Jupiter Timeline

Jupiter Timeline

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Timeline of discovery of Solar System planets and their moons

The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the discoverer(s) listed. Historically the naming of moons did not always match the times of their discovery. Traditionally, the discoverer enjoys the privilege of naming the new object however, some neglected to do so (E. E. Barnard stated he would "defer any suggestions as to a name" [for Amalthea] "until a later paper" [1] but never got around to picking one from the numerous suggestions he received) or actively declined (S. B. Nicholson stated "Many have asked what the new satellites [Lysithea and Carme] are to be named. They will be known only by the numbers X and XI, written in Roman numerals, and usually prefixed by the letter J to identify them with Jupiter." [2] ). The issue arose nearly as soon as planetary satellites were discovered: Galileo referred to the four main satellites of Jupiter using numbers while the names suggested by his rival Simon Marius gradually gained universal acceptance. The International Astronomical Union (IAU) eventually started officially approving names in the late 1970s.


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 岁 ) 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.

Timeline of astronomy

Mayan astronomers discover an 18.7-year cycle in the rising and setting of the Moon. From this they created the first almanacs – tables of the movements of the Sun, Moon, and planets for the use in astrology. In 6th century BC Greece, this knowledge is used to predict eclipses.

Anaxagoras produced a correct explanation for eclipses and then described the Sun as a fiery mass larger than the Peloponnese , as well as attempting to explain rainbows and meteors . He was the first to explain that the Moon shines due to reflected light from the Sun. [1] [2] [3]

Around this date, Babylonians use the zodiac to divide the heavens into twelve equal segments of thirty degrees each, the better to record and communicate information about the position of celestial bodies. [4]

Plato, a Greek philosopher, founds a school (the Platonic Academy) that will influence the next 2000 years. It promotes the idea that everything in the universe moves in harmony and that the Sun, Moon, and planets move around Earth in perfect circles.

Aristarchus of Samos proposes heliocentrism as an alternative to the Earth-centered universe. His heliocentric model places the Sun at its center, with Earth as just one planet orbiting it. However, there were only a few people who took the theory seriously.

The earliest recorded sighting of Halley's Comet is made by Chinese astronomers. Their records of the comet's movement allow astronomers today to predict accurately how the comet's orbit changes over the centuries.

Hipparchus of Nicaea calculates the first model of the solar system based on trigonometry and determines the precession of the equinoxes.

The Magi - probably Persian astronomers/astrologers (Astrology) - observed a planetary conjunction on Saturday (Sabbath) April 17, 6 BC that signified the birth of a great Hebrew king: Jesus. [5]

The astronomer Shi Shen is believed to have cataloged 809 stars in 122 constellations, and he also made the earliest known observation of sunspots.

Ptolemy publishes his star catalogue, listing 48 constellations and endorses the geocentric (Earth-centered) view of the universe. His views go unquestioned for nearly 1500 years in Europe and are passed down to Arabic and medieval European astronomers in his book the Almagest.

The Hindu cosmological time cycles explained in the Surya Siddhanta, give the average length of the sidereal year (the length of the Earth's revolution around the Sun) as 365.2563627 days, which is only 1.4 seconds longer than the modern value of 365.256363004 days. [6] This remains the most accurate estimate for the length of the sidereal year anywhere in the world for over a thousand years.

Indian mathematician-astronomer Aryabhata, in his Aryabhatiya first identifies the force gravity to explain why objects do not fall when the Earth rotates, [7] propounds a geocentric Solar System of gravitation, and an eccentric elliptical model of the planets, where the planets spin on their axis and follow elliptical orbits, the Sun and the Moon revolve around the Earth in epicycles. He also writes that the planets and the Moon do not have their own light but reflect the light of the Sun and that the Earth rotates on its axis causing day and night and also that the Sun rotates around the Earth causing years.

Indian mathematician-astronomer Brahmagupta, in his Brahma-Sphuta-Siddhanta, first recognizes gravity as a force of attraction, and briefly describes the second law of Newton's law of universal gravitation. He gives methods for calculations of the motions and places of various planets, their rising and setting, conjunctions, and calculations of the solar and lunar eclipses.

The Sanskrit works of Aryabhata and Brahmagupta, along with the Sanskrit text Surya Siddhanta, are translated into Arabic, introducing Arabic astronomers to Indian astronomy.

Muhammad al-Fazari and Yaʿqūb ibn Ṭāriq translate the Surya Siddhanta and Brahmasphutasiddhanta, and compile them as the Zij al-Sindhind, the first Zij treatise. [8]

The first major Arabic work of astronomy is the Zij al-Sindh by al-Khwarizimi. The work contains tables for the movements of the Sun, the Moon, and the five planets known at the time. The work is significant as it introduced Ptolemaic concepts into Islamic sciences. This work also marks the turning point in Arabic astronomy. Hitherto, Arabic astronomers had adopted a primarily research approach to the field, translating works of others and learning already discovered knowledge. Al-Khwarizmi's work marked the beginning of nontraditional methods of study and calculations. [9]

al-Farghani wrote Kitab fi Jawani ("A compendium of the science of stars"). The book primarily gave a summary of Ptolemic cosmography. However, it also corrected Ptolemy based on findings of earlier Arab astronomers. Al-Farghani gave revised values for the obliquity of the ecliptic, the precessional movement of the apogees of the Sun and the Moon, and the circumference of the Earth. The books were widely circulated through the Muslim world and even translated into Latin. [10]

The earliest surviving astrolabe is constructed by Islamic mathematician–astronomer Mohammad al-Fazari. Astrolabes are the most advanced instruments of their time. The precise measurement of the positions of stars and planets allows Islamic astronomers to compile the most detailed almanacs and star atlases yet.

Abū Rayḥān al-Bīrūnī discussed the Indian heliocentric theories of Aryabhata, Brahmagupta and Varāhamihira in his Ta'rikh al-Hind (Indica in Latin). Biruni stated that the followers of Aryabhata consider the Earth to be at the center. In fact, Biruni casually stated that this does not create any mathematical problems. [11]

Abu Sa'id al-Sijzi, a contemporary of Abu Rayhan Biruni, defended the theory that Earth revolves around its axis.

Chinese astronomers record the sudden appearance of a bright star. Native-American rock carvings also show the brilliant star close to the Moon. This star is the Crab supernova exploding.

Abu Ubayd al-Juzjani published the Tarik al-Aflak. In his work, he indicated the so-called "equant" problem of the Ptolemic model. Al-Juzjani even proposed a solution to the problem. In al-Andalus, the anonymous work al-Istidrak ala Batlamyus (meaning "Recapitulation regarding Ptolemy"), included a list of objections to the Ptolemic astronomy.

One of the most important works in the period was Al-Shuku ala Batlamyus ("Doubts on Ptolemy"). In this, the author summed up the inconsistencies of the Ptolemic models. Many astronomers took up the challenge posed in this work, namely to develop alternate models that evaded such errors.

Islamic and Indian astronomical works (including Aryabhatiya and Brahma-Sphuta-Siddhanta) are translated into Latin in Córdoba, Spain in 1126, introducing European astronomers to Islamic and Indian astronomy.

Indian mathematician-astronomer Bhāskara II, in his Siddhanta Shiromani, calculates the longitudes and latitudes of the planets, lunar and solar eclipses, risings and settings, the Moon's lunar crescent, syzygies, and conjunctions of the planets with each other and with the fixed stars, and explains the three problems of diurnal rotation. He also calculates the planetary mean motion, ellipses, first visibilities of the planets, the lunar crescent, the seasons, and the length of the Earth's revolution around the Sun to 9 decimal places.

Al-Bitruji proposed an alternative geocentric system to Ptolemy's. He also declared the Ptolemaic system as mathematical, and not physical. His alternative system spread through most of Europe during the 13th century, with debates and refutations of his ideas continued to the 16th century. [12] [13]

Mo'ayyeduddin Urdi develops the Urdi lemma, which is later used in the Copernican heliocentric model.

Nasir al-Din al-Tusi resolved significant problems in the Ptolemaic system by developing the Tusi-couple as an alternative to the physically problematic equant introduced by Ptolemy. [14] His Tusi-couple is later used in the Copernican model.

Tusi's student Qutb al-Din al-Shirazi, in his The Limit of Accomplishment concerning Knowledge of the Heavens, discusses the possibility of heliocentrism.

Najm al-Din al-Qazwini al-Katibi, who also worked at the Maraghah observatory, in his Hikmat al-'Ain, wrote an argument for a heliocentric model, though he later abandoned the idea. [ citation needed ]

Ibn al-Shatir (1304–1375), in his A Final Inquiry Concerning the Rectification of Planetary Theory, eliminated the need for an equant by introducing an extra epicycle, departing from the Ptolemaic system in a way very similar to what Copernicus later also did. Ibn al-Shatir proposed a system that was only approximately geocentric, rather than exactly so, having demonstrated trigonometrically that the Earth was not the exact center of the universe. His rectification is later used in the Copernican model.

Nicolaus Copernicus publishes De revolutionibus orbium coelestium containing his theory that Earth travels around the Sun. However, he complicates his theory by retaining Plato's perfect circular orbits of the planets.

A brilliant supernova (SN 1572 - thought, at the time, to be a comet) is observed by Tycho Brahe, who proves that it is traveling beyond Earth's atmosphere and therefore provides the first evidence that the heavens can change.

Dutch eyeglass maker Hans Lippershey tries to patent a refracting telescope (the first historical record of one). The invention spreads rapidly across Europe, as scientists make their own instruments. Their discoveries begin a revolution in astronomy.

Johannes Kepler publishes his New Astronomy. In this and later works, he announces his three laws of planetary motion, replacing the circular orbits of Plato with elliptical ones. Almanacs based on his laws prove to be highly accurate.

Galileo Galilei publishes Sidereus Nuncius describing the findings of his observations with the telescope he built. These include spots on the Sun, craters on the Moon, and four satellites of Jupiter. Proving that not everything orbits Earth, he promotes the Copernican view of a Sun-centered universe.

As the power and the quality of the telescopes increase, Christiaan Huygens studies Saturn and discovers its largest satellite, Titan. He also explains Saturn's appearance, suggesting the planet is surrounded by a thin ring.

Scottish astronomer James Gregory describes his "gregorian" reflecting telescope, using parabolic mirrors instead of lenses to reduce chromatic aberration and spherical aberration, but is unable to build one.

Isaac Newton publishes his first copy of the book Philosophiae Naturalis Principia Mathematica, establishing the theory of gravitation and laws of motion. The Principia explains Kepler's laws of planetary motion and allows astronomers to understand the forces acting between the Sun, the planets, and their moons.

Edmond Halley calculates that the comets recorded at 76-year intervals from 1456 to 1682 are one and the same. He predicts that the comet will return again in 1758. When it reappears as expected, the comet is named in his honor.

French astronomer Nicolas de Lacaille sails to southern oceans and begins work compiling a catalog of more than 10000 stars in the southern sky. Although Halley and others have observed from the Southern Hemisphere before, Lacaille's star catalog is the first comprehensive one of the southern sky.

Amateur astronomer William Herschel discovers the planet Uranus, although he at first mistakes it for a comet. Uranus is the first planet to be discovered beyond Saturn, which was thought to be the most distant planet in ancient times.

Charles Messier publishes his catalog of star clusters and nebulas. Messier draws up the list to prevent these objects from being identified as comets. However, it soon becomes a standard reference for the study of star clusters and nebulas and is still in use today.

William Herschel splits sunlight through a prism and with a thermometer, measures the energy given out by different colours. He notices a sudden increase in energy beyond the red end of the spectrum, discovering invisible infrared and laying the foundations of spectroscopy.

Italian astronomer Giuseppe Piazzi discovers what appears to be a new planet orbiting between Mars and Jupiter, and names it Ceres. William Herschel proves it is a very small object, calculating it to be only 320 km in diameter, and not a planet. He proposes the name asteroid, and soon other similar bodies are being found. We now know that Ceres is 932 km in diameter, and is now considered to be a dwarf planet.

Joseph von Fraunhofer builds the first accurate spectrometer and uses it to study the spectrum of the Sun's light. He discovers and maps hundreds of fine dark lines crossing the solar spectrum. In 1859 these lines are linked to chemical elements in the Sun's atmosphere. Spectroscopy becomes a method for studying what stars are made of.

Friedrich Bessel successfully uses the method of stellar parallax, the effect of Earth's annual movement around the Sun, to calculate the distance to 61 Cygni, the first star other than the Sun to have its distance from Earth measured. Bessel's is a truly accurate measurement of stellar positions, and the parallax technique establishes a framework for measuring the scale of the universe.

German amateur astronomer Heinrich Schwabe, who has been studying the Sun for the past 17 years, announces his discovery of a regular cycle in sunspot numbers - the first clue to the Sun's internal structure.

Irish astronomer William Parsons, 3rd Earl of Rosse completes the first of the world's great telescopes, with a 180-cm mirror. He uses it to study and draw the structure of nebulas, and within a few months discovers the spiral structure of the Whirlpool Galaxy.

French physicists Jean Foucault and Armand Fizeau take the first detailed photographs of the Sun's surface through a telescope - the birth of scientific astrophotography. Within five years, astronomers produce the first detailed photographs of the Moon. Early film is not sensitive enough to image stars.

A new planet, Neptune, is identified by German astronomer Johann Gottfried Galle while searching in the position suggested by Urbain Le Verrier. Le Verrier has calculated the position and size of the planet from the effects of its gravitational pull on the orbit of Uranus. An English mathematician, John Couch Adams, also made a similar calculation a year earlier.

Astronomers notice a new bright emission line in the spectrum of the Sun's atmosphere during an eclipse. The emission line is caused by an element's giving out light, and British astronomer Norman Lockyer concludes that it is an element unknown on Earth. He calls it helium, from the Greek word for the Sun. Nearly 30 years later, helium is found on Earth.

An American astronomer Henry Draper takes the first photograph of the spectrum of a star (Vega), showing absorption lines that reveal its chemical makeup. Astronomers begin to see that spectroscopy is the key to understanding how stars evolve. William Huggins uses absorption lines to measure the redshifts of stars, which give the first indication of how fast stars are moving.

A comprehensive survey of stars, the Henry Draper Catalogue, is published. In the catalog, Annie Jump Cannon proposes a sequence of classifying stars by the absorption lines in their spectra, which is still in use today.

Ejnar Hertzsprung establishes the standard for measuring the true brightness of a star. He shows that there is a relationship between color and absolute magnitude for 90% of the stars in the Milky Way Galaxy. In 1913, Henry Norris Russell published a diagram that shows this relationship. Although astronomers agree that the diagram shows the sequence in which stars evolve, they argue about which way the sequence progresses. Arthur Eddington finally settles the controversy in 1924.

Williamina Fleming publishes her discovery of white dwarf stars.

Henrietta Swan Leavitt discovers the period-luminosity relation for Cepheid variables, whereas the brightness of a star is proportional to its luminosity oscillation period. It opened a whole new branch of possibilities of measuring distances on the universe, and this discovery was the basis for the work done by Edwin Hubble on extragalactic astronomy.

German physicist Karl Schwarzschild uses Albert Einstein's theory of general relativity to lay the groundwork for black hole theory. He suggests that if any star collapse to a certain size or smaller, its gravity will be so strong that no form of radiation will escape from it.

Edwin Hubble discovers a Cepheid variable star in the "Andromeda Nebula" and proves that Andromeda and other nebulas are galaxies far beyond our own. By 1925, he produces a classification system for galaxies.

Cecilia Payne-Gaposchkin discovers that hydrogen is the most abundant element in the Sun's atmosphere, and accordingly, the most abundant element in the universe by relating the spectral classes of stars to their actual temperatures and by applying the ionization theory developed by Indian physicist Meghnad Saha. This opens the path for the study of stellar atmospheres and chemical abundances, contributing to understand the chemical evolution of the universe.

Edwin Hubble discovered that the universe is expanding and that the farther away a galaxy is, the faster it is moving away from us. Two years later, Georges Lemaître suggests that the expansion can be traced to an initial "Big Bang".

By applying new ideas from subatomic physics, Subrahmanyan Chandrasekhar predicts that the atoms in a white dwarf star of more than 1.44 solar masses will disintegrate, causing the star to collapse violently. In 1933, Walter Baade and Fritz Zwicky describe the neutron star that results from this collapse, causing a supernova explosion.

Clyde Tombaugh discovers the dwarf planet Pluto at the Lowell Observatory in Flagstaff, Arizona. The object is so faint and moving so slowly that he has to compare photos taken several nights apart.

Karl Jansky detects the first radio waves coming from space. In 1942, radio waves from the Sun are detected. Seven years later radio astronomers identify the first distant source - the Crab Nebula, and the galaxies Centaurus A and M87.

German physicist Hans Bethe explains how stars generate energy. He outlines a series of nuclear fusion reactions that turn hydrogen into helium and release enormous amounts of energy in a star's core. These reactions use the star's hydrogen very slowly, allowing it to burn for billions of years.

The largest telescope in the world, with a 5.08m (200 in) mirror, is completed at Palomar Mountain in California. At the time, the telescope pushes single-mirror telescope technology to its limits - large mirrors tend to bend under their own weight.

July 29 marks the beginning of the NASA (National Aeronautics and Space Administration), agency newly created by the United States to catch up with Soviet space technologies. It absorbs all research centers and staffs of the NACA (National Advisory Committee for Aeronautics), an organization founded in 1915.

Russia and the US both launch probes to the Moon, but NASA's Pioneer probes all failed. The Russian Luna program was more successful. Luna 2 crash-lands on the Moon's surface in September, and Luna 3 returns the first pictures of the Moon's farside in October.

Cornell University astronomer Frank Drake performed the first modern SETI experiment, named "Project Ozma", after the Queen of Oz in L. Frank Baum's fantasy books. [15]

Mariner 2 becomes the first probe to reach another planet, flying past Venus in December. NASA follows this with the successful Mariner 4 mission to Mars in 1965, both the US and Russia send many more probes to planets through the rest of the 1960s and 1970s.

Dutch-American astronomer Maarten Schmidt measures the spectra of quasars, the mysterious star-like radio sources discovered in 1960. He establishes that quasars are active galaxies, and among the most distant objects in the universe.

Arno Penzias and Robert Wilson announce the discovery of a weak radio signal coming from all parts of the sky. Scientists figure out that this must be emitted by an object at a temperature of -270 °C. Soon it is recognized as the remnant of the very hot radiation from the Big Bang that created the universe 13 billion years ago, see Cosmic microwave background. This radio signal is emitted by the electron in hydrogen flipping from pointing up or down and is approximated to happen once in a million years for every particle. Hydrogen is present in interstellar space gas throughout the entire universe and most dense in nebulae which is where the signals originate. Even though the electron of hydrogen only flips once every million years the mere quantity of hydrogen in space gas makes the presence of these radio waves prominent.

Russian Luna 9 probe makes the first successful soft landing on the Moon in January, while the US lands the far more complex Surveyor missions, which follows up to NASA's Ranger series of crash-landers, scout sites for possible manned landings.

Jocelyn Bell Burnell and Antony Hewish detected the first pulsar, an object emitting regular pulses of radio waves. Pulsars are eventually recognized as rapidly spinning neutron stars with intense magnetic fields - the remains of a supernova explosion.

The Uhuru satellite, designed to map the sky at X-ray wavelengths, is launched by NASA. The existence of X-rays from the Sun and a few other stars has already been found using rocket-launched experiments, but Uhuru charts more than 300 X-ray sources, including several possible black holes.

Charles Thomas Bolton was the first astronomer to present irrefutable evidence of the existence of a black hole.

The Russian probe Venera 9 lands on the surface of Venus and sends back the first picture of its surface. The first probe to land on another planet, Venera 7 in 1970, had no camera. Both break down within an hour in the hostile atmosphere.

NASA's Viking 1 and Viking 2 space probes arrive at Mars. Each Viking mission consists of an orbiter, which photographs the planet from above, and a lander, which touches down on the surface, analyzes the rocks, and searches unsuccessfully for life.

On September 5 The Voyager 1 space probe launched by NASA to study the Jovian system, Saturnian system and the interstellar medium.

The first infrared astronomy satellite, IRAS, is launched. It must be cooled to extremely low temperatures with liquid helium, and it operates for only 300 days before the supply of helium is exhausted. During this time it completes an infrared survey of 98% of the sky.

The returning Halley's Comet is met by a fleet of five probes from Russia, Japan, and Europe. The most ambitious is the European Space Agency's Giotto spacecraft, which flies through the comet's coma and photographs the nucleus.

The Magellan probe, launched by NASA, arrives at Venus and spends three years mapping the planet with radar. Magellan is the first in a new wave of probes that include Galileo, which arrives at Jupiter in 1995, and Cassini which arrives at Saturn in 2004.

The Hubble Space Telescope, the first large optical telescope in orbit, is launched using the Space Shuttle, but astronomers soon discovered that it is crippled by a problem with its mirror. A complex repair mission in 1993 allows the telescope to start producing spectacular images of distant stars, nebulae, and galaxies.

The Cosmic Background Explorer satellite produces a detailed map of the background radiation remaining from the Big Bang. The map shows "ripples", caused by slight variations in the density of the early universe – the seeds of galaxies and galaxy clusters.

The 10-meter Keck telescope on Mauna Kea, Hawaii, is completed. The first revolutionary new wave of telescopes, the Keck's main mirror is made of 36 six-sided segments, with computers to control their alignment. New optical telescopes also make use of interferometry – improving resolution by combining images from separate telescopes.

Mike Brown and his team discovered Eris a large body in the outer Solar System [16] which was temporarily named as (2003) UB313 . Initially, it appeared larger than Pluto and was called the tenth planet. [17]

International Astronomical Union (IAU) adopted a new definition of planet. A new distinct class of objects called dwarf planets was also decided. Pluto was redefined as a dwarf planet along with Ceres and Eris, formerly known as (2003) UB313 . Eris was named after the IAU General Assembly in 2006. [18] [19]

2008 TC3 becomes the first Earth-impacting meteoroid spotted and tracked prior to impact.

(May 2) First visual proof of the existence of black holes is published. Suvi Gezari's team in Johns Hopkins University, using the Hawaiian telescope Pan-STARRS 1, record images of a supermassive black hole 2.7 million light-years away that is swallowing a red giant. [20]

In October 2013, the first extrasolar asteroid is detected around white dwarf star GD 61. It is also the first detected extrasolar body which contains water in liquid or solid form. [21] [22] [23]

On July 14, with the successful encounter of Pluto by NASA's New Horizons spacecraft, the United States became the first nation to explore all of the nine major planets recognized in 1981. Later on September 14, LIGO was the first to directly detect gravitational waves. [24]

In August 2017, a neutron star collision that occurred in the galaxy NGC 4993 produced the gravitational wave signal GW170817, which was observed by the LIGO/Virgo collaboration. After 1.7 seconds, it was observed as the gamma-ray burst GRB 170817A by the Fermi Gamma-ray Space Telescope and INTEGRAL, and its optical counterpart SSS17a was detected 11 hours later at the Las Campanas Observatory. Further optical observations e.g. by the Hubble Space Telescope and the Dark Energy Camera, ultraviolet observations by the Swift Gamma-Ray Burst Mission, X-ray observations by the Chandra X-ray Observatory and radio observations by the Karl G. Jansky Very Large Array complemented the detection. This was the first instance of a gravitational wave event that was observed to have a simultaneous electromagnetic signal, thereby marking a significant breakthrough for multi-messenger astronomy. [25] Non-observation of neutrinos is attributed to the jets being strongly off-axis. [26]

China's Chang'e 4 became the first spacecraft to perform a soft landing on the lunar far side.

In April 2019, the Event Horizon Telescope Collaboration obtained the first image of a black hole which was at the center of galaxy M87, providing more evidence for the existence of supermassive black holes in accordance with general relativity. [27]

India launched its second lunar probe called Chandrayaan 2 with an orbiter that was successful and a lander called Vikram along with a rover called Pragyan which failed just 2.1 km above the lunar south pole.

NASA launches Mars 2020 to Mars with a Mars rover that was named Perseverance by seventh grader Alexander Mather in a naming contest. [28]

Crafting a legacy on screen

Mark Millar's "Jupiter's Legacy" Netflix debut was a long time coming. After heeding Stan Lee's advice, Millar conceptualized the series in 2008, but the first issue wasn't published until 2013. Millar handled the words while Frank Quitely covered the series' illustrations, and Pete Doherty took on the lettering. Millar told The Hollywood Reporter that the "Jupiter's Legacy" comics span over 20 issues, noting that it's the longest thing he's published. However, the Netflix series covers five issues over a single eight-episode season.

Compared to comic book universes like DC and Marvel, eight years between publishing the first comic and landing a massive Netflix deal for the series isn't exactly a long wait time. Some comics take decades to get to the big (or small) screen, so getting it done in less than a decade is impressive. Not that "Jupiter's Legacy" is Mark Millar's first foray into Hollywood — the writer's work was adapted into several massively popular film series, including the "Kingsman" franchise and "Kick-Ass."

It was only a matter of time before "Jupiter's Legacy" added to the ranks. And let's face it: right on the heels of a global pandemic and economic disaster, 2021 was the most appropriate year that a series covering financial ruin and ethical dilemmas could come out.


Before the invention of the telescope, Humans had discovered this planet in the night sky. ( TNG : " Loud As A Whisper " okudagram)

In the late 1970s, this planet was surveyed by Pioneer 11, which discovered the planet's magnetic field and magnetosphere. ( TNG : " Loud As A Whisper " okudagram)

In 2143, the NX-Alpha was destroyed near Jupiter shortly after breaking the warp 2 barrier. By 2151, Jupiter Station in orbit of Jupiter served as a repair facility to Earth Starfleet and the Earth Cargo Service. ( ENT : " Silent Enemy ", " Fortunate Son ", " First Flight ", et al.)

That year, Charles Tucker III planned to take Enterprise NX-01 up to warp 4.5 once the ship had passed Jupiter. ( ENT : " Broken Bow ")

An image of Jupiter appeared in Daniels' database on two occasions when Captain Jonathan Archer accessed it in 2152. ( ENT : " Shockwave ", " Future Tense ")

In 2257, the Klingon fleet passed through the Jovian system on its way towards Earth. Later, on a course to Vulcan, the USS Discovery passed through the system, flying close to Jupiter. ( DIS : " Will You Take My Hand? ")

A close-up image of Jupiter was contained in the library computer aboard the USS Enterprise. This image was flashed on a viewscreen when the Talosians scanned the Enterprise computer in 2254. ( TOS-R : " The Cage ")

According to Arex, the cosmic cloud encountered by the Enterprise in 2269 was twice the diameters of Jupiter, Saturn, and Neptune in size. ( TAS : " One of Our Planets Is Missing ")

In the 2270s, the Enterprise flew past Jupiter on its way to intercept V'ger. ( Star Trek: The Motion Picture )

By the early 24th century a shuttle route had been established "from Jupiter to Saturn and back, once a day, every day," know as "the Jovian Run." Both Edward Jellico and Geordi La Forge used to pilot shuttles on this route early in their Starfleet careers. ( TNG : " Chain of Command, Part II ")

According to a sarcastic remark by Lewis Zimmerman, tours of the lava flows on Jupiter's third moon were popular by 2377. ( VOY : " Life Line ")


Initial concept Edit

Jupiter traces its history ultimately to the PGM-11 Redstone missile, the US's first nuclear ballistic missile. While it was entering service, Wernher von Braun's Army Ballistic Missile Agency (ABMA) team at Redstone Arsenal began to consider an upgraded version using the LR89 rocket engine being developed by Rocketdyne for the Air Force's Atlas missile project. Using the LR89 and adding a second stage would allow the new design to reach 1,000 nautical miles (1,900 km 1,200 mi), [1] a dramatic improvement over the Redstone's roughly 60 miles (97 km).

As Rocketdyne continued working on the LR89, it appeared that it could be improved to increase thrust over the promised 120,000 pounds-force (530,000 N). In 1954, the Army asked Rocketdyne to provide a similar design with a thrust of 135,000 pounds-force (600,000 N). [2] During this same period, the weight of nuclear warheads was rapidly falling, and by combining this engine with a warhead of 2,000 pounds (910 kg) they could build a single-stage missile able to reach 1,500 nautical miles (2,800 km 1,700 mi) while being significantly less complicated and easier to handle in the field than a two-stage model. This engine was continually upgraded, ultimately reaching 150,000 pounds-force (670,000 N). [1] This last model, known to the Army as the NAA-150-200, became much better known by its Rocketdyne model number, S-3. [3]

Navy SLBM interest Edit

Around the same time, the US Navy was looking for ways to join the nuclear club, and had been focusing mostly on cruise missiles and similar systems. Some consideration had been given to the use of ballistic missiles on ships, but Admiral Hyman Rickover, "father" of the nuclear submarine, was skeptical that this could be done, and was worried it would take up funding needed elsewhere. [4] Another skeptic of missiles was the Chief of Naval Operations, Robert B. Carney. [5]

Lower-ranking Navy officials became increasingly interested when the Army and Air Force began serious development of their long-range missiles. In an attempt to bypass high-ranking Navy officials, who remained uninterested in the concept, the Navy liaison to the Killian Committee championed the cause. The Committee took up the concept, and in September 1955 released a report calling for the development of a sea-based missile system. [5]

The Navy's disinterest in missiles had been greatly reduced with the August 1955 appointment of Admiral Arleigh Burke to replace Carney. Burke was convinced the Navy had to get into the missile field as rapidly as possible, and was well aware that the Air Force would oppose any such endeavor. Instead, he approached the Army, and found that the proposed Jupiter fit the range goals needed by the Navy. [5]

Development begins Edit

The issue of who would be given the go-ahead to build an IRBM by this time had reached the Joint Chiefs of Staff (JCS), who proved unable to reach a decision. This forced the Secretary of Defense Charles Erwin Wilson to move ahead without an official recommendation from the military. He saw the Navy interest as a reasonable argument to continue the Army project in any event, and on 8 November 1955 approved both programs. The Air Force would develop IRBM No. 1, or SM-75 (for "strategic missile"), the Army would develop their design as IRBM No. 2 or SM-78. The Navy would develop systems to launch the Army missile from ships and, later, submarines. [5] [6]

The requirement for shipboard storage and launching dictated the size and shape of the Jupiter. The original Army design was 92 feet (28 m) long and 95 inches (2,400 mm) in diameter. The Navy stated they were not interested in anything longer than 50 feet (15 m). The ABMA team responded by increasing the diameter to 105 inches (2,700 mm). This precluded it from being carried aboard contemporary cargo aircraft, limiting it to sea and road. Even with this change, they were unable to reduce its length enough to suit the Navy. They suggested that they begin with a 60 foot (18 m) long version and then scale it down as improvements in the engines were worked into the design. This was rejected, and after briefly considering a 55 foot (17 m) version, finally settled on the 58 foot (18 m) version. [7]

On 2 December 1955, the secretaries of the Army and Navy publicly announced the dual Army–Navy program to create a land- and sea-based MRBM. In April 1956, as part of a widespread effort to assign names to various missile projects, the Army's effort was given the name "Jupiter" and the Air Force's became "Thor". [1]

Accuracy and mission Edit

Redstone provided an accuracy of 300 metres (980 ft) at its maximum range, which, when combined with its large warhead, allowed it to attack hard targets like protected airbases, bridges, command and control sites, as well as other strategic targets like railway marshaling yards and pre-attack concentration areas. This was in keeping with the Army's view of nuclear weapons, which was in effect more powerful artillery. They saw the weapons as part of a large-scale battle in Europe, in which both sides would use nuclear weapons during a limited war that did not include the use of strategic weapons on each other's cities. In that case, "if wars were to be kept limited, such weapons would have to be capable of hitting only tactical targets." This approach saw the support of a number of influential theorists, notably Henry Kissinger, and was seized on as a uniquely Army mission. [8]

The original goal for the new longer-range design was to match Redstone's accuracy at the Jupiter's much-extended range. That is, if Redstone could reach 300 m at 60 miles, the new design would provide a circular error probable on the order of 7 kilometres (4.3 mi). As development continued, it became clear the ABMA team, under the direction of Fritz Mueller, could improve on that. This led to a period in which "The Army would lay down a particular accuracy, and wait for our arguments whether it was possible. We had to promise a lot, but were fortunate." [9]

This process ultimately delivered a design intended to provide 0.5 miles (0.80 km) accuracy at the full range, an order of magnitude better than Redstone and four times better than the best INS designs being used by the Air Force. The system was so accurate that a number of observers expressed their skepticism about the Army's goals, with the WSEG suggesting they were hopelessly optimistic. [9]

The Air Force was dead set against Jupiter. They argued that nuclear weapons were not simple new artillery, and that their employment would immediately trigger a response that might result in a strategic exchange. This would especially be true if the Army launched a long-range weapon like Jupiter, which could reach cities in the Soviet Union and could not immediately be distinguished as attacking a military or civilian target. They suggested that any such launch would trigger a strategic response, and as such, the Army should not be given any long-range weapons. [9]

However, as von Braun's team went from success to success, and with Atlas still years from operational deployment, it was clear that Jupiter represented a threat to the Air Force's desired hegemony over strategic forces. This led to them starting their own MRBM program Thor, in spite of having repeatedly dismissed the medium-range role in the past. [10] The fighting between the Army and Air Force grew through 1955 and 1956 until practically every missile system the Army was involved in was being attacked in the press. [11]

Navy exit Edit

The Navy was concerned from the start about Jupiter's cryogenic propellants, but at the time there was no other option. Given the size and weight of contemporary nuclear weapons, only a large liquid-fuel rocket engine provided the energy needed to meet the Navy's range goal of launching from safe areas in the Atlantic Ocean. They justified the risk thus:

We were prepared to take the chance that we might lose a submarine or two through accidental explosions. But, then, there are some of us who enjoy, or at lease [sic] are acclimated to, the idea of risking our lives." [12]

All of this changed radically in the summer of 1956, when Project Nobska brought together leading scientists to consider antisubmarine warfare. As part of this workshop, Edward Teller stated that by 1963 a 1 megaton warhead would be reduced to only 600 pounds (270 kg). [13] Rocketry experts at the same meeting suggested that an intermediate-range weapon carrying one of these weapons could be built using solid propellant. Even in this case, the missile would be much smaller than Jupiter Jupiter was expected to weigh 160,000 pounds (73,000 kg), while estimates of a solid-fuel missile with similar range were closer to 30,000 pounds (14,000 kg), along with a similar reduction in size which was of paramount importance to a submarine design. [14]

The Navy announced their desire to develop their own missile that summer, initially under the name Jupiter-S. After intensive follow-up studies, the Navy withdrew from the Jupiter program in December 1956. This was officially announced by the Army in January 1957. [15] In its place, the Navy began development of what was then known as the Fleet Ballistic Missile Program, and the missile was later renamed Polaris, their first submarine-launched ballistic missile (SLBM). [16] Rickover, one of the few remaining skeptics, was won over by pointing out that a properly designed submarine was needed specifically for this role, and he would be called upon to produce it. Rickover was from that point on a staunch ally of the program. [17]

Saved from cancellation Edit

On 4 October 1957, the Soviets successfully launched Sputnik I from their R-7 Semyorka ICBM. The US was aware of these efforts and had already talked to the press about it, suggesting that if the Soviets launched a satellite first it would be no big deal. [18] To their surprise, the press exploded in rage over the affair. Having spent over a decade working on similar missiles, like Atlas, the fact that the Soviets could beat them was a serious blow, and prompted a deep review of the ongoing programs. [19]

One problem noted from the start was that the internecine fighting between the Army and Air Force was leading to significant duplication of effort, with little to show for it. The Department of Defense responded by creating the Advanced Research Projects Agency (ARPA), whose initial mission was to look over all of the ongoing projects and select ones based solely on their technical merits. [20]

At the same time, the fighting had begun to have negative political effects. In a 26 November 1956 memorandum, recently appointed US Secretary of Defense Charles Erwin Wilson attempted to end the fighting. His solution was to limit the Army to weapons with 200-mile (320 km) range, and those involved in surface-to-air defense to only 100 miles (160 km). [21] The memo also placed limits on Army air operations, severely limiting the weight of the aircraft it was allowed to operate. To some degree this simply formalized what had largely already been the case in practice, but Jupiter fell outside the range limits and the Army was forced to hand them to the Air Force. [22]

The Air Force, of course, had no interest in taking over a weapon system they had long argued was not needed. However, ARPA's studies clearly showed it was an excellent system, and as it was ready to enter production, any Air Force thoughts about canceling it were immediately quashed. New orders for 32 prototypes and 62 operational missiles were soon placed, bringing the total number of Jupiters to be built to 94. The first, hand-built at ABMA, would be delivered by the end of FY57, and the first production models from Chrysler's Michigan Ordnance Missile Plant near Warren, Michigan between FY58 and FY61. [20]

Lingering complaints Edit

A primary complaint about Jupiter was that the design's shorter range placed it within relatively easy striking distance of Soviet weapons, both missiles and aircraft. Thor, based in the UK, would likely have more warning of an impending attack. [a] This is precisely the reason that the Army spent considerable effort on making Jupiter mobile, in order to make surprise attacks difficult without prior aerial reconnaissance missions. [9]

However, in November 1958, the Air Force decided Jupiter would be launched from fixed emplacements. Army General Maxwell Taylor argued this was done deliberately, noting that:

. a mobile missile needs Army-type troops to move, emplace, protect and fire it. a decision to organize mobile ballistic missile units would in logic have led to transferring the operational use of the weapon back to the Army – where it should have been all the time. [9]

To offset the possibility of air attack, the systems were upgraded to allow a launch within 15 minutes of a launch order. [20]

Rocketdyne tested the first S-3 engine at their Santa Susana, California facilities in November 1955. A mock-up was delivered to ABMA in January 1956, followed by the first prototype engines in July 1956. Testing of these engines began in September 1956 at ABMA's new Power Plant Test Stand. This demonstrated a number of problems with unstable combustion, leading to the failure of four engines by November. To continue testing, the engine was temporarily derated back to 135,000 lbf and was successfully tested at this level in January 1957. Continued work on the engine developed several sub-versions, finally reaching the design goal of 150,000 lbf in the S-3D model. [23]

The 135,000 pound engine, also used in the first Thor and Atlas tests, had conical thrust chambers, but the 150,000 pound model switched to bell-shaped thrust chambers. Unlike Thor and Atlas, which had two small vernier engines for roll control, Jupiter gimbaled the turbine exhaust. The early test model Jupiters had two small gas jets powered off the turbine exhaust, the gimbaled exhaust pipe not being introduced until late 1958. [ citation needed ]

Static tests Edit

In 1954 Test Laboratory director Karl Heimburg began construction of the Static Test Stand for Redstone testing. This was still under construction when it was re-purposed for Jupiter, and finally completed in January 1957. [24] A Jupiter was installed in the stand that month, and fired for the first time on 12 February 1957. This almost ended in disaster when a small explosion went off in the liquid oxygen (LOX) pump, and as the missile sat there the LOX boiled off and threatened to burst the tanks. The day was saved when the foreman, Paul Kennedy, ran to the missile and connected a pressure line to drain the oxygen buildup in the tank. The problem was later traced to the lubricant used in the pump, which tended to burst into flames in contact with LOX. A new lubricant was introduced, along with a series of changes to the test stand to help retain control in these situations. [25]

Flight tests Edit

Kurt Debus had led the construction of launch pads for Redstone missiles at Cape Canaveral, Florida, building the twin LC-5 and LC-6 pads about 500 feet (150 m) apart with a common blockhouse located 300 feet (91 m) away between the two. Redstone testing moved to these pads from the smaller LC-4 on 20 April 1955, with the launch of the seventh Redstone from LC-6. Envisioning an extended test program, a second set of similar pads began construction in 1956, LC-26 A and B the only major difference was the blockhouse was located slightly further away, about 400 feet (120 m). In late 1957 a set of parallel railway tracks running just east of the pads was added, allowing an A-frame gantry to be rolled to any of the four pads. [26]

Jupiters were delivered to the Cape strapped to wheeled trailers and flown to the Cape's "Skid Strip" on C-124s. They were then moved to Hangar R at the Cape Industrial Area where the nose cone was mated with the missile, and electrical checkout was performed. It was then moved on the trailer to the pads, about 3.5 miles (5.6 km) south, where they were lifted to vertical by a crane on the movable gantry. Just to the north of the launch area was the Air Force's LC-17 for Thor, and LC-18 used for Thor and the Navy's Vanguard. After the Army's head start, the Air Force had since caught up and attempted its first Thor launch on 26 January 1957, which ended with the missile exploding on the launch pad. [27]

Jupiter test flights commenced with the launch of AM-1A (ABMA Missile 1A) on 1 March 1957 from LC-5. This missile was equipped with the lower-thrust interim engine. The vehicle performed well until past 50 seconds into launch when control started to fail, leading to breakup at T+73 seconds. It was deduced that turbopump exhaust was sucked up by the partial vacuum in the area behind the missile and began to burn in the tail section. The heat burned through the control wiring, so extra insulation was added there on future flights. An identical AM-1B was quickly readied and launched on 26 April. AM-1B's flight went entirely according to plan up to T+70 seconds when the missile started becoming unstable in flight and finally broke up at T+93 seconds. The failure was deduced to have been the result of propellant slosh due to bending modes induced by the steering maneuvers needed to perform the flight trajectory. The solution to this problem involved testing several types of baffles in a Jupiter center section until discovering a suitable type for both the LOX and fuel tanks. [27]

The third Jupiter, also numbered AM-1, was quickly equipped with the baffles and launched on 31 May, slightly over a month after AM-1B, traveling a full 1,247 nautical miles (2,309 km 1,435 mi) downrange. This version had a slightly improved S-3 engine with 139,000 pounds-force (620,000 N) thrust. AM-2 flew from LC-26A on 28 August, and successfully tested the separation of the rocket body from the reentry vehicle section before splashing down at 1,460 nautical miles (2,700 km 1,680 mi). AM-3 flew from LC-26B on 23 October, including the ablative heat shield and the new ST-90 INS. This test flew a planned distance of 1,100 nautical miles (2,000 km 1,300 mi). [27]

AM-3A launched on 26 November and all went according to plan until T+101 seconds when engine thrust abruptly terminated. The missile broke up at T+232 seconds. On 18 December, AM-4 lost thrust T+117 seconds and fell into the ocean 149 nautical miles (276 km 171 mi) downrange. These failures were traced to an inadequate turbopump design that resulted in a string of failures in the Jupiter, Thor, and Atlas programs, all of which used a variant of the same Rocketdyne engine. Testing then paused for five months while Rocketdyne came up with a number of fixes and the Army retrofitted all its Jupiters with the redesigned pumps. [27] In spite of these failures, Jupiter was declared operational on 15 January 1958.

Taking the time to also fully rate the engine to 150,000 lbf, the new engine was first flown on AM-5 on 18 May 1958 from LC-26B, reaching a planned 1,247 nautical miles (2,309 km 1,435 mi). AM-5 also carried the real nose cone design, which separated from the rocket body, spun up the warhead, and separated to allow the warhead to continue on its own. The warhead section was equipped with a parachute and was recovered by the Navy some 28 nautical miles (52 km 32 mi) from its predicted splashdown point. [27]

AM-6B included both the production nose cone and the ST-90 INS during its launch from LC-26B on 17 July 1958. This time the Navy recovered it only 1.5 nautical miles (2.8 km 1.7 mi) from its planned splash down point 1,241 nautical miles (2,298 km 1,428 mi) downrange. AM-7 flew 1,207 nautical miles (2,235 km 1,389 mi) on 27 August, testing a new solid fuel rocket for spinup, replacing the older hydrogen peroxide model. AM-9 was launched on 10 October, the first Jupiter to carry the fully functional turbine exhaust roll control system. The flight failed however a pinhole leak in the thrust transducer area started a thrust section fire and loss of vehicle control. The Range Safety Officer destroyed the missile at T+49 seconds. [27]

Afterwards, there was only one more failure in the Jupiter program, AM-23 on 15 September 1959, which developed a leak in a nitrogen bottle that led to depressurization of the RP-1 tank and almost immediate loss of control at liftoff. The missile wobbled from side to side and the RP-1 tank began to break apart starting at T+7 seconds. The Jupiter flipped upside down, dumping out the contents of the RP-1 tank, followed by total vehicle breakup at T+13 seconds, just before the Range Safety Officer could issue the flight termination command. Flying debris struck and damaged a Juno II on the adjacent LC-5. This particular launch was carrying a biological nose cone with mice and other specimens (which did not survive). [28]

Through the early 1960s, a number of Jupiters were launched by the forces of other countries, as well as the Air Force, as part of ongoing combat training. The last launch of this sort was by the Italian Air Force, CM-106, which took place from LC-26B on 23 January 1963. [29]

Biological flights Edit

Jupiter missiles were used in a series of suborbital biological test flights. On 13 December 1958, Jupiter AM-13 was launched from Cape Canaveral, Florida with a Navy-trained South American squirrel monkey named Gordo on board. The nose cone recovery parachute failed to operate and Gordo did not survive the flight. Telemetry data sent back during the flight showed that the monkey survived the 10 g (100 m/s²) of launch, eight minutes of weightlessness and 40 g (390 m/s²) of reentry at 10,000 mph (4.5 km/s). The nose cone sank 1,302 nautical miles (2,411 km) downrange from Cape Canaveral and was not recovered.

Another biological flight was launched on 28 May 1959. Aboard Jupiter AM-18 were a seven-pound (3.2 kg) American-born rhesus monkey, Able, and an 11-ounce (310 g) South American squirrel monkey, Baker. The monkeys rode in the nose cone of the missile to an altitude of 300 miles (480 km) and a distance of 1,500 miles (2,400 km) down the Atlantic Missile Range from Cape Canaveral. [30] They withstood accelerations of 38 g and were weightless for about nine minutes. A top speed of 10,000 mph (4.5 km/s) was reached during their 16-minute flight.

After splashdown the Jupiter nosecone carrying Able and Baker was recovered by the seagoing tug USS Kiowa (ATF-72). The monkeys survived the flight in good condition. Able died four days after the flight from a reaction to anesthesia while undergoing surgery to remove an infected medical electrode. Baker lived for many years after the flight, finally succumbing to kidney failure on 29 November 1984 at the United States Space and Rocket Center in Huntsville, Alabama.

In April 1958, under the command of President Eisenhower, the U.S. Department of Defense notified the Air Force it had tentatively planned to deploy the first three Jupiter squadrons (45 missiles) in France. However, in June 1958 the new French President Charles de Gaulle refused to accept basing any Jupiter missiles in France. This prompted U.S. to explore the possibility of deploying the missiles in Italy and Turkey. The Air Force was already implementing plans to base four squadrons (60 missiles)—subsequently redefined as 20 Royal Air Force squadrons each with three missiles—of PGM-17 Thor IRBMs in Britain on airfields stretching from Yorkshire to East Anglia.

In 1958, the United States Air Force activated the 864th Strategic Missile Squadron at ABMA. Although the USAF briefly considered training its Jupiter crews at Vandenberg AFB, California, it later decided to conduct all of its training at Huntsville. In June and September of the same year the Air Force activated two more squadrons, the 865th and 866th.

In April 1959, the secretary of the Air Force issued implementing instructions to USAF to deploy two Jupiter squadrons to Italy. The two squadrons, totaling 30 missiles, were deployed at 10 sites in Italy from 1961 to 1963. They were operated by Italian Air Force crews, but USAF personnel controlled arming the nuclear warheads. The deployed missiles were under command of 36th Strategic Interdiction Air Brigade (36ª Aerobrigata Interdizione Strategica, Italian Air Force) at Gioia del Colle Air Base, Italy.

In October 1959, the location of the third and final Jupiter MRBM squadron was settled when a government-to-government agreement was signed with Turkey. The U.S. and Turkey concluded an agreement to deploy one Jupiter squadron on NATO's southern flank. One squadron totaling 15 missiles was deployed at five sites near İzmir, Turkey from 1961 to 1963, operated by USAF personnel, with the first flight of three Jupiter missiles turned over to the Türk Hava Kuvvetleri (Turkish Air Force) in late October 1962, but USAF personnel retaining control of nuclear warhead arming.

On four occasions between mid-October 1961 and August 1962, Jupiter mobile missiles carrying 1.4 megatons of TNT (5.9 PJ) nuclear warheads were struck by lightning at their bases in Italy. In each case, thermal batteries were activated, and on two occasions, tritium-deuterium "boost" gas was injected into the warhead pits, partially arming them. After the fourth lightning strike on a Jupiter MRBM, the USAF placed protective lightning strike-diversion tower arrays at all of the Italian and Turkish Jupiter MRBM missiles sites.

In 1962, a Bulgarian MiG-17 reconnaissance airplane was reported to have crashed into an olive grove near one of the U.S. Jupiter missile launch sites in Italy, after overflying the site. [31]

By the time the Turkish Jupiters had been installed, the missiles were already largely obsolete and increasingly vulnerable to Soviet attacks. All Jupiter MRBMs were removed from service by April 1963, as a backdoor trade with the Soviets in exchange for their earlier removal of MRBMs from Cuba.

Deployment sites Edit

Jupiter squadrons consisted of 15 missiles and approximately 500 military personnel with five "flights" of three missiles each, manned by five officers and 10 NCOs. To reduce vulnerability, the flights were located approximately 30 miles apart, with the triple launcher emplacements separated by a distance of several hundred miles.

The ground equipment for each emplacement was housed in approximately 20 vehicles including two generator trucks, a power distribution truck, short- and long-range theodolites, a hydraulic and pneumatic truck and a liquid oxygen truck. Another trailer carried 6000 gallons of fuel and three liquid oxygen trailers each carried 4,000 US gallons (15,000 l 3,300 imp gal).

The missiles arrived at the emplacement on large trailers while still on the trailer, the crew attached the hinged launch pedestal to the base of the missile which was hauled to an upright position using a winch. Once the missile was vertical, fuel and oxidizer lines were connected and the bottom third of the missile was encased in a "flower petal shelter", consisting of wedge-shaped metal panels, allowing crew members to service the missiles in all weather conditions. Stored empty, on 15-minute combat status in an upright position on the launch pad, the firing sequence included filling the fuel and oxidizer tanks with 68,000 lb (31,000 kg) of LOX and 30,000 lb (14,000 kg) of RP-1, while the guidance system was aligned and targeting information loaded. Once the fuel and oxidizer tanks were full, the launch controlling officer and two crewmen in a mobile launch control trailer could launch the missiles.

Each squadron was supported by a receipt, inspection and maintenance (RIM) area to the rear of the emplacements. RIM teams inspected new missiles and provided maintenance and repair to missiles in the field. Each RIM area also housed 25 tons of liquid oxygen and nitrogen generating plants. Several times a week, tanker trucks carried the fuel from the plant to the individual emplacements.

  • Length: 60 ft (18.3 m)
  • Diameter: 8 ft 9 in (2.67 m)
  • Total Fueled Weight: 108,804 lb (49,353 kg)
  • Empty Weight: 13,715 lb (6,221 kg)
  • Oxygen (LOX) Weight: 68,760 lb (31,189 kg)
  • RP-1 (kerosene) Weight: 30,415 lb (13,796 kg)
  • Thrust: 150,000 lbf (667 kN)
  • Engine: Rocketdyne LR79-NA (Model S-3D)
  • ISP: 247.5 s (2.43 kN·s/kg)
  • Burning time: 2 min. 37 sec.
  • Propellant consumption rate: 627.7 lb/s (284.7 kg/s)
  • Range: 1,500 mi (2,400 km)
  • Flight time: 16 min 56.9 sec
  • Cutoff velocity: 8,984 mph (14,458 km/h) – Mach 13.04
  • Reentry velocity: 10,645 mph (17,131 km/h) – Mach 15.45
  • Acceleration: 13.69 g (134 m/s²)
  • Peak deceleration: 44.0 g (431 m/s²)
  • Peak altitude: 390 mi (630 km)
  • CEP 4,925 ft (1,500 m)
  • Warhead: 1.45 Mt Thermonuclear W49 – 1,650 lb (750 kg)
  • Fusing: Proximity and Impact
  • Guidance: Inertial

The Saturn I and Saturn IB rockets were manufactured by using a single Jupiter propellant tank, in combination with eight Redstone rocket propellant tanks clustered around it, to form a powerful first stage launch vehicle.

The Jupiter MRBM was also modified by adding upper stages, in the form of clustered Sergeant-derived rockets, to create a space launch vehicle called Juno II, not to be confused with the Juno I which was a Redstone-Jupiter-C missile development. There is also some confusion with another U.S. Army rocket called the Jupiter-C, which were Redstone missiles modified by lengthening the fuel tanks and adding small solid-fueled upper stages.

Specifications (Juno II launch vehicle) Edit

The Juno II was a four-stage rocket derived from the Jupiter IRBM. It was used for 10 satellite launches, six of which failed. It launched Pioneer 3 (a partial success), Pioneer 4, Explorer 7, Explorer 8, and Explorer 11.

  • Juno II total length: 24.0 m
  • Orbit payload to 200 km: 41 kg
  • Escape velocity payload: 6 kg
  • First launch date: 6 December 1958
  • Last launch date: 24 May 1961

There were 46 test launches, all launched from Cape Canaveral Missile Annex, Florida. [32]

1957 Edit

Rocket S/N Launch Site Payload Function Orbit Outcome Remarks
1957-03-01 Jupiter AM-1A CCAFS LC-5 Missile test Suborbital Failure First flight of Jupiter. Thrust section overheating led to control failure and missile breakup T+74 seconds.
1957-04-26 Jupiter AM-1B CCAFS LC-5 Missile test Suborbital Failure Propellant slosh led to control failure and missile breakup T+93 seconds.
1957-05-31 Jupiter AM-1 CCAFS LC-5 Missile test Suborbital Success
1957-08-28 Jupiter AM-2 CCAFS LC-26A Missile test Suborbital Success
1957-10-23 Jupiter AM-3 CCAFS LC-26B Missile test Suborbital Success
1957-11-27 Jupiter AM-3A CCAFS LC-26B Missile test Suborbital Failure Turbopump failure caused loss of thrust T+101 seconds. Missile broke up T+232 seconds.
1957-12-19 Jupiter AM-4 CCAFS LC-26B Missile test Suborbital Failure Turbopump failure caused loss of thrust T+116 seconds. Missile remained structurally intact until impact with the ocean.

1958 Edit

Rocket S/N Launch Site Payload Function Orbit Outcome Remarks
1958-05-18 Jupiter AM-5 CCAFS LC-26B Missile test Suborbital Success
1958-07-17 Jupiter AM-6B CCAFS LC-26B Missile test Suborbital Success
1958-08-27 Jupiter AM-7 CCAFS LC-26A Missile test Suborbital Success
1958-10-10 Jupiter AM-9 CCAFS LC-26B Missile test Suborbital Failure Hot exhaust gas leak caused thrust section fire and loss of control. RSO T+49 seconds.
1958-12-06 Juno II AM-11 CCAFS LC-5 Pioneer 3 Lunar orbiter High suborbital Partial failure Premature first stage cutoff
1958-12-13 Jupiter AM-13 CCAFS LC-26B Biological nose cone w/ squirrel monkey Missile test Suborbital Success

1959 Edit

Rocket S/N Launch Site Payload Function Orbit Outcome Remarks
1959-01-22 Jupiter CM-21 CCAFS LC-5 Missile test Suborbital Success First flight of production Chrysler-built Jupiter
1959-02-27 Jupiter CM-22 CCAFS LC-26B Missile test Suborbital Success
1959-03-03 Juno II AM-14 CCAFS LC-5 Pioneer 4 Lunar orbiter TEO Success First successful American lunar probe
1959-04-04 Jupiter CM-22A CCAFS LC-26B Missile test Suborbital Success
1959-05-07 Jupiter AM-12 CCAFS LC-26B Missile test Suborbital Success
1959-05-14 Jupiter AM-17 CCAFS LC-5 Missile test Suborbital Success
1959-05-28 Jupiter AM-18 CCAFS LC-26B Biological nose cone Missile test Suborbital Success
1959-07-16 Juno II AM-16 CCAFS LC-5 Explorer 6 Scientific LEO Failure Electrical short in the guidance system caused loss of control at liftoff. RSO T+5 seconds.
1959-08-14 Juno II AM-19B CCAFS LC-26B Beacon 2 Scientific LEO Failure Premature first stage cutoff
1959-08-27 Jupiter AM-19 CCAFS LC-5 Missile test Suborbital Success
1959-09-15 Jupiter AM-23 CCAFS LC-26B Biological nose cone Missile test Suborbital Failure Pressure gas leak led to loss of control at liftoff. Missile self-destructed T+13 seconds.
1959-10-01 Jupiter AM-24 CCAFS LC-6 Missile test Suborbital Success
1959-10-13 Juno II AM-19A CCAFS LC-5 Explorer 7 Scientific LEO Success
1959-10-22 Jupiter AM-31 CCAFS LC-26A Missile test Suborbital Success
1959-11-05 Jupiter CM-33 CCAFS LC-6 Missile test Suborbital Success
1959-11-19 Jupiter AM-25 CCAFS LC-26B Missile test Suborbital Success
1959-12-10 Jupiter AM-32 CCAFS LC-6 Missile test Suborbital Success
1959-12-17 Jupiter AM-26 CCAFS LC-26B Missile test Suborbital Success

1960 Edit

Rocket S/N Launch Site Payload Function Orbit Outcome Remarks
1960-01-26 Jupiter AM-28 CCAFS LC-26B Missile test Suborbital Success
1960-03-23 Juno II AM-19C CCAFS LC-26B Explorer Scientific LEO Failure Third stage failed to ignite
1960-10-20 Jupiter CM-217 CCAFS LC-26A Missile test Suborbital Success
1960-11-03 Juno II AM-19D CCAFS LC-26B Explorer 8 Scientific LEO Success

1961 Edit

Rocket S/N Launch Site Payload Function Orbit Outcome Remarks
1961-02-25 Juno II AM-19F CCAFS LC-26B Explorer 10 Scientific LEO Failure Third stage failed to ignite
1961-04-22 Jupiter CM-209 CCAFS LC-26A Missile test Suborbital Success
1961-04-27 Juno II AM-19E CCAFS LC-26B Explorer 11 Scientific LEO Success
1961-05-24 Juno II AM-19G CCAFS LC-26B Explorer 12 Scientific LEO Failure Second stage failed to ignite. Final flight of Juno II
1961-08-05 Jupiter CM-218 CCAFS LC-26A Missile test Suborbital Success
1961-12-06 Jupiter CM-115 CCAFS LC-26A Missile test Suborbital Success

1962 Edit

Rocket S/N Launch Site Payload Function Orbit Outcome Remarks
1962-04-18 Jupiter CM-114 CCAFS LC-26A Missile test Suborbital Success
1962-08-01 Jupiter CM-111 CCAFS LC-26A Missile test Suborbital Success

1963 Edit

Rocket S/N Launch Site Payload Function Orbit Outcome Remarks
1963-01-22 Jupiter CM-106 CCAFS LC-26A Missile test Suborbital Success Final flight of Jupiter

The Marshall Space Flight Center in Huntsville, Alabama displays a Jupiter missile in its Rocket Garden.

The U.S. Space & Rocket Center in Huntsville, Alabama displays two Jupiters, including one in Juno II configuration, in its Rocket Park.

An SM-78/PMG-19 is on display at the Air Force Space & Missile Museum at Cape Canaveral, Florida. The missile had been present in the rocket garden for many years until 2009 when it was taken down and given a complete restoration. [33] This pristine artifact is now in sequestered storage in Hangar R on Cape Canaveral AFS and cannot be viewed by the general public.

A Jupiter (in Juno II configuration) is displayed in the Rocket Garden at Kennedy Space Center, Florida. It was damaged by Hurricane Frances in 2004, [34] but was repaired and subsequently placed back on display.

A PGM-19 is on display at the National Museum of the United States Air Force in Dayton, Ohio. The missile was obtained from the Chrysler Corporation in 1963. For decades it was displayed outside the museum, before being removed in 1998. The missile was restored by the museum's staff and was returned to display in the museum's new Missile Silo Gallery in 2007. [35]

A PGM-19 is on display at the South Carolina State Fairgrounds in Columbia, South Carolina. The missile, named Columbia, was presented to the city in the early 1960s by the US Air Force. It was installed at the fairgrounds in 1969 at a cost of $10,000. [36]

The Frontiers of Flight Museum at Dallas Love Field in Dallas, Texas, has a Jupiter missile on display outdoors.

Dec 19, 2020 8:07 AM Jupiter enters Aquarius
May 13, 2021 6:36 PM Jupiter enters Pisces
Jul 28, 2021 8:42 AM Jupiter Rx enters Aquarius
Dec 28, 2021 11:09 PM Jupiter enters Pisces
May 10, 2022 7:22 PM Jupiter enters Aries

Oct 28, 2022 1:10 AM Jupiter Rx enters Pisces
Dec 20, 2022 9:32 AM Jupiter enters Aries
May 16, 2023 1:20 PM Jupiter enters Taurus
May 25, 2024 7:14 PM Jupiter enters Gemini
Jun 9, 2025 5:02 PM Jupiter enters Cancer
Jun 30, 2026 1:52 AM Jupiter enters Leo
Jul 26, 2027 12:49 AM Jupiter enters Virgo
Aug 24, 2028 1:08 AM Jupiter enters Libra
Sep 24, 2029 2:23 AM Jupiter enters Scorpio
Oct 22, 2030 7:14 PM Jupiter enters Sagittarius

Jan 17, 2010 9:10 PM Jupiter enters Pisces
June 6, 2010 2:27 AM Jupiter enters Aries
Sep 9, 2010 12:49 AM Jupiter Rx enters Pisces
Jan 22, 2011 12:11 PM Jupiter enters Aries
June 4, 2011 9:56 AM Jupiter enters Taurus
June 11, 2012 1:22 PM Jupiter enters Gemini
June 25, 2013 9:40 PM Jupiter enters Cancer
Jul 16, 2014 6:30 AM Jupiter enters Leo

Aug 11, 2015 7:11 AM Jupiter enters Virgo
Sep 9, 2016 7:18 AM Jupiter enters Libra
Oct 10, 2017 9:20 AM Jupiter enters Scorpio
Nov 8, 2018 7:38 AM Jupiter enters Sagittarius
Dec 2, 2019 1:20 PM Jupiter enters Capricorn

Feb 14, 2000 4:40 PM Jupiter enters Taurus
June 30, 2000 3:35 AM Jupiter enters Gemini
July 12, 2001 8:03 PM Jupiter enters Cancer
Aug 1, 2002 1:20 PM Jupiter enters Leo
Aug 27, 2003 5:26 AM Jupiter enters Virgo
Sep 24, 2004 11:23 PM Jupiter enters Libra
Oct 25, 2005 10:51 PM Jupiter enters Scorpio
Nov 24, 2006 -1:43 AM Jupiter enters Sagittarius
Dec 18, 2007 3:11 PM Jupiter enters Capricorn
Jan 5, 2009 10:41 AM Jupiter enters Aquarius

Aug 18, 1990 3:30 AM Jupiter enters Leo
Sep 12, 1991 2:00 AM Jupiter enters Virgo
Oct 10, 1992 9:26 AM Jupiter enters Libra
Nov 10, 1993 3:15 AM Jupiter enters Scorpio
Dec 9, 1994 5:54 AM Jupiter enters Sagittarius
Jan 3, 1996 2:22 AM Jupiter enters Capricorn
Jan 21, 1997 10:13 AM Jupiter enters Aquarius
Feb 4, 1998 5:52 AM Jupiter enters Pisces
Feb 12, 1999 8:23 PM Jupiter enters Aries
June 28, 1999 5:29 AM Jupiter enters Taurus
Oct 23, 1999 1:48 AM Jupiter Rx enters Aries

Oct 27, 1980 5:10 AM Jupiter enters Libra
Nov 26, 1981 9:19 PM Jupiter enters Scorpio
Dec 25, 1982 8:57 PM Jupiter enters Sagittarius
Jan 19, 1984 10:04 AM Jupiter enters Capricorn
Feb 6, 1985 10:35 AM Jupiter enters Aquarius
Feb 20, 1986 11:05 AM Jupiter enters Pisces
Mar 2, 1987 1:41 PM Jupiter enters Aries
Mar 8, 1988 10:44 AM Jupiter enters Taurus
July 21, 1988 8:00 PM Jupiter enters Gemini
Nov 30, 1988 3:53 PM Jupiter Rx enters Taurus
Mar 10, 1989 10:26 PM Jupiter enters Gemini
July 30, 1989 7:50 PM Jupiter enters Cancer

Apr 30, 1970 2:43 AM Jupiter Rx enters Libra
Aug 15, 1970 1:58 PM Jupiter enters Scorpio
Jan 14, 1971 3:49 AM Jupiter enters Sagittarius
June 4, 1971 10:12 PM Jupiter Rx enters Scorpio
Sep 11, 1971 11:33 AM Jupiter enters Sagittarius
Feb 6, 1972 2:37 PM Jupiter enters Capricorn
July 24, 1972 12:42 PM Jupiter Rx enters Sagittarius
Sep 25, 1972 2:20 PM Jupiter enters Capricorn
Feb 23, 1973 4:28 AM Jupiter enters Aquarius
Mar 8, 1974 6:11 AM Jupiter enters Pisces
Mar 18, 1975 11:47 AM Jupiter enters Aries
Mar 26, 1976 5:25 AM Jupiter enters Taurus
Aug 23, 1976 6:24 AM Jupiter enters Gemini
Oct 16, 1976 4:24 PM Jupiter Rx enters Taurus
Apr 3, 1977 10:42 AM Jupiter enters Gemini
Aug 20, 1977 8:43 AM Jupiter enters Cancer
Dec 30, 1977 6:50 PM Jupiter Rx enters Gemini
Apr 11, 1978 7:12 PM Jupiter enters Cancer
Sep 5, 1978 4:31 AM Jupiter enters Leo
Feb 28, 1979 6:35 PM Jupiter Rx enters Cancer
Apr 20, 1979 3:30 AM Jupiter enters Leo
Sep 29, 1979 6:23 AM Jupiter enters Virgo

Mar 1, 1960 8:10 AM Jupiter enters Capricorn
June 9, 1960 9:52 PM Jupiter Rx enters Sagittarius
Oct 25, 1960 11:01 PM Jupiter enters Capricorn
Mar 15, 1961 3:01 AM Jupiter enters Aquarius
Aug 12, 1961 4:54 AM Jupiter Rx enters Capricorn
Nov 3, 1961 9:49 PM Jupiter enters Aquarius
Mar 25, 1962 5:07 PM Jupiter enters Pisces
Apr 3, 1963 10:19 PM Jupiter enters Aries
Apr 12, 1964 1:52 AM Jupiter enters Taurus
Apr 22, 1965 9:32 AM Jupiter enters Gemini
Sep 21, 1965 -1:40 AM Jupiter enters Cancer
Nov 16, 1965 10:08 PM Jupiter Rx enters Gemini
May 5, 1966 10:52 AM Jupiter enters Cancer
Sep 27, 1966 9:19 AM Jupiter enters Leo
Jan 15, 1967 10:50 PM Jupiter Rx enters Cancer
May 23, 1967 4:21 AM Jupiter enters Leo
Oct 19, 1967 6:51 AM Jupiter enters Virgo
Feb 26, 1968 10:33 PM Jupiter Rx enters Leo
June 15, 1968 10:44 AM Jupiter enters Virgo
Nov 15, 1968 5:44 PM Jupiter enters Libra
Mar 30, 1969 4:36 PM Jupiter Rx enters Virgo
July 15, 1969 9:30 AM Jupiter enters Libra
Dec 16, 1969 10:55 AM Jupiter enters Scorpio

Apr 15, 1950 3:58 AM Jupiter enters Pisces
Sep 14, 1950 10:23 PM Jupiter Rx enters Aquarius
Dec 1, 1950 2:57 PM Jupiter enters Pisces
Apr 21, 1951 9:57 AM Jupiter enters Aries
Apr 28, 1952 4:50 PM Jupiter enters Taurus
May 9, 1953 11:33 AM Jupiter enters Gemini
May 24, 1954 12:43 AM Jupiter enters Cancer
June 12, 1955 8:07 PM Jupiter enters Leo
Nov 17, 1955 1:01 AM Jupiter enters Virgo
Jan 17, 1956 9:04 PM Jupiter Rx enters Leo
July 7, 1956 3:01 PM Jupiter enters Virgo
Dec 12, 1956 9:17 PM Jupiter enters Libra
Feb 19, 1957 10:37 AM Jupiter Rx enters Virgo
Aug 6, 1957 10:11 PM Jupiter enters Libra
Jan 13, 1958 7:52 AM Jupiter enters Scorpio
Mar 20, 1958 2:13 PM Jupiter Rx enters Libra
Sep 7, 1958 4:52 AM Jupiter enters Scorpio
Feb 10, 1959 8:46 AM Jupiter enters Sagittarius
Apr 24, 1959 9:10 AM Jupiter Rx enters Scorpio
Oct 5, 1959 10:40 AM Jupiter enters Sagittarius
May 16, 1940 3:54 AM Jupiter enters Taurus
May 26, 1941 8:48 AM Jupiter enters Gemini
June 10, 1942 6:36 AM Jupiter enters Cancer

June 30, 1943 5:46 PM Jupiter enters Leo
July 25, 1944 9:04 PM Jupiter enters Virgo
Aug 25, 1945 2:06 AM Jupiter enters Libra
Sep 25, 1946 6:19 AM Jupiter enters Scorpio
Oct 23, 1947 10:00 PM Jupiter enters Sagittarius
Nov 15, 1948 5:38 AM Jupiter enters Capricorn
Apr 12, 1949 2:18 PM Jupiter enters Aquarius
June 27, 1949 2:29 PM Jupiter Rx enters Capricorn
Nov 30, 1949 3:08 PM Jupiter enters Aquarius

June 26, 1930 5:42 PM Jupiter enters Cancer
July 17, 1931 3:52 AM Jupiter enters Leo
Aug 11, 1932 3:16 AM Jupiter enters Virgo
Sep 10, 1933 1:11 AM Jupiter enters Libra
Oct 11, 1934 -1:55 AM Jupiter enters Scorpio
Nov 8, 1935 9:56 PM Jupiter enters Sagittarius
Dec 2, 1936 3:39 AM Jupiter enters Capricorn
Dec 19, 1937 11:06 PM Jupiter enters Aquarius
May 14, 1938 3:46 AM Jupiter enters Pisces
July 29, 1938 11:01 PM Jupiter Rx enters Aquarius
Dec 29, 1938 1:34 PM Jupiter enters Pisces
May 11, 1939 10:08 AM Jupiter enters Aries
Oct 29, 1939 7:44 PM Jupiter Rx enters Pisces
Dec 20, 1939 12:03 PM Jupiter enters Aries


Jupiter was the king of the moons since recently, having a total of 79 known satellites. Recently, Saturn dethroned Jupiter having a total of 82 known satellites. These rankings can change as observations continue.

Out of the 79 satellites, 63 are less than 10 km / 6.2 mi in diameter, and have only been observed since 1975. The Galilean moons, Io, Europa, Ganymede, and Callisto are large enough to be seen from Earth with binoculars. They are among the largest satellites discovered in the Solar System with Ganymede being the largest out of all the satellites in our solar system.

Jupiter has both regular moons and irregular moons with further sub-divisions.

Regular moons

The regular moons of Jupiter consists of the Galilean moons and an inner group of 4 small moons with diameters less than 200 km / 124 mi, and orbits with radii less than 200.000 km / 124.274 mi. They all have orbital inclinations of less than half a degree. The Galilean moons orbit between 400.000 and 2.000.000 km – 248.548 mi and 1.242.742 mi. These moons are believed to have been formed together with Jupiter since they have nearly circular orbits near the plane of Jupiter’s equator.


Despite being the largest known satellite in the solar system, it lacks a substantial atmosphere. It is the 9 th largest object in the solar system with a diameter of 5.268 km / 3.273 mi and is 8% larger than the planet Mercury, although only 45% as massive.

It was named after the mythological cupbearer of the Greek gods, who was kidnapped by Zeus for this purpose. It is the only moon known to have a magnetic field and though it posseses a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System.

Outward from Jupiter, it is the seventh satellite completing an orbit around Jupiter in about 7 Earth days. It is in a 1:2:4 orbital resonance with the moons Europa and Io. It is comprised mostly of equal amounts of silicate rock and water ice, having an iron-rich, liquid core, and an internal ocean that may contain more water than all of Earth’s oceans combined.

A third of its surface is covered by dark regions covered in impact craters and a light region, crosscut by extensive grooves and ridges possibly due to tectonic activity due to tidal heating. It has a thin atmosphere comprised of oxygen, ozone and other elements. There is some speculation on the potential habitability of Ganymede's ocean.

The innermost and third-largest of the four Galilean moons of Jupiter, Io is the fourth-largest moon the solar system with the highest density and the least amount of water molecules of any known astronomical object in the Solar System.

Named after the mythological character Io, a priestess of Hera who became one of Zeus’ lovers, Io is the most geological active object in the Solar system having over 400 active volcanoes.

This extreme geological activity is due to tidal heating caused from friction generated within Io’s interior as it is pulled between Jupiter and the other Galilean moons.

converted PNM file

It takes Io 1.77 Earth-days to orbit Jupiter. It is tidally locked to Jupiter, showing only one side to its parent planet, and has a mean radius of 1.131 miles / 1.821 km, slightly larger than Earth’s moon.

Many of Io’s volcanoes produce plumes of 500 km / 300 mi above the surface. More than 100 mountains are uplifted by extensive compression at the base of Io’s silicate crust. Some of these peaks are taller than Mount Everest, the highest point on Earth’s surface.

Io is composed primarily of silicate rock that surrounds a molten iron core. The plains of Io are coated with sulfur and sulfur-dioxide frost. The materials produced by Io’s volcanism make up its thin atmosphere, and result in the large plasma torus around Jupiter.


Europa is the smallest of the four Galilean moons and the sixth largest of all the moons in the Solar System. It was named after the Phoenician mother of King Minos of Crete and lover of Zeus.

It is slightly smaller than Earth’s moon having a diameter of 3.100 km / 1.900 mi. It is primarily made of silicate rock and has a water-ice crust, and a probably iron-nickel core.

Its atmosphere is thin, composed primarily of oxygen. The surface is very smooth. In fact it is the smoothest of any known solid object in the Solar System. The apparent youth of the smoothness of the surface led to the hypothesis that a water ocean exists beneath it, which could conceivably harbor extraterrestrial life.

Currently, Europa probably has the highest of either having or developing life, and thus it is one of the most closely studied objects in the solar system.


Callisto is the second-largest moon of Jupiter and the third-largest moon in the Solar System after Ganymede and Saturn’s moon Titan. It has a diameter of about 4.821 km / 2.995 mi, having about 99% the diameter of the planet Mercury but only a third of its mass.

Named after a nymph of Greek mythology, also another one of Zeus’s lovers, Callisto is the farthest Galilean moon orbiting Saturn at a distance of 1.8 million km. It is not in a orbital resonance like the other three Galilean moons and thus it is not appreciably tidally heated like the others. It is tidally locked with Jupiter and it is less affected by Jupiter’s magnetosphere than the other inner satellites because of its remote orbit.

It is composed primarily out of equal amounts of rock and ices, with a density of about 1.83 g/cm 3 , the lowest of Jupiter’s satellites. Investigations by the Galileo spacecraft suggest that Callisto has a silicate core and possibly a subsurface ocean of liquid water at depths of 100 km.

Interestingly, the surface of Callisto is the oldest and most heavily cratered in the Solar System. It has an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen.

The presence of an ocean within Callisto opens the possibility that it could harbor life but conditions are thought to be less favorable than on Europa. Regardless, it is considered the most suitable planet for a human base for future exploration of the Jovian system due to low radiation levels.

Irregular Moons

The irregular moons are small and have elliptical and inclined orbits. They are thought to be captured asteroids or fragments of captured asteroids. Their exact number is unknown but they are further divided into sub-divisions – groups, in which they share similar orbital elements and thus may have a common origin.

There are 4 groups:

  • The Himalia group – a clustered group of moons with orbits around 11 million to 12 million km / 6 to 7 million mi from Jupiter.
  • The Ananke group – a group with a retrograde orbit with rather indistinct borders, averaging from 21 million km / 13 million mi from Jupiter with an average inclination of 149 degrees.
  • The Carme group – they are a group with a fairly distinct retrograde orbit that averages from 23 million km / 14 million mi from Jupiter with an average inclination of 165 degrees.
  • The Pasiphae group – a very dispersed and only vaguely distinct retrograde group that covers all the outermost moons.
  • There are three irregular moons that stand out from these groups:
  • Themisto – it orbits halfway between the Galilean moons and the Himalia group.
  • Carpo – it is at the inner edge of the Ananke group and orbits Jupiter in prograde direction.
  • Valetudo – this moon has a prograde orbit but overlaps the retrograde groups and may result in future collisions with those groups.

Discovery of Jupiter

No one can definitively say when the discovery of Jupiter took place nor who discovered it. Why is it so hard? It is one of the five planets that can be seen in the night sky. Only Venus and the Moon are brighter. Frankly, it is nearly impossible to miss. NASA lists the planet as having been discovered by the Ancients. The planet is called Marduk in ancient Babylonian texts, Zeus in early Greek manuscripts, and Jupiter in Roman antiquity.

What is known are some of the firsts in the exploration of Jupiter. In 1610, Galileo Galilei turned his rudimentary telescope on Jupiter, and realized that it had 4 large moons orbiting it: Io, Europa, Ganymede and Callisto. This was an important discovery, because it demonstrated that Earth was not the center of the Universe as proponents of the geocentric view believed.

In the1660s, Giovanni Cassini used his telescope to discover spots and bands across the surface of Jupiter, and was able to estimate the planet’s rotational period. He is thought to be the first to observe the planet’s Great Red Spot, a giant storm that is still raging. Imagine a single storm that rages for over 450 years and is larger than the Earth.

The first spacecraft to visit Jupiter up close was NASA’s Pioneer 10 in 1973. That mission was closely followed by Pioneer 11 in 1974. Both of NASA’s Voyager spacecraft flew past in 1979, sending back many of the famous pictures we’re all familiar with. Since then, the Ulysses solar probe, NASA’s Cassini spacecraft and New Horizons have all made flybys of the planet.

The only spacecraft to actually orbit Jupiter was NASA’s Galileo mission, which went into orbit in 1995. NASA scientists were not satisfied with a few orbits of Jupiter. They wanted to see a bit more of the Jovian system, so Galileo was sent to observe a few moons. Galileo is credited as being the first spacecraft to observe a comet hitting a planet(Jupiter), first to flyby an asteroid, first to discover an asteroid with a moon, and it was the first to measure the crushing atmospheric pressure of Jupiter with a descent probe. The mission discovered evidence of subsurface saltwater on Europa, Ganymede and Callisto and revealed the intensity of the volcanic activity on Io.

We may not know the exact date of the discovery of Jupiter, but we know many first about the planet. Even now, scientists are planning the next mission and hoping to be the first to discover something about the Jovian system.

Here are some images of the Jupiter flyby from NASA’s New Horizons spacecraft, and an article about Cassini’s flyby of Jupiter.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Watch the video: Timeline of Jupiter in my pocket galaxy