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Jupiter Astronomical symbol of Jupiter
Jupiter by Cassini-Huygens.jpg
Photo of Jupiter from Cassini.
Adjectives Jovian
Orbital characteristics
Epoch J2000
Aphelion 816,520,800 km (5.4581 AU)
Perihelion 740,573,600 km (4.9504 AU)
778,547,200 km (5.2043 AU)
Eccentricity 0.048775
4,331.572 days
11.85920 yr
398.88 days
13.07 km/s
Inclination 1.305° to Ecliptic
6.09° to Sun's equator
0.32° to Invariable plane
Known satellites 67
Physical characteristics
Mean radius
69,911±6 km
Flattening 0.06487 ± 0.00015
6.21796×1010 km²
121.9 Earths
Volume 1.43128×1015 km³
1321.3 Earths
Mass 1.8986×1027 kg
317.83 Earths
Mean density
1.326 g/cm³
24.79 m/s²
2.528 g
59.5 km/s
9.925 h
Equatorial rotation velocity
12.6 km/s
45,300 km/h
North pole declination

0.343 (bond)

0.52 (geom.)
Surface temp. min mean max
1 bar level 165 K
0.2 bar 112 K
-1.6 to -2.94
Angular diameter
29.8" — 50.1"
Surface pressure
20–200 kPa (cloud layer)
27 km
Composition by volume
87.8 to 91.8% Hydrogen (H2)
8.2 to 12.2% Helium
~0.3% Methane
~0.026% Ammonia
~0.003% Hydrogen deuteride (HD)
0.0006% Ethane
0.0004% water
ammonium hydrosulfide(NH4SH)

Jupiter is the largest planet in the Solar System. It is the fifth planet from the Sun. Jupiter is classified as a gas giant, both because it is so large and due to the fact that it is made up mostly of gas. The other gas giants are Saturn, Uranus, and Neptune.

Jupiter can be seen with the naked eye. It was known to the ancient Romans, who named it after their god Jupiter, he was known for causing lightning strikes on Earth. Jupiter is the third brightest object in the night sky. Only the Earth's moon and Venus are brighter.

Jupiter has at least 67 moons. Of these, 55 are very small and less than five kilometres wide. The four largest moons of Jupiter are Io, Europa, Ganymede, and Callisto. They are collectively called the Galilean moons, because they were discovered by the Italian astronomer Galileo Galilei.



Jupiter, Earth size comparison
Jupiter, Earth size comparison

Jupiter is the biggest planet in the Solar System with a diameter of 142,984 km. This is eleven times bigger than the diameter of Earth. The volume of Jupiter is 1,317 times the volume of Earth, in other words, 1,317 Earth-sized objects could fit inside it.

Jupiter has a mass of 1.8986×1027 kg, or about 318 Earths. Jupiter is twice as massive as all the other planets in the Solar System put together. It gives off more heat than it gets from the sun. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere. Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including Earth.

Jupiter shrinks by about 2 cm each year. When it was first formed, Jupiter was much hotter and was about twice its current diameter.

Inner structure

Jupiter interior
This illustrates Jupiter's interior. In the upper layers the atmosphere changes to a liquid state above a thick layer of metallic hydrogen. In the center there may be a solid core of heavier elements

Jupiter is thought to consist of a dense core with a mixture of elements, a surrounding layer of liquid metallic hydrogen with some helium, and an outer layer predominantly of molecular hydrogen. Beyond this basic outline, there is still considerable uncertainty.

The core region may be surrounded by dense metallic hydrogen, which extends outward to about 78% of the radius of the planet. The core is often described as rocky, but its detailed composition is unknown, as are the properties of materials at the temperatures and pressures of those depths.


Parachute deployment
Gallileo Probe shortly after parachute deployment, descent through the Jupiter atmosphere

Jupiter's upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules. Thus, Jupiter's atmosphere is approximately 75% hydrogen and 24% helium, with the remaining one percent consisting of other elements. The atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, and sulfur.

The outermost layer of the atmosphere contains crystals of frozen ammonia. The interior contains denser materials, it is roughly 71% hydrogen, 24% helium, and 5% other elements.

Jupiter diagram
Diagram of Jupiters characteristics

Further into the planet it is so hot and the pressure so high that helium becomes a liquid and precipitates or rains further down into the planet. Jupiter seems to be made of similar gases to Saturn. Rainfalls of diamonds have been suggested to occur on Jupiter, as well as on Saturn and ice giants Uranus and Neptune.

Above the unknown inner core is an outer core. The outer core of Jupiter is thick, liquid hydrogen. The pressure is high enough to make the hydrogen solid, but then it melts because of the heat.

Cloud layers

High Above Jupiter's Clouds

The cloud layer is only 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 idea 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. The water clouds are assumed to generate thunderstorms in the same way as terrestrial thunderstorms, driven by the heat rising from the interior.

Jupiter has many bands of clouds going horizontally across its surface. The brown and orange colours are caused when sunlight passes through or refracts with the many gases in the atmosphere. The light parts are called zones and the darker are called belts.

Jupiter from Voyager 1
View of Jupiter's clouds with the Great Red Spot at top right, taken from Voyager 1

The zones and belts often interact with each other. This causes huge storms. Wind speeds of 360 kilometres per hour (km/h) are common on Jupiter. To show the difference, the strongest tropical storms on Earth are about 100 km/h.

Most of the clouds on Jupiter are made of ammonia. There may also be clouds of water vapour similar to clouds on Earth. Spacecrafts such as Voyager 1 have seen lightning on the surface of the planet. Scientists think it was water vapour because lightning needs water vapour. These lightning bolts have been measured as up 1,000 times as powerful as those on Earth.

Great Red Spot

Great Red Spot From Voyager 1
This view of Jupiter's Great Red Spot and its surroundings was obtained by Voyager 1 in 1979, the white oval storm directly below the Great Red Spot is approximately the same diameter as Earth

One of the biggest features in Jupiter's atmosphere is the Great Red Spot. It is a huge storm which is bigger than the entire Earth. The Great Red Spot is a 300-year old storm, it is known to have been in existence since at least 1831, and possibly since 1665. Storms can last for hours or as long as hundreds of years in the case of the Great Red Spot. The oval object rotates counterclockwise, within a period of about six days. The maximum altitude of this storm is about 8 km (5 mi) above the surrounding cloud-tops. The storm is large enough to be visible through Earth-based telescopes.

Storms such as this are common within the turbulent atmospheres of giant planets. Jupiter also has white ovals and brown ovals, which are lesser unnamed storms. White ovals tend to consist of relatively cool clouds within the upper atmosphere. Brown ovals are warmer and located within the "normal cloud layer". Such storms can last as little as a few hours or stretch on for centuries.

Great red spot PJ07 053 Detail v1
The Great Red Spot of Jupiter, as seen by the Juno Spacecraft

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 several 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 color from white to red.

Mathematical models suggest that the storm is stable and may be a permanent feature of the planet. However, it has significantly decreased in size since its discovery and is decreasing in length by about 930 km (580 mi) per year.

In April 2017, scientists reported the discovery of a "Great Cold Spot" in Jupiter's thermosphere at its north pole that is 24,000 km (15,000 mi) across, 12,000 km (7,500 mi) wide, and 200 °C (360 °F) cooler than surrounding material.

Magnetic field

Aurorae on the north pole of Jupiter as viewed by Hubble
Infrared view of Jupiter's southern lights, taken by the Jovian Infrared Auroral Mapper

Jupiter's magnetic field that is similar to Earth's, though it is fourteen times as strong as that of Earth, it the strongest in the Solar System (except for sunspots). It also has a magnetosphere much bigger and stronger than Earth's. The field traps radiation belts much stronger than Earth's Van Allen radiation belts, strong enough to endanger any spacecraft travelling past or to Jupiter.

The magnetic field is probably caused by the large amounts of liquid metallic hydrogen in the core of Jupiter. Due to its magnetic field trapping particles from the Sun, Jupiter is surrounded by very powerful radiation belts which would kill anyone who entered them.

Jupiter's magnetic field is the largest single planetary thing in the Solar System. It is 26 million kilometers across, making it about 20 times bigger than the Sun. It has a tail that extends past Saturn's orbit. If it could be seen from Earth, it would appear to be five times the size of the full moon.

The four largest moons of Jupiter and many of the smaller ones orbit or go around the planet within the magnetic field. This protects them from the solar wind. Jupiter's magnetic field is so large, it reaches the orbit of Saturn 7.7 million miles (12 million km) away. The Earth's magnetosphere does not even cover its moon, less than a quarter of a million miles (400,000 km) away.

Ring system

Jupiter Rings ca
An illustration of Jupiter's ring system showing the four main components

Jupiter also has a thin planetary ring system. These rings are very difficult to see, and so they were not discovered until NASA's Voyager 1 probe went to Jupiter in 1979. There are four parts to Jupiter's rings. The closest ring to Jupiter is called the Halo Ring. The next ring is called the Main Ring. It is about 6,440 km (4,002 mi) wide and only 30 km (19 mi) thick.

The Main and Halo rings of Jupiter are made of small, dark particles. The third and fourth rings, called the Gossamer Rings, are transparent (see through) and are made from microscopic debris and dust. This dust probably comes from small meteors striking the surface of Jupiter's moons. The third ring is called the Amalthea Gossamer Ring. The outer ring is the Thebe Gossamer Ring, the outer edge of this ring is about 220,000 km (136,702 mi) from Jupiter.


Jupiter System Montage - GPN-2000-000451
Jupiter and its four planet-size moons, called the Galilean satellites

The orbit of a planet is the time and path it takes to go around the Sun. In the amount of time it takes for Jupiter to orbit the Sun one time, the Earth orbits the Sun 11.86 times. One year on Jupiter is equal to 11.86 years on Earth. The average distance between Jupiter and the Sun is 778 million kilometres. This is five times the distance between Earth and the Sun.

Jupiter is not tilted on its axis as much as the Earth or Mars. This causes it to have no seasons, for example Summer or Winter. Jupiter rotates, or spins around very quickly. This causes the planet to bulge in the middle. Jupiter is the fastest spinning planet in the Solar System. It completes one rotation or spin in 10 hours.


Ulysses at Jupiter H1
Ulysses was launchedin 1990. It headed out to Jupiter for the gravity-assist manoeuvre that swung the craft into its unique solar orbit

Jupiter's large gravity has had a big effect on the Solar System. Jupiter protects the inner planets from comets by pulling them towards itself. Jupiter has been called the Solar System's vacuum cleaner, because of its immense gravity well and location near the inner Solar System. It receives the most frequent comet impacts of the Solar System's planets. Jupiter experiences about 200 times more asteroid and comet impacts than Earth. Two groups of asteroids, called Trojan asteroids, have settled into Jupiter's orbit round the Sun. One group is called the Trojans and the other group is called the Greeks. They go around the Sun at the same time as Jupiter.


From Earth

Conjunction of Jupiter and Moon
Conjunction of Jupiter and the Moon as seen from Earth

Jupiter is the third brightest object in the night sky, after the Moon and Venus. Because of that, people have always been able to see it from Earth. The first person known to really study the planet was Galileo Galilei in 1610. He was the first person to see Jupiter's moons Io, Europa, Ganymede and Callisto. This was because he used a telescope, unlike anyone before him.

No new moons were discovered for more than two hundred years. In 1892, astronomer E.E Barnard found a new moon using his observatory in California. He called the moon Amalthea. It was the last of Jupiter's 67 moons to be discovered by human observation through a telescope. Now, a small telescope will usually show Jupiter's four Galilean moons and the prominent cloud belts across Jupiter's atmosphere. A large telescope will show Jupiter's Great Red Spot when it faces Earth.

In 1994, bits of the comet Shoemaker Levy-9 hit Jupiter. It was the first time a collision or crash between two Solar System objects had been directly seen by people.


Io highest resolution true color
Io - true color

Jupiter has 67 known moons. The four largest were seen by Galileo with his primitive telescope, and nine more can be seen from Earth with modern telescopes. The rest of the moons have been identified by spacecraft. The smallest moon (S/2003 J 12) is only one kilometre across. The largest, Ganymede, has a diameter of 5,262 kilometres. It is bigger than the planet Mercury and is the largest moon in the solar system.

The other three Galilean moons are Io, Europa and Callisto. Because of the way they orbit Jupiter, gravity affects three of these moons greatly. The friction caused by the gravity of Europa and Ganymede pulling on Io makes it the most volcanic object in the Solar System. It has over 400 volcanoes, more than three times as many as Earth. Jupiter's moon Europa is thought to have a giant ocean below its surface.


New Horizons launch
NASA’s New Horizons spacecraft roars into the blue sky aboard an Atlas V rocket 2006

Seven spacecraft have flown past Jupiter since 1973. These were Pioneer 10 (1973), Pioneer 11 (1974), Voyagers 1 and 2 (1979), Ulysses (1992 and 2004), Cassini (2000), New Horizons (2006) and the NASA's Juno mission which arrived at Jupiter on July 4, 2016, and is expected to complete 37 orbits over 20 months. The mission plan called for Juno to study the planet in detail from a polar orbit.

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. 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.

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. As the spacecraft passed behind the planet, it observed flashes of lightning in the night side atmosphere.

Voyager and Jupiter (34685663916)
Voyager and Jupiter

The Ulysses probe was sent to study the Sun. It only went to Jupiter after it had finished its main mission. Ulysses had no cameras so it took no photographs. In 2006, the Cassini spacecraft, on its way to Saturn, took some very good, very clear pictures of the planet. Cassini also found a moon and took a picture of it but it was too far away to show the details.

The New Horizons probe flew by Jupiter for a gravity assist en route to Pluto. Its closest approach was on February 28, 2007. 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. Imaging of the Jovian system began September 4, 2006.

A Whole New Jupiter (34849964096)
This image shows Jupiter’s south pole, as seen by NASA’s Juno spacecraft

The Galileo mission in 1995 was the first spacecraft to go into orbit around Jupiter. It flew around the planet for seven years and studied all of the four biggest moons. It launched a probe into the planet to get information about Jupiter's atmosphere. The probe travelled to a depth of about 150 km before it was crushed by the weight of all the gas above it. The Galileo spacecraft was also crushed in 2003 when NASA steered the craft into the planet on purpose. They did this so that the craft could not crash into Europa, a moon which scientists think might have life.

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

The next planned mission to the Jovian system will be the European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in 2022, followed by NASA's Europa Clipper mission in 2025. Jovian in English means anything relating to Jupiter — the god or the planet. Sometimes the four outer planets are called the Jovian planets.

Human exploration

Callisto base
An artist’s rendering of a human exploration base on Callisto, Jupiter’s second largest moon

While scientists require further evidence to determine the extent of a rocky core on Jupiter, its Galilean moons provide the potential opportunity for future human exploration. Particular targets are Europa, due to its potential for life, and Callisto, due to its relatively low radiation dose. In 2003, NASA proposed a program called Human Outer Planets Exploration (HOPE) that involved sending astronauts to explore the Galilean moons. NASA has projected a possible attempt some time in the 2040s. In the Vision for Space Exploration policy announced in January 2004, NASA discussed missions beyond Mars, mentioning that a "human research presence" may be desirable on Jupiter's moons.

JPL Visions of the Future, Europa
The under-ice ocean as a must-see location on Europa moon. Fictional space tourism poster from JPL’s Visions of the Future

NASA has theorized on the feasibility of mining the atmospheres of the outer planets, particularly for helium-3, an isotope of helium that is rare on Earth and could have a very high value per unit mass as thermonuclear fuel. Factories stationed in orbit could mine the gas and deliver it to visiting craft. However, the Jovian system in general poses particular disadvantages for colonization because of the severe radiation conditions prevailing in Jupiter's magnetosphere and the planet's particularly deep gravitational well.

Ganymede is the Solar System's largest moon and the Solar System's only known moon with a magnetosphere, but this does not shield it from cosmic radiation. Callisto is farther from Jupiter's strong radiation belt. One of the main targets chosen by the HOPE study was Callisto. The possibility of building a surface base on Callisto was proposed, because of the low radiation levels at its distance from Jupiter and its geological stability. Callisto is the only Galilean satellite for which human exploration is feasible. The levels of ionizing radiation on Io, Europa, and Ganymede are hostile to human life, and adequate protective measures have yet to be devised.

It could be possible to build a surface base that would produce fuel for further exploration of the Solar System. In 1997, the Artemis Project designed a plan to colonize Europa. According to this plan, explorers would drill down into the Europan ice crust, entering the assumed subsurface ocean, where they would inhabit artificial air pockets.

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 408,894 km
February 4, 2004 120,000,000 km
Cassini December 30, 2000 10,000,000 km
New Horizons February 28, 2007 2,304,535 km

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