics
Jupiter is a gas giant, meaning its chemical composition is primarily hydrogen and helium. These materials are classified as gasses in planetary geology, a term that does not denote the state of matter. It is the largest planet in the Solar System, with a diameter of at its equator, giving it a volume 1,321 times that of the Earth. Its average density, 1.326 g/cm3, is lower than those of the four terrestrial planets.Composition
The atmosphere of Jupiter is approximately 76% hydrogen and 24% helium by mass. By volume, the upper atmosphere is about 90% hydrogen and 10% helium, with the lower proportion owing to the individual helium atoms being more massive than the molecules of hydrogen formed in this part of the atmosphere. The atmosphere contains trace amounts of elemental carbon, oxygen, sulfur, and neon, as well as ammonia, water vapour, phosphine, hydrogen sulfide, and hydrocarbons like methane, ethane and benzene. Its outermost layer contains crystals of frozen ammonia. The planet's interior is denser, with a composition of roughly 71% hydrogen, 24% helium, and 5% other elements by mass.The atmospheric proportions of hydrogen and helium are close to the theoretical composition of the primordial solar nebula. Neon in the upper atmosphere consists of 20 parts per million by mass, which is about a tenth as abundant as in the Sun. Jupiter's helium abundance is about 80% that of the Sun due to the precipitation of these elements as helium-rich droplets, a process that happens deep in the planet's interior.
Based on spectroscopy, Saturn is thought to be similar in composition to Jupiter, but the other giant planets Uranus and Neptune have relatively less hydrogen and helium and relatively more of the next most common elements, including oxygen, carbon, nitrogen, and sulfur. These planets are known as ice giants because during their formation, these elements are thought to have been incorporated into them as ice; however, they probably contain very little ice.