Does Jupiter rotate at the same speed at every depth?

Does Jupiter rotate at the same speed at every depth?

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Jupiter rotates in less than 10 hours. Its rotation is differential, with the upper layers of the atmosphere spinning a bit faster at the equator than at higher latitudes. Do the inner layers of Jupiter rotate at the same (angular) speed as the outmost layers of the atmosphere?

No. The deep interior of the planet rotates as (nearly) a rigid body (Guillot et al. 2018), while the outer part of the planet undergoes differential rotation. Therefore the interior and exterior rotation cannot match at all latitudes simultaneously.


Although the composition of Jupiter is similar to that of our Sun, it failed to ignite in nuclear fusion. A nuclear fusion reaction similar to that of the Sun requires extreme gravity to compress the hydrogen down to a point where the extreme pressure and temperature pack the hydrogen atoms into helium, which is the energy source for the sun and most stars. ¹ This is also what makes the Sun burn bright. Despite the fact that Jupiter is made of vast quantities of hydrogen, it is not nearly enough to ignite the planet in nuclear fusion. The minimum amount of mass required for an object to ignite in true nuclear fusion is 80 times that of Jupiter, which is considered to be a red dwarf star.¹ Astronomers draw the line between a brown dwarf, a planet, and a star depending on a variety of factors such as the ignition of nuclear fusion. Although there is a distinction made between Jupiter, brown dwarfs, and stars, one can conclude that there is a definite connection between the planet Jupiter and all stars. This realization begs a variety of questions: Can Jupiter be classified as a star, or as a brown dwarf? Could Jupiter become a star? Could nuclear fusion on Jupiter be triggered, and if so what would happen to our Solar System? This web page will answer these research questions as well as highlight how Jupiter is very similar in composition and structure when compared to a star such as the Sun. We will also explore how Jupiter is ultimately and inherently different from the Sun and all other stars due to its size, orbit, magnetic field, and rotation.


Jupiter is most likely the oldest planet in the Solar System. [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 is sufficiently cold for volatiles such as water to condense into solids. [25] It first assembled a large solid core before accumulating its gaseous atmosphere. As a consequence, the core must have formed before the solar nebula began to dissipate after 10 million years. Formation models suggest Jupiter grew to 20 times the mass of the Earth in under a million years. The orbiting mass created a gap in the disk, thereafter slowly increasing to 50 Earth masses in 3–4 million years. [24]

According to the "grand tack hypothesis", Jupiter would have begun to form at a distance of roughly 3.5 AU. As the young planet accreted mass, interaction with the gas disk orbiting the Sun and orbital resonances with Saturn [25] caused it to migrate inward. [26] This would have upset the orbits of what are believed to be super-Earths orbiting closer to the Sun, causing them to collide destructively. Saturn would later have begun to migrate inwards too, much faster than Jupiter, leading to the two planets becoming locked in a 3:2 mean motion resonance at approximately 1.5 AU. This in turn would have changed the direction of migration, causing them to migrate away from the Sun and out of the inner system to their current locations. [27] These migrations would have occurred over an 800,000 year time period, [26] with all of this happening over a time period of up to 6 million years after Jupiter began to form (3 million being a more likely figure). [28] This departure would have allowed the formation of the inner planets from the rubble, including Earth. [29]

However, the formation timescales of terrestrial planets resulting from the grand tack hypothesis appear inconsistent with the measured terrestrial composition. [30] Moreover, the likelihood that the outward migration actually occurred in the solar nebula is very low. [31] In fact, some models predict the formation of Jupiter's analogues whose properties are close to those of the planet at the current epoch. [32]

Other models have Jupiter forming at distances much further out, such as 18 AU. [33] [34] In fact, based on Jupiter's composition, researchers have made the case for an initial formation outside the molecular nitrogen (N2) snowline, which is estimated at 20-30 AU, [35] [36] and possibly even outside the argon snowline, which may be as far as 40 AU. Having formed at one of these extreme distances, Jupiter would then have migrated inwards to its current location. This inward migration would have occurred over a roughly 700,000 year time period, [33] [34] during an epoch approximately 2–3 million years after the planet began to form. Saturn, Uranus and Neptune would have formed even further out than Jupiter, and Saturn would also have migrated inwards.

Jupiter is one of the four gas giants, being primarily composed of gas and liquid rather than solid matter. It is the largest planet in the Solar System, with a diameter of 142,984 km (88,846 mi) at its equator. [37] The average density of Jupiter, 1.326 g/cm 3 , is the second highest of the giant planets, but lower than those of the four terrestrial planets. [38]


Jupiter's upper atmosphere is about 90% hydrogen and 10% helium by volume. Since helium atoms are more massive than hydrogen atoms, Jupiter's atmosphere is approximately 75% hydrogen and 24% helium by mass, with the remaining one percent consisting of other elements. The atmosphere contains trace amounts of methane, water vapour, ammonia, and silicon-based compounds. There are also fractional amounts of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, and sulfur. The outermost layer of the atmosphere contains crystals of frozen ammonia. Through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have also been found. [39] The interior of Jupiter contains denser materials—by mass it is roughly 71% hydrogen, 24% helium, and 5% other elements. [40] [41]

The atmospheric proportions of hydrogen and helium are close to the theoretical composition of the primordial solar nebula. 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. [42] Helium is also depleted to about 80% of the Sun's helium composition. This depletion is a result of precipitation of these elements as helium-rich droplets deep in the interior of the planet. [43]

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 abundant elements, including oxygen, carbon, nitrogen, and sulfur. [44] As their volatile compounds are mainly in ice form, they are called ice giants.

Mass and size

Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined—this 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. [45] Jupiter is much larger than Earth and considerably less dense: its volume is that of about 1,321 Earths, but it is only 318 times as massive. [7] [46] Jupiter's radius is about one tenth the radius of the Sun, [47] and its mass is one thousandth the mass of the Sun, so the densities of the two bodies are similar. [48] A "Jupiter mass" ( M J or M Jup) 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 M J, while Kappa Andromedae b has a mass of 12.8 M J. [49]

Theoretical models indicate that if Jupiter had much more mass than it does at present, it would shrink. [50] For small changes in mass, the radius would not change appreciably, and above 160% [50] of the current mass the interior would become so much more compressed under the increased pressure that its volume would decrease despite the increasing amount of matter. As a result, Jupiter is thought to have about as large a diameter as a planet of its composition and evolutionary history can achieve. [51] The process of further shrinkage with increasing mass would continue until appreciable stellar ignition was achieved, as in high-mass brown dwarfs having around 50 Jupiter masses. [52]

Although Jupiter would need to be about 75 times more massive to fuse hydrogen and become a star, the smallest red dwarf is only about 30 percent larger in radius than Jupiter. [53] [54] Despite this, Jupiter still radiates more heat than it receives from the Sun the amount of heat produced inside it is similar to the total solar radiation it receives. [55] This additional heat is generated by the Kelvin–Helmholtz mechanism through contraction. This process causes Jupiter to shrink by about 1 mm/yr. [56] [57] When formed, Jupiter was hotter and was about twice its current diameter. [58]

Internal structure

Before the early 21st century, most scientists expected Jupiter to either consist of a dense core, a surrounding layer of liquid metallic hydrogen (with some helium) extending outward to about 80% of the radius of the planet, [59] and an outer atmosphere consisting predominantly of molecular hydrogen, [57] or perhaps to have no core at all, consisting instead of denser and denser fluid (predominantly molecular and metallic hydrogen) all the way to the center, depending on whether the planet accreted first as a solid body or collapsed directly from the gaseous protoplanetary disk. When the Juno mission arrived in July 2016, [21] it found that Jupiter has a very diffuse core that mixes into its mantle. [60] [61] A possible cause is an impact from a planet of about ten Earth masses a few million years after Jupiter's formation, which would have disrupted an originally solid Jovian core. [62] [63] It is estimated that the core is 30–50% of the planet's radius, and contains heavy elements 7–25 times the mass of Earth. [64]

Above 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 only 33 K. [65] In this state, there are no distinct liquid and gas phases—hydrogen is said to be in a supercritical fluid state. It is convenient to treat hydrogen as gas extending downward from the cloud layer to a depth of about 1,000 km, [55] and as liquid in deeper layers. Physically, there is no clear boundary—the gas smoothly becomes hotter and denser as depth increases. [66] [67] Rain-like droplets of helium and neon precipitate downward through the lower atmosphere, depleting the abundance of these elements in the upper atmosphere. [43] [68] Calculations suggest that helium drops separate from metalic hydrogen at a radius of 60,000 km (11,000 km below the cloudtops) and merge again at 50,000 km (22,000 km beneath the clouds). [69] Rainfalls of diamonds have been suggested to occur, as well as on Saturn [70] and the ice giants Uranus and Neptune. [71]

The temperature and pressure inside Jupiter increase steadily inward, this is observed in microwave emission and required because the heat of formation can only escape by convection. At the pressure level of 10 bars (1 MPa), the temperature is around 340 K (67 °C 152 °F). The hydrogen is always supercritical (that is, it never encounters a first-order phase transition) even as it changes gradually from a molecular fluid to a metallic fluid at around 100–200 GPa, where the temperature is perhaps 5,000 K (4,730 °C 8,540 °F). The temperature of Jupiter's diluted core is estimated at around 20,000 K (19,700 °C 35,500 °F) or more with an estimated pressure of around 4,500 GPa. [72]


Jupiter has the deepest planetary atmosphere in the Solar System, spanning over 5,000 km (3,000 mi) in altitude. [73] [74]

Cloud layers

Jupiter is perpetually covered with clouds composed of ammonia crystals, and possibly ammonium hydrosulfide. The clouds are in the tropopause and are in bands of 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. [75] The zones have been observed to vary in width, colour and intensity from year to year, but they have remained sufficiently stable for scientists to name them. [46]

The cloud layer is about 50 km (31 mi) deep, and consists of at least two decks of clouds: a thick lower deck and a thin clearer region. There may also be a thin layer of water clouds underlying the ammonia layer. Supporting the presence of water clouds are the flashes of lightning detected in the atmosphere of Jupiter. These electrical discharges can be up to a thousand times as powerful as lightning on Earth. [76] The water clouds are assumed to generate thunderstorms in the same way as terrestrial thunderstorms, driven by the heat rising from the interior. [77] The Juno mission revealed the presence of "shallow lightning" which originates from ammonia-water clouds relatively high in the atmosphere. [78] These discharges carry "mushballs" of water-ammonia slushes covered in ice, which fall deep into the atmosphere. [79] 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. [80] [81]

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 phosphorus, sulfur or possibly hydrocarbons. [55] [82] These colourful compounds, known as chromophores, mix with the warmer lower deck of clouds. The zones are formed when rising convection cells form crystallising ammonia that masks out these lower clouds from view. [83]

Jupiter's low axial tilt means 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 the temperatures at the cloud layer. [46]

Great Red Spot and other vortices

The best known feature of Jupiter is the Great Red Spot, [84] a persistent anticyclonic storm located 22° south of the equator. It is known to have existed since at least 1831, [85] and possibly since 1665. [86] [87] Images by the Hubble Space Telescope have shown as many as two "red spots" adjacent to the Great Red Spot. [88] [89] The storm is visible through Earth-based telescopes with an aperture of 12 cm or larger. [90] The oval object rotates counterclockwise, with a period of about six days. [91] The maximum altitude of this storm is about 8 km (5 mi) above the surrounding cloudtops. [92] The Spot's composition and the source of its red color remain uncertain, although photodissociated ammonia reacting with acetylene is a robust candidate to explain the coloration. [93]

The Great Red Spot is larger than the Earth. [94] Mathematical models suggest that the storm is stable and will be a permanent feature of the planet. [95] 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). [96] 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), [96] and was decreasing in length by about 930 km (580 mi) per year. [94] [97]

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 center and eight others around it, while its southern counterpart also consists of a center vortex but is surrounded by five large storms and a single smaller one. [98] [ better source needed ] These polar structures are caused by the turbulence in Jupiter's atmosphere and can be compared with the hexagon at Saturn's north pole.

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 first observed in 1938. The merged feature was named Oval BA and has been nicknamed "Red Spot Junior." It has since increased in intensity and changed from white to red. [99] [100] [101]

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. Interactions between charged particles generated from Io and the planet's strong magnetic field likely resulted in redistribution of heat flow, forming the Spot. [103]


Jupiter's magnetic field is fourteen times stronger than Earth's, ranging from 4.2 gauss (0.42 mT) at the equator to 10–14 gauss (1.0–1.4 mT) at the poles, making it the strongest in the Solar System (except for sunspots). [83] This field is thought to be generated by eddy currents—swirling movements of conducting materials—within the liquid metallic hydrogen core. The volcanoes on the moon Io emit large amounts of sulfur dioxide, forming a gas torus along the moon's orbit. The gas is ionised in the 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 that produces bursts in the range of 0.6–30 MHz which are detectable from Earth with consumer-grade shortwave radio receivers. [104] [105]

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 the solar wind. [55]

The magnetosphere of Jupiter is responsible for intense episodes of radio emission from the planet's polar regions. Volcanic activity on Jupiter's moon Io injects gas into Jupiter's magnetosphere, producing a torus of particles about the planet. As Io moves through this torus, the interaction generates Alfvén waves that carry ionised 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 solar radio output. [106]

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. [107] The average distance between Jupiter and the Sun is 778 million km (about 5.2 times the average distance between Earth and the Sun, or 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. [108] The orbital plane of Jupiter is inclined 1.31° compared to Earth. Because the eccentricity of its orbit is 0.048, Jupiter is slightly over 75 million km nearer the Sun at perihelion than aphelion. [7]

The axial tilt of Jupiter is relatively small, only 3.13°, so its seasons are insignificant compared to those of Earth and Mars. [109]

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. The planet is an oblate spheroid, meaning that the diameter across its equator is longer than the diameter measured between its poles. On Jupiter, the equatorial diameter is 9,275 km (5,763 mi) longer than the polar diameter. [67]

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 three systems are used as frames of reference, particularly when graphing the motion of atmospheric features. System I applies to latitudes from 10° N to 10° S its period is the planet's shortest, at 9h 50m 30.0s. System II applies at all latitudes north and south of these its period is 9h 55m 40.6s. System III was defined by radio astronomers and corresponds to the rotation of the planet's magnetosphere its period is Jupiter's official rotation. [110]

Jupiter is usually the fourth brightest object in the sky (after the Sun, the Moon, and Venus) [83] 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 [13] at opposition down to [13] −1.66 during conjunction with the Sun. The mean apparent magnitude is −2.20 with a standard deviation of 0.33. [13] The angular diameter of Jupiter likewise varies from 50.1 to 29.8 arc seconds. [7] Favorable oppositions occur when Jupiter is passing through perihelion, an event that occurs once per orbit. [111]

Because the orbit of Jupiter is outside that of Earth, the phase angle of Jupiter as viewed from Earth never exceeds 11.5° thus, Jupiter always appears nearly fully illuminated when viewed through Earth-based telescopes. It was only during spacecraft missions to Jupiter that crescent views of the planet were obtained. [112] A small telescope will usually show Jupiter's four Galilean moons and the prominent cloud belts across Jupiter's atmosphere. [113] A large telescope will show Jupiter's Great Red Spot when it faces Earth. [114]

Pre-telescopic research

Observation of Jupiter dates back to at least the Babylonian astronomers of the 7th or 8th century BC. [115] The ancient Chinese knew Jupiter as the "Suì Star" (Suìxīng 歲星 ) and established their cycle of 12 earthly branches based on its approximate number of years the Chinese language still uses its name (simplified as 歲 ) when referring to years of age. By the 4th century BC, these observations had developed into the Chinese zodiac, [116] with each year associated with a Tai Sui star and god controlling the region of the heavens opposite Jupiter's position in the night sky these beliefs survive in some Taoist religious practices and in the East Asian zodiac's twelve animals, now often popularly assumed to be related to the arrival of the animals before Buddha. The Chinese historian Xi Zezong has claimed that Gan De, an ancient Chinese astronomer, reported a small star "in alliance" with the planet, [117] which may indicate a sighting of one of Jupiter's moons with the unaided eye. If true, this would predate Galileo's discovery by nearly two millennia. [118] [119]

A 2016 paper reports that trapezoidal rule was used by Babylonians before 50 BCE for integrating the velocity of Jupiter along the ecliptic. [120] In his 2nd century work the Almagest, the Hellenistic astronomer Claudius Ptolemaeus constructed a geocentric planetary model based on deferents and epicycles to explain Jupiter's motion relative to Earth, giving its orbital period around Earth as 4332.38 days, or 11.86 years. [121]

Ground-based telescope research

In 1610, Italian polymath Galileo Galilei discovered the four largest moons of Jupiter (now known as the Galilean moons) using a telescope thought to be the first telescopic observation of moons other than Earth's. One day after Galileo, Simon Marius independently discovered moons around Jupiter, though he did not publish his discovery in a book until 1614. [122] It was Marius's names for the major moons, however, that stuck: Io, Europa, Ganymede, and Callisto. These findings were the first discovery of celestial motion not apparently centred on Earth. The discovery was a major point in favor of Copernicus' heliocentric theory of the motions of the planets Galileo's outspoken support of the Copernican theory led to him being tried and condemned by the Inquisition. [123]

During the 1660s, Giovanni Cassini used a new telescope to discover spots and colourful bands, observe that the planet appeared oblate, and estimate the planet's rotation period. [124] In 1690 Cassini noticed that the atmosphere undergoes differential rotation. [55]

The Great Red Spot may have been observed as early as 1664 by Robert Hooke and in 1665 by Cassini, although this is disputed. The pharmacist Heinrich Schwabe produced the earliest known drawing to show details of the Great Red Spot in 1831. [125] The Red Spot was reportedly lost from sight on several occasions between 1665 and 1708 before becoming quite conspicuous in 1878. It was recorded as fading again in 1883 and at the start of the 20th century. [126]

Both Giovanni Borelli and Cassini made careful tables of the motions of Jupiter's moons, allowing predictions of when the moons would pass before or behind the planet. By the 1670s, it was observed that when Jupiter was on the opposite side of the Sun from Earth, these events would occur about 17 minutes later than expected. Ole Rømer deduced that light does not travel instantaneously (a conclusion that Cassini had earlier rejected), [41] and this timing discrepancy was used to estimate the speed of light. [127]

In 1892, E. E. Barnard observed a fifth satellite of Jupiter with the 36-inch (910 mm) refractor at Lick Observatory in California. This moon was later named Amalthea. [128] It was the last planetary moon to be discovered directly by visual observation. [129] An additional eight satellites were discovered before the flyby of the Voyager 1 probe in 1979. [d]

In 1932, Rupert Wildt identified absorption bands of ammonia and methane in the spectra of Jupiter. [130]

Three long-lived anticyclonic features termed white ovals were observed in 1938. For several decades they remained as separate features in the atmosphere, sometimes approaching each other but never merging. Finally, two of the ovals merged in 1998, then absorbed the third in 2000, becoming Oval BA. [131]

Radiotelescope research

In 1955, Bernard Burke and Kenneth Franklin detected bursts of radio signals coming from Jupiter at 22.2 MHz. [55] The period of these bursts matched the rotation of the planet, and they used this information to refine the rotation rate. Radio bursts from Jupiter were found to come in two forms: long bursts (or L-bursts) lasting up to several seconds, and short bursts (or S-bursts) lasting less than a hundredth of a second. [132]

Scientists discovered that there are three forms of radio signals transmitted from Jupiter:

  • Decametric radio bursts (with a wavelength of tens of metres) vary with the rotation of Jupiter, and are influenced by the interaction of Io with Jupiter's magnetic field. [133]
  • Decimetric radio emission (with wavelengths measured in centimetres) was first observed by Frank Drake and Hein Hvatum in 1959. [55] The origin of this signal was a torus-shaped belt around Jupiter's equator. This signal is caused by cyclotron radiation from electrons that are accelerated in Jupiter's magnetic field. [134]
  • Thermal radiation is produced by heat in the atmosphere of Jupiter. [55]


Since 1973, a number of automated spacecraft have visited Jupiter, most notably the Pioneer 10 space probe, the first spacecraft to get close enough to Jupiter to send back revelations about its properties and phenomena. [135] [136] Flights to planets within the Solar System are accomplished at a cost in energy, which is described by the net change in velocity of the spacecraft, or delta-v. Entering a Hohmann transfer orbit from Earth to Jupiter from low Earth orbit requires a delta-v of 6.3 km/s, [137] which is comparable to the 9.7 km/s delta-v needed to reach low Earth orbit. [138] Gravity assists through planetary flybys can be used to reduce the energy required to reach Jupiter, albeit at the cost of a significantly longer flight duration. [139]

Flyby missions

Flyby missions
Spacecraft Closest
Pioneer 10 December 3, 1973 130,000 km
Pioneer 11 December 4, 1974 34,000 km
Voyager 1 March 5, 1979 349,000 km
Voyager 2 July 9, 1979 570,000 km
Ulysses February 8, 1992 [140] 408,894 km
February 4, 2004 [140] 120,000,000 km
Cassini December 30, 2000 10,000,000 km
New Horizons February 28, 2007 2,304,535 km

Beginning in 1973, several spacecraft have performed planetary flyby maneuvers that brought them within observation range of Jupiter. The Pioneer missions obtained the first close-up images of Jupiter's atmosphere and several of its moons. They discovered that the radiation fields near the planet were much stronger than expected, but both spacecraft managed to survive in that environment. The trajectories of these spacecraft were used to refine the mass estimates of the Jovian system. Radio occultations by the planet resulted in better measurements of Jupiter's diameter and the amount of polar flattening. [46] [141]

Six years later, the Voyager missions vastly improved the understanding of the Galilean moons and discovered Jupiter's rings. They also confirmed that the Great Red Spot was anticyclonic. Comparison of images showed that the Red Spot had changed hue since the Pioneer missions, turning from orange to dark brown. A torus of ionised atoms was discovered along Io's orbital path, and volcanoes were found on the moon's surface, some in the process of erupting. As the spacecraft passed behind the planet, it observed flashes of lightning in the night side atmosphere. [46] [142]

The next mission to encounter Jupiter was the Ulysses solar probe. It performed a flyby maneuver to attain a polar orbit around the Sun. During this pass, the spacecraft studied Jupiter's magnetosphere. Ulysses has no cameras so no images were taken. A second flyby six years later was at a much greater distance. [140]

In 2000, the Cassini probe flew by Jupiter on its way to Saturn, and provided higher-resolution images. [143]

The New Horizons probe flew by Jupiter in 2007 for a gravity assist en route to Pluto. [144] The probe's cameras measured plasma output from volcanoes on Io and studied all four Galilean moons in detail, as well as making long-distance observations of the outer moons Himalia and Elara. [145]

Galileo mission

The first spacecraft to orbit Jupiter was the Galileo probe, which entered orbit on December 7, 1995. [51] It orbited the planet for over seven years, conducting multiple flybys of all the Galilean moons and Amalthea. The spacecraft also witnessed the impact of Comet Shoemaker–Levy 9 as it approached Jupiter in 1994, giving a unique vantage point for the event. Its originally designed capacity was limited by the failed deployment of its high-gain radio antenna, although extensive information was still gained about the Jovian system from Galileo. [146]

A 340-kilogram titanium atmospheric probe was released from the spacecraft in July 1995, entering Jupiter's atmosphere on December 7. [51] It parachuted through 150 km (93 mi) of the atmosphere at a speed of about 2,575 km/h (1600 mph) [51] and collected data for 57.6 minutes before the signal was lost at a pressure of about 23 atmospheres and a temperature of 153 °C. [147] It melted thereafter, and possibly vapourised. The Galileo orbiter itself experienced a more rapid version of the same fate when it was deliberately steered into the planet on September 21, 2003, at a speed of over 50 km/s to avoid any possibility of it crashing into and possibly contaminating the moon Europa, which may harbor life. [146]

Data from this mission revealed that hydrogen composes up to 90% of Jupiter's atmosphere. [51] The recorded temperature was more than 300 °C (570 °F) and the windspeed measured more than 644 km/h (>400 mph) before the probes vapourised. [51]

Juno mission

NASA's Juno mission arrived at Jupiter on July 4, 2016, and was expected to complete thirty-seven orbits over the next twenty months. [21] The mission plan called for Juno to study the planet in detail from a polar orbit. [148] On August 27, 2016, the spacecraft completed its first fly-by of Jupiter and sent back the first ever images of Jupiter's north pole. [149] Juno would complete 12 science orbits before the end of its budgeted mission plan, ending July 2018. [150] In June of that year, NASA extended the mission operations plan to July 2021, and in January of that year the mission was extended to September 2025 with four lunar flybys: one of Ganymede, one of Europa, and two of Io. [151] [152] When Juno reaches the end of the mission, it will perform a controlled deorbit and disintegrate into Jupiter's atmosphere. During the mission, the spacecraft will be exposed to high levels of radiation from Jupiter's magnetosphere, which may cause future failure of certain instruments and risk collision with Jupiter's moons. [153] [154]

Canceled missions and future plans

There has been great interest in studying Jupiter's icy moons in detail because of the possibility of subsurface liquid oceans on Europa, Ganymede, and Callisto. Funding difficulties have delayed progress. NASA's JIMO (Jupiter Icy Moons Orbiter) was cancelled in 2005. [155] A subsequent proposal was developed for a joint NASA/ESA mission called EJSM/Laplace, with a provisional launch date around 2020. EJSM/Laplace would have consisted of the NASA-led Jupiter Europa Orbiter and the ESA-led Jupiter Ganymede Orbiter. [156] However, ESA had formally ended the partnership by April 2011, citing budget issues at NASA and the consequences on the mission timetable. Instead, ESA planned to go ahead with a European-only mission to compete in its L1 Cosmic Vision selection. [157]

These plans were realized as the European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in 2022, [158] followed by NASA's Europa Clipper mission, scheduled for launch in 2024. [159] Other proposed missions include the Chinese National Space Administration's Interstellar Express, a pair of probes to launch in 2024 that would use Jupiter's gravity to explore either end of the heliosphere, and NASA's Trident, which would launch in 2025 and use Jupiter's gravity to bend the spacecraft on a path to explore Neptune's moon Triton.

Jupiter has 79 known natural satellites. [6] [160] Of these, 60 are less than 10 km in diameter. [161] The four largest moons are Io, Europa, Ganymede, and Callisto, collectively known as the "Galilean moons", and are visible from Earth with binoculars on a clear night. [162]

Galilean moons

The moons discovered by Galileo—Io, Europa, Ganymede, and Callisto—are among the largest in the Solar System. The orbits of three of them (Io, Europa, and Ganymede) form a pattern known as a Laplace resonance for every four orbits that Io makes around Jupiter, Europa makes exactly two orbits and Ganymede makes exactly one. This resonance causes the gravitational effects of the three large moons to distort their orbits into elliptical shapes, because each moon receives an extra tug from its neighbors at the same point in every orbit it makes. The tidal force from Jupiter, on the other hand, works to circularise their orbits. [163]

The eccentricity of their orbits causes regular flexing of the three moons' shapes, with Jupiter's gravity stretching them out as they approach it and allowing them to spring back to more spherical shapes as they swing away. This tidal flexing heats the moons' interiors by friction. [164] This is seen most dramatically in the volcanic activity of Io (which is subject to the strongest tidal forces), [164] and to a lesser degree in the geological youth of Europa's surface, which indicates recent resurfacing of the moon's exterior. [165]


Jupiter's moons were traditionally classified into four groups of four, based on commonality of their orbital elements. [166] This picture has been complicated by the discovery of numerous small outer moons since 1999. Jupiter's moons are currently divided into several different groups, although there are several moons which are not part of any group. [167]

The eight innermost regular moons, which have nearly circular orbits near the plane of Jupiter's equator, are thought to have formed alongside Jupiter, whilst the remainder are irregular moons and are thought to be captured asteroids or fragments of captured asteroids. Irregular moons that belong to a group share similar orbital elements and thus may have a common origin, perhaps as a larger moon or captured body that broke up. [168] [169]

Regular moons
Inner group The inner group of four small moons all have diameters of less than 200 km, orbit at radii less than 200,000 km, and have orbital inclinations of less than half a degree.
Galilean moons [170] These four moons, discovered by Galileo Galilei and by Simon Marius in parallel, orbit between 400,000 and 2,000,000 km, and are some of the largest moons in the Solar System.
Irregular moons
Himalia group A tightly clustered group of moons with orbits around 11,000,000–12,000,000 km from Jupiter. [171]
Ananke group This retrograde orbit group has rather indistinct borders, averaging 21,276,000 km from Jupiter with an average inclination of 149 degrees. [169]
Carme group A fairly distinct retrograde group that averages 23,404,000 km from Jupiter with an average inclination of 165 degrees. [169]
Pasiphae group A dispersed and only vaguely distinct retrograde group that covers all the outermost moons. [172]

Planetary rings

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. [173] These rings appear to be made of dust, rather than ice as with Saturn's rings. [55] The main ring is probably made of material ejected from the satellites Adrastea and Metis. Material that would normally fall back to the moon is pulled into Jupiter because of its strong gravitational influence. The orbit of the material veers towards Jupiter and new material is added by additional impacts. [174] In a similar way, the moons Thebe and Amalthea probably produce the two distinct components of the dusty gossamer ring. [174] There is also evidence of a rocky ring strung along Amalthea's orbit which may consist of collisional debris from that moon. [175]

Along with the Sun, the gravitational influence of Jupiter has helped shape the Solar System. The orbits of most of the system's planets lie closer to Jupiter's orbital plane than the Sun's equatorial plane (Mercury is the only planet that is closer to the Sun's equator in orbital tilt). The Kirkwood gaps in the asteroid belt are mostly caused by Jupiter, and the planet may have been responsible for the Late Heavy Bombardment event in the inner Solar System's history. [176]

In addition to its moons, Jupiter's gravitational field controls numerous asteroids that have settled into the regions of the Lagrangian points preceding and following Jupiter in its orbit around the Sun. These are known as the Trojan asteroids, and are divided into Greek and Trojan "camps" to commemorate the Iliad. The first of these, 588 Achilles, was discovered by Max Wolf in 1906 since then more than two thousand have been discovered. [177] The largest is 624 Hektor. [178]

Most short-period comets belong to the Jupiter family—defined as comets with semi-major axes smaller than Jupiter's. Jupiter family comets are thought to form in the Kuiper belt outside the orbit of Neptune. During close encounters with Jupiter their orbits are perturbed into a smaller period and then circularised by regular gravitational interaction with the Sun and Jupiter. [179]

Due to the magnitude of Jupiter's mass, the centre of gravity between it and the Sun lies just above the Sun's surface, the only planet in the Solar System for which this is true. [180] [181]


Jupiter has been called the Solar System's vacuum cleaner [183] because of its immense gravity well and location near the inner Solar System there are more impacts on Jupiter, such as comets, than on the Solar System's other planets. [184] It was thought that Jupiter partially shielded the inner system from cometary bombardment. [51] However, recent computer simulations suggest that Jupiter does not cause a net decrease in the number of comets that pass through the inner Solar System, as its gravity perturbs their orbits inward roughly as often as it accretes or ejects them. [185] This topic remains controversial among scientists, as some think it draws comets towards Earth from the Kuiper belt while others think that Jupiter protects Earth from the Oort cloud. [186] Jupiter experiences about 200 times more asteroid and comet impacts than Earth. [51]

A 1997 survey of early astronomical records and drawings suggested that a certain dark surface feature discovered by astronomer Giovanni Cassini in 1690 may have been an impact scar. The survey initially produced eight more candidate sites as potential impact observations that he and others had recorded between 1664 and 1839. It was later determined, however, that these candidate sites had little or no possibility of being the results of the proposed impacts. [187]

The planet Jupiter has been known since ancient times. It is visible to the naked eye in the night sky and can occasionally be seen in the daytime when the Sun is low. [188] To the Babylonians, this object represented their god Marduk. They used Jupiter's roughly 12-year orbit along the ecliptic to define the constellations of their zodiac. [46] [189]

The Romans called it "the star of Jupiter" (Iuppiter Stella), as they believed it to be sacred to the principal god of Roman mythology, whose name comes from the Proto-Indo-European vocative compound *Dyēu-pəter (nominative: *Dyēus-pətēr, meaning "Father Sky-God", or "Father Day-God"). [190] In turn, Jupiter was the counterpart to the mythical Greek Zeus (Ζεύς), also referred to as Dias (Δίας), the planetary name of which is retained in modern Greek. [191] The ancient Greeks knew the planet as Phaethon ( Φαέθων ), meaning "shining one" or "blazing star". [192] [193] As supreme god of the Roman pantheon, Jupiter was the god of thunder, lightning, and storms, and appropriately called the god of light and sky.

The astronomical symbol for the planet, , is a stylised representation of the god's lightning bolt. The original Greek deity Zeus supplies the root zeno-, used to form some Jupiter-related words, such as zenographic. [e] 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 astrological influence. [194] In Germanic mythology, Jupiter is equated to Thor, whence the English name Thursday for the Roman dies Jovis. [195]

In Vedic astrology, Hindu astrologers named the planet after Brihaspati, the religious teacher of the gods, and often called it "Guru", which literally means the "Heavy One". [196] In Central Asian Turkic myths, Jupiter is called Erendiz or Erentüz, from eren (of uncertain meaning) and yultuz ("star"). There are many theories about the meaning of eren. These peoples calculated the period of the orbit of Jupiter as 11 years and 300 days. They believed that some social and natural events connected to Erentüz's movements on the sky. [197] The Chinese, Vietnamese, Koreans, and Japanese called it the "wood star" (Chinese: 木星 pinyin: mùxīng ), based on the Chinese Five Elements. [198] [199] [200]

The tempestuous atmosphere of Jupiter, captured by the Wide Field Camera 3 on the Hubble Space Telescope in infrared.

Differential Rotation

In a rotating solid body, regions that are adjacent at one point in time will remain adjacent as the body rotates. This means that points further from the rotation centre will travel at greater speeds than those closer in.

If only one period spacing pattern is detected and analysed for a star, it is difficult to detect differential rotation. A rigidly rotating model will often provide the best solution.

Differential Rotation. The change in solar rotation rate with latitude. Low latitudes rotate at a faster angular rate (approx. 14 degrees per day) than do high latitudes (approx. 12 degrees per day). For example, the equatorial rotation period is 27.7 days compared to 28.6 days at latitude 40 degrees.

The rotation of a body in which different parts of the body have different periods of rotation. This is true of the sun, Jovian planets, and the disk of the galaxy.
Differentiation .

occurs for gaseous bodies like the Sun or for planets with thick atmospheres .

. The rotation of a body such as a gaseous planet or the Sun so that different parts are rotating at different speeds. For example, a star or planet which rotates faster at its equator than it does at its poles.
Diffraction. The spreading out of light as it passes the edge of an obstacle.

(a) Of a stellar cluster or galaxy, the "orbiting" of stars nearer the center faster than those at the edge. Of a single body (such as the Sun or a gaseous planet), the axial rotation of equatorial latitudes faster than polar latitudes. [A84] .

In a fluid body, such as a star or gas giant planet, the equatorial regions rotate more rapidly than the poles. As shown, a consequence of this is that a set of points lined up on the central meridian will become spread out in longitude over the course of a rotation.

is the difference in the angular speeds of different parts of the galactic disk so stars closer to the center complete a greater fraction of their orbit in a given time.

The tendency for a gaseous sphere, such as a jovian planet or the Sun, to rotate at a different rate at the equator than at the poles. For a galaxy or other object, a condition where the angular speed varies with location within the object.

of the Galaxy can stretch it out into spiral features.

of the disk around the star smears these over-dense regions into spiral waves.
"Although it had been speculated that planets can produce spiral arms, we now think we know how," said team member Zhaohuan Zhu, of Princeton University.

is the most pronounced of any planet in the Solar System, and results in strong latitudinal wind shear and violent storms. The three most impressive were all spotted in 1989 by the Voyager 2 space probe, and then named based on their appearances.

in our galaxy can be used to determine the distance of a source when its radial velocity is known.
F. Expansion Parallax
The distance to an expanding object like a supernova remnant such as Tycho can be determined by measuring: .

of the Sun causes eventual twisting of the magnetic fields. Eventually, the magnetic field undoes itself as rotation continues.

, and how is it observed on Jupiter? HINT
3. Describe some of the ways in which the Voyager mission changed our perception of Jupiter.
4. What is the Great Red Spot? What is known about the source of its energy? HINT .

the condition in which different parts of an object rotate at different speeds one example would be a spiral galaxy whose inner regions rotate faster than its outer regions. dipole a pair of equal and oppositely charged or magnetized poles separated by a distance.

Sunspots are the most obvious manifestation of the Sun's magnetic energy and form when

winds up and intensifies magnetic fields below the surface. The fields become buoyant and break through the surface, creating a sunspot group.

The Sun does rotate, but because it is a large gaseous sphere, not all parts rotate at the same speed. This is known as a

ATMOSPHERE The layers of gases which surround a star, like our Sun, or a planet, like our Earth.

in Jupiter's deep interior:
Clusters of Cyclones Encircling Jupiter's Poles: .

We don't know for sure, but we suspect that the

and convection going on under the photosphere can wrap up and tangle the Sun's magnetic field. As a magnetic field line gets twisted and stretched out by the Sun's wacky rotation, a part of it can erupt near the Sun's surface, producing a sunspot.

The difference in period is caused by

. (S. L. Rucinski et al., Publications of the Astronomical Society of the Pacific, vol. 116, p. 1093, 2004.) .

In the solar dynamo model of the Sun,

of the solar plasma causes the meridional magnetic field to stretch into an azimuthal magnetic field, a process called the omega-effect. The reverse process is called the alpha-effect.[40] .

It ends up fragmenting and those fragments get moved around by the, in this case, it's that everything is rotating and you end up with a certain amount of

. It's not a big deal with the earth but it does act to add to the motion.

Although the Sun's magnetic field is only about twice as strong as Earth's overall, the

of the Sun concentrates the field in some places, where it can be as much as 3,000 times as strong as on Earth.

The behavior of the Sun's magnetic field is strongly influenced by the combination of convective currents, which bring the charged plasma from deep within the Sun to the Sun's surface, and the

of the outer layers of the Sun.

Jupiter's upper atmosphere undergoes

, an effect first noticed by Giovanni Cassini (1690). The rotation of Jupiter's polar atmosphere is

5 minutes longer than that of the equatorial atmosphere. In addition, bands of clouds of different latitudes flow in opposing directions on the prevailing winds.

Vilhelm Bjerknes theorized in 1926 that spots are the erupting ends of magnetic vortices broken by the Sun's

. Various elaborations on this idea have been proposed, but the cause of sunspots is still uncertain.

Magnetic fields within the Sun are stretched out and wound around the Sun by

- the change in rotation rate as a function of latitude and radius within the Sun. This is called the omega-effect after the Greek letter used to represent rotation.

The outer layers of the Sun exhibit

: at the equator the surface rotates once every 25.4 days near the poles it's as much as 36 days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen in the gas planets.

The polar regions complete a rotation in 12 hours being the most pronounced

of any planet in the Solar System, resulting in strong latitudinal wind shear.
Orbital Resonances .

If the material originally making up a spiral arm of a spiral galaxy remains in the arm, then the

of the galaxy should wind up the arm in a time which is short compared to the age of the galaxy.

The Revengian ecosystem is powered by the

The star has "a combination of

and concentration of starspot activity at different stellar latitudes from year to year" (Guidos et al, 2000, in pdf). Useful catalogue numbers and designations for the star include: 58 Eri, HR 1532, Gl 177, Hip 22263, HD 30495, BD-17 954, SAO 149888, and LTT 2088.

It also emits radio waves, ultraviolet rays, and X-rays. The Earth's atmosphere protects us from the harmful effects of the ultraviolet rays and the X-rays. The Sun does rotate, but because it is a large gaseous sphere, not all parts rotate at the same speed. This is known as a

A rigid body such as the Earth will clearly have a single rotation rate. But since the Sun is made of gas, different parts of it rotate at different speeds. Near the Sun's equator, it completes one rotation every 27 Earth days. But near the poles, it's about 31 Earth days. This is called "

With GONG data, it will be possible to constrain the interior temperature and density structure of the sun, and to infer its

Does Jupiter rotate at the same speed at every depth? - Astronomy

Jupiter and the other giant planets are made mostly of hydrogen. Hydrogen is very explosive. We have also seen lightning on some of the giant planets. Why doesn't the lightning make the hydrogen explode?

When hydrogen explodes, it does so by combining with oxygen in the following reaction:

If there is no oxygen, then the explosion cannot take place. While the gas giants are made mostly of hydrogen, they have very little oxygen in their atmospheres.

In fact, the Earth is the only planet with an oxygen-rich atmosphere. The reason is that on Earth, plants and bacteria that perform photosynthesis release oxygen. There is no known photosynthetic life on any other planet, so they have only trace amounts of oxygen in their atmospheres.

This page was last updated June 28, 2015.

About the Author

Britt Scharringhausen

Britt studies the rings of Saturn. She got her PhD from Cornell in 2006 and is now a Professor at Beloit College in Wisconson.

7 Jupiter Is The King Of Spin

Jupiter takes just under 10 hours to complete a full rotation on its axis, compared with 24 hours here on Earth. A day on Jupiter varies from nine hours and 56 minutes at both poles to nine hours and 50 minutes around the equator of the giant planet. This exceedingly fast rotation causes Jupiter to bulge out at the equator and flatten at top, causing the giant to be around 7 percent wider at the equator than it is at the poles. This rotation speed is exceptional when one considers the sheer size of the great planet, which allows it to reign high in yet another category: the shortest day in the planetary system.

Being a gaseous planet, Jupiter does not rotate as a solid sphere like Earth does. Instead, it rotates slightly faster at the equator than at the polar regions, at a speed of 50,000 kilometers (30,000 mi) per hour an hour&mdash27 times faster than the earth rotates.

The Planet Jupiter

Jupiter is the fifth closest planet to our Sun and is the first planet beyond the relatively small, inner four, rocky planets. It is the first of the four "gas giant" planets in proximity to the Sun. Jupiter has 300 times the mass of Earth, but is less dense. It is by far the largest planet in our solar system and has 2 1/2 times the mass of all the solar system's planets put together. Jupiter has 63 known satellites and like Saturn, there is a large number of very small satellites orbiting Jupiter from about seven million to 13 million miles away. In addition, the tiny satellites are all similar in structure, suggesting that they are pieces from a parent body. Jupiter's average distance from the Sun is 480 million miles and takes nearly 12 years to make one revolution. Like the rest of the gas giants, Jupiter has a ring, albeit small and flat. Its rotation is the fastest of all solar system planets, rotating once on its axis every 10 hours. This means at the equator, Jupiter is moving at 22,000 mph, compared with 1,000 mph for the Earth. See what this does to Jupiter's weather below. (For the curious, the small object to the lower left of Jupiter in the photograph above is Ganymede, one of its four large inner moons).

Atmosphere and Weather: Jupiter's extremely dense and relatively dry atmosphere is composed of a mixture of hydrogen, helium and much smaller amounts of methane and ammonia. The same mixture of elements which made Jupiter also made the Sun. It is reasonable to assume, that under more extreme conditions, Jupiter could have evolved into a double-star companion to our Sun. However, Jupiter would have had to become at least 80 times more massive to become a star.

The atmosphere is probably a few hundred miles in depth, pulled toward the surface by the intense gravity. Closer to the surface, the gases become more dense, and likely turn into a compound of slurry. Pioneer's 10 and 11 found evidence that the planet itself is composed almost entirely of liquid hydrogen and that there likely is no real interface between the atmosphere and surface. Jupiter's rocky core lies well below the "surface" and is very hot (around 36,000 degrees F.) due to gravitational compression (compression is a heating process). But Jupiter is much too small and cool to ignite nuclear fusion reactions which are required to become a star.

As mentioned above, Jupiter's extremely fast rotation flattens the globe at the poles and drives extremely changeable weather patterns in the clouds which envelope the planet. The clouds are likely made of ammonia ice crystals, changing to ammonia droplets further down. It is estimated that the temperature of the cloud tops are about -280 degrees F. Overall, Jupiter's average temperature is -238 degrees F. Since Jupiter is only tilted slightly more then 3 degrees on its axis, seasonal fluctuations are minimal.

Jupiter is basically a turbulent, stormy, whirlpool of wind, banded with variable belts and a giant "Red Spot." This giant Red Spot is an oval shaped, counter-clockwise moving storm and is four times larger than our Earth. The storm is by far the largest of similar ovals found on other parts of Jupiter and the other gas giants. Jupiter's wind appears to be driven by internal heat rather than from solar insolation. A probe dropped by the Galileo spacecraft late in 1995 provided evidence of wind speeds of more than 400 mph and some lightning.

QUICK FACTS (Data is from NASA Goddard)

Average distance from Sun 482,300,000 miles
Perihelion 459,100,000 miles
Aphelion 506,300,000 miles
Sidereal Rotation 9.925 Earth hours
Length of Day 9.925 Earth hours
Sidereal Revolution 11.87 Earth years
Diameter at Equator 88,650 miles (largest planet)
Tilt of axis 3.13 degrees
Moons 79 known
Atmosphere Hydrogen (90%), Helium (10%), trace amounts of methane and ammonia
Discoverer Unknown
Discovery Date Prehistoric


Average distance from Sun: Average distance from the center of a planet to the center of the Sun.
Perihelion: The point in a planet's orbit closest to the Sun.
Aphelion: The point in a planet's orbit furthest from the Sun.
Sidereal Rotation: The time for a body to complete one rotation on its axis relative to the fixed stars such as our Sun. Earth's sidereal rotation is 23 hours, 57 minutes.
Length of Day: The average time for the Sun to move from the Noon position in the sky at a point on the equator back to the same position. Earth's length of day = 24 hours
Sidereal Revolution: The time it takes to make one complete revolution around the Sun.
Axis tilt: Imagining that a body's orbital plane is perfectly horizontal, the axis tilt is the amount of tilt of the body's equator relative to the body's orbital plane. Earth is tilted an average of 23.45 degrees on its axis.

A side note: Beginning on July 16, 1994, 21 large fragments of the comet Shoemaker-Levy 9 bombarded Jupiter over a six day period. The fragments impacted the planet in a systematic order, one after the other at 134,000 mph. This provided a pyrotechnic show of unbelievable proportions. The impact of the comet's fragments released massive plumes of gas into Jupiter's atmosphere, emitting huge fireballs and leaving scarring behind. One of the largest fragments impacted Jupiter with a force of 6 million megatons of TNT and produced a plume about 1,500 miles high and 5,000 miles wide. It left a dark discoloration larger than Earth. The top image to the left shows an impact from fragment "G" on Jupiter. This picture was taken by Peter McGregor at the Mount Stromlo and Siding Observatories on July 18, 1994.

The bottom image displays residual scarring from comet fragments "G" "D" and "L", taken by Dan Burton at the Texas A&M observatory on July 20, 1994. The dark discoloration at the lower left is from fragments "G" and "D". The lower right impact is from fragment "L".


Q2.1: What are the impact times and impact locations?

Q2.2: Can the collision be observed with radio telescopes?

For those interested in radio observations during the SL9 impact, Leonard Garcia of the University of Florida has made some information available. The following files are available via anonymous ftp on the University of Florida, Department of Astronomy site in the /pub/jupiter directory:

The antenna required to observe Jupiter may be as simple as a dipole antenna constructed with two pieces of wire 11 feet 8.4 inches in length, connected to a 50 ohm coax cable. This antenna should be laid out on a East-West line and raised above the ground by at least seven feet. A Directional Discontinuity Ring Radiator (DDRR) antenna is also easy to construct and can be made from 1/2 inch copper tubing 125.5 inches in length (21Mhz). The copper tube should be bent into a loop and placed 5 inches above a metallic screen. A good preamp is required for less sensitive shortwave receivers [39].

Society of Amateur and Radio Astronomers (SARA) say that amateur radio astronomers may have to wait approximately three hours after impact for the impact sites to rotate to the central meridian of Jupiter before anything unusual is detected. This wait is typical due to the Jovian decametric synchrotron emissions being emitted as a beam of radiation. Due to the large time differential from impact to radio observations any disturbance may have settled and not be detected. SARA suggest that the radio observer begin the watch approximately 30 minutes before the fragments hit to four hour after.

Q2.3: Will light from the explosions be reflected by any moons?

The following files contain information concerning the reflection of light by Jupiter's moons and are available at SEDS.LPL.Arizona.EDU :

Also, monitoring the eclipses of the Galilean satellites after the impacts may yield valuable scientific data with the moons serving as sensitive probes of any cometary dust in Jupiter's atmosphere. The geometry of the eclipses is such that the satellites pass through the shadow at roughly the same latitude as the predicted comet impacts. There is an article in the first issue of CCD Astronomy involving these observations. The article says that if the dust were to obscure sunlight approximately 120 kilometers above Jupiter's cloud tops, Io could be more that 3 percent (0.03 magnitudes) fainter than normal at mideclipse [40].

Q2.4: What are the orbital parameters of the comet?

In the abstract "The Orbit of Comet Shoemaker-Levy 9 about Jupiter" by D.K. Yeomans and P.W. Chodas (1994, BAAS, 26, 1022), the elements for the brightest fragment Q are listed. These elements are Jovicentric and for Epoch 1994Jul15 (J2000 ecliptic):

Q2.5: Why did the comet break apart?

Furthermore, images of Callisto and Ganymede show crater chains which may have resulted from the impact of a shattered comet similar to Shoemaker- Levy 9 [3,17]. The satellite with the best example of aligned craters is Callisto with 13 crater chains. There are three crater chains on Ganymede. These were first thought to be from basin ejecta in other words secondary craters [27]. See in /pub/astro/SL9/images for images of crater chains (gipul.gif and chain.gif).

There are also a few examples of crater chains on our Moon. Jay Melosh and Ewen Whitaker have identified 2 possible crater chains on the moon which would be generated by near-Earth tidal breakup. One is called the "Davy chain" and it is very tiny but shows up as a small chain of craters aligned back toward Ptolemaeus. In near opposition images, it appears as a high albedo line in high phase angle images, you can see the craters themselves. The second is between Almanon and Tacitus and is larger (comparable to the Ganymede and Callisto chains in size and length). There is an Apollo 11 image of a crater chain on the far side of the moon at in /pub/astro/SL9/images (moonchain.gif).

Q2.6: What are the sizes of the fragments?

The new images, taken with the Hubble telescope's new Wide Field and Planetary Camera-II instrument in 1994, have given us an even clearer view of this fascinating object, which should allow a refinement of the size estimates. Some astronomers now suggest that the fragments are about 1 km or smaller. In addition, the new images show strong evidence for continuing fragmentation of some of the remaining nuclei, which will be monitored by the Hubble telescope over the next two weeks. One can get an idea of the relative sizes of the fragments by considering the relative brightnesses:

The "brightness index" subjectively rates comet fragment brightnesses, 3 being brightest. Brightnesses are eyeballed from the press-released HST image where possible.

Q2.7: How long is the fragment train?

Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?

Galileo will get a direct view of the impacts rather than the grazing limb view previously expected. The Ida image data playback was scheduled to end at the end of June, so there should be no tape recorder conflicts with observing the comet fragments colliding with Jupiter. The problem is how to get the most data played back when Galileo will only be transmitting at 10 bps. One solution is to have both Ulysses and Galileo record the event and and store the data on their respective tape recorders. Ulysses observations of radio emissions data will be played back first and will at least give the time of each comet fragment impact. Using this information, data can be selectively played back from Galileo's tape recorder. From Galileo's perspective, Jupiter will be 60 pixels wide and the impacts will only show up at about 1 pixel, but valuable science data can still collected in the visible and IR spectrum along with radio wave emissions from the impacts.

The impact points are also viewable by both Voyager spacecraft, especially Voyager 2. Jupiter will appear as 2.5 pixels from Voyager 2's viewpoint and 2.0 pixels for Voyager 1. However, it is doubtful that the Voyagers will image the impacts because the onboard software that controls the cameras has been deleted, and there is insufficient time to restore and test the camera software. The only Voyager instruments likely to observe the impacts are the ultraviolet spectrometer and planetary radio astronomy instrument. Voyager 1 will be 52 AU from Jupiter and will have a near-limb observation viewpoint. Voyager 2 will be in a better position to view the collision from a perspective of looking down on the impacts, and it is also closer at 41 AU.

Read More

With so much variety among the brown dwarf speeds already measured, it surprised the authors of the new study that the three fastest brown dwarfs ever found have almost the exact same spin rate (about one full rotation per hour) as each other. This cannot be attributed to the brown dwarfs having formed together or being at the same stage in their development, as they are physically different: One is a warm brown dwarf, one is cold, and the other falls between them. Since brown dwarfs cool as they age, the temperature differences suggest these brown dwarfs are different ages.

The authors aren&rsquot chalking this up to coincidence. They think the members of the speedy trio have all reached a spin speed limit beyond this, a brown dwarf could break apart.

All rotating objects generate centripetal force, which increases the faster the object spins. On a carnival ride, this force can threaten to throw riders from their seats in stars and planets, it can tear the object apart. Before a spinning object breaks apart it will often start bulging around its midsection as it deforms under the pressure. Scientists call this oblation. Saturn, which rotates once every 10 hours like Jupiter, has a perceptible oblation. Based on the known characteristics of the brown dwarfs, they likely have similar degrees of oblation, according to the paper authors.

Locklin on science

A friend of mine asked me if I thought there were actual open questions in physics, ones that individuals or small groups could make a contribution to (as opposed to things like the Higgs boson which require 4000 people and billions of dollars to suss out). Here is a list I came up with. I don’t think it is definitive, and for all I know, some of these problems may no longer be open questions as of today, but I didn’t find anything better on the internets. It may be of interest to young researchers wishing to make a real contribution to human knowledge. Or maybe it’s just something to bullshit about.

Unlike other such lists, there are no silly cosmological or quantum gravitic types of questions on it. I think these are unanswerable questions, and not presently solvable by Baconian science. Essentially, such questions are metaphysical. They can’t presently be solved even in concept by making observations about reality. We’d still like to know the answers to such questions as how to unify gravity with the other forces, but it’s effectively a sort of mathematical philosophic enquiry, rather than normative science.

The other aspect of my “open questions” is they could conceivably be solved by an individual or a small team. I had to use my judgement on that, such as it is. I think these are all interesting and worthy mysteries ones which could be of great import to the human race. I suppose they vary quite a bit in importance, but all of ’em are interesting.