Flying the Juno Spacecraft Towards Jupiter: Kristen Francis

Flying the Juno Spacecraft Towards Jupiter: Kristen Francis

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A reconstruction shows what the northern and southern auroras looked like to Juno as it approached Jupiter, passed over the north pole, travelled to the southern hemisphere to pass over the southern pole, and finally receded from Jupiter

Unfortunately, the probe does not have an X-ray instrument on board, so the researchers must combine data collected by Juno with data from other instruments, including the Chandra and XMM-Newton satellites.

Dr Dunn said: 'If we can start to connect the X-ray signatures with the physical processes that produce them, then we can use those signatures to understand other bodies across the universe such as brown dwarfs, exoplanets or maybe even neutron stars.

Researchers from UCL found that high-energy X-ray emissions at Jupiter's south pole consistently pulse every 11 minutes. But pulses at the north pole (pictured) are erratic, increasing and decreasing in brightness independent of the south pole


Earth's auroras are produced by interactions between charged particles from the sun as they enter the atmosphere.

Two processes are involved, depending on the type of aurora.

Intense auroras are generated by the acceleration of electrons, while weaker auroras arise from the scattering of magnetically trapped electrons.

Until now, it was though that auroras on Jupiter were produced in the same way as intense auroras on Earth.

But during a recent flyover of Jupiter, Nasa's Juno probe detected accelerating electrons, although this didn't seem to produce intense auroras.

Instead, the observations indicate that Jupiter's auroras are generated in the same way as weaker auroras on Earth.

'It is a very powerful and important step towards understanding X-rays throughout the Universe and one that we only have while Juno is conducting measurements simultaneously with Chandra and XMM-Newton.'

One of the theories for the mismatched northern and southern lights is that Jupiter's auroras form separately when the planet's magnetic field interacts with solar winds.

The researchers suggest that the magnetic field lines vibrate, producing waves that carry charged particles towards the poles.

These waves then change in speed and direction of travel until they collide with Jupiter's atmosphere, generating X-ray pulses.

Using the XMM-Newton and Chandra X-ray observatories in May to June 2016 and March 2007, the authors produced maps of Jupiter's X-ray emissions and identified an X-ray hot spot at each pole.

Each hot spot covers an area much bigger than the surface of the Earth.

Studying each to identify patterns of behaviour, they found that the hot spots have very different characteristics.

A video shows a series of images of Jupiter's northern aurora, taken by Juno in the northern hemisphere on 2 February 2017

Dr Licia Ray, co-author of the study, said: 'The behaviour of Jupiter's X-ray hot spots raises important questions about what processes produce these auroras.

'We know that a combination of solar wind ions and ions of oxygen and sulphur, originally from volcanic explosions from Jupiter's moon, Io, are involved.

'However, their relative importance in producing the X-ray emissions is unclear.'


The Juno probe reached Jupiter last year after a five-year, 1.8 billion-mile journey from Earth.

Following a successful braking manoeuvre, it has now entered into a long polar orbit flying to within 3,100 miles (5,000 km) of the planet's swirling cloud tops.

The probe will skim to within just 4,200 km of the planet's clouds once a fortnight - too close to provide global coverage in a single image.

No previous spacecraft has orbited so close to Jupiter, although two others have been sent plunging to their destruction through its atmosphere.

To complete its risky mission Juno will have to survive a circuit-frying radiation storm generated by Jupiter's powerful magnetic field. The maelstrom of high energy particles travelling at nearly the speed of light is the harshest radiation environment in the Solar System.

To cope with the conditions, the spacecraft is protected with special radiation-hardened wiring and sensor shielding.

Its all-important 'brain' - the spacecraft's flight computer - is housed in an armoured vault made of titanium and weighing almost 400 pounds (172kg).

Juno is in a harsh radiation environment, so its delicate electronics are housed in a special titanium vault. Eventually, Juno will succumb to the intense radiation and will be commanded to plunge into Jupiter's atmosphere to avoid any collision with the planet's moons. Pictured is a 1/5 scale model size of the solar-powered Juno spacecraft

Professor Graziella Branduardi-Raymont, co-author of the study, added: 'What I find particularly captivating in these observations, especially at the time when Juno is making measurements in situ, is the fact that we are able to see both of Jupiter's poles at once, a rare opportunity that last occurred ten years ago.

'Comparing the behaviours at the two poles allows us to learn much more of the complex magnetic interactions going on in the planet's environment.'

The researchers now hope to keep tracking the activity of Jupiter's poles over the next two years to see if this previously unreported behaviour is commonplace.


The Atlas V was developed by Lockheed Martin Commercial Launch Services (LMCLS) as part of the U.S. Air Force Evolved Expendable Launch Vehicle (EELV) program and made its inaugural flight on 21 August 2002. The vehicle operates from SLC-41 at Cape Canaveral Space Force Station (CCSFS) and SLC-3E at Vandenberg Air Force Base. LMCLS continued to market the Atlas V to commercial customers worldwide until January 2018, when United Launch Alliance (ULA) assumed control of commercial marketing and sales. [9] [10]

Atlas V first stage Edit

The Atlas V first stage, the Common Core Booster (CCB), is 3.8 m (12 ft) in diameter and 32.5 m (107 ft) in length. It is powered by one Russian RD-180 main engine burning 284,450 kg (627,100 lb) of liquid oxygen and RP-1. The booster operates for about four minutes, providing about 4 MN (900,000 lbf) of thrust. [11] Thrust can be augmented with up to five Aerojet strap-on solid rocket boosters, each providing an additional 1.27 MN (290,000 lbf) of thrust for 94 seconds.

The Atlas V is the newest member of the Atlas family. Compared to the Atlas III vehicle, there are numerous changes. Compared to the Atlas II, the first stage is a near-redesign. There was no Atlas IV.

The main differences between the Atlas V and earlier Atlas I and II family rockets are:

  • The first stage tanks no longer use stainless steelmonocoque pressure stabilized "balloon" construction. The tanks are isogridaluminum and are structurally stable when unpressurized. [11]
  • Use of aluminum, with a higher thermal conductivity than stainless steel, requires insulation for the liquid oxygen. The tanks are covered in a polyurethane-based layer. [citation needed]
  • Accommodation points for parallel stages, both smaller solids and identical liquids, are built into first-stage structures. [11]
  • The "1.5 staging" technique is no longer used, having been discontinued on the Atlas III with the introduction of the Russian RD-180 engine. [11] The RD-180 features a single turbopump feeding dual combustion chambers and nozzles burning kerosene/liquid oxygen propellants.
  • As with the Atlas III, the oxygen tank is larger relative to the fuel tank to accommodate the mixture ratio of the RD-180.
  • The main-stage diameter increased from 3.0 to 3.7 m (9.8 to 12.1 ft). [12]

Centaur upper stage Edit

The Centaur upper stage uses a pressure-stabilized propellant-tank design and cryogenic propellants. The Centaur stage for Atlas V is stretched 1.7 m (5 ft 7 in) relative to the Atlas IIAS Centaur and is powered by either one or two Aerojet Rocketdyne RL10A-4-2 engines, each engine developing a thrust of 99.2 kN (22,300 lbf). The inertial navigation unit (INU) located on the Centaur provides guidance and navigation for both the Atlas and Centaur and controls both Atlas and Centaur tank pressures and propellant use. The Centaur engines are capable of multiple in-space starts, making possible insertion into low Earth parking orbit, followed by a coast period and then insertion into GTO. A subsequent third burn following a multi-hour coast can permit direct injection of payloads into geostationary orbit. [13] As of 2006 [update] , the Centaur vehicle had the highest proportion of burnable propellant relative to total mass of any modern hydrogen upper stage and hence can deliver substantial payloads to a high-energy state. [14]

Star 48 third stage Edit

Star 48 is a type of solid rocket motor used by many space propulsion and launch vehicle stages. It was developed primarily by Thiokol Propulsion, and is now, after several mergers, manufactured by Northrop Grumman’s Space Systems division. A Star 48B stage is also one of the few man-made items sent on escape trajectories out of the Solar System, although it is derelict since its use. It has been used once on the Atlas V as a third stage for the New Horizons mission.

Payload fairing Edit

Atlas V payload fairings are available in two diameters, depending on satellite requirements. The 4.2 m (14 ft) diameter fairing, [15] originally designed for the Atlas II booster, comes in three different lengths: the original 9 m (30 ft) version and extended 10 and 11 m (33 and 36 ft) versions, first flown respectively on the AV-008/Astra 1KR and AV-004/Inmarsat-4 F1 missions. Fairings of up to 7.2 m (24 ft) diameter and 32.3 m (106 ft) length have been considered but were never implemented. [8]

A 5.4 m (18 ft) diameter fairing, with an internally usable diameter of 4.57 m (15.0 ft), was developed and built by RUAG Space [16] in Switzerland. The RUAG fairing uses carbon fiber composite construction and is based on a similar flight-proven fairing for the Ariane 5. Three configurations are manufactured to support the Atlas V: 20.7 m (68 ft), 23.4 m (77 ft), and 26.5 m (87 ft) long. [16] While the classic 4.2 m (14 ft) fairing covers only the payload, the RUAG fairing is much longer and fully encloses both the Centaur upper stage and the payload. [17]

Many systems on the Atlas V have been the subject of upgrade and enhancement both prior to the first Atlas V flight and since that time. Work on a new Fault Tolerant Inertial Navigation Unit (FTINU) started in 2001 to enhance mission reliability for Atlas vehicles by replacing the existing non-redundant navigation and computing equipment with a fault-tolerant unit. [18] The upgraded FTINU first flew in 2006, [19] [ full citation needed ] and in 2010 a follow-on order for more FTINU units was awarded. [20] [ full citation needed ] Later in the decade, the FTINU was replaced with avionics common to both the Atlas V and Delta IV. [ citation needed ]

In 2015, ULA announced that the Aerojet Rocketdyne-produced AJ-60A solid rocket boosters (SRBs) currently in use on Atlas V will be superseded by new GEM 63 boosters produced by Northrop Grumman Innovation Systems. The extended GEM-63XL boosters will also be used on the Vulcan Centaur launch vehicle that will replace the Atlas V. [21] The first Atlas V launch with GEM 63 boosters happened on 13 November 2020. [22]

Proposals and design work to human-rate the Atlas V began as early as 2006, with ULA's parent company Lockheed Martin reporting an agreement with Bigelow Aerospace that was intended to lead to commercial private trips to low Earth orbit (LEO). [23]

Human-rating design and simulation work began in earnest in 2010, with the award of US$6.7 million in the first phase of the NASA Commercial Crew Program (CCP) to develop an Emergency Detection System (EDS). [24]

As of February 2011, ULA had received an extension to April 2011 from NASA and was finishing up work on the EDS. [25]

NASA solicited proposals for CCP phase 2 in October 2010, and ULA proposed to complete design work on the EDS. At the time, NASA's goal was to get astronauts to orbit by 2015. Then-ULA President and CEO Michael Gass stated that a schedule acceleration to 2014 was possible if funded. [26] Other than the addition of the Emergency Detection System, no major changes were expected to the Atlas V rocket, but ground infrastructure modifications were planned. The most likely candidate for the human-rating was the N02 configuration, with no fairing, no solid rocket boosters, and dual RL10 engines on the Centaur upper stage. [26]

On 18 July 2011, NASA and ULA announced an agreement on the possibility of certifying the Atlas V to NASA's standards for human spaceflight. [27] ULA agreed to provide NASA with data on the Atlas V, while NASA would provide ULA with draft human certification requirements. [27] In 2011, the human-rated Atlas V was also still under consideration to carry spaceflight participants to the proposed Bigelow Commercial Space Station. [28]

In 2011, Sierra Nevada Corporation (SNC) picked the Atlas V to be the booster for its still-under-development Dream Chaser crewed spaceplane. [29] The Dream Chaser was intended to launch on an Atlas V, fly a crew to the ISS, and landing horizontally following a lifting-body reentry. [29] However, in late 2014 NASA did not select the Dream Chaser to be one of the two vehicles selected under the Commercial Crew competition.

On 4 August 2011, Boeing announced that it would use the Atlas V as the initial launch vehicle for its CST-100 crew capsule. CST-100 will take NASA astronauts to the International Space Station (ISS) and was also intended to service the proposed Bigelow Commercial Space Station. [30] [31] A three-flight test program was projected to be completed by 2015, certifying the Atlas V/CST-100 combination for human spaceflight operations. [31] The first flight was expected to include an Atlas V rocket integrated with an uncrewed CST-100 capsule, [30] the second flight an in-flight launch abort system demonstration in the middle of that year, [31] and the third flight a crewed mission carrying two Boeing test-pilot astronauts into LEO and returning them safely at the end of 2015. [31] These plans did not materialize.

In 2014, NASA selected the Boeing CST-100 space capsule as part of the CCD program after extensive delays. Atlas V is the launch vehicle of the CST-100. The first launch of an uncrewed CST-100 capsule occurred atop a human-rated Atlas V on the morning of 20 December 2019, however an anomaly with the Mission Elapsed Time clock aboard the CST-100 caused the spacecraft to enter a suboptimal orbit. [32] As a result, the CST-100 could not achieve orbital insertion to reach the International Space Station, and instead deorbited after two days.

Each Atlas V booster configuration has a three-digit designation. The first digit shows the diameter (in meters) of the payload fairing and has a value of "4" or "5" for fairing launches and "N" for crew capsule launches (as no payload fairing is used when a crew capsule is launched). The second digit indicates the number of solid rocket boosters (SRBs) attached to the base of the rocket and can range from "0" through "3" with the 4 m (13 ft) fairing, and "0" through "5" with the 5 m (16 ft) fairing. As seen in the first image, all SRB layouts are asymmetrical. The third digit represents the number of engines on the Centaur stage, either "1" or "2".

For example, an Atlas V 551 has a 5-meter fairing, 5 SRBs, and 1 Centaur engine, whereas an Atlas V 431 has a 4-meter fairing, 3 SRBs, and 1 Centaur engine. [33] The Atlas V N22 with no fairing, two SRBs, and 2 Centaur engines was first launched in 2019. The flight carried the Starliner vehicle for its first orbital test flight.

As of June 2015 [update] , all versions of the Atlas V, its design and production rights, and intellectual property rights are owned by ULA and Lockheed Martin. [34]

Capabilities Edit

List date: 8 August 2019 [35] Mass to LEO numbers are at an inclination of 28.5°.

Launch cost Edit

Before 2016, pricing information for Atlas V launches was limited. In 2010, NASA contracted with ULA to launch the MAVEN mission on an Atlas V 401 for approximately US$187 million. [41] The 2013 cost of this configuration for the U.S. Air Force under their block buy of 36 rockets was $164 million. [42] In 2015, the TDRS-M launch on an Atlas 401 cost NASA US$132.4 million. [43]

Starting in 2016, ULA provided pricing for the Atlas V through its RocketBuilder website, advertising a base price for each rocket configuration, which ranges from $109 million for the 401 up to $153 million for the 551. [1] Each additional SRB adds an average of US$6.8 million to the cost of the rocket. Customers can also choose to purchase larger payload fairings or additional launch service options. NASA and Air Force launch costs are often higher than equivalent commercial missions due to additional government accounting, analysis, processing, and mission assurance requirements, which can add US$30–80 million to the cost of a launch. [44]

In 2013, launch costs for commercial satellites to GTO averaged about $100 million, significantly lower than historic Atlas V pricing. [45] However, in recent years [ clarification needed ] the price of an Atlas V [401] has dropped from approximately US$180 million to US$109 million, [ citation needed ] in large part due to competitive pressure that emerged in the launch services marketplace during the early 2010s. ULA CEO Tory Bruno stated in 2016 that ULA needs at least two commercial missions each year in order to stay profitable going forward. [46] ULA is not attempting to win these missions on purely lowest purchase price, stating that it "would rather be the best value provider". [47] ULA suggests that customers will have much lower insurance and delay costs because of the high Atlas V reliability and schedule certainty, making overall customer costs close to that of using competitors like the SpaceX Falcon 9. [48]

Historically proposed versions Edit

In 2006, ULA offered an Atlas V Heavy option that would use three Common Core Booster (CCB) stages strapped together to lift a 29,400 kg (64,800 lb) payload to low Earth orbit. [49] ULA stated at the time that 95% of the hardware required for the Atlas V Heavy has already been flown on the Atlas V single-core vehicles. [8] The lifting capability of the proposed rocket was to be roughly equivalent to the Delta IV Heavy, [8] which uses RS-68 engines developed and produced domestically by Aerojet Rocketdyne.

A 2006 report, prepared by the RAND Corporation for the Office of the Secretary of Defense, stated that Lockheed Martin had decided not to develop an Atlas V heavy-lift vehicle (HLV). [50] The report recommended for the U.S. Air Force and the National Reconnaissance Office (NRO) to "determine the necessity of an EELV heavy-lift variant, including development of an Atlas V Heavy", and to "resolve the RD-180 issue, including coproduction, stockpile, or United States development of an RD-180 replacement". [51]

In 2010, ULA stated that the Atlas V Heavy variant could be available to customers 30 months from the date of order. [8]

In late 2006, the Atlas V program gained access to the tooling and processes for 5 meter diameter stages used on Delta IV when Boeing and Lockheed Martin space operations were merged into the United Launch Alliance. This led to a proposal to combine the 5 meter diameter Delta IV tankage production processes with dual RD-180 engines, resulting in the Atlas Phase 2.

An Atlas V PH2-Heavy consisting of three 5 meter stages in parallel with six RD-180s was considered in the Augustine Report as a possible heavy lifter for use in future space missions, as well as the Shuttle-derived Ares V and Ares V Lite. [52] If built, the Atlas PH2-Heavy was projected to be able to launch a payload mass of approximately 70 t (69 long tons 77 short tons) into an orbit of 28.5° inclination. [52] Neither of the Atlas V Phase 2 proposals progressed to development work.

The Atlas V Common Core Booster was to have been used as the first stage of the joint US-Japanese GX rocket, which was scheduled to make its first flight in 2012. [53] GX launches would have been from the Atlas V launch complex at Vandenberg Air Force Base, SLC-3E. However, the Japanese government decided to cancel the GX project in December 2009. [54]

Out-licensing rejected by ULA

In May 2015, a consortium of companies, including Aerojet and Dynetics, sought to license the production or manufacturing rights to the Atlas V using the AR1 engine in place of the RD-180. The proposal was rejected by ULA. [55]

  • First ULA Atlas launch
  • First Atlas V night launch
  • First three-burn Atlas V mission
    Commercial Launch Services launch
  • Heaviest payload launched by an Atlas until the launch of MUOS-1 in 2012.
  • Largest comsat in the world at time of launch until the launch of TerreStar-1 in 2009 by Ariane 5 and then Telstar 19V on 21 July 2018 by Falcon 9.
  • 200th Centaur launch [92]
  • Heaviest payload launched by an Atlas until launch of MUOS-2
  • First GPS satellite launched by an Atlas V
  • Longest Atlas V mission to date

Notable missions Edit

The first payload, the Hot Bird 6 communications satellite, was launched to geostationary transfer orbit (GTO) on 21 August 2002 by an Atlas V 401. [ citation needed ]

On 12 August 2005, the Mars Reconnaissance Orbiter was launched aboard an Atlas V 401 rocket from Space Launch Complex 41 at Cape Canaveral Air Force Station (CCAFS). The Centaur upper stage of the launch vehicle completed its burns over a 56-minute period and placed MRO into an interplanetary transfer orbit towards Mars [61]

On 19 January 2006, New Horizons was launched by a Lockheed Martin Atlas V 551 rocket. A third stage was added to increase the heliocentric (escape) speed. This was the first launch of the Atlas V 551 configuration with five solid rocket boosters, and the first Atlas V with a third stage. [ citation needed ]

On 6 December 2015, Atlas V lifted its heaviest payload to date into orbit – a 16,517-pound (7,492 kg) Cygnus resupply craft. [157]

On 8 September 2016, the OSIRIS-REx Asteroid Sample Return Mission was launched on an Atlas V 411 rocket. It was scheduled to arrive at the asteroid Bennu in 2018 and return with a sample ranging from 60 grams to 2 kilograms in 2023. [ citation needed ]

The first four Boeing X-37B spaceplane missions were successfully launched with the Atlas V. The X-37B, also known as the Orbital Test Vehicle (OTV), is a reusable robotic spacecraft operated by USAF that can autonomously conduct landings from orbit to a runway. [158] The first four X-37B flights were launched on Atlas V's from Cape Canaveral Air Force Station in Florida with subsequent landings taking place on the Space Shuttle 15,000-foot (4,600 m) runway located at Vandenberg Air Force Base in California. [ citation needed ]

On 20 December 2019, the first Starliner crew capsule was launched in Boe-OFT uncrewed test flight. The Atlas V carrier rocket performed flawlessly but an anomaly with the spacecraft left it in a wrong orbit. The orbit was too low to reach the flight's destination of ISS, and the mission was subsequently cut short.

Mission success record Edit

The rocket had 86 launches with only one failure and 76 consecutive successful launches since 11 October 2007.

In its 85 launches (as of October 2020), starting with its first launch in August 2002, Atlas V has achieved a 100% mission success rate and a 97.65% vehicle success rate. [159] This is in contrast to the industry success rate of 90%–95%. [160] However, there have been two anomalous flights that – while still successful in their mission – prompted a grounding of the Atlas fleet while investigations determined the root cause of their problems.

The first anomalous event in the use of the Atlas V launch system occurred on 15 June 2007, when the engine in the Centaur upper stage of an Atlas V shut down early, leaving its payload – a pair of NROL-30 ocean surveillance satellites – in a lower than intended orbit. The cause of the anomaly was traced to a leaky valve, which allowed fuel to leak during the coast between the first and second burns. The resulting lack of fuel caused the second burn to terminate 4 seconds early. [161] Replacing the valve led to a delay in the next Atlas V launch. [68] However, the customer (the National Reconnaissance Office) categorized the mission as a success. [162] [163]

A flight on 23 March 2016, suffered an underperformance anomaly on the first-stage burn and shut down 5 seconds early. The Centaur proceeded to boost the Orbital Cygnus payload, the heaviest on an Atlas to date, into the intended orbit by using its fuel reserves to make up for the shortfall from the first stage. This longer burn cut short a later Centaur disposal burn. [164] An investigation of the incident revealed that this anomaly was due to a fault in the main engine mixture-ratio supply valve, which restricted the flow of fuel to the engine. The investigation and subsequent examination of the valves on upcoming missions led to a delay of the next several launches. [165]

In 2014, geopolitical and U.S. political considerations led to an effort to replace the Russian-supplied RD-180 engine used on the first-stage booster of the Atlas V. Formal study contracts were issued in June 2014 to a number of U.S. rocket-engine suppliers. [166] The results of those studies have led a decision by ULA to develop the new Vulcan Centaur launch vehicle to replace the existing Atlas V and Delta IV. [167]

In September 2014, ULA announced a partnership with Blue Origin to develop the BE-4 LOX/methane engine to replace the RD-180 on a new first-stage booster. As the Atlas V core is designed around RP-1 fuel and cannot be retrofitted to use a methane-fueled engine, a new first stage is being developed. This booster will have the same first-stage tankage diameter as the Delta IV and will be powered by two 2,400 kN (540,000 lbf) thrust BE-4 engines. [166] [168] [169] The engine was already in its third year of development by Blue Origin, and ULA expected the new stage and engine to start flying no earlier than 2019.

Vulcan will initially use the same Centaur upper stage as on Atlas V, later to be upgraded to ACES. [168] It will also use a variable number of optional solid rocket boosters, called the GEM 63XL, derived from the new solid boosters planned for Atlas V. [21]

As of 2017, the Aerojet AR1 rocket engine was under development as a backup plan for Vulcan. [170]

As of November 2020 [update] , no replacement was expected before mid-2021. [171]

Notable payloads Edit

Core stage of an Atlas V being raised to a vertical position.

X-37B OTV-1 (Orbital Test Vehicle) being encased in its payload fairing for its 22 April 2010, launch.

An Atlas V 541 is moved to the launch pad.

Atlas V 401 on launch pad

An Atlas V 551 with the New Horizons probe launches from Launch Pad 41 in Cape Canaveral.

What is pressure?

Have you ever gone swimming at the deep end of a pool? Did you notice that your ears started to hurt a little bit when you were under water? The deeper you dive, the more water there is on top of you. All of that water presses on your body&ndashand that's pressure.

The same type of pressure happens in Jupiter's core. Under low pressure, particles of hydrogen and helium, called molecules, have lots of room to bounce around. This is when hydrogen and helium are gases.

However, the weight of all this hydrogen and helium is really heavy. This weight presses down toward the planet's core, creating high pressure. The molecules run out of room to bounce around, so instead, they slow down and crowd together. This creates a liquid.


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

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

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

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

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


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

The atmospheric proportions of hydrogen and helium are close to the theoretical composition of the primordial solar nebula. Neon in the upper atmosphere only consists of 20 parts per million by mass, which is about a tenth as abundant as in the Sun. [42] Helium is also depleted to about 80% of the Sun's helium composition. This depletion is a result of precipitation of these elements as helium-rich droplets deep in the interior of the planet. [43]

Based on spectroscopy, Saturn is thought to be similar in composition to Jupiter, but the other giant planets Uranus and Neptune have relatively less hydrogen and helium and relatively more of the next most abundant elements, including oxygen, carbon, nitrogen, and sulfur. [44] As their volatile compounds are mainly in ice form, they are called ice giants.

Mass and size

Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined—this is so massive that its barycentre with the Sun lies above the Sun's surface at 1.068 solar radii from the Sun's centre. [45] Jupiter is much larger than Earth and considerably less dense: its volume is that of about 1,321 Earths, but it is only 318 times as massive. [7] [46] Jupiter's radius is about one tenth the radius of the Sun, [47] and its mass is one thousandth the mass of the Sun, so the densities of the two bodies are similar. [48] A "Jupiter mass" ( M J or M Jup) is often used as a unit to describe masses of other objects, particularly extrasolar planets and brown dwarfs. For example, the extrasolar planet HD 209458 b has a mass of 0.69 M J, while Kappa Andromedae b has a mass of 12.8 M J. [49]

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

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

Internal structure

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

Above the layer of metallic hydrogen lies a transparent interior atmosphere of hydrogen. At this depth, the pressure and temperature are above molecular hydrogen's critical pressure of 1.3 MPa and critical temperature of only 33 K. [65] In this state, there are no distinct liquid and gas phases—hydrogen is said to be in a supercritical fluid state. It is convenient to treat hydrogen as gas extending downward from the cloud layer to a depth of about 1,000 km, [55] and as liquid in deeper layers. Physically, there is no clear boundary—the gas smoothly becomes hotter and denser as depth increases. [66] [67] Rain-like droplets of helium and neon precipitate downward through the lower atmosphere, depleting the abundance of these elements in the upper atmosphere. [43] [68] Calculations suggest that helium drops separate from metalic hydrogen at a radius of 60,000 km (11,000 km below the cloudtops) and merge again at 50,000 km (22,000 km beneath the clouds). [69] Rainfalls of diamonds have been suggested to occur, as well as on Saturn [70] and the ice giants Uranus and Neptune. [71]

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


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

Cloud layers

Jupiter is perpetually covered with clouds composed of ammonia crystals, and possibly ammonium hydrosulfide. The clouds are in the tropopause and are in bands of different latitudes, known as tropical regions. These are subdivided into lighter-hued zones and darker belts. The interactions of these conflicting circulation patterns cause storms and turbulence. Wind speeds of 100 metres per second (360 km/h 220 mph) are common in zonal jet streams. [75] The zones have been observed to vary in width, colour and intensity from year to year, but they have remained sufficiently stable for scientists to name them. [46]

The cloud layer is about 50 km (31 mi) deep, and consists of at least two decks of clouds: a thick lower deck and a thin clearer region. There may also be a thin layer of water clouds underlying the ammonia layer. Supporting the presence of water clouds are the flashes of lightning detected in the atmosphere of Jupiter. These electrical discharges can be up to a thousand times as powerful as lightning on Earth. [76] The water clouds are assumed to generate thunderstorms in the same way as terrestrial thunderstorms, driven by the heat rising from the interior. [77] The Juno mission revealed the presence of "shallow lightning" which originates from ammonia-water clouds relatively high in the atmosphere. [78] These discharges carry "mushballs" of water-ammonia slushes covered in ice, which fall deep into the atmosphere. [79] Upper-atmospheric lightning has been observed in Jupiter's upper atmosphere, bright flashes of light that last around 1.4 milliseconds. These are known as "elves" or "sprites" and appear blue or pink due to the hydrogen. [80] [81]

The orange and brown colours in the clouds of Jupiter are caused by upwelling compounds that change colour when they are exposed to ultraviolet light from the Sun. The exact makeup remains uncertain, but the substances are thought to be phosphorus, sulfur or possibly hydrocarbons. [55] [82] These colourful compounds, known as chromophores, mix with the warmer lower deck of clouds. The zones are formed when rising convection cells form crystallising ammonia that masks out these lower clouds from view. [83]

Jupiter's low axial tilt means that the poles always receive less solar radiation than the planet's equatorial region. Convection within the interior of the planet transports energy to the poles, balancing out the temperatures at the cloud layer. [46]

Great Red Spot and other vortices

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

The Great Red Spot is larger than the Earth. [94] Mathematical models suggest that the storm is stable and will be a permanent feature of the planet. [95] However, it has significantly decreased in size since its discovery. Initial observations in the late 1800s showed it to be approximately 41,000 km (25,500 mi) across. By the time of the Voyager flybys in 1979, the storm had a length of 23,300 km (14,500 mi) and a width of approximately 13,000 km (8,000 mi). [96] Hubble observations in 1995 showed it had decreased in size to 20,950 km (13,020 mi), and observations in 2009 showed the size to be 17,910 km (11,130 mi). As of 2015 [update] , the storm was measured at approximately 16,500 by 10,940 km (10,250 by 6,800 mi), [96] and was decreasing in length by about 930 km (580 mi) per year. [94] [97]

Juno missions show that there are several polar cyclone groups at Jupiter's poles. The northern group contains nine cyclones, with a large one in the center and eight others around it, while its southern counterpart also consists of a center vortex but is surrounded by five large storms and a single smaller one. [98] [ better source needed ] These polar structures are caused by the turbulence in Jupiter's atmosphere and can be compared with the hexagon at Saturn's north pole.

In 2000, an atmospheric feature formed in the southern hemisphere that is similar in appearance to the Great Red Spot, but smaller. This was created when smaller, white oval-shaped storms merged to form a single feature—these three smaller white ovals were first observed in 1938. The merged feature was named Oval BA and has been nicknamed "Red Spot Junior." It has since increased in intensity and changed from white to red. [99] [100] [101]

In April 2017, a "Great Cold Spot" was discovered in Jupiter's thermosphere at its north pole. This feature is 24,000 km (15,000 mi) across, 12,000 km (7,500 mi) wide, and 200 °C (360 °F) cooler than surrounding material. While this spot changes form and intensity over the short term, it has maintained its general position in the atmosphere for more than 15 years. It may be a giant vortex similar to the Great Red Spot, and appears to be quasi-stable like the vortices in Earth's thermosphere. Interactions between charged particles generated from Io and the planet's strong magnetic field likely resulted in redistribution of heat flow, forming the Spot. [103]


Jupiter's magnetic field is fourteen times stronger than Earth's, ranging from 4.2 gauss (0.42 mT) at the equator to 10–14 gauss (1.0–1.4 mT) at the poles, making it the strongest in the Solar System (except for sunspots). [83] This field is thought to be generated by eddy currents—swirling movements of conducting materials—within the liquid metallic hydrogen core. The volcanoes on the moon Io emit large amounts of sulfur dioxide, forming a gas torus along the moon's orbit. The gas is ionised in the magnetosphere, producing sulfur and oxygen ions. They, together with hydrogen ions originating from the atmosphere of Jupiter, form a plasma sheet in Jupiter's equatorial plane. The plasma in the sheet co-rotates with the planet, causing deformation of the dipole magnetic field into that of a magnetodisk. Electrons within the plasma sheet generate a strong radio signature that produces bursts in the range of 0.6–30 MHz which are detectable from Earth with consumer-grade shortwave radio receivers. [104] [105]

At about 75 Jupiter radii from the planet, the interaction of the magnetosphere with the solar wind generates a bow shock. Surrounding Jupiter's magnetosphere is a magnetopause, located at the inner edge of a magnetosheath—a region between it and the bow shock. The solar wind interacts with these regions, elongating the magnetosphere on Jupiter's lee side and extending it outward until it nearly reaches the orbit of Saturn. The four largest moons of Jupiter all orbit within the magnetosphere, which protects them from the solar wind. [55]

The magnetosphere of Jupiter is responsible for intense episodes of radio emission from the planet's polar regions. Volcanic activity on Jupiter's moon Io injects gas into Jupiter's magnetosphere, producing a torus of particles about the planet. As Io moves through this torus, the interaction generates Alfvén waves that carry ionised matter into the polar regions of Jupiter. As a result, radio waves are generated through a cyclotron maser mechanism, and the energy is transmitted out along a cone-shaped surface. When Earth intersects this cone, the radio emissions from Jupiter can exceed the solar radio output. [106]

Jupiter is the only planet whose barycentre with the Sun lies outside the volume of the Sun, though by only 7% of the Sun's radius. [107] The average distance between Jupiter and the Sun is 778 million km (about 5.2 times the average distance between Earth and the Sun, or 5.2 AU) and it completes an orbit every 11.86 years. This is approximately two-fifths the orbital period of Saturn, forming a near orbital resonance. [108] The orbital plane of Jupiter is inclined 1.31° compared to Earth. Because the eccentricity of its orbit is 0.048, Jupiter is slightly over 75 million km nearer the Sun at perihelion than aphelion. [7]

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

Jupiter's rotation is the fastest of all the Solar System's planets, completing a rotation on its axis in slightly less than ten hours this creates an equatorial bulge easily seen through an amateur telescope. The planet is an oblate spheroid, meaning that the diameter across its equator is longer than the diameter measured between its poles. On Jupiter, the equatorial diameter is 9,275 km (5,763 mi) longer than the polar diameter. [67]

Because Jupiter is not a solid body, its upper atmosphere undergoes differential rotation. The rotation of Jupiter's polar atmosphere is about 5 minutes longer than that of the equatorial atmosphere three systems are used as frames of reference, particularly when graphing the motion of atmospheric features. System I applies to latitudes from 10° N to 10° S its period is the planet's shortest, at 9h 50m 30.0s. System II applies at all latitudes north and south of these its period is 9h 55m 40.6s. System III was defined by radio astronomers and corresponds to the rotation of the planet's magnetosphere its period is Jupiter's official rotation. [110]

Jupiter is usually the fourth brightest object in the sky (after the Sun, the Moon, and Venus) [83] at opposition Mars can appear brighter than Jupiter. Depending on Jupiter's position with respect to the Earth, it can vary in visual magnitude from as bright as −2.94 [13] at opposition down to [13] −1.66 during conjunction with the Sun. The mean apparent magnitude is −2.20 with a standard deviation of 0.33. [13] The angular diameter of Jupiter likewise varies from 50.1 to 29.8 arc seconds. [7] Favorable oppositions occur when Jupiter is passing through perihelion, an event that occurs once per orbit. [111]

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

Pre-telescopic research

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

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

Ground-based telescope research

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

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

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

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

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

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

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

Radiotelescope research

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

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

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


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

Flyby missions

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

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

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

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

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

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

Galileo mission

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

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

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

Juno mission

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

Canceled missions and future plans

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

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

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

Galilean moons

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

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


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

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

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

Planetary rings

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

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

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

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

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


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

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

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

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

The astronomical symbol for the planet, , is a stylised representation of the god's lightning bolt. The original Greek deity Zeus supplies the root zeno-, used to form some Jupiter-related words, such as zenographic. [e] Jovian is the adjectival form of Jupiter. The older adjectival form jovial, employed by astrologers in the Middle Ages, has come to mean "happy" or "merry", moods ascribed to Jupiter's astrological influence. [194] In Germanic mythology, Jupiter is equated to Thor, whence the English name Thursday for the Roman dies Jovis. [195]

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

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

Quick Facts

Namesake: King of the ancient Roman gods

Discovered: Known to the ancients

Planet type: Gas Giant

Number of moons: 53 confirmed | 26 provisional (79 total)

Diameter: 88,846 miles (142,984 kilometers)

Length of day: 9.93 hours

Length of year: 11.86 Earth Years

Distance from Sun: 5.1 Astronomical Units (Earth=1)

Surface temperature*: -160 degrees Fahrenheit (-110 degrees Celsius )

This amazing video shows what it's like to zoom through space on NASA's daredevil Jupiter probe

NASA's Juno spacecraft, which is roughly the size of a basketball court, is currently zooming around Jupiter some 600 million miles away from Earth.

And it's taking some truly amazing photos.

A handful of pictures released by NASA in August show the first-ever views of Jupiter's poles, plus wild new infrared images and audio of its auroras. The Juno mission's leader has said the imagery "looks like nothing we have seen or imagined before."

But there are many, many other Juno images we're not readily seeing — so mathematician Gerald Eichstädt is continuously assembling them into a "marble movie" of Jupiter, as we learned from Emily Lakdawalla at her Planetary Society blog.

The animated video below shows the view from Juno's only visible-light camera, called JunoCam. You can even imagine you're riding Juno while watching it.

The "marble" of Jupiter is at the center and its four biggest, Galilean moons — Europa, Ganymede, Io, and Callisto — are orbiting around it as brightened dots:

The clip looks sped-up because JunoCam only takes photos once every 15 to 30 minutes, Lakdawalla writes in the description for the YouTube video.

But wait for the frightening moment about 1 minute and 50 seconds into the clip, when it looks like Juno is going to slam into the largest planet in the solar system.

What you're seeing is the pinnacle of a highly elliptical and scary-looking orbit — and the only reason Juno is able to get such unprecedented views of the world:

At the tightest part of the orbital loop, Jupiter's gravity accelerates Juno to a blistering 130,000 mph, or about 75 times faster than a bullet shot out of a gun.

The main reason Juno pulls off these acrobatics is so that it does not die.

Jupiter's powerful magnetic field whips up a sickening amount of harmful radiation that can fry electronics, and in particular solar panels. So it's best to bolt around the planet and then get out of there as fast as possible.

NASA could have powered Juno with a rare radioactive material called plutonium-238, allowing the robot to orbit more closely, but the space agency is running very, very low on the stuff. So instead, it opted for solar energy (and crazy orbits).

Lakdawalla says Eichstädt wrote an algorithm to continuously build out the video using images she's ripping from a buried page of the Juno mission's website.

Eichstädt is also using the Juno data to make cool animations like the one below. Each frame shows how far a Galilean moon moves over 21 hours (the trail of dots), and there are 46 frames, giving a total of about 6 weeks of time compressed into a few seconds.

Io orbits the closest, followed by Europa, then Ganymede, and the farthest (about 1.2 million miles away) is Callisto:

So far the latest "marble movie" covers about 1.5 orbits, since Juno is into its second of 36 flybys scientists have planned.

"This is a work in progress eventually the animation should cover through October 18," Lakdawalla wrote — when Juno will make another death-defying flyby of Jupiter.

Once the mission ends, however, Juno won't live on as a relic of humanity's exploration. To protect any aliens that might be living on icy moons such as Europa and Ganymede, NASA intends to fly the $1 billion probe to its doom — right into Jupiter's seemingly bottomless clouds.


DNA: Scientists who've studied the planet's history using data from NASA's Juno space probe, which will study the composition of the planet's atmosphere until 2021

In fact, they add that proto-planets would've frequently collided in the early days of the solar system.

'We suggest that collisions were common in the young Solar System and that a similar event may have also occurred for Saturn, contributing to the structural differences between Jupiter and Saturn.'

They also tested the theory that Jupiter's fragmented nucleus was caused by weather erosion or the possibility that it always contained core gas.

But the study concluded that a colossal collision was most-likely responsible.


Experts have studied recent evidence gathered from Nasa's Juno spacecraft to reveal the reason why gases form bands on Jupiter.

Clouds of ammonia at Jupiter's outer atmosphere are carried along by jet streams to form Jupiter's regimented coloured bands.

Jupiter's jet streams reach as deep as 1,800 miles (3,000 km) below Jupiter's clouds, which are shades of white, red, orange, brown and yellow.

The gas in the interior of Jupiter is magnetised, which researchers believe explains why the jet streams go as deep as they do but don't go any deeper.

There are also no continents and mountains below Jupiter's atmosphere to obstruct the path of the jet stream.

This makes the jet streams on Jupiter simpler than those on Earth and cause less turbulence in it's upper atmosphere.

Our galaxy is home to a bewildering variety of Jupiters: hot ones, cold ones, giant versions of our own giant, pint-sized pretenders only half as big around.

Astronomers say that in our galaxy alone, a billion or more Jupiter-like worlds could be orbiting stars other than our sun. And we can use them to gain a better understanding of our solar system and our galactic environment, including the prospects for finding life. We need only turn our instruments and probes to our own backyard.

We just need to see Jupiter as an exoplanet.

Jupiter cousin WASP-12b


The video above shows Juno arriving at the system, and slowing down enough to be captured by Jupiter's powerful gravity. As the probe approaches the planet, the video shows some of Jupiter's 67 moons circling their host planet

The fifth planet from the sun and the heftiest in the solar system, Jupiter is known as a gas giant — a ball of mainly hydrogen and helium — unlike rocky Earth and Mars.

But scientists still do not know exactly what lies at its centre, or whether it formed within its current orbit, or migrated from elsewhere in the solar system.

Among the lingering questions are how much water exists, if it has a a solid core, and why Jupiter's southern and northern lights are the brightest in the solar system.

The first part of the video shows the long journey to Jupiter, when the planet hardly appears to change in size. Juno's very rapid descent into the Jupiter system is shown in the video's last 25 seconds (pictured)

There is also the mystery of its Great Red Spot.

Recent observations by the Hubble Space Telescope revealed the centuries-old monster storm in Jupiter's atmosphere is shrinking.

The spacecraft will end its mission in 2018 when it takes a swan dive into Jupiter's atmosphere and disintegrates, a necessary sacrifice to prevent any chance of accidentally crashing into the planet's potentially habitable moons.

Juno launched in 2011. This image shows an Atlas V rocket carrying the Juno spacecraft lifts off from Space Launch Complex-41 in Cape Canaveral, Florida. It was the first step in Juno's 1.8 billion-mile voyage to the gas giant planet, Jupiter


The Juno probe reached Jupiter in July after a five-year, 1.8 billion-mile journey from Earth.

Following a successful braking manoeuvre, it entered into a long polar orbit flying to within 3,100 miles (5,000 km) of the planet's swirling cloud tops.

The probe skimmed to within just 4,200 km of the planet's clouds once a fortnight - too close to provide global coverage in a single image.

No previous spacecraft has orbited so close to Jupiter, although two others have been sent plunging to their destruction through its atmosphere.

To complete its risky mission Juno had to survive a circuit-frying radiation storm generated by Jupiter's powerful magnetic field.

The maelstrom of high energy particles travelling at nearly the speed of light is the harshest radiation environment in the solar system.

To cope with the conditions, the spacecraft is protected with special radiation-hardened wiring and sensor shielding.

Its all-important 'brain' - the spacecraft's flight computer - is housed in an armoured vault made of titanium and weighing almost 400 pounds (172kg).

The Earth-based observations supplement the suite of advanced instrumentation on the Juno spacecraft, filling in the gaps in Juno's spectral coverage and providing the wider global and temporal context to Juno's close-in observations.

Juno was launched on 5 August, 2011. During more than 30 orbital flybys of the Jovian world, it will probe beneath the obscuring ammonia and hydrogen sulfide cloud cover and study the auroras to learn more about the planet's origins, structure, atmosphere and magnetosphere.

Juno's name comes from Greek and Roman mythology. Jupiter, the father of the Roman gods, drew a veil of clouds around himself to hide his mischief. But his wife - the goddess Juno - was able to peer through the clouds and reveal Jupiter's true nature.

With its billowy clouds and colourful stripes, Jupiter is an extreme world that likely formed first, shortly after the sun.

Unlocking its history may hold clues to understanding how Earth and the rest of the solar system developed.

Named after the Roman god Jupiter's cloud-piercing wife, Juno is only the second mission designed to spend time at Jupiter.

Galileo, which launched in 1989, circled Jupiter for 14 years, beaming back splendid views of the planet and its numerous moons.

It uncovered signs of an ocean beneath the icy surface of Europa, considered a top target in the search for life outside Earth.

The trek to Jupiter, spanning nearly five years and 1.8 billion miles (2.8 billion kilometres), took Juno on a tour of the inner solar system followed by a swing past Earth that catapulted it beyond the asteroid belt between Mars and Jupiter.

Juno is in a harsh radiation environment, so its delicate electronics are housed in a special titanium vault. Eventually, Juno will succumb to the intense radiation and will be commanded to plunge into Jupiter's atmosphere to avoid any collision with the planet's moons. Pictured is a 1/5 scale model size of the solar-powered Juno spacecraft

Along with the scientific instruments Juno is also carrying three tiny passengers in the form of Lego figures, made from spacecraft-grade Aluminium. The three models include models of the god Jupiter, his wife and mission namesake the goddess Juno, and astronomer Galileo


— 1.8 billion miles (2.8 billion kilometres)

That's the total distance travelled from launch to arrival. Juno's journey wasn't a straight shot. Because the rocket that carried Juno wasn't powerful enough to boost it directly to Jupiter, it took a longer route. It looped around the inner solar system and then swung by Earth, using our planet as a gravity slingshot to hurtle toward the outer solar system.

— 3,100 miles (5,000 kilometres)

That's how close Juno will fly to Jupiter's cloud tops. It will pass over the poles a total of 37 times during the mission on a path that avoids the most intense radiation, before it plunges into the planet's atmosphere.

That's the time it takes for radio signals from Jupiter to reach Earth. During the encounter, Juno will fire its main engine for about a half hour to slow down. By the time ground controllers receive word that it started, the engine burn would have been completed, and if all goes as planned, Juno would be in orbit.

That's how long the mission will last. Because Juno is in a harsh radiation environment, its delicate electronics are housed in a special titanium vault. Eventually, Juno will succumb to the intense radiation and will be commanded to plunge into Jupiter's atmosphere to avoid any collision with the planet's moons.

Juno carries a suite of nine instruments to explore Jupiter from its interior to its atmosphere. It will map Jupiter's gravity and magnetic fields and track how much water is in the atmosphere. Its colour camera dubbed JunoCam will snap close-ups of Jupiter's swirling clouds, polar regions and shimmering southern and northern lights.

Three massive solar wings extend from Juno, making it the most distant solar-powered spacecraft. The panels can generate 500 watts of electricity, enough to power the instruments

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