Jupiter is the fifth planet from the Sun and by far the largest. Jupiter is more than twice as massive as all the other planets combined (the mass of Jupiter is 318 times that of Earth).
orbit: 778,330,000 km (5.20 AU) from Sun
diameter: 142,984 km (equatorial)
mass: 1.900e27 kg
History of Jupiter
Jupiter is the fourth brightest object in the sky (after the Sun, the Moon and Venus). It has been known since prehistoric times as a bright “wandering star”. But in 1610 when Galileo first pointed a telescope at the sky he discovered Jupiter’s four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons) and recorded their motions back and forth around Jupiter. This was the first discovery of a center of motion not apparently centered on the Earth. It was a major point in favor of Copernicus’s heliocentric theory of the motions of the planets (along with other new evidence from his telescope: the phases of Venus and the mountains on the Moon). Galileo’s outspoken support of the Copernican theory got him in trouble with the Inquisition. Today anyone can repeat Galileo’s observations (without fear of retribution 🙂 using binoculars or an inexpensive telescope.
Jupiter was first visited by Pioneer 10 in 1973 and later by Pioneer 11, Voyager 1, Voyager 2 and Ulysses. The spacecraft Galileo orbited Jupiter for eight years. It is still regularly observed by the Hubble Space Telescope.
The gas planets do not have solid surfaces, their gaseous material simply gets denser with depth (the radii and diameters quoted for the planets are for levels corresponding to a pressure of 1 atmosphere). What we see when looking at these planets is the tops of clouds high in their atmospheres (slightly above the 1 atmosphere level).
Jupiter is about 90% hydrogen and 10% helium (by numbers of atoms, 75/25% by mass) with traces of methane, water, ammonia and “rock”. This is very close to the composition of the primordial Solar Nebula from which the entire solar system was formed. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium.
Our knowledge of the interior of Jupiter (and the other gas planets) is highly indirect and likely to remain so for some time. (The data from Galileo’s atmospheric probe goes down only about 150 km below the cloud tops.)
Jupiter probably has a core of rocky material amounting to something like 10 to 15 Earth-masses.
Above the core lies the main bulk of the planet in the form of liquid metallic hydrogen. This exotic form of the most common of elements is possible only at pressures exceeding 4 million bars, as is the case in the interior of Jupiter (and Saturn). Liquid metallic hydrogen consists of ionized protons and electrons (like the interior of the Sun but at a far lower temperature). At the temperature and pressure of Jupiter’s interior hydrogen is a liquid, not a gas. It is an electrical conductor and the source of Jupiter’s magnetic field. This layer probably also contains some helium and traces of various “ices”.
The outermost layer is composed primarily of ordinary molecular hydrogen and helium which is liquid in the interior and gaseous further out. The atmosphere we see is just the very top of this deep layer. Water, carbon dioxide, methane and other simple molecules are also present in tiny amounts.
Recent experiments have shown that hydrogen does not change phase suddenly. Therefore the interiors of the jovian planets probably have indistinct boundaries between their various interior layers.
Three distinct layers of clouds are believed to exist consisting of ammonia ice, ammonium hydrosulfide and a mixture of ice and water. However, the preliminary results from the Galileo probe show only faint indications of clouds (one instrument seems to have detected the topmost layer while another may have seen the second). But the probe’s entry point (left) was unusual — Earth-based telescopic observations and more recent observations by the Galileo orbiter suggest that the probe entry site may well have been one of the warmest and least cloudy areas on Jupiter at that time.
Data from the Galileo atmospheric probe also indicate that there is much less water than expected. The expectation was that Jupiter’s atmosphere would contain about twice the amount of oxygen (combined with the abundant hydrogen to make water) as the Sun. But it now appears that the actual concentration much less than the Sun’s. Also surprising was the high temperature and density of the uppermost parts of the atmosphere.
Jupiter and the other gas planets have high velocity winds which are confined in wide bands of latitude. The winds blow in opposite directions in adjacent bands. Slight chemical and temperature differences between these bands are responsible for the colored bands that dominate the planet’s appearance. The light colored bands are called zones; the dark ones belts. The bands have been known for some time on Jupiter, but the complex vortices in the boundary regions between the bands were first seen by Voyager. The data from the Galileo probe indicate that the winds are even faster than expected (more than 400 mph) and extend down into as far as the probe was able to observe; they may extend down thousands of kilometers into the interior. Jupiter’s atmosphere was also found to be quite turbulent. This indicates that Jupiter’s winds are driven in large part by its internal heat rather than from solar input as on Earth.
The vivid colors seen in Jupiter’s clouds are probably the result of subtle chemical reactions of the trace elements in Jupiter’s atmosphere, perhaps involving sulfur whose compounds take on a wide variety of colors, but the details are unknown.
The colors correlate with the cloud’s altitude: blue lowest, followed by browns and whites, with reds highest. Sometimes we see the lower layers through holes in the upper ones.
The Great Red Spot (GRS) has been seen by Earthly observers for more than 300 years (its discovery is usually attributed to Cassini, or Robert Hooke in the 17th century). The GRS is an oval about 12,000 by 25,000 km, big enough to hold two Earths. Other smaller but similar spots have been known for decades. Infrared observations and the direction of its rotation indicate that the GRS is a high-pressure region whose cloud tops are significantly higher and colder than the surrounding regions. Similar structures have been seen on Saturn and Neptune. It is not known how such structures can persist for so long.
Jupiter radiates more energy into space than it receives from the Sun. The interior of Jupiter is hot: the core is probably about 20,000 K. The heat is generated by the Kelvin-Helmholtz mechanism, the slow gravitational compression of the planet. (Jupiter does NOT produce energy by nuclear fusion as in the Sun; it is much too small and hence its interior is too cool to ignite nuclear reactions.) This interior heat probably causes convection deep within Jupiter’s liquid layers and is probably responsible for the complex motions we see in the cloud tops. Saturn and Neptune are similar to Jupiter in this respect, but oddly, Uranus is not.
Jupiter is just about as large in diameter as a gas planet can be. If more material were to be added, it would be compressed by gravity such that the overall radius would increase only slightly. A star can be larger only because of its internal (nuclear) heat source. (But Jupiter would have to be at least 80 times more massive to become a star.)
Jupiter has a huge magnetic field, much stronger than Earth’s. Its magnetosphere extends more than 650 million km (past the orbit of Saturn!). (Note that Jupiter’s magnetosphere is far from spherical — it extends “only” a few million kilometers in the direction toward the Sun.) Jupiter’s moons therefore lie within its magnetosphere, a fact which may partially explain some of the activity on Io. Unfortunately for future space travelers and of real concern to the designers of the Voyager and Galileo spacecraft, the environment near Jupiter contains high levels of energetic particles trapped by Jupiter’s magnetic field. This “radiation” is similar to, but much more intense than, that found within Earth’s Van Allen belts. It would be immediately fatal to an unprotected human being.
The Galileo atmospheric probe discovered a new intense radiation belt between Jupiter’s ring and the uppermost atmospheric layers. This new belt is approximately 10 times as strong as Earth’s Van Allen radiation belts. Surprisingly, this new belt was also found to contain high energy helium ions of unknown origin.
Jupiter has rings like Saturn’s, but much fainter and smaller (right). They were totally unexpected and were only discovered when two of the Voyager 1 scientists insisted that after traveling 1 billion km it was at least worth a quick look to see if any rings might be present. Everyone else thought that the chance of finding anything was nil, but there they were. It was a major coup. They have since been imaged in the infra-red from ground-based observatories and by Galileo.
Unlike Saturn’s, Jupiter’s rings are dark (albedo about .05). They’re probably composed of very small grains of rocky material. Unlike Saturn’s rings, they seem to contain no ice.
Particles in Jupiter’s rings probably don’t stay there for long (due to atmospheric and magnetic drag). The Galileo spacecraft found clear evidence that the rings are continuously resupplied by dust formed by micrometeor impacts on the four inner moons, which are very energetic because of Jupiter’s large gravitational field. The inner halo ring is broadened by interactions with Jupiter’s magnetic field.
In July 1994, Comet Shoemaker-Levy 9 collided with Jupiter with spectacular results (left). The effects were clearly visible even with amateur telescopes. The debris from the collision was visible for nearly a year afterward with HST.
When it is in the nighttime sky, Jupiter is often the brightest “star” in the sky (it is second only to Venus, which is seldom visible in a dark sky). The four Galilean moons are easily visible with binoculars; a few bands and the Great Red Spot can be seen with a small astronomical telescope. There are several Web sites that show the current position of Jupiter (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program.
Interesting Facts about Jupiter
- Jupiter is the fifth planet from the sun. It is 483 million miles (777 million kilometres) away from the Sun.
- The planet Jupiter is one of five planets which are visible from Earth with the naked eye. It’s the fourth brightest object in the Solar System. Only the Sun, Venus and the Moon are brighter in the night’s sky.
- Jupiter is named after the Roman king of the gods. This is probably because of its size. It has a diameter of 86,881 miles(139,822 kilometres) making it the biggest planet in the solar system by far. It would take a massive 1000 Earths to fill Jupiter! All the other planets could fit in there in one go!
- Jupiter has 67 moons orbiting the planet. And these are just the confirmed ones, and there are potentially more undiscovered! They have been put into three different groups. Inner moons which orbit closest to Jupiter, Galilean moons which are the largest ones and outer moons which are much smaller and further away.
- Galileo (1564-1642) discovered Jupiter’s moons. The planet itself is large enough to be seen with the naked eye, but it was not until the telescope was invented that we could see its moons.
- Jupiters largest moon is called Ganymede and is the biggest one in the solar system. If it were orbiting the Sun instead of Jupiter, it would most likely be classed as a planet and is only slightly smaller than Mars. Ganymede was discovered by Galileo Galilei in 1610, along with three other moons, Io, Europa and Callisto. These are the largest of Jupiters moons and are called the Galilean Moons.
- A day on Jupiter is 9 hours and 55 minutes. This is how long the planet takes to rotate on its axis. Jupiter has the shortest days of all eight planets.
- Jupiter takes 4328 earth days to orbit the Sun. Making a year on Jupiter the same as 11.86 Earth years.
- Jupiter has very faint rings around it. These rings are very dark, unlike Saturn’s better known bright ones. They are mostly made up of dust and small rock pieces. They were found by a NASA mission in 1980.
- Jupiter has a strong magnetic field. It is up to fourteen times stronger than the magnetic field on Earth. This is thought to be because of its rapid rotation and its layer of liquid hydrogen.
- Jupiter only has a small axial tilt of 3.13 degrees and so does not experience seasons like Earth and Mars.
- Jupiter has a Great Red Spot. This was first observed in 1664 and is a huge storm that has been raging on the planet for as long as we have been able to see it.
- Jupiter has the largest atmosphere in the Solar System. It is made up of hydrogen, helium, methane and ammonia.
- Jupiter is surrounded by very thick clouds. These are estimated to be 30 miles (50 kilometres) thick. They are thought to be made up of two layers, a very thick one and a smaller thing one.
- It is not known whether Jupiter has a solid surface. Below the clouds are thousands of miles of layers of hydrogen and helium gas. Underneath that is liquid hydrogen. Further below that liquid hydrogen becomes hot liquid metal. It is not yet known whether a solid core lies underneath it all, the temperatures would have destroyed any equipment we sent there to find out.
- Jupiter has lots of gravity. This is due to its size. If you took a heavy item to Jupiter, it would weigh much more than it does on Earth.
- Jupiter is the first of the planets known as the Gas Giants. The gas giants are planets made up mostly of gases with very little rock material at their cores. The other gas giants are Saturn, Uranus and Neptune.
- Eight spacecraft have visited Jupiter to this point. These are Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini, Ulysses and the New Horizons mission.
- There are others planned for the future and much more to learn about this planet. The European Space Agency has a mission planned called Jupiter Icy Moon Explorer (JUICE), which will explore the Jovian moons around Jupiter in 2022. This mission will pay particular attention to Ganymede and will remain in orbit around Jupiter’s largest satellite.
Jupiter has 79 known satellites : the four large Galilean moons plus many more small ones some of which have not yet been named:
- Jupiter is very gradually slowing down due to the tidal drag produced by the Galilean satellites. Also, the same tidal forces are changing the orbits of the moons, very slowly forcing them farther from Jupiter.
- Io, Europa and Ganymede are locked together in a 1:2:4 orbital resonance and their orbits evolve together. Callisto is almost part of this as well. In a few hundred million years, Callisto will be locked in too, orbiting at exactly twice the period of Ganymede (eight times the period of Io).
- Jupiter’s satellites are named for other figures in the life of Zeus (mostly his numerous lovers).
- Many more small moons have been discovered recently but have not as yet been officially confirmed or named. The most up to date info on them can be found at Scott Sheppard’s site.
Values for the smaller moons are approximate. Many more small moons are not listed here.
(distance is from Jupiter’s center to the ring’s inner edge)
More about Jupiter and its satellites
- more Jupiter images
- from NSSDC
- Voyager Jupiter Science Summary
- Galileo Education and Public Outreach (including the latest images)
- Jupiter’s Rings from JPL
- Galileo report on Jupiter’s rings (1998)
- Jupiter’s Ring System
- Jupiter Events from TAMU
- Online from Jupiter, NASA information about the Galileo mission for K-12 educators
- The Discovery of the Galilean Satellites
- Jovian System Nomenclature Tables
- Preliminary! Galileo Probe Results from JPL and ARC and LANL
- Galileo Probe Mission “Quick-look” Science Summary 1/25/96 from ARC
- Galileo science report 3/18/96
- Galileo Probe Results suggest our theories of the origin of the solar system need revision
- The Jupiter Satellite Page by Scott Sheppard
- Galileo’s atmospheric probe provides our first direct measurements of Jupiter’s atmosphere, our first real data about the chemistry of a gas planet. The initial data indicate a major new mystery — why is there so little water in Jupiter’s atmosphere? There is a building consensus that the probe encountered an unusually dry area but more details are needed.
- Just how deep into the interior do the zonal winds extend? What mechanism drives them?
- Why is the GRS so persistent? There are actually several theoretical models that seem to work. We need more data to decide between them.
- How can we get more direct information about the interior? Liquid metallic hydrogen has been produced in a lab at Lawrence Livermore National Laboratory but much about its properties is still unknown.
- Why are Jupiter’s rings so dark while Saturn’s are so bright?