Jupiter
Fifth planet from the Sun From Wikipedia, the free encyclopedia
Fifth planet from the Sun From Wikipedia, the free encyclopedia
Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than 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 eleven times that of Earth, and a tenth that of the Sun. Jupiter orbits the Sun at a distance of 5.20 AU (778.5 Gm), with an orbital period of 11.86 years. 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 captured by New Horizons space probe. The small spot on top of Jupiter is the shadow cast by its moon Ganymede. | |||||||||||||
| Designations | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Pronunciation | /ˈdʒuːpɪtər/ [1] | ||||||||||||
Named after | Jupiter | ||||||||||||
| Adjectives | Jovian /ˈdʒoʊviən/ | ||||||||||||
| Symbol | .svg){kind=small} | ||||||||||||
| Orbital characteristics[2] | |||||||||||||
| Epoch J2000 | |||||||||||||
| Aphelion | 5.4570 AU (816.363 million km) | ||||||||||||
| Perihelion | 4.9506 AU (740.595 million km) | ||||||||||||
| 5.2038 AU (778.479 million km) | |||||||||||||
| Eccentricity | 0.0489 | ||||||||||||
| |||||||||||||
| 398.88 d | |||||||||||||
Average orbital speed | 13.06 km/s | ||||||||||||
| 20.020°[4] | |||||||||||||
| Inclination | |||||||||||||
| 100.464° | |||||||||||||
| January 21, 2023[6] | |||||||||||||
| 273.867°[4] | |||||||||||||
| Known satellites | 95 (as of 2023[update])[7] | ||||||||||||
| Physical characteristics[2][8][9] | |||||||||||||
| 69911 km[lower-alpha 1] 10.973 of Earth's | |||||||||||||
Equatorial radius | 71492 km[lower-alpha 1] 11.209 R🜨 (of Earth's) 0.10276 R☉ (of Sun's) | ||||||||||||
Polar radius | 66854 km[lower-alpha 1] 10.517 of Earth's | ||||||||||||
| Flattening | 0.06487 | ||||||||||||
| 6.1469×1010 km2 120.4 of Earth's | |||||||||||||
| Volume | 1.4313×1015 km3[lower-alpha 1] 1,321 of Earth's | ||||||||||||
| Mass | 1.8982×1027 kg | ||||||||||||
Mean density | 1.326 g/cm3[lower-alpha 2] | ||||||||||||
Equatorial surface gravity | 24.79 m/s2 2.528 g0[lower-alpha 1][citation needed] | ||||||||||||
| 0.2756±0.0006[11] | |||||||||||||
Equatorial escape velocity | 59.5 km/s[lower-alpha 1] | ||||||||||||
| 9.9258 h (9 h 55 m 33 s)[3] | |||||||||||||
| 9.9250 hours (9 h 55 m 30 s) | |||||||||||||
Equatorial rotation velocity | 12.6 km/s | ||||||||||||
| 3.13° (to orbit) | |||||||||||||
North pole right ascension | 268.057°; 17h 52m 14s[12] | ||||||||||||
North pole declination | 64.495°[12] | ||||||||||||
| 0.503 (Bond)[13] 0.538 (geometric)[14] | |||||||||||||
| Temperature | 88 K (−185 °C) (blackbody temperature) | ||||||||||||
| |||||||||||||
| −2.94[15] to −1.66[15] | |||||||||||||
| −9.4[16] | |||||||||||||
| 29.8" to 50.1" | |||||||||||||
| Atmosphere[2] | |||||||||||||
Surface pressure | 200–600 kPa (30–90 psi) (opaque cloud deck)[17] | ||||||||||||
| 27 km (17 mi) | |||||||||||||
| Composition by volume | |||||||||||||
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. Hydrogen constitutes 90% of Jupiter's volume, followed by helium, which forms 25% of its mass and 10% of its volume. The ongoing contraction of Jupiter's interior generates more heat than the planet receives from the Sun. Its internal structure is believed to consist of an outer mantle of fluid metallic hydrogen and a diffuse inner core of denser material. Because of its rapid rate of rotation, one turn in ten hours, Jupiter is an oblate spheroid; it has a slight but noticeable bulge around the equator. 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 at least 1831.
Jupiter is surrounded by a faint system of planetary rings and has a powerful magnetosphere, the second-largest contiguous structure in the Solar System (after the heliosphere). Jupiter forms a system of 95 known moons and probably many more, including the four large moons discovered by Galileo Galilei in 1610: Io, Europa, Ganymede, and Callisto. Ganymede, the largest of the four, is larger than the planet Mercury. Callisto is the second largest; Io and Europa are each about the size of Earth's Moon.
Since 1973, Jupiter has been visited by nine robotic probes: seven flybys and two dedicated orbiters, with one more en route and one awaiting launch.
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.[18] 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.[19] The planetary symbol for Jupiter, .svg){kind=small}
, descends from a Greek zeta with a horizontal stroke, ⟨Ƶ⟩, as an abbreviation for Zeus.[20][21]
In Latin, Iovis is the genitive case of Iuppiter, i.e. Jupiter. It is associated with the etymology of Zeus ('sky father'). The English equivalent, Jove, is only known to have come into use as a poetic name for the planet around the 14th century.[22]
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.[23]
The original Greek deity Zeus supplies the root zeno-, which is used to form some Jupiter-related words, such as zenographic.[lower-alpha 3]
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.[24] 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.[25] The planet began as a solid core, which then accumulated its gaseous atmosphere. As a consequence, the planet must have formed before the solar nebula was fully dispersed.[26] 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.[24] When the proto-Jupiter grew larger than 50 Earth masses it created a gap in the solar nebula.[24] Thereafter, the growing planet reached its final mass in 3–4 million years.[24][26] Since Jupiter is made of the same elements as the Sun (hydrogen and helium) it has been suggested that the Solar System might have been early in its formation a system of multiple protostars, which are quite common, with Jupiter being the second but failed protostar. But the Solar System never developed into a system of multiple stars and Jupiter today does not qualify as a protostar or brown dwarf since it does not have enough mass to fuse hydrogen.[27][28][29][30]
According to the "grand tack hypothesis", Jupiter began to form at a distance of roughly 3.5 AU (520 million km; 330 million mi) from the Sun. As the young planet accreted mass, interaction with the gas disk orbiting the Sun and orbital resonances with Saturn caused it to migrate inward.[25][31] This upset the orbits of several super-Earths orbiting closer to the Sun, causing them to collide destructively.[32] 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 1.5 AU (220 million km; 140 million mi) from the Sun.[33] This changed the direction of migration, causing them to migrate away from the Sun and out of the inner system to their current locations.[32] All of this happened over a period of 3–6 million years, with the final migration of Jupiter occurring over several hundred thousand years.[31][34] Jupiter's migration from the inner solar system eventually allowed the inner planets—including Earth—to form from the rubble.[35]
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.[36] Jupiter would likely have settled into an orbit much closer to the Sun if it had migrated through the solar nebula.[37] 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.[26] Other models predict Jupiter forming at distances much farther out, such as 18 AU (2.7 billion km; 1.7 billion mi).[38][39]
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.[40]
Based on Jupiter's composition, researchers have made the case for an initial formation outside the molecular nitrogen (N2) snow line, which is estimated at 20–30 AU (3.0–4.5 billion km; 1.9–2.8 billion mi) from the Sun, and possibly even outside the argon snow line, which may be as far as 40 AU (6.0 billion km; 3.7 billion mi).[41][42] 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,[38][39] 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.[38]
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 142,984 km (88,846 mi) at its equator, giving it a volume 1,321 times that of the Earth.[2][43] Its average density, 1.326 g/cm3,[lower-alpha 4] is lower than those of the four terrestrial planets.[45][46]
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.[47] The atmosphere contains trace amounts of elemental carbon, oxygen, sulfur, and neon,[48] as well as ammonia, water vapour, phosphine, hydrogen sulfide, and hydrocarbons like methane, ethane and benzene.[49] Its outermost layer contains crystals of frozen ammonia.[50] The planet's interior is denser, with a composition of roughly 71% hydrogen, 24% helium, and 5% other elements by mass.[51][52]
The atmospheric proportions of hydrogen and helium are close to the theoretical composition of the primordial solar nebula.[53] Neon in the upper atmosphere only consists of 20 parts per million by mass, which is about a tenth as abundant as in the Sun.[54] 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.[55][56]
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.[57] 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 little ice today.[58]
Jupiter is about ten times larger than Earth (11.209 R🜨) and smaller than the Sun (0.10276 R☉). Jupiter's mass is 318 times that of Earth;[2] 2.5 times that of all the other planets in the Solar System combined. It is so massive that its barycentre with the Sun lies above the Sun's surface at 1.068 solar radii from the Sun's centre.[59][60]: 6 Jupiter's radius is about one tenth the radius of the Sun,[61] and its mass is one thousandth the mass of the Sun, as the densities of the two bodies are similar.[62] A "Jupiter mass" (MJ or MJup) is often used as a unit to describe masses of other objects, particularly extrasolar planets and brown dwarfs. For example, the extrasolar planet HD 209458 b has a mass of 0.69 MJ, while the brown dwarf Gliese 229 b has a mass of 60.4 MJ.[63][64]
Theoretical models indicate that if Jupiter had over 40% more mass, the interior would be so compressed that its volume would decrease despite the increasing amount of matter. For smaller changes in its mass, the radius would not change appreciably.[65] As a result, Jupiter is thought to have about as large a diameter as a planet of its composition and evolutionary history can achieve.[66] The process of further shrinkage with increasing mass would continue until appreciable stellar ignition was achieved.[67] Although Jupiter would need to be about 75 times more massive to fuse hydrogen and become a star,[68] its diameter is sufficient as the smallest red dwarf may be only slightly larger in radius than Saturn.[69]
Jupiter radiates more heat than it receives through solar radiation, due to the Kelvin–Helmholtz mechanism within its contracting interior.[70]: 30 [71] This process causes Jupiter to shrink by about 1 mm (0.039 in) per year.[72][73] At the time of its formation, Jupiter was hotter and was about twice its current diameter.[74]
Before the early 21st century, most scientists proposed one of two scenarios for the formation of Jupiter. If the planet accreted first as a solid body, it would consist of a dense core, a surrounding layer of fluid metallic hydrogen (with some helium) extending outward to about 80% of the radius of the planet,[75] and an outer atmosphere consisting primarily of molecular hydrogen.[73] Alternatively, if the planet collapsed directly from the gaseous protoplanetary disk, it was expected to completely lack a core, consisting instead of a denser and denser fluid (predominantly molecular and metallic hydrogen) all the way to the centre. Data from the Juno mission showed that Jupiter has a diffuse core that mixes into its mantle, extending for 30–50% of the planet's radius, and comprising heavy elements with a combined mass 7–25 times the Earth.[76][77][78][79][80] This mixing process could have arisen during formation, while the planet accreted solids and gases from the surrounding nebula.[81] Alternatively, it could have been caused by an impact from a planet of about ten Earth masses a few million years after Jupiter's formation, which would have disrupted an originally compact Jovian core.[82][83]
Outside the layer of metallic hydrogen lies a transparent interior atmosphere of hydrogen. At this depth, the pressure and temperature are above molecular hydrogen's critical pressure of 1.3 MPa and critical temperature of 33 K (−240.2 °C; −400.3 °F).[84] In this state, there are no distinct liquid and gas phases—hydrogen is said to be in a supercritical fluid state. The hydrogen and helium gas extending downward from the cloud layer gradually transitions to a liquid in deeper layers, possibly resembling something akin to an ocean of liquid hydrogen and other supercritical fluids.[70]: 22 [85][86][87] Physically, the gas gradually becomes hotter and denser as depth increases.[88][89]
Rain-like droplets of helium and neon precipitate downward through the lower atmosphere, depleting the abundance of these elements in the upper atmosphere.[55][90] Calculations suggest that helium drops separate from metallic hydrogen at a radius of 60,000 km (37,000 mi) (11,000 km (6,800 mi) below the cloud tops) and merge again at 50,000 km (31,000 mi) (22,000 km (14,000 mi) beneath the clouds).[91] Rainfalls of diamonds have been suggested to occur, as well as on Saturn[92] and the ice giants Uranus and Neptune.[93]
The temperature and pressure inside Jupiter increase steadily inward as the heat of planetary formation can only escape by convection.[56] At a surface depth where the atmospheric pressure level is 1 bar (0.10 MPa), the temperature is around 165 K (−108 °C; −163 °F). The region where supercritical hydrogen changes gradually from a molecular fluid to a metallic fluid spans pressure ranges of 50–400 GPa with temperatures of 5,000–8,400 K (4,730–8,130 °C; 8,540–14,660 °F), respectively. The temperature of Jupiter's diluted core is estimated to be 20,000 K (19,700 °C; 35,500 °F) with a pressure of around 4,000 GPa.[94]
The atmosphere of Jupiter is primarily composed of molecular hydrogen and helium, with a smaller amount of other compounds such as water, methane, hydrogen sulfide, and ammonia.[95] Jupiter's atmosphere extends to a depth of approximately 3,000 km (2,000 mi) below the cloud layers.[94]
Jupiter is perpetually covered with clouds of ammonia crystals, which may contain ammonium hydrosulfide as well.[96] The clouds are located in the tropopause layer of the atmosphere, forming bands at different latitudes, known as tropical regions. These are subdivided into lighter-hued zones and darker belts. The interactions of these conflicting circulation patterns cause storms and turbulence. Wind speeds of 100 metres per second (360 km/h; 220 mph) are common in zonal jet streams.[97] The zones have been observed to vary in width, colour and intensity from year to year, but they have remained stable enough for scientists to name them.[60]: 6
The cloud layer is about 50 km (31 mi) deep and consists of at least two decks of ammonia clouds: a thin, clearer region on top and a thicker, lower deck. There may be a thin layer of water clouds underlying the ammonia clouds, as suggested by flashes of lightning detected in the atmosphere of Jupiter.[98] These electrical discharges can be up to a thousand times as powerful as lightning on Earth.[99] The water clouds are assumed to generate thunderstorms in the same way as terrestrial thunderstorms, driven by the heat rising from the interior.[100] The Juno mission revealed the presence of "shallow lightning" which originates from ammonia-water clouds relatively high in the atmosphere.[101] These discharges carry "mushballs" of water-ammonia slushes covered in ice, which fall deep into the atmosphere.[102] Upper-atmospheric lightning has been observed in Jupiter's upper atmosphere, bright flashes of light that last around 1.4 milliseconds. These are known as "elves" or "sprites" and appear blue or pink due to the hydrogen.[103][104]
The orange and brown colours in the clouds of Jupiter are caused by upwelling compounds that change colour when they are exposed to ultraviolet light from the Sun. The exact makeup remains uncertain, but the substances are thought to be made up of phosphorus, sulfur or possibly hydrocarbons.[70]: 39 [105] These colourful compounds, known as chromophores, mix with the warmer clouds of the lower deck. The light-coloured zones are formed when rising convection cells form crystallising ammonia that hides the chromophores from view.[106]
Jupiter has a low axial tilt, thus ensuring that the poles always receive less solar radiation than the planet's equatorial region. Convection within the interior of the planet transports energy to the poles, balancing out temperatures at the cloud layer.[60]: 54
A well-known feature of Jupiter is the Great Red Spot,[107] a persistent anticyclonic storm located 22° south of the equator. It was first observed in 1831,[108] and possibly as early as 1665.[109][110] Images by the Hubble Space Telescope have shown two more "red spots" adjacent to the Great Red Spot.[111][112] The storm is visible through Earth-based telescopes with an aperture of 12 cm or larger.[113] The oval object rotates counterclockwise, with a period of about six days.[114] The maximum altitude of this storm is about 8 km (5 mi) above the surrounding cloud tops.[115] The Spot's composition and the source of its red colour remain uncertain, although photodissociated ammonia reacting with acetylene is a likely explanation.[116]
The Great Red Spot is larger than the Earth.[117] Mathematical models suggest that the storm is stable and will be a permanent feature of the planet.[118] However, it has significantly decreased in size since its discovery. Initial observations in the late 1800s showed it to be approximately 41,000 km (25,500 mi) across. By the time of the Voyager flybys in 1979, the storm had a length of 23,300 km (14,500 mi) and a width of approximately 13,000 km (8,000 mi).[119] Hubble observations in 1995 showed it had decreased in size to 20,950 km (13,020 mi), and observations in 2009 showed the size to be 17,910 km (11,130 mi). As of 2015[update], the storm was measured at approximately 16,500 by 10,940 km (10,250 by 6,800 mi),[119] and was decreasing in length by about 930 km (580 mi) per year.[117][120] In October 2021, a Juno flyby mission measured the depth of the Great Red Spot, putting it at around 300–500 kilometres (190–310 mi).[121]
Juno missions show that there are several polar cyclone groups at Jupiter's poles. The northern group contains nine cyclones, with a large one in the centre and eight others around it, while its southern counterpart also consists of a centre vortex but is surrounded by five large storms and a single smaller one for a total of 7 storms.[122][123]
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In 2000, an atmospheric feature formed in the southern hemisphere that is similar in appearance to the Great Red Spot, but smaller. This was created when smaller, white oval-shaped storms merged to form a single feature—these three smaller white ovals were formed in 1939–1940. The merged feature was named Oval BA. It has since increased in intensity and changed from white to red, earning it the nickname "Little Red Spot".[124][125]
In April 2017, a "Great Cold Spot" was discovered in Jupiter's thermosphere at its north pole. This feature is 24,000 km (15,000 mi) across, 12,000 km (7,500 mi) wide, and 200 °C (360 °F) cooler than surrounding material. While this spot changes form and intensity over the short term, it has maintained its general position in the atmosphere for more than 15 years. It may be a giant vortex similar to the Great Red Spot, and appears to be quasi-stable like the vortices in Earth's thermosphere. This feature may be formed by interactions between charged particles generated from Io and the strong magnetic field of Jupiter, resulting in a redistribution of heat flow.[126]
Jupiter's magnetic field is the strongest of any planet in the Solar System,[106] with a dipole moment of 4.170 gauss (0.4170 mT) that is tilted at an angle of 10.31° to the pole of rotation. The surface magnetic field strength varies from 2 gauss (0.20 mT) up to 20 gauss (2.0 mT).[127] This field is thought to be generated by eddy currents—swirling movements of conducting materials—within the fluid, metallic hydrogen core. At about 75 Jupiter radii from the planet, the interaction of the magnetosphere with the solar wind generates a bow shock. Surrounding Jupiter's magnetosphere is a magnetopause, located at the inner edge of a magnetosheath—a region between it and the bow shock. The solar wind interacts with these regions, elongating the magnetosphere on Jupiter's lee side and extending it outward until it nearly reaches the orbit of Saturn. The four largest moons of Jupiter all orbit within the magnetosphere, which protects them from solar wind.[70]: 69
The volcanoes on the moon Io emit large amounts of sulfur dioxide, forming a gas torus along its orbit. The gas is ionized in Jupiter's magnetosphere, producing sulfur and oxygen ions. They, together with hydrogen ions originating from the atmosphere of Jupiter, form a plasma sheet in Jupiter's equatorial plane. The plasma in the sheet co-rotates with the planet, causing deformation of the dipole magnetic field into that of a magnetodisk. Electrons within the plasma sheet generate a strong radio signature, with short, superimposed bursts in the range of 0.6–30 MHz that are detectable from Earth with consumer-grade shortwave radio receivers.[128][129] As Io moves through this torus, the interaction generates Alfvén waves that carry ionized matter into the polar regions of Jupiter. As a result, radio waves are generated through a cyclotron maser mechanism, and the energy is transmitted out along a cone-shaped surface. When Earth intersects this cone, the radio emissions from Jupiter can exceed the radio output of the Sun.[130]
Jupiter has a faint planetary ring system composed of three main segments: an inner torus of particles known as the halo, a relatively bright main ring, and an outer gossamer ring.[132] These rings appear to be made of dust, whereas Saturn's rings are made of ice.[70]: 65 The main ring is most likely made out of material ejected from the satellites Adrastea and Metis, which is drawn into Jupiter because of the planet's strong gravitational influence. New material is added by additional impacts.[133] In a similar way, the moons Thebe and Amalthea are believed to produce the two distinct components of the dusty gossamer ring.[133] There is evidence of a fourth ring that may consist of collisional debris from Amalthea that is strung along the same moon's orbit.[134]
Jupiter is the only planet whose barycentre with the Sun lies outside the volume of the Sun, though by only 7% of the Sun's radius.[135][136] The average distance between Jupiter and the Sun is 778 million km (5.2 AU) and it completes an orbit every 11.86 years. This is approximately two-fifths the orbital period of Saturn, forming a near orbital resonance.[137] The orbital plane of Jupiter is inclined 1.30° compared to Earth. Because the eccentricity of its orbit is 0.049, Jupiter is slightly over 75 million km nearer the Sun at perihelion than aphelion,[2] which means that its orbit is nearly circular. This low eccentricity is at odds with exoplanet discoveries, which have revealed Jupiter-sized planets with very high eccentricities. Models suggest this may be due to there being only two giant planets in our Solar System, as the presence of a third or more giant planets tends to induce larger eccentricities.[138]
The axial tilt of Jupiter is relatively small, only 3.13°, so its seasons are insignificant compared to those of Earth and Mars.[139]
Jupiter's rotation is the fastest of all the Solar System's planets, completing a rotation on its axis in slightly less than ten hours; this creates an equatorial bulge easily seen through an amateur telescope. Because Jupiter is not a solid body, its upper atmosphere undergoes differential rotation. The rotation of Jupiter's polar atmosphere is about 5 minutes longer than that of the equatorial atmosphere.[140] The planet is an oblate spheroid, meaning that the diameter across its equator is longer than the diameter measured between its poles.[89] On Jupiter, the equatorial diameter is 9,276 km (5,764 mi) longer than the polar diameter.[2]
Three systems are used as frames of reference for tracking planetary rotation, particularly when graphing the motion of atmospheric features. System I applies to latitudes from 7° N to 7° S; its period is the planet's shortest, at 9h 50 m 30.0s. System II applies at latitudes north and south of these; its period is 9h 55 m 40.6s.[141] System III was defined by radio astronomers and corresponds to the rotation of the planet's magnetosphere; its period is Jupiter's official rotation.[142]
Jupiter is usually the fourth brightest object in the sky (after the Sun, the Moon, and Venus),[106] although at opposition Mars can appear brighter than Jupiter. Depending on Jupiter's position with respect to the Earth, it can vary in visual magnitude from as bright as −2.94 at opposition down to −1.66 during conjunction with the Sun.[15] The mean apparent magnitude is −2.20 with a standard deviation of 0.33.
